Lay Summaries Archive
Read Lay Summaries from previous volumes of Functional Ecology here:
- Volume 27 Issue 6
- Volume 27 Issue 5
- Lay summaries for Volume 27 Issue 4 including the Special feature: Mechanisms of Plant Competition and the Extended Spotlight: Responses to global climate change: Insights from organismal physiology.)
- Volume 27 Issue 3 (including lay summaries for the Special Feature: Plant-Microbe-Insect Interactions).
- Volume 27 Issue 2
- Volume 27 Issue 1 (including lay summaries for the Special Feature: The Ecology of Stress)
- Volume 26 Issue 6 (including lay summaries for the Special Feature: Invasions and Infections)
- Volume 26 Issue 5
- Volume 26 Issue 4
- Volume 26 Issue 3
- Volume 26 Issue 2
- Volume 26 Issue 1
- Volume 25 Issue 6
- Volume 25 Issue 5
Early View Lay Summaries
- Structural, compositional and trait differences between native and non-native dominated grassland patches Molinari & D'Antonio
- Maternal effects of carotenoid supplementation in an ornamented cichlid fish Brown et al
- Breeding timing in relation to quality at hatching affect the survival of king penguin chicks. Stier et al
- Garden plants for flower-visiting insects-- quantifying variation in attractiveness Garbuzov & Ratnieks
- Slow animals, fast invaders: the strain of snails that invaded the world. Nespolo et al
- Are there evolutionary consequences of plant-soil feedbacks along soil gradients? Schweitzer et al
- Thinner whales reduce energy investment in their foetus. Christiansen et al
- Predator-prey dynamics and the plasticity of predator body size DeLong et al
- Exercise changes behaviour Sinclair et al
- Elevated maternal temperature enhances offspring disease resistance in Daphnia magna Garbutt et al
- Herbivores change how shrubs affect ecosystems services Soliveres & Eldridge
- Adaptive maternal and paternal effects: gamete plasticity in response to parental stress Jensen et al
- Temporal patterns in immunity, infection load, and disease susceptibility: understanding the drivers of host responses in the amphibian-chytrid fungus system. Gervasi et al
- Stem-stored water: a good strategy for plants to survive short dry periods but not long