Lay Summaries Archive

Read Lay Summaries from previous volumes of Functional Ecology here:

Early View Lay Summaries

 

Competition between genotypes of a dominant grass

Cynthia C. Chang and Melinda D. SmithGreenhouse competition experiment on Andropogon gerardii under different resource conditions.

Plants compete for essential resources like light, water, and nitrogen, and understanding how plants coexist when these resources are limiting helps explain how they persist in a changing environment. Dominant species, the most abundant species in a community, are ecologically important because they contribute a disproportionate amount to ecosystem functions like productivity, invasion resistance, and resilience to climate change. Therefore, it is particularly important to understand how individuals within a dominant species coexist when resources are limiting.

We studied four of the most common genotypes within a dominant grass species, Andropogon gerardii, which is known to play a large role in grassland ecosystem function. We conducted a competition experiment under low and high light, water, and nitrogen combinations. Genotypes were grown alone, in competition with the same genotypes (e.g. A with A, intragenotypic competition), and in competition with a different genotype (e.g. A with B, intergenotypic competition).

We found that all 4 genotypes make demands on different resources, which provides evidence for niche complementarity (genotypes occupy different niches, and thus together are able to maximize resource uptake) and helps explain how they are able to coexist. In addition, we found that genotypes differed in their above and belowground biomass, as well as reproductive output, and that both resource conditions and competitive environment affected these genotype traits. No single genotype dominated under all resource combinations, which helps to explain how environmental variability plays a large role in coexistence within this species. Together, these results provide insight into how genetic diversity within this dominant species is maintained and its potential effect on important ecosystem processes.

Image caption: Greenhouse competition experiment on Andropogon gerardii under different resource conditions.
This paper can be found online (not typeset or proofed) here

 

Poor food quality for hosts lowers transmission potential of their parasites.

Rachel M. Penczykowski, Brian C. P. Lemanski, R. Drew Sieg, Spencer R. Hall, Jessica Housley Ochs, Julia Kubanek, and Meghan A. Duffy Daphnia dentifera host infected with the fungal parasite Metschnikowia bicuspidata. Photograph credit: Isabella Oleksy.

Share this summary: Google+Linkedin

Consumers face wide variation in resource quality across habitats and through time. In this study, we focused on how the quality of food available to hosts affects the ability of parasites to infect and replicate within them. For instance, hosts that eat higher quality food might be more resistant to infection if they are in better overall condition or can meet nutritional demands of immune function. On the other hand, better fed hosts may provide more fuel for the parasite to use for its own growth. Food quality may also influence host growth or behaviour in ways that affect the probability of encountering parasites and becoming infected. To differentiate among mechanisms such as these, we manipulated resource quality (high quality green alga vs. low quality cyanobacterium) for a freshwater zooplankton host. The host becomes infected by accidentally ingesting spores of a fungal parasite while filter feeding. We hypothesized that hosts fed the lower quality resource would have slower growth, consume parasite spores at a lower rate (due to a known positive relationship between body size and feeding rate for this species), and consequently have lower infection risk. In addition, we expected that the production of new parasite spores would be lower in hosts fed low quality food. As hypothesized, hosts on the low quality diet had low infection risk because of their small size and low rate of parasite exposure. Smaller hosts also yielded fewer parasite spores. However, there was also an effect of food quality on foraging behaviour independent of body size, and hosts that were switched from high to low quality food at the time of parasite exposure had much lower feeding rate and corresponding infection risk than expected for their body size. In a second experiment, we tested chemical traits of the low quality resource which might have driven these effects. Our study highlights that changes in food quality can alter multiple traits of hosts and parasites, and illustrates how those mechanisms can be experimentally disentangled. This is especially relevant for freshwater ecosystems, where excess nutrient loading often causes shifts from green algae to cyanobacteria.

Image caption: Daphnia dentifera host infected with the fungal parasite Metschnikowia bicuspidata. Photograph credit: Isabella Oleksy.
This paper can be found online here.

 

Pollinator behaviour can rescue plants from the negative effects of small population size.

Ryan D. Phillips, Felix Steinmeyer, Myles H.M. Menz, Todd E. Erickson and Kingsley W. DixonA New Holland Honeyeater feeding on the nectar of Anigozanthos flavidus.

Share this summary: Google+Linkedin

Small population size in plants is associated with reduced reproduction through two contrasting mechanisms. Smaller populations attract fewer pollinators leading to reduced fruit set. Alternatively, a smaller pool of potential mates leads to an increased risk of inbreeding and lower-quality seeds. Consequently, in many species small populations will be at increased risk of extinction.

As pollinators, birds offer several potential advantages over nectar foraging insects. Some species move large distances between isolated plant populations, maintaining gene flow and fruit set. Further, communities of nectarivorous birds are characterised by frequent aggression as they defend nectar resources within their territories. This disrupts foraging birds from the typical foraging pattern of nectar feeding animals, which move between closely related, neighbouring plants.

We investigated how pollinator behaviour and abundance changes with plant population size and its consequences for fruit set and seed fitness. We studied the Evergreen Kangaroo Paw (Anigozanthus flavidus), a species endemic to south-western Australia but commonly cultivated for its attractive bird-pollinated flowers. We used a newly discovered germination stimulant to remove inter-population variation in seed dormancy when assessing seed fitness.

Pollination by Western Spinebills occurred at all populations of A. flavidus, while the behavioural dominant New Holland Honeyeater pollinated only the largest populations. Up to 31% of foraging periods were interrupted by aggression from pollinators, suggesting that territorial behaviour will substantially increase pollen dispersal. Western Spinebills visited fewer stems per plant than New Holland Honeyeaters, a behaviour that reduces self-pollination. There was no relationship between seed germinability, seeds produced per capsule or fruit set and plant population size, suggesting that the foraging behaviour of Western Spinebills mitigates the potential reduction in seed production and germinability with small population size.

Our findings highlight that, even within a group of similar pollinators, differences in behaviour can have important implications for the fitness of plants in small populations, with the potential for some pollinators to provide unexpected levels of resilience. Further, our work highlights the potential advantages of bird pollination for plants in small populations, suggesting a mechanism for the frequent evolution of bird pollination in the south-west Australian biodiversity hotspot.

Image caption: A New Holland Honeyeater feeding on the nectar of Anigozanthos flavidus.
This paper can be found online here.

 

How do floral signals in the ultraviolet spectrum influence pollinator behavior?

Matthew H. Koski and Tia-Lynn AshmanFlowers of Argentina anserina in the human-visible spectrum (top) appear uniformly yellow, however in the UV spectrum (bottom) flowers display a distinct bullseye pattern..

Share this summary: Google+Linkedin

Color patterns on flowers can enhance pollinators’ ability to recognize flowers and orient to pollen and nectar rewards, increasing both pollinator foraging efficiency and pollination success. Interestingly, many flowers have color patterns in the ultraviolet (UV) spectrum that are visible to insects but not to the naked human eye. The most common pattern is that in which petals absorb UV at the base and reflect UV at the tips of petals, making a bullseye pattern. UV reflection has been shown to increase pollinator visitation relative to UV absorption, and the UV bullseye pattern has long been purported to function as a nectar guide for pollinators, that is, orient pollinators to floral rewards. To investigate how bees and flies respond to variation in floral UV patterns, we performed experiments with flowers of the widespread plant, silverweed cinquefoil (Argentina anserine), which has uniformly yellow flowers in the human-visible color spectrum, but a distinct UV bullseye. We compared visitation and pollinating behaviors between flowers that had a UV bullseye and those that were manipulated to be either uniformly UV absorbing, UV reflecting, or to display an inverted bullseye (reflective petal bases and absorptive tips). We found that flowers with a bullseye pattern were more apparent to bees and flies than flowers that either absorbed or reflected UV. However, the likelihood of pollinator foraging and orienting to the center of flowers once they landed was not enhanced by the presence of the bullseye pattern. Flowers with the common bullseye pattern were also more apparent, and received more foraging visits than those with the inverse pattern. Our results suggest that patterns in the UV spectrum, rather than UV reflection alone can be important for mediating pollinator visitation. Our results also imply that plants with the common UV bullseye pattern may have higher pollination success than those with the inverse pattern which is a rare phenotype in nature. Since the presence of a bullseye did not increase the likelihood of pollinator foraging or orienting to the center relative to flowers without a bullseye (absorbing or reflecting), our findings do not support that this common floral pattern acts as a nectar guide in this system.

Image caption: Flowers of Argentina anserina in the human-visible spectrum (top) appear uniformly yellow, however in the UV spectrum (bottom) flowers display a distinct bullseye pattern.
This paper can be found online here.

 

Caterpillar feeding rates evolve in response to climate change.

Jessica K. Higgins, Heidi J. MacLean, Lauren B. Buckley and Joel G. KingsolverA Colias caterpillar after measurement of feeding rate. Image credit: Jessica Higgins.

Share this summary: Google+Linkedin

Climate has changed in recent decades, and will continue to change in the near future. Can plant and animal populations evolve to keep up? Several studies document evolutionary changes in seasonal timing or body size in response to recent climate warming, but evidence for evolution of thermal physiology has been limited by a lack of historical data. We take advantage of physiological studies from the 1970s to examine how Colias caterpillar feeding rates have changed over the past 40 years in California and Colorado in response to changing climate. We also looked at two additional populations (one in North Carolina and another in Colorado) to see if the populations are specifically adapted to their local temperatures.

We found that each population of caterpillars displayed a unique maximum feeding rate and optimal temperature for feeding. The population from the highest elevation showed an interesting pattern where the optimal temperature for feeding was much higher than the maximum air temperature experienced at that location. This may seem paradoxical, but because at high elevations it is often too cold for the caterpillars to feed, whenever it is warm the caterpillars eat with reckless abandon!

By comparing our data to historical data from these populations, we measured changes in climate and in caterpillars’ temperature responses over the past 40 years. Overall, the average air temperature near our study sites in California and Colorado has only slightly increased during this time, but the frequency of high temperatures has increased dramatically at both sites. Seemingly to accommodate these newly variable temperature regimes, the modern California population of caterpillars had higher feeding at both low and high temperatures than their ancestors. Interestingly, the optimal feeding temperature has not changed. In Colorado, modern caterpillars had a higher optimal temperature, and higher feeding rates at high temperatures, than their 1970s counterparts.

Rapid evolution of physiological traits in response to recent climate change has rarely been shown. This work highlights how thermal adaptation may be one way for some species to cope with hotter, more variable climates in the future.

Image caption: A Colias caterpillar after measurement of feeding rate. Image credit: Jessica Higgins.

 

Linking dietary shifts and reproductive failure in seabirds.

Nicole D. Kowalczyk, Andre Chiaradia, Tiana J. Preston & Richard D. Reina  Little penguin chick. Photo courtesy of Simon Lim.

Share this summary: Google+Linkedin

Breeding failure in seabirds has been attributed to declines in key prey abundance, the quality of prey, and overall prey diversity. However, identifying which aspect of diet is responsible for reproductive failure is challenging due to the difficulties associated with measuring prey intake and measuring the actual availability and abundance of those resources.

Little penguins (Eudyptula minor) provide a unique opportunity to understand the links between resource availability and reproductive success. The St Kilda little penguin colony has a short foraging range and displays narrow dietary diversity. These factors improve our ability to identify how changes in resources influence their reproduction. Anchovy has played a big role in the diet of the St Kilda little penguin colony and its contribution has ranged from 36% - 78% between years 2004 and 2008. This strong dependence on anchovy led to the prediction that changes in its distribution and abundance would have a negative impact on the reproductive success of this penguin colony.

In this study, we used published indices of actual prey abundance and availability within Port Phillip Bay, over two years with low anchovy abundance, to investigate how changes in prey abundance would influence the diet and breeding success of the colony.

We found that the sharp decline of anchovy in 2010 had a negative impact on little penguin reproduction. However, in 2011, despite the relatively low anchovy abundance, their breeding success was extremely high. These results indicate that the decrease of anchovy itself was not the only cause for low reproductive success. Low anchovy levels in combination with the scarcity of alternative prey likely led to the low breeding success in 2010. Our results show that little penguins are resilient to changes in their preferred prey but their ability to adapt to these changes is determined by the availability of alternative prey species.

Image caption: Little penguin chick. Photo courtesy of Simon Lim.
This paper can be found online here.

 

Orientation and speed of wind gusts causing abscission of wind-dispersed seeds influences dispersal distance.

David Savage, Catherine P. Borger and Michael Renton  Close up of fleabane flower heads. Courtesy of C. P. Borger.

Share this summary: Google+Linkedin

The seeds of many plants are removed from the plant by passing winds, and are regularly blown over hundreds of metres. Many plant species (e.g. dandelions) have developed seeds with structures that act like parachutes, and this greatly increases the distance that seeds are typically blown. This gives the plant an important advantage, as the further its seeds are blown, the quicker it can spread into new areas, and the more likely it is to survive in fragmented and highly dynamic environments.

The distance that wind-blown seeds travel from their parent is significantly influenced by the initial wind gust that removes the seed from the parent. If the seed is released into fast moving winds, it is likely to travel farther than if released into slow moving winds. Consequently, plants have evolved so that the bond between the seed and the plant can only be broken by sufficiently fast winds. In addition, some plant species have evolved so that upward wind gusts are more likely to remove seeds than downward gusts.

In this paper, we consider Conyza bonariensis (fleabane, a significant weed in Australia) as a case study, and examine the influence of the initial wind gust that removes the seed from the plant on the subsequent distance travelled. We demonstrate that the seeds of C. bonariensis are more easily removed from the plant by wind gusts with an upward orientation than horizontal or downward wind gusts and that seeds released into upward moving wind gusts are likely to travel farther than seeds released into horizontal or downward wind gusts. However, we also show that the influence of wind-orientation is correlated with wind speed, and as the speed of the initial wind gust is increased, the influence of wind orientation becomes less pronounced.

Image caption: Close up of fleabane flower heads. Courtesy of C. P. Borger.
This paper can be found online here.

 

 

Experimental evidence that maternal corticosterone controls adaptive offspring sex ratios.

Sarah R. Pryke, Lee A. Rollins, Simon C. Griffith & William A. ButtemerGouldian finches. Photo provided by authors.

Recent studies have shown that female birds can have a remarkable degree of control over whether they produce sons or daughters. However, it is unknown how females are able to control the sex of their offspring. One idea is that differences in levels of hormones circulating in the female during egg production may influence this process. Here we experimentally altered levels of the stress hormone, corticosterone, in egg laying Gouldian finches. Individual females received both corticosterone (which elevates stress levels, although corticosterone levels remained within the natural range for these birds) and metrypone implants (which reduces stress levels) in random order (i.e. such that each female bred under both treatments).

Females with corticosterone implants had highly elevated levels of circulating (plasma) corticosterone and overproduced sons, whereas when the same females were treated with metrypone they exhibited very low stress levels and overproduced daughters. In this species, females naturally show large variations in both corticosterone levels and offspring sex ratio adjustment in response to quality of their partners (male quality is signalled through genetically-determined head colouration - red or black). Previous studies have shown that females breeding with genetically incompatible males (of the opposite head colour) have very high daughter mortality (>80%), and when females are constrained to breeding with incompatible males they exhibit highly elevated stress responses and also adaptively overproduce sons. Therefore, the current study suggests that female hormonal state, and particularly elevated stress levels, may provide the mechanism for female birds to adjust the sex of their offspring.

Image caption: Simochromis pleurospilus with young. Photograph by Christoph Grüter.
This paper can be found online here.

 

Structural, compositional and trait differences between native and non-native dominated grassland patches.

Nicole A. Molinari and Carla M. D'Antonio  Invaded grassland dominated by ripgut brome.

Humans are moving species around the globe at unprecedented rates. These actions are resulting in the introduction of species into locations where they were not previously found. Many non-native species have little impact on the regions they invade, yet others form visually conspicuous, seemingly monotypic stands across portions of the landscape. Often the rise to dominance of a non-native species coincides with the loss or decline of native species including those that might have previously been dominant. We surveyed adjacent native and non-native dominated grassland patches to understand how a shift in dominance (native to non-native) affects physical structure, resource availability and species composition.

We found that grassland patches dominated by the non-native annual grass, ripgut brome, were homogenous in terms of their architecture and composed of denser vegetation and leaf litter relative to patches dominated by the native perennial grass, purple needle grass. These differences in physical structure are responsible for a threefold reduction in available light at the soil surface and likely contribute to the lower diversity associated with ripgut brome invaded patches. We also found that among species that coexist with the dominant, flowering began earlier and seed size and plant height were greater in invaded grassland patches relative to uninvaded patches. Our results suggest that species that are better suited (taller, earlier phenology and larger seed size) for low light availability are those that coexist with ripgut brome and this is consistent with our hypothesis that changes in physical structure with ripgut brome invasion is an important driver of community and trait composition.

The traits of species able to coexist with invaders are rarely considered when assessing community change following invasion, however this may be a powerful approach for predicting community turnover in environments with high anthropogenic pressures, such as disturbance and nutrient enrichment. It also provides a powerful means for selecting species to introduce when trying to enhance native diversity in an otherwise invaded community.

Image caption: Invaded grassland dominated by ripgut brome (Bromus diandrus). Photo credited to Nicole Molinari.
The article is available as accepted (not yet typeset or proofed) here.

 

Maternal effects of carotenoid supplementation in an ornamented cichlid fish

Alexandria C. Brown, Heather M. Leonard, Kevin J. McGraw and Ethan D. Clotfelter Female convict cichlid with her brood of eggs.  Photo credit: Alexandria C. Brown.

Pigments called "carotenoids" are responsible for the yellow, orange, or red colors of many animals. Animals can't make their own—they have to eat carotenids as part of their natural diet. Carotenoids might also support health in other ways, by acting as antioxidants or immunostimulants. Carotenoid-based body color uses up a portion of the carotenoids that the animal eats, so a prospective mate might be able to tell how healthy an animal is by how much color he or she can show off! Females that have carotenoid-based body colors might have it extra tough: she might also have to share her carotenoids with her young to keep them healthy. We used a cichlid fish species (Amatitlania siquia) in which females, but not males, have carotenoid-based ventral coloration to find out if carotenoids in maternal diets might enhance offspring survival. Indeed, we found that offspring from mothers that ate carotenoids grew larger and survived better than the offspring from unsupplemented mothers. However, carotenoid-fed mothers did not share more carotenoids with their young, so we conclude that the benefits of carotenoid supplementation to offspring must be transferred indirectly.

Image caption: Female convict cichlid with her brood of eggs. Photo credit: Alexandria C. Brown.
The article is available as accepted (not yet typeset or proofed) here.

 

Breeding timing in relation to quality at hatching affect the survival of king penguin chicks.

Antoine Stier, Vincent A. Viblanc, Sylvie Massemin-Challet, Yves Handrich, Sandrine Zahn, Emilio R. Rojas, Claire Saraux, Maryline Le Vaillant, Onésime Prud’homme, Edith Grosbellet, Jean-Patrice Robin, Pierre Bize and Francois CriscuoloKing penguin feeding its offspring. Photo provided by authors.

The king penguin (Aptenodytes patagonicus) , an emblematic species of the sub-Antarctic, has a unique breeding cycle. Chicks are raised for more than a year, including over the Austral winter when food resources are scarce and chick growth is interrupted. As a consequence, chicks need to grow and accumulate enough body reserves during the first weeks of their life to survive the harsh winter period. Growth is completed the following summer, when conditions are propitious again, before reaching independence and leaving for sea. Breeding timing is then critical for this species, and birds that breed late in the season have low chances of successfully raising a chick.

However, because a few late chicks generally make it through the winter, some adults will nonetheless attempt reproduction late in the breeding season despite very low chances of success. But why do some late chicks survive when others don’t? Is survival random or linked to specific characteristics of the chicks or their parents?

To answer these questions, we investigated differences in morphological and physiological traits related to stress and ageing between early and late chicks, shortly after hatching (day 10). We tested if such differences could explain chick survival up to departure at sea.

Despite being heavier than early chicks at 10 days, late chicks presented higher levels of stress hormone (corticosterone), higher levels of oxidative damage on cell components such as DNA and shorter telomeres (i.e. protective DNA structures that cap the end of chromosomes). For both early and late chicks, high body mass close to hatching was a strong predictor of survival up to the winter period and beyond. Importantly, in late chicks only, high levels of stress hormone and long telomeres were significant predictors of survival up to winter and to fledging, respectively.

These results suggest that the survival of late-chicks is clearly not random but linked to a combination of parent and offspring quality in relation to their environment.

Image caption: King penguin feeding its offspring. Photo provided by authors.

The article is available as accepted (not yet typeset or proofed) here.

 

Slow animals, fast invaders: the strain of snails that invaded the world.

Roberto F. Nespolo, José Luis Bartheld, Avia González, Andrea Bruning, Derek A. Roff, Leonardo D. Bacigalup & Juan Diego Gaitán-Espitia Marked snail in an enclosure. Photo provided by authors.

Many of the common terrestrial snails of our gardens have their origin in Europe or North Africa, but have invaded most of the human-populated areas of the World, thanks to our help with hitchhiking. In addition to their dispersal abilities, invasive species commonly exhibit special features for rapid spread in the invaded region, such as high fecundity. Here, phenotypic variation is very important in determining adaptive capacities, since populations can respond to natural selection only if there is variation in traits. With this idea in mind, we studied the populations of garden snails in Chile, in order to analyse phenotypic variation in traits related to performance and fitness. Phenotypic variation can have many origins, but natural selection provokes responses only if there exists additive genetic variation (that is, variation from many genes of small effect). The main index of additive genetic variation is its ratio with phenotypic variation, known as heritability. No previous information on heritability existed for terrestrial molluscs, but morphology was known to have high heritability in the original European populations. During four years, we studied three Chilean snail populations, across a range of 1300 km, which served as a starting colony for a pedigree-based experiment that permitted the computation of heritability, and other sources of phenotypic variation. To our surprise, we found very low heritability, including morphological traits, which contrasts sharply with what is known about the original populations. We also found that our populations, despite being separated by 1300 kilometers, were hardly differentiated. Hence, it appears that the process of colonizing was undertaken by a fast growing, undifferentiated strain of snails –an invasive strain- that spread rapidly through Chile and other countries. This process prevented local adaptation and differentiation.

Image caption: Marked snail in an enclosure. Photo provided by authors.

 

Special Feature: Climate Change and Species Range Shifts

Are there evolutionary consequences of plant-soil feedbacks along soil gradients?

Jennifer A. Schweitzer, Ivan Juric, Tess F. J. van de Voorde, Keith Clay, Wim H. van der Putten and Joseph K. Bailey  Figure provided by authors.

As most gardeners appreciate, plants have traits that change their surrounding soils. Such plant-soil linkages are fundamental to understanding ecological patterns such as community succession through time, whether invasive species can persist, and overall patterns of diversity due to the ability of plants to co-exist. However, the role of plant-soil linkages and their evolutionary potential has been largely ignored. The model results reported here indicate that feedbacks between soils and plants may commonly result in evolutionary interactions. The simulation model indicates that plant traits can change when they influence soil processes and plant traits can be selected in response to how they change soils. However, the magnitude of feedbacks and how strongly they evolve depend on the amount of gene flow and the strength of selective gradients over time. These results suggest that plant-soil feedback can lead to evolution in plants and reveals new research directions for further study with both theoretical and practical applications (for example, for crops and forest rotation practices). Questions addressing trade-offs and relationships between positive and negative feedbacks, how feedbacks may influence the evolution of diversity across landscapes, as well as the role of adaptation and maladaptation (how well matched or mis-matched plants are to soils), represent important frontiers in plant-soil feedback studies, contributing to a framework for better understanding evolution that occurs when species interact with each other and their surrounding environments.

Image caption: Figure provided by authors.

 

Thinner whales reduce energy investment in their foetus.

Fredrik Christiansen, Gisli A. Víkingsson, Marianne H. Rasmussen and David Lusseau  Minke whale foetus. Photo taken by Gisli Vikingsson.

We know that the maternal body condition of mammals affects foetus development. Surprisingly though, little is known about the relationship between female body condition and foetus growth in the largest animals on the planet, the whales. In this study, we looked at the relationship between foetus growth and female body condition in minke whales in Icelandic waters. Minke whales migrate to Iceland every summer to feed, in order to build up their fat reserves, including their blubber layer. For pregnant females, the energy contained in the blubber plays an important role in supporting the development of the foetus during gestation. Thus, it can be expected that a reduction in the blubber volume of pregnant females will lead to a reduction in the amount of energy that can be invested in the foetus. To investigate this, we used information from pregnant minke whales previously caught around Iceland between 2003 and 2007, when the volume of their blubber layer was estimated, together with the length of their foetuses. Minke whale foetuses increased almost linearly in length through the feeding season, at a rate of about 1cm per day. While accounting for this daily growth in foetus length, we found that female body condition, measures as the relative difference between the blubber volume of individual females and the average of all pregnant females, had a nonlinear effect on foetal length. Females that were in relatively poor body condition (below the average blubber volume) had smaller foetuses, proportionately to their condition. This suggests that females in poorer condition reduce the amount of energy that they invest in their offspring even at this early stage of pregnancy. This is probably to avoid worsening their condition and therefore risking their own survival. Females that were in better condition (above the average blubber volume) however did not carry larger foetuses than females of average condition. This suggests that there might be an upper limit to how much energy a female can invest in her foetus. This study is the first to demonstrate that maternal body condition can affect foetus growth in large whales.

Image caption: Minke whale foetus. Photo taken by Gisli Vikingsson.

 

Exercise changes behaviour

Elektra L. E. Sinclair, Carolina R. Noronha de Souza, Ashley J. W. Ward & Frank Seebacher Mosquitofish (Gambusia holbrooki) with marking. Photo provided by authors

The importance of physical activity for humans is well known. Exercise is essential for good health and for prevention and reversal of conditions such as obesity and diabetes. However, exercise is also an integral part of the ecology of most other animals. Migration, foraging, and behavioural interactions all require considerable levels of physical activity. The success of animals in their natural environment may be curtailed if their capacity for locomotion is inadequate to fulfil these functions. Regular physical activity, or exercise, can lead to a training effect that improves the capacity for locomotion. This is well known to people who go running regularly or engage in similar activities. For wild animals, improved locomotor capacity may remove a physical constraint and thereby influence the performance of behaviours such as migration or interactions with other individuals. Additionally, exercise can alter the production of hormones and thereby influence the psychological state of animals and their motivation for behaviour or movement. In other words, exercise can have a profound influence on behaviour.

We tested this hypothesis in a small invasive fish, the mosquitofish, Gambusia holbrooki. We show that fish which exercised by swimming against a current, such as that experienced in natural streams, had greater endurance capacity. Surprisingly, these fish were also more willing to take risks and explore new environments, and were a lot more aggressive than fish which lived in still water. We were able to show that the increased aggression and exploration resulted from an increased capacity for sustained exercise. However, the willingness to take risks was independent of this physical training effect, and is more likely due to changes in hormone levels. Our data show that the behaviour of animals can be modified by the physical environment, and the need for physical activity it imposes on individuals. These relationships are important for understanding movement and dispersal of animals, as well as their motivation to move - including the motivation to exercise in humans.

Mosquitofish (Gambusia holbrooki) with marking. Photo provided by authors

 

Adaptive maternal and paternal effects: gamete plasticity in response to parental stress

Natasha Jensen, Richard M. Allen, & Dustin J. MarshallAdult Hydroides diramphus with its feeding tentacles extended. Photograph by Richard Allen

In organisms with external fertilisation, gametes are exposed to the vagaries of naturally varying environments. Given their small size and relatively unsophisticated organisation, gametes are particularly vulnerable to environmental stress. While mothers have been shown to adjust the traits of their offspring to increase performance, few studies have examined whether fathers also manipulate gamete traits to improve their performance. This study shows that, in a marine invertebrate that experiences natural fluctuations in salinity, fathers alter their sperm to cope with changes in the environment. Specifically, fathers exposed to low salinity environments produced sperm that were more resistant to low salinity themselves. This increased resistance to low salinity during the gamete phase carried through to positively affect salinity tolerance during the larval phase, raising the possibility of nongenetic paternal effects, a poorly understood phenomenon. We suggest that future studies incorporate the potential for parental manipulations of gamete traits into their investigations of stress, since to ignore such effects could result in the mis-estimation of the effects of stress on gamete performance.

Image caption: Adult Hydroides diramphus with its feeding tentacles extended. Photograph by Richard Allen

 

Temporal patterns in immunity, infection load, and disease susceptibility: understanding the drivers of host responses in the amphibian-chytrid fungus system.

Stephanie S. Gervasi, Emily G. Hunt, Malcolm Lowry and Andrew R. Blaustein Photo provided by authors.

Many pathogens infect a wide range of host species, but not all hosts respond similarly to infection. For example, a single pathogen may cause rapid mortality when it infects one species, but cause no harm to another. Among-species variation in pathogen susceptibility, including differences in how hosts acquire, transmit, and persist with infection is important, because it can alter the abundance of pathogens and affect the probability of a pathogen persisting or going extinct within an ecological system. One trait that may underlie variation in species-specific susceptibility to pathogens is host immunity.

We examined the relationship between disease susceptibility (survival rate), quantitative infection load, and several measures of immunity in two different amphibian species, the Pacific tree frog and the Cascades frog, over a 15 day time-course of pathogen exposure. For both species, we compared responses of uninfected control animals to animals experimentally exposed to amphibian chytrid fungus. We found qualitative and quantitative differences in the way that hosts responded to the fungus. Species exhibited differential patterns of survival, contrasting trends in infection load over time, and variation in the direction and magnitude of immunological responses. Changes in immunity detected as soon as 24h and 48h after pathogen exposure suggest that initial host-pathogen contact may drive disease progression. Responses detected in the blood of amphibians suggest that this skin fungus may also change systemic-level responses. Our experimental work reveals the complexity of host-pathogen interactions and the importance of experimental comparative approaches to understanding the drivers of host susceptibility.

Variation in host responses to pathogens can drive disease dynamics over space and time, and understanding these differences is critical in this host-pathogen system since the chytrid fungus is associated with amphibian population declines worldwide.

Image caption: Photo provided by authors.

 

Stem-stored water: a good strategy for plants to survive short dry periods but not long droughts

Anna E. Richards, Ian J. Wright, Tanja I. Lenz and Amy E. ZanneTop photo: low rainfall, high nutrient woodland site at Round Hill nature reserve; Lower photo: high rainfall, low nutrient forest site at Ku-ring-gai Chase National Park.

Plants need water to survive and grow. However, reliance on water from soil makes plants vulnerable to unpredictable rainfall events. One way to overcome the mismatch between supply and demand for water is for plants to store water in their woody stems. Plants can use this water to survive for longer during dry conditions. The extent to which plants use stem-stored water varies from very little (relying mostly on uptake of water from the soil) to a considerable amount (up to half of a plants’ daily water requirements may come from stem stores). Plants that have woody stems adapted to storing a lot of water are more vulnerable to cavitation (breaking) of the cellular tubes that transport water. When plants stems become very dry and experience excessive cavitation they may eventually die.

In this study we measured how much plants rely on stem-stored water when growing in high rainfall areas, where dry periods are short, compared to plants growing in low rainfall areas, where long droughts are common. We measured branches sampled from 16 plant species growing in a high rainfall zone (1220mm per year) in Ku-ring-gai Chase National Park near Sydney, and 16 plant species growing in a low rainfall zone (390 mm per year) in Round Hill nature reserve in outback New South Wales, Australia. In each rainfall zone we collected half the plant species from soils with high levels of nutrients, and half from soils with low levels of nutrients.

We found that plants growing in high rainfall areas and on high nutrient soils used more stem stored water for growth than plants growing under low rainfall or on low nutrient soils. This is because plants growing in low rainfall areas, where long and unpredictable droughts are common, must have stems that are very resistant to cavitation. Wood that is very resistant to cavitation cannot release as much stored water as wood that is less resistant to cavitation. In the future droughts are predicted to become more frequent and longer in high rainfall areas of Australia. Therefore, we may see a shift in these areas to plant communities that are dominated by species that rely less on stem-stored water.

Image caption: Top photo: low rainfall, high nutrient woodland site at Round Hill nature reserve; Lower photo: high rainfall, low nutrient forest site at Ku-ring-gai Chase National Park.

 

Nectar Seekers Sneak Insect Snacks!

Elizabeth L. Clare, Holger R. Goerlitz, Violaine A. Drapeau, Marc W. Holderied, Amanda M. Adams, Juliet Nagel, Elizabeth R. Dumont, Paul D.N. Hebert, M. Brock Fenton  Glossophaga soricina is commonly associated with nectar feeding but it is also an efficient insectivore using it's quite echolocation to sneak up on prey.

Pallas’s long-tongued bat, Glossphaga soricina, is an important pollinator in the Neotropics. These bats find immobile flowers using a variety of sensory cues such as smell, spatial memory, and echolocation. However, they also often catch insects by echolocation to supplement this plant-based diet. While we have known they are capable of this task for some time, the mechanism they used was not clear. Using echolocation to detect and approach a stationary flower is different from detecting and tracking flying insects which move about trying to avoid capture. While some flowers provide bats with acoustic nectar guides, which make them easy to detect using echolocation, many insects use bat-detecting ears to avoid hunting bats.

Our genetic analysis indicates these bats can consume noctuid moths which have bat-detecting ears. To determine how they approach insect prey we used sound recordings and infrared video to monitor Pallas’s long-tongued bats detecting and approaching tethered mealworms. Our bats did not produce the rapid sequence of echolocation pulses that are associated with attacks on insects in most other bats that hunt aerial prey. The echolocation calls of Pallas’s long-tongued bats were high in frequency but low in intensity. When we compared the bats’ echolocation calls to the moths’ auditory abilities, we found that the low intensity echolocation calls were not loud enough to trigger the auditory neurons of moths with ears. In effect, the echolocation of G. soricina is too quiet for the moths to hear and allows them to sneak up on their target using a stealth tactic.

The European barbastelle (Barbastella barbastellus) uses a similar tactic when hunting flying insects and sneaks up on moths with bat detecting ears. It was previously the only bat species shown to use this strategy. Glossophaga soricina belongs to a large family of bats commonly called “whispering bats” because many of them emit relatively quiet echolocation calls for foraging within dense vegetation. Our analysis suggests that more bats than previously thought may benefit from this stealthy approach that prevents auditory-guided evasion of eared prey.

Image caption: Glossophaga soricina is commonly associated with nectar feeding but it is also an efficient insectivore using it's quite echolocation to sneak up on prey.

 

Herbivores in a small world: long-term movement patterns of herbivorous coral reef fishes are defined by small-world network dynamics

Rebecca J. Fox & David R. BellwoodThe movements of the steep-head parrotfish between points along its reef habitat (lower insert) fit the same pattern as a theoretical “small-world” network (top insert). Photo credit: Saspotato, Creative Commons (www.creativecommons.org).

The function or role of an organism within an ecosystem is defined not just by what that organism does, but the area over which it does it. This spatial dimension is an important, yet often overlooked, aspect of ecosystem function. Within coral reef ecosystems, grazing by large herbivorous fishes is critical in maintaining the balance between coral and algae and therefore a key process in reef ecosystem functioning. However, the spatial dynamics of these roving herbivores and the implications of their dynamics for the overall resilience of herbivory on reefs are not well understood.

In this study we used passive acoustic telemetry to track the movements of three species of roving herbivorous fishes along one of the fringing reefs of the Great Barrier Reef, Australia over a period of 12 months. Along a 3km stretch of reef we moored underwater receivers that listened for transmissions from the tags that had been surgically inserted into individual fishes at the site. These receivers logged the identity and time stamp of every tagged fish that passed within range.

Analysing the movement dynamics of fishes along the reef, we discovered that most individuals of the three species examined in our study impacted on only limited segments of reef. When moving between distant parts of reef, they tended to do so along direct routes, rather than from area to neighbouring area. This resulted in a pattern of movement resembling the hub-and-spoke network of an airline. We found that the dynamics of most individuals could be characterised as small-world networks such as those built on the theory of six degrees of separation. Such networks are generally stable in the face of random shocks, suggesting that the process of herbivory is resilient to random disturbances. However, these networks are extremely vulnerable to targeted attack. In the case of these reef herbivores, that could be thought of as targeted fishing effort or the destruction of individual pockets of habitat.

Viewed from a network perspective, the dynamics of reef herbivores confirm the need to maintain high herbivore abundances across all reef habitats in order to preserve the integrity of the grazing function on reefs. The application of network analyses to telemetry data may have applications across other ecosystems and provide an interesting opportunity to examine organism movements in a dynamic, rather than just a static context.

Image caption: The movements of the steep-head parrotfish between points along its reef habitat (lower insert) fit the same pattern as a theoretical "small-world" network (top insert). Photo credit: Saspotato, Creative Commons (www.creativecommons.org) .

 

Adaptive maternal plasticity in yellow dung flies

Claudia C. Buser, Paul I. Ward, Luc F. Bussière In the foreground, a female dung fly (olive-coloured and smaller than her larger and yellow mate, who is positioned dorsally and engaged in post-copulatory guarding) lays eggs on a cow pat in close proximity to other flies, seen just beyond the plane of focus. Photo by Roland Gautier.

When animals encounter environmental variation that alters the relative payoffs of different traits, they are often able to change their phenotype in response to these environmental conditions in a way that enhances fitness (a phenomenon known as adaptive phenotypic plasticity). For female animals, some of the most important plastic traits involve responses to conditions affecting offspring survival and performance. In animals without direct parental care, adaptive maternal plasticity should involve alterations of the number and provisioning of offspring, or adjustments in mating preferences in response to prevailing environmental conditions.

Mate choice can take place before, but also after copulation (e.g. females favouring the use of sperm from a certain male when fertilizing their eggs). Very few studies unequivocally demonstrate active post-copulatory sperm choice. Consequently, the prevalence of sperm choice and its importance relative to premating choice or other forms of plasticity in female reproduction remain unclear.

We independently manipulated maternal exposure to cues of larval competition intensity and the actual competition experienced by larval yellow dung flies (see Figure 1). We did this by mating each experimental female with two differently sized males. During the subsequent egg laying bout, we exposed females either to dung containing the eggs of other yellow dung flies, or to dung without any potential competitors. We then split each female’s brood into two different rearing environments, one of which included competition with siblings, and one without competition, such that in half of our trials, female perceptions matched larval experiences, while in half they did not. This experiment allows us to simultaneously assess several forms of maternal plasticity, including post-copulatory choice, and to detect subtle interactions between environmental variation and maternal perceptions of changes in environmental conditions. Although we do not find strong evidence that females select the sperm of certain males over others in a context-dependent way, we do provide general evidence of impressive adaptive maternal plasticity in response to cues of larval competition, illustrating the subtlety and complexity of adaptive maternal plasticity within variable environments.

Image caption: In the foreground, a female dung fly (olive-coloured and smaller than her larger and yellow mate, who is positioned dorsally and engaged in post-copulatory guarding) lays eggs on a cow pat in close proximity to other flies, seen just beyond the plane of focus. Photo by Roland Gautier.

 

Male offspring affect sisters’ reproduction later in life. A study in marmots and rabbits.

Raquel Monclús, Dietrich von Holst, Daniel T. Blumstein, Heiko G. Rödel Female yellow-bellied marmot and one of her pups at the entrance of the burrow (credit: Julien Martin). Bottom: Sibling European rabbits around their burrow (Credit: D. von Holst).

The events that happen during early life are known to have long lasting consequences because animals are often more flexible when young. Most animals are raised with siblings, with whom they have to share parental resources, such as food and space. Moreover, in mammals, siblings from the same litter share a common prenatal environment, the mother’s uterus. Male foetuses start producing testosterone, which diffuses across the membranes, reaching adjacent foetuses. Testosterone has a masculinising effect on females and, as the number of males in the womb increases, females become more masculinised. This is seen in terms of their morphology, physiology, and behaviour. The consequences of this pre-natal masculinisation are long-lasting. In general, females raised in male-biased litters are more aggressive, are less receptive to males, as well as less preferred by males, and start reproducing later in life. Most of these facts are known from laboratory experiments, but have hardly ever been tested in the wild. For that, we used two well-studied populations: yellow-bellied marmots at the Rocky Mountain Biological Laboratory, Colorado, USA, and European rabbits studied in a 2 ha field enclosure at the University of Bayreuth, Germany. We looked at the reproductive performance of marmot and rabbit females coming from varying litter sex-compositions, and different group densities. We found that for both species, females from male-biased litters delayed the onset of reproduction during their first breeding seasons. At least in marmots, the effects were still apparent as late as 4 years after birth. That has important consequences as both species live in temperate climates, and pups are usually time-constrained to grow and store fat before the winter starts. Therefore, those born earlier in the season have greater chances of surviving the winter, and thus of reaching adulthood. However, rabbits under high densities brought forward the onset of breeding, compared to non-masculinised females. Whereas masculinisation might seem maladaptive in most scenarios, masculinised females are better able to monopolise resources, which are normally limiting when group densities are high. We highlight the importance of considering the consequences of early events in naturalistic settings to understand the dynamics of a population.

Image caption: Female yellow-bellied marmot and one of her pups at the entrance of the burrow (credit: Julien Martin). Bottom: Sibling European rabbits around their burrow (Credit: D. von Holst).
This paper can be found online (not typeset or proofed) here.

 

Food availability and developmental plasticity.

Alexander Kotrschal, Sönke Szidat and Barbara Taborsky A Simochromis pleurospilus male. Photo provided by authors.

That the conditions experienced during childhood impact on our adult life is general knowledge. Bad habits picked up as children are hard to get rid of as adults or traumatic childhood experiences can lead to serious psychological problems in grown-ups. But a developing body may also adapt to circumstances and so help master those circumstances. For example, virtually all top athletes have started training for their sports as young children.

Using an African cichlid fish from Lake Tanganyika, East Africa, we investigated how different levels of food availability early in life influence the ability to digest food later in life. We fed our fish very much or very little food during the first seven months of their life, which is their whole juvenile period. Then, at two years of age we tested how well they could digest their food. By comparing the caloric content of their food and their faeces, we found that animals that had previously experienced food shortages were better able to extract energy from their food. Because we also found heavier digestive organs in those low-food fish we conclude that the sparse food during early life lead to an increased investment into the digestive system.

Those underfed fish therefore prepared themselves for a life of hunger because a more efficient digestive system likely proves beneficial in times of food shortage. Fish reared on all-they-can-eat diets, on the other hand, had no need to invest into effective guts because even a less efficient digestion is enough to thrive if food is abundant.

Image caption: A Simochromis pleurospilus male. Photo provided by authors. This paper can be found online (not typeset or proofed) here.

 

 

 

 

Alternative overwintering strategies in an Antarctic midge: freezing versus cryoprotective dehydration.

Yuta Kawarasaki, Nicholas M. Teets, David L. Denlinger, Richard E. Lee, Jr  Larvae of the Antarctic midge, (Belgica antarctica.) Photo credit: Richard E. Lee, Jr. (or R. E. Lee).

To freeze, or not to freeze: that is the question for surviving winter in many temperate and polar insects. Most species are freeze intolerant, and their survival depends on avoidance of internal ice formation by supercooling. Although relatively uncommon, some species can survive the multi-faceted stresses associated with internal ice formation. Generally, freeze avoidance and freeze tolerance are considered mutually-exclusive strategies for low-temperature survival and each is characterized by a unique set of limitations and advantages; yet, a few species can employ either depending on the prevailing environmental conditions.

One such species is the terrestrial midge, Belgica antarctica, which is endemic to the Antarctic Peninsula. Larvae of B. antarctica survive winter either by freeze tolerance or by cryoprotective dehydration. Cryoprotective dehydration is a relatively new addition to our understanding of freeze-avoidance strategies employed by polar invertebrates. Although the underlying cellular processes associated with this strategy are similar to those of freeze tolerance, little is known about potential trade-offs of overwintering in these states. As the only insect with the capacity to tolerate freezing and to cryoprotectively dehydrate, B. antarctica is an ideal model to compare the benefits and costs of these strategies.

Both freezing and cryoprotective dehydration effectively promoted larval survival during our 32-day-experimental exposure to simulated overwintering temperatures. Freezing had little effect on larval body water content or on the concentration of salts and organic molecules in the hemolymph(body fluids). In contrast, cryoprotective dehydration at -5°C resulted in a progressive loss of body water, causing a four-fold increase in the concentration of hemolymph fluids. Also, freezing and cryoprotective dehydration produced distinctly different patterns of breakdown of glycogen (a sugar storage compound, similar to starch in plants); however, post-recovery levels of glycogen were similar in these two groups, as were total fats. In summary, we conclude that freezing and cryoprotective dehydration were both effective in promoting winter survival of larvae, with only minor differences in energetic costs. Whether larvae freeze or become cryoprotectively dehydrated ultimately depends on the moisture condition of their microhabitat. Thus, the physiological flexibility of B. antarctica to overwinter in these alternative states likely contributed to its geographic range distribution that extends further south than any other free-living insect.

Image caption: Larvae of the Antarctic midge, Belgica antarctica. Photo credit: Richard E. Lee, Jr. (or R. E. Lee).
This paper can be found online (not typeset or proofed) here.

 

Insects fall from smooth bark surfaces which help to defend trees.

Scott Ferrenberg and Jeffry B. MittonA mountain pine beetle attacking a pine tree elicits a defensive resin response.

Tree bark is a first line of defense against pathogens and insect attack. Bark has long been known to contain defensive chemicals to deter pests, but there is less understanding of how bark anatomy influences tree defense. Decades ago, scientists pondered why so many tropical trees had smooth surfaced bark. A hypothesis emerged that smooth surfaces hinder the ability of insects and plants to grip a tree’s bark, thus reducing damage from pests and parasitic plants. While the hypothesis of “smooth bark defense” was eventually dismissed, it was never scientifically tested with regard to insects.

We tested the smooth bark defense hypothesis using bark beetles (mountain pine beetle) as our model insects and limber pines as our model trees. The mountain pine beetle is a widespread, destructive insect specialized to attack pines, and thus a notable effect of bark texture on its success is unexpected. Limber pines are also widespread in western North America, and commonly have both smooth and rough bark surfaces on the same tree stem.

We conducted field surveys to determine if mountain pine beetles can successfully attack limber pines with smooth versus rough bark, and experimentally tested the ability of beetles to grip the different bark textures in timed trials. Mountain pine beetles were unable to grip smooth bark and quickly fell from its surface, but easily gripped rough bark. Field surveys reinforced the finding that mountain pine beetle attacks are overwhelmingly found on rough bark surfaces, and virtually absent from smooth bark. Thus, mountain pine beetles’ difficulty gripping smooth bark leads to significantly fewer beetle attacks on trees with greater coverage of smooth bark than rough.

Our results indicate that smooth surfaced bark can defend trees against insects. This finding is important because tree mortality from insects is increasing worldwide in response to global climate change. For example, recent epidemics of the mountain pine beetle in North America have impacted forests from southern California to Alaska, leaving billions of dead pine trees in their wake. Understanding traits that give trees greater resistance to insects can improve forest management, and improve future studies of ecology and evolution.

Image caption: A mountain pine beetle attacking a pine tree elicits a defensive resin response.
This paper can be found online (not typeset or proofed) here.

 

Hovering on a high fructose diet

Chris Chin Wah Chen and Kenneth Collins Welch, Jr.A male ruby-throated hummingbird (Archilochus colubris) hovers at a feeder placed inside a respirometry mask.

Recent studies suggest that even “normal” dietary intake of sugar can be harmful to one’s health. In particular, the increasing presence of fructose in our diets is linked to the current obesity epidemic. While our muscles can make use, to a limited extent, of circulating glucose to fuel our exercise metabolism, we cannot metabolize fructose very well in our muscles. Instead, the fructose in our sugary drinks and processed foods is destined for our liver, where it is preferentially used to synthesize fat.

Unlike humans, some animals evolved on a sugar diet equally rich in glucose and fructose. Hovering hummingbirds are rare among vertebrates in their ability to rapidly make use of ingested sugars to fuel energetically expensive hovering flight, powering up to 100% of their metabolic needs with the sugars they drink, while humans athletes max out at around 30%. Still, until now, we haven’t understood to what extent hummingbirds can use the 50% of the sugar in their nectar meals that is glucose versus the 50% that is fructose. We studied the oxidation of specially labelled glucose and fructose solutions in hovering ruby-throated hummingbirds. Our study shows that hummingbirds begin using newly ingested sugars to fuel hovering flight within minutes and can fuel as much as 100% of their intense hovering metabolism with either glucose or fructose. These data suggest that hummingbirds may even be able to oxidize fructose in flight muscle tissues at rates high enough to satisfy metabolic demands that are, pound for pound, 10 times those of an elite human athlete.

By relying on newly ingested sugars to fuel flight hummingbirds can reserve precious fat stores to see them through the overnight fasting period, or to power migratory flights. These results hint at unique adaptations for fructose use in hummingbird muscles and demonstrate the remarkable convergence of diet, behaviour, and most notably, physiology that enables their high energy lifestyle.

A male ruby-throated hummingbird (Archilochus colubris) hovers at a feeder placed inside a respirometry mask.
This article is available online for free here.

 

Finding a recipe to help honeybees survive stress.

C. Ruth Archer, Christian W. W. Pirk, Geraldine A. Wright & Sue W. Nicolson  Honeybee. Photograph by Ludwig Eksteen.

Honeybees pollinate many important crop species and wild flowers and so play a key role in preserving high agricultural output and biodiversity. However, honeybees, like other insect pollinators, are experiencing population declines in many parts of the world. These declines could have severe agricultural and ecological implications. Therefore, it is important that we understand why bees are in decline.

Increasingly it appears that bees are being exposed to multiple interacting stressors, such as pesticides, disease and land use changes, which together reduce their survival. Crucially, land use changes may reduce the quality and quantity of floral resources, which could lead to poor nutrition in bees. This may increase their vulnerability to other stressors. While there is some evidence for nutrition affecting survival under stress in solitary insects such as caterpillars, we have no information for social insects. Our experiments test directly whether nutrition affects stress resistance in honeybees.

Using bees from four colonies of Apis mellifera scutellata, we set up groups of 100 queenless, newly-emerged workers in cages in incubators. Bees were fed different diets containing specific ratios of protein (casein) and carbohydrate (sucrose), and were subjected to two different stresses. One was the neurotoxin nicotine, which is chemically related to the neonicotinoids, long-lasting systemic pesticides that have recently been banned in the EU. The other stress was lower temperature: bees were kept at 30oC instead of the normal 35oC that is maintained in the brood area of a hive. Food consumption and survival of the bees were measured over a 14 day period.

We found that low temperatures and nicotine interacted to reduce survival in bees that ate low protein, high carbohydrate ratio diets. However, bees on high protein diets did better. We also carried out an experiment where bees were offered a choice of diets and could vary their nutrient intake. Again, the combined stress, but not the individual stresses, reduced survival. Surprisingly, when these bees were exposed to both stresses, they did not shift their intake towards higher protein to improve their survival.

As seen in other studies, a combination of stresses can be lethal for bees: a combination of multiple stressors might “push our pollinators over the edge”. However, bees did not meet this combination of stressors by adjusting their intake towards higher protein. This may be because the hive is a comparatively stable environment; selection for flexible nutrient regulation to increase stress resistance may not be as strong in honeybees as in solitary insects.

Image caption: Honeybee. Photograph by Ludwig Eksteen.
This paper can be found online here.

 

Context-dependent costs and constraints of begging and non-begging activity by Common Grackle nestlings at the scale of the nanoclimate.

Barb Glassey, Melanie Gunson and Robert Muir Common Grackle nestlings in a heterogeneous nest environment. Photograph provided by authors.

Both adult and young seabirds move to cooler areas of shade under hot, sunny conditions, behaviour that has been shown to reduce body temperature and energy expenditure. Young passerines, which are perching birds, are however confined to the nest, where direct exposure to solar radiation at even moderate temperatures can increase their body temperature, stimulate heat stress behaviours and potentially impact their ability to beg for food. The nests of Common Grackles (Quiscalus quiscula) are of the open-cup type (not covered or located in a cavity), and under sunny conditions patches of sun and shade, differing in temperature and solar radiation, are created within the nest cup, a scale referred to as the nanoclimate. Grackle nestlings can detect sun and shade within the nest cup and when exposed to sunlight respond by shade-seeking, i.e. moving to cooler shaded areas.

We were interested in exploring 1) whether moving to shade within the nest cup was a strategy used by nestlings to reduce the effect of solar radiation on heat gain and energy expenditure, and 2) if the energetic cost of nestling activities such as movement and begging was higher in the sun compared to the shade, which would suggest that the cost depends on the environmental context. We first conducted an experiment in which nestlings were assigned to one of two types of nest environments: one with patches of sun and shade or one in full sun without access to shade. We videotaped the behaviour of nestlings and measured body temperature.

The body temperature of nestlings without access to shade was significantly higher, and nestlings spent more time moving around the nest cup (shade-seeking) and panting, suggesting increased metabolic expenditure. To test this hypothesis, we measured energy expenditure in the lab under conditions of simulated sun and shade. The lab experiments confirm that nestlings use less energy in the shade. Furthermore, not only was begging in the sun more energetically costly than begging in the shade, but our results suggest that the duration of time that nestlings can beg may be reduced by exposure to sunlight, meaning that the environmental context imposes a behavioural constraint.

Image caption: Common Grackle nestlings in a heterogeneous nest environment. Photograph provided by authors.
This paper can be found online here.

 

Antipredator defences of young are independently determined by genetic inheritance, maternal effects and own early experience in mouthbrooding cichlids.

Ariane Stratmann and Barbara TaborskySimochromis pleurospilus with young. Photograph by Christoph Grüter.

Predation is one of the most important forces of natural selection, which has given rise to a broad range of adaptations in prey animals to defend themselves against predator attacks. Usually, young animals are particularly vulnerable to predation. Especially shortly after birth they may become an easy treat for predators because of their small size and limited escape ability. Therefore, any anti-predator defences existing in new-borns are likely to greatly enhance their survival chances during the dangerous early life stages. To understand how such defences can evolve and function effectively, we need to understand their developmental origins. A comprehensive understanding of variation in anti-predator defences thus requires the examination of innate factors, environmentally induced parental influences and the learning from experience of young animals. It has been shown previously that each of these possibilities can influence certain aspects of anti-predator strategies in young animals. Here we developed a novel approach to study all three sources of anti-predator defences together in an integrative experimental approach. We expected that the different origins of anti-predator defences would interact to affect the behaviour and growth of our study species, the mouthbrooding cichlid fish Simochromis pleurospilus. Unexpectedly, however, genetic inheritance, maternal effects and learnt predator experience affected the defences of young fish independently of each other. We found that (i) the olfactory recognition of a predator was genetically determined, (ii) maternal effects mediated a growth boost shortly after the young had reached independence of maternal brood care, and (iii) the wariness fish showed towards predators later in life was altered by direct experience of the smell of the predator during the larval stage. Apparently, in our study species, the maternally induced growth boost is limited to a short but critical time window, when young undergo a niche shift from the deeper adult habitat to a more shallow juvenile habitat, and when they particularly benefit from a large size when predation risk is high. Instead, an individual’s own environmental sampling of predation risk, combined with an innate predisposition to recognize predators, may enable the best prediction of predation risk for young in the juvenile habitat.

Image caption: Simochromis pleurospilus with young. Photograph by Christoph Grüter.
This paper can be found online here.

 

Floral neighbourhood is important for red clover pollination.

Stein J. HeglandTwo field workers, Torkjel and Håvard, observed bumblebee visits to red clover at the same time for 30 minutes each time. We did this five times during the main part of the pollination season (July). Afterwards we counted flowers in the immediate neighbourhood and also in the surroundings to test the questions posed in this study. Photo: Stein J. Hegland.

Plants compete against each other, trying to draw pollinators to their flowers by using colour, size, odour and other attractants. On the other hand, plants may also find it advantageous to grow in a neighbourhood with many other flowers, because bees and other pollinators may prefer to visit such areas above those with fewer flowers. We still know little about the relative importance of negative (competition) and positive (called facilitation) interrelationships among plants for attracting pollinators.

Imagine you are a flower: can it be an advantage to live together with other flowers because this increases your success in attracting pollinators? But if there are many flowers at the other end of the meadow, do these flowers then compete with you? That is what I wanted to find out and test. To perform such a test, I collected data from twelve different locations in meadows around the village Kaupanger by the Sognefjord in Norway. I counted quantities of flowers both close and further away from red clover flowers at the same time as I counted the number of bumblebees visiting these red clover flowers.

My findings suggests that the floral neighbourhood of the red clover flowers is indeed important for whether plants compete or have positive effects on each other’s attraction of pollinators. When there were many flowers near red clover there were more bumblebees visiting each single flower, especially those with similar colours to red clover. However, when the amount of purple flowers increased further away (in this case 2.5 to 10 m away), the red clovers that I studied attracted fewer bumblebees. The advantage of living together thus resulted in more bumblebees visiting red clover which also allowed these flowers to produce more seeds. If the quantity of flowers in a given spot is reduced by, for example, human activity, that may reduce the amount of offspring for plant species dependent on pollinators for seed production. On the other hand, the findings may be used to attract more pollinators to specific flowers or places in gardens, parks or in agricultural fields.

Image caption: Two field workers, Torkjel and Håvard, observed bumblebee visits to red clover at the same time for 30 minutes each time. We did this five times during the main part of the pollination season (July). Afterwards we counted flowers in the immediate neighbourhood and also in the surroundings to test the questions posed in this study. Photo: Stein J. Hegland.
This paper can be found online here.

 

The kinematics of swimming with a sword.

Christopher E. Oufiero, Kristine Jugo, Theodore Garland, Jr.  Photo provided by authors.

Sexual selection, i.e. selection for increased reproductive success, often results in bizarre, exaggerated morphological structures, which increase the number of matings or success during competition with other members of the same sex. However, these exaggerated structures may hinder the bearer’s ability to function, and therefore impose a cost. For example, exaggerated fins in fish that evolve through sexual selection may increase drag, and thus the amount of energy needed to move, or alter the manner in which the fish swim. Many studies have examined the effects of sexually selected fins on locomotor performance, but few have examined the effects of these exaggerated fins on the kinematics of locomotion. Using four species of swordtail and platyfish (Xiphophorus), as well as an experimental reduction of sword length in X. alvarezi, we examined the effect of the sexually selected sword on the kinematics of steady swimming. Unlike some other sexually selected traits, the sword is directly linked to the main propulsive system, the caudal fin (the tail fin). An elongation of the caudal fin into the sword may hinder a male’s ability to swim and decrease how much the tail is moved (tail beat amplitude) or how fast the tail is moved (tail beat frequency). Conversely, males may compensate for the sword by increasing tail beat amplitude or tail beat frequency. We found that among four species with naturally varying sword length, there are few differences in the way they swim. The two species with the longest swords (X. alvarezi and X. nigrensis) did not differ in their tail beat amplitudes or frequencies from the species with no sword (X. meyeri), suggesting either no cost or compensation for the sword. We also found that experimentally removing the sword increases tail beat amplitude, but has no effect on tail beat frequency; the effect on the males of ‘training’ with the sword (which is not permanent but may be present for several weeks) may be an ability to generate more thrust when the tail is completely removed. Taken together, our results suggest that the diversity of caudal fin shape due to sexual selection has minimal impact on a male’s functional abilities to swim.

Image caption: Photo provided by authors.
This paper can be found online here.

 

Charcoal effects on tree seedlings.

Nathalie Pluchon, Michael J. Gundale, Marie-Charlotte Nilsson, Paul Kardol and David A. Wardle Salix charcoal Photograph provided by authors.

Fire is a major disturbance in many ecosystems worldwide including the boreal forest, and significant quantities of charcoal can be input to the soil from fire. However, the mechanisms by which charcoal affects plant growth are poorly understood, and little is known about the factors that influence how charcoal effects plant growth. Seedlings from four common boreal tree species were grown in each of two contrasting soils which were amended by nine different charcoal types (each from a different species) in a greenhouse experiment. Charcoal addition had either positive or neutral effects on seedling growth, with great variability among charcoal types. The charcoal types that had the strongest positive effect were those that had the greatest concentrations of phosphate and total phosphorus, and in some cases were derived from woods that had the highest total phosphorus concentration. Addition of charcoal had a stronger positive effect on plant growth on soil with the lowest levels of phosphate and total phosphorus. Generally, charcoal derived from angiosperms (deciduous broad-leafed trees) stimulated seedling growth more than charcoal from gymnosperms (evergreen conifers). Further, angiosperm seedlings were on average stimulated more by charcoal addition than were gymnosperm seedlings. These results indicate that charcoal produced by fire could contribute to the initial dominance of angiosperm trees in post-fire succession, and suggests a possible feedback whereby charcoal from angiosperm tree species favors growth of angiosperm seedlings. This study highlights a new means by which functional trait variation among tree species could potentially exert “after-life” effects in forested ecosystems through influencing traits of the charcoal that they produce following wildfire, with potentially important consequences for plant growth and community and ecosystem properties during post-fire succession.

Image caption: Salix charcoal Photograph provided by authors.
This paper can be found online here.

 

Root trait hierarchy ranks grasses’ competitive ability.

Florian Fort, Pablo Cruz and Claire Jouany Greenhouse experiment. Photo courtesy of authors.

Attempting to understand how the species that live together in plant communities are selected is one of the oldest pursuits in ecological research. The idea that greater diversity in plant features allows plants to coexist more easily was established in Darwin’s statement that species more closely related compete more intensely for resources than species with different strategies. This led scientists to suggest that the more species’ features differ, the more they have differing "niches" and the less they interact, and as a result, the more they are able to live together. However, recent work suggests that when species’ features are related to resource-acquisition strategies, the more species differ, the less they are able to live together. If the competitive abilities of the species are too different, some competitive species may out-compete others, leading to the eradication of poor competitors from the community.

To determine whether species compete more strongly when they have similar or different features, we conducted a greenhouse experiment with four species, two with root characteristics of slow-growing species (nominally poor competitors) and two with root characteristics of fast-growing species (nominally efficient competitors). They were grown alone and in pairs under two levels of water and phosphorus availability. We measured the intensity of competition between species pairs by comparing the aboveground biomass production of plants grown alone and in pairs. At the same time, we measured species’ roots to assess differences in their root strategies.

For all features measured, when species were grown in high water- and phosphorus-availability conditions, the species pairs with the most difference in root strategy had the most unequal interactions, with one species strongly affecting the other and being little affected in return. In contrast, when species pairs were grown in dry conditions, the degree of competition did not depend on differences in root strategy. These results show that having different root strategies did not allow species to reduce or avoid competition.

Image caption: Greenhouse experiment. Photo courtesy of authors.
This paper can be found online here.

 

Marine crustaceans lack coherence in warming responses.

Katelyn T. Faulkner, Susana Clusella-Trullas, Lloyd S. Peck & Steven L. Chown  Marion Island species examined in this study: specimens of the amphipod Hyale hirtipalma preserved after tolerance trials and the isopod Exosphaeroma gigas and. Photos provided by authors.

Recent analyses of temperature tolerance and geographic distributions of species at global scales suggest that responses to warming are more predictable in marine than terrestrial systems. However, this generality has not been tested consistently across regions and taxonomic groups. In particular, only a limited number of studies incorporate both basal tolerance and its plasticity for marine organisms. In addition, the influences of plasticity and rates of temperature change on tolerance will likely complicate predictions of future responses of these organisms to climate change.

In this study, we investigated basal upper thermal tolerance (the highest temperature at which cessation of coordinated locomotion is detected), the extent of phenotypic plasticity and the impacts of different rates of temperature change on this trait in five species of intertidal crustaceans. The species originated from three distinct thermal regimes, incorporating sampling on South African shores and sub-Antarctic Marion Island.

We show that for intertidal crustaceans, there are significant and complex interactions among basal temperature tolerance, phenotypic plasticity and the thermal environment, which translate to very different long-term responses across species. In addition, populations from warmer latitudes have a lower warming tolerance, owing to a smaller margin between the upper thermal tolerance and the maximum microsite temperature, and have lower plasticity than those from cooler regions. These findings are robust when accounting for microsite variation within geographical locations and changes in body condition during experimental trials. Thus, this study indicates that the responses of marine organisms to ocean warming are likely to be less coherent than expected and forecasts need to incorporate explicit spatial scales and multiple approaches.

Image caption: Marion Island species examined in this study: the isopod Exosphaeroma gigas and specimens of the amphipod Hyale hirtipalma preserved after tolerance trials. Photos provided by authors.
This paper can be found online here.

 

How grasshoppers respond to road noise: Developmental plasticity and population differentiation in acoustic signalling.

Ulrike Lampe, Klaus Reinhold, Tim Schmoll  Male of the acridid grasshopper Chorthippus biguttulus. Image courtesy of Ulrike Lampe.

Anthropogenic noise is a prominent example of how humans influence the behaviour of various animal species in their natural habitats. Acoustically communicating animals produce signals to transmit information to rivals, potential mates, offspring, or even predators. These signals are frequently masked by anthropogenic noise, challenging animals to find ways of preserving information transfer under increased noise levels. Some species produce louder signals, others produce signals with elevated frequencies or elongated signals to ensure successful communication.

As reported in this journal, in a previous study we found that Chorthippus biguttulus grasshoppers from roadside populations, which are exposed to low-frequency noise pollution, produced courtship songs with higher frequency components in the range between 6-10 kHz. In the present study, we wanted to find out which mechanisms underlie these potentially adaptive differences and used a common garden approach to disentangle developmental plasticity from other possible sources of variation (i.e. genetic differentiation).

We collected grasshopper nymphs from seven roadside and five non-roadside populations and transferred them to the laboratory, where they were assigned to two different experimental treatment groups. One group was exposed to road noise recordings 24 hours a day, whereas the other group was reared under quiet conditions. Adult males were transferred to a separate, quiet room 24-72 hours before we recorded their courtship songs under standardized, quiet conditions.

Our results demonstrate that grasshoppers from roadside habitats produced signals with higher frequency maxima in the low-frequency band of their signals, corroborating the result from our previous study (see above). Intriguingly, we found that males from the noisy treatment also produced signals with elevated frequency maxima, suggesting an important and as yet unknown role of developmental plasticity in shaping song traits as a response to human-induced noise pollution. Furthermore, we found that the syllable to pause ratio, a substructure of grasshopper songs which is relevant for female mate choice, was higher in males from roadside habitats indicating a potential additional strategy to prevent masking of grasshopper courtship song by ambient noise.

Image Caption: Male of the acridid grasshopper Chorthippus biguttulus. Image courtesy of Ulrike Lampe.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Maternal and paternal contributions to pathogen resistance dependent on development stage in a whitefish (Salmonidae)

Emily S. Clark, Manuel Pompini, Lucas Marques da Cunha, & Claus Wedekind Whitefish (Coregonus palaea) at late embryonic stage (© Manuel Pompini, University of Lausanne)

The damage that an infection can cause to an individual host depends not only on the type of pathogen but also on host characteristics. Among the potentially important host characteristics are the individual’s own genetics, maternal environmental effects (i.e. non-genetic maternal contributions such as immune-relevant substances that mothers put into eggs), its developmental stage, its current condition, and its history of infections. The relative importance of these factors is difficult to determine, unless half-sib families (i.e. those having one parent in common) can be produced in vitro, and the resulting embryos can be reared separately and in large numbers under controlled laboratory conditions. Only a few vertebrates are suitable for such an experimental approach, and among them are salmonid fish (i.e. the family of fish including salmon, trout, whitefish and grayling).

We sampled a natural population of the whitefish Coregonus palaea during their spawning season, collected eggs and sperm from several adults, and used these gametes for in vitro fertilizations to produce all possible half-sib families. More than 10,000 of the resulting embryos were then singly raised under controlled laboratory conditions. Samples of each half-sib family were either kept unexposed to infections or were exposed to one of two strains of the pathogenic bacterium Pseudomonas fluorescens. The embryos were exposed at one of four different time points in order also to study the effects of developmental stage. Both strains proved to be virulent to their fish host as they reduced growth and delayed hatching. One strain also caused some mortality. Our experimental design therefore allowed us to study the separate and combined effects of genetics, maternal environmental effects, developmental stage, and pathogen strain on embryo growth and survival. We found that all these factors mattered.

Vulnerability to infection increased markedly over embryo development. This change coincided with a distinct shift in the importance of maternal environmental effects relative to genetic effects on embryo survival. Although the relative contributions of maternal environmental and genetic effects on susceptibility changed over time, the overall differences between half-sib families largely remained, i.e. some half-sib families were consistently more susceptible than others over different developmental stages. Our experiment demonstrates that the relative importance of maternal and paternal contributions to an embryo’s susceptibility to an infection varies over time.

Image caption: Whitefish (Coregonus palaea) at late embryonic stage (© Manuel Pompini, University of Lausanne).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted versionhere.

 

 

Energetic adjustments in freely breeding-fasting king penguin: does colony density matter?

Vincent A. Viblanc, Claire Saraux, Nelly Malosse and René GroscolasIncubating king penguin. Photo courtesy of Nelly Malosse.

For seabirds, reproduction is a tricky business. Those animals forage at sea but breed while fasting on land. Success therefore depends on how well they manage their energy stores. In addition, breeding often means gathering in dense, potentially stressful, colonies where aggressive neighbours actively defend small breeding territories. While the fasting capacities of seabirds have been studied in captive and non-breeding conditions, we know little about the energy adjustments of birds freely breeding in their colonial environment. This study shows that, in order to save energy during their month-long breeding fast including both courtship and incubation, sub-Antarctic male king penguins (Aptenodytes patagonicus) progressively decrease their overall body activity, but do not depress their core body temperature. Interestingly, monitoring daily changes in heart rate as a reflection of daily changes in energy expenditure revealed striking differences between males breeding early versus late in the breeding season. Early in the season, male’s heart rate was found to decrease daily during most of courtship, but to increase again 3 days before egg laying and during incubation. Late in the season however, heart rate remained stable over the same period. The heart rate increase observed in early breeding males was strongly associated with a marked increase in colony density over time, as more and more pairs gathered at the colony to breed. In contrast, no such pattern occurred in late breeding males, for which colony density was high and steady. Those intriguing findings point a suspicious finger at the role of social density in affecting the energetics of colonial seabirds and suggest a potential energy cost to breeding at high densities.

Image caption: Incubating king penguin. Photo courtesy of Nelly Malosse.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Decomposition of dung from African large herbivores is mediated by soil arthropods and the balance of nutrients.

Judith Sitters, Marc-Jacques Maechler, Peter J. Edwards, Werner Suter and Harry Olde Venterink Set-up of dung decomposition experiment in Saadani National Park, Tanzania. Fresh dung was placed in small bags on the soil surface in a woodland site. The bags were protected from animals by a fence of chicken wire. Photo credit: Judith Sitters.

In the savannas of Africa large herbivores, such as giraffe, buffalo and wildebeest are abundant and deposit their dung across the landscape. Herbivore dung contains the nutrients nitrogen (N) and phosphorus (P), which will be returned to the soil and are important for plant growth. So the decomposition of herbivore dung and especially the speed at which nutrients are released from dung are important steps in the nutrient cycle and vegetation productivity of savannas.

Dung decomposition and N and P release rates from dung are affected by the chemical composition of dung and especially the ratio of carbon (C) to the nutrients N and P. This dung C:N:P ratio differs per herbivore species and likely depends on what plant type the herbivores feed on (feeding strategy) and how they digest their food (digestive physiology). In addition dung decomposition is affected by soil arthropods, like dung beetles and termites, which feed on the dung and increase its nutrient release.

In this study we collected fresh dung from different herbivore species in a savanna in Tanzania. With this dung we measured the release rates of N and P and related them to dung C:N:P ratio and activities of soil arthropods. We showed that dung C:N:P ratio differed among herbivore species and that these differences were partly related to the herbivores’ feeding strategy and digestive physiology. The C:N:P ratio of the dung influenced the release of N and P and when N was more abundant in the dung it was released faster than P and vice versa. In contrast, soil arthropods surprisingly increased the release rate of the least abundant nutrient when they were present. This is a new finding and more studies are needed to better understand the role that dung C:N:P ratio plays in the use of dung nutrients by soil arthropods.

We concluded that dung C:N:P ratio, the presence of soil arthropods and interactions amongst these factors have a strong influence upon the availabilities of N and P in the soil and hence the functioning of savanna ecosystems.

Image caption: Set-up of dung decomposition experiment in Saadani National Park, Tanzania. Fresh dung was placed in small bags on the soil surface in a woodland site. The bags were protected from animals by a fence of chicken wire. Photo credit: Judith Sitters.
This paper can be found online here.

The article is available as accepted (not yet typeset or proofed) here.

 

 

How does a floral colour-changing species differ from its non-colour-changing congener? – a comparison of trait combinations and their effects on pollination.

Miki F. Suzuki and Kazuharu Ohashi Flowers of colour-changing (Weigela coraeensis) and non-colour-changing (W. hortensis) species. Photo credited to Miki F. Suzuki.

Ecological interactions between plants and pollinators have driven the evolution of floral traits and their combinations. Floral colour change—the retention of old, nonreproductive, rewardless, but fully turgid flowers in altered colour—is a good example of such pollinator-mediated floral evolution. This trait syndrome has been considered as a plant strategy for enhancing pollinator attraction while minimizing visits to nonreproductive flowers. Considering that the perceptive and cognitive abilities of most pollinators are basically similar, these advantages should apply in most systems. It seems paradoxical, therefore, that floral colour change occurs in only a portion of plant species.

This divergence may be explained if floral colour change adds as yet unknown costs or benefits under specific conditions. To explore such possibilities, we compared combinations of floral traits and pollination consequences between a floral colour changing (Weigela coraeensis) and a noncolour changing (W. hortensis) species in a shared environment.

Flowers of W. coraeensis secreted nectar for an initial 2-3 days and remain white, after which they persist for a few days with reddish colours and reduced nectar production. Flowers of W. hortensis also secreted nectar for the first 2-3 days. They persisted for a few more days with the same colour and reduced nectar production, but did so only when pollinators were scarce. At our site, both species retained their flowers for 4-5 days, because only W. coraeensis received sufficient pollen grains. The difference in pollination consequences can be attributed to the bees’ preference for the colour changers. In addition to their higher nectar productivity, only W. coraeensis offered bees colour difference as a visual cue to choose rewarding flowers. These results indicate that floral colour change yields an additional benefit of attracting bee-like pollinators that return preferentially to easily exploitable plants.

Based on the results, we provide a novel hypothesis to explain why colour changers and nonchangers both persist: colour changers will be successful only when the benefits of enhancing both conspicuousness and exploitability by pollinators outweigh the cost of doing so. When plants under environmental stress can increase pollinator visits solely by enhancing conspicuousness, in contrast, the cost saving can become advantageous—as in the noncolour changer, W. hortensis.

Image caption: Flowers of colour-changing (Weigela coraeensis) and non-colour-changing (W. hortensis) species. Photo credited to Miki F. Suzuki.
The article is available as accepted (not yet typeset or proofed) here.

 

 

Soil hypha mediated movement of allelochemicals: arbuscular mycorrhizae extend the bioactive zone of juglone.

Michaela Achatz, E. Kathryn Morris, Frank Müller, Monika Hilker, Matthias C.Rillig.  Tomato plants at harvest time for experiment 3 in the paper (addition of juglone and presence of a mycorrhizal fungus). Photograph by Michaela Achatz.

Allelopathy is a biological phenomenon, where plants produce natural chemical products and release them to the environment. These chemicals can influence the surrounding vegetation by affecting its growth, development, reproduction and distribution.

One of the best documented and oldest known examples of plants which produce allelochemicals is the American black walnut (Juglans nigra L. ), but other species of the family Juglandaceae also produce the chemical responsible, juglone. This toxic compound is released into the environment in different ways, like leaching into the soil or by root exudation, and can therefore reach toxic levels in the soil with potential consequences for the surrounding vegetation.

We here focus on the role of fungi inhabiting the soil, in particular on arbuscular mycorrhizal fungi, which are ubiquitous and are associated with most vascular plants. We wanted to find out if the presence of these fungi plays a significant role in soil transport processes of the allelochemical compound juglone and therefore results in growth reductions of juglone-sensitive plants. To cover a range of scales from ecological realism to high experimental control, we conducted one field study and two greenhouse experiments, in which we used tomato as a sensitive plant in various experimental settings.

Throughout this study we found increased juglone transfer if mycorrhizal fungal hyphae were present, resulting in reduced growth of tomato “target” plants.

We therefore conclude that mycorrhizal fungi play an important role in extending the zone of influence of allelopathic compounds. We suggest that the presence of soil hyphae in natural systems increase the effectiveness of allelochemical transport; this is important for understanding how allelopathy works in the field.

Image caption: Tomato plants at harvest time for experiment 3 in the paper (addition of juglone and presence of a mycorrhizal fungus). Photograph by Michaela Achatz.

here.

 

The fitness implications of adaptation via phenotypic plasticity and maternal effects.

Thomas H. G. Ezard, Roshan Prizak & Rebecca B. Hoyle A family of swans in the River Witham.  © Copyright John Bennett and licensed for reuse under this Creative Commons Licence: CC BY-SA 2.0.

Individuals need to track environmental change and ensure their behaviour and morphology are well-suited to prevailing conditions. The challenge for all individuals is to spot the most relevant cue that can correctly predict the environment. Here, we use a theoretical model that includes two ways in which individuals can modify their traits (height or weight, for example) over and above genetic transmission alone. This trait flexibility can arise from within-generation and/or maternally induced effects. The relative impacts of these forms of trait flexibility depend on the predictability of environmental change and the lag between juvenile development and adult reproduction (and therefore selection). We show how maternal effects that slow adaptation can maximise fitness by keeping more offspring closer to the target value for the trait. If the environmental change is frequent, then within-generational flexibility plays a larger role, but both forms act together to deliver well-adapted traits. We should strive to study both within- and transgenerational plasticity in the same studies.

Image caption:
The article is available as accepted (not yet typeset or proofed) here.

 

Linking microhabitat structure, morphology and locomotor performance traits in a recent radiation of dwarf chameleons.

Jessica M. da Silva, Anthony Herrel, G. John Measey, Bieke Vanhooydonck, and Krystal A. Tolley Natal Midlands dwarf chameleon (Bradypodion thamnobates). Photo provided by Krystal Tolley.

Adaptive radiation is a process where an ancestral species rapidly evolves into a multitude of new and different physical forms, often because new resources or habitats become available. The species adapt to their new environment with modified physical features to take advantage of the new environment. One way to illustrate an adaptive radiation is to look at how species, with these differing physical traits, perform in the new environments. Movement for example, is an extremely important aspect, and can include running, jumping, clinging, and climbing.

Chameleons, unlike most other lizards, move slowly and rely upon crypsis to avoid predation, but also to ambush prey. Their slow cryptic movement is augmented by specialised adaptations, including a prehensile tail and clamp-like feet that are particularly useful for clinging onto narrow branches and slowly moving between perches. We have found that a group of dwarf chameleon species from KwaZulu-Natal Province in South Africa have multiple physical forms that reflect adaptations to forest and grasslands. We measured their tail and foot grip strength on different size perches, and found that forest chameleons grip harder on broad perches than do grassland species. These performance differences correspond to their physical differences: chameleons in forested habitats (which have thick perches), possess relatively longer tails and larger feet than do chameleons in grasslands (which have thin perches), because it enables them to grip harder on the broader perches found there. These means they are adapted to the features of the habitats, and that physical differences in foot size between forms enables them to better utilize their respective habitats. The adaptive radiation in these chameleons therefore, is all about getting a good grip.

Image caption: Natal Midlands dwarf chameleon (Bradypodion thamnobates). Photo provided by Krystal Tolley

Article available in its As Accepted form (not yet typeset or proofed) here

Search the Site

Search

Site Adverts

 
Virtual Issue on Ecophysiological forecasting: predicting adaptation and limits to adaptation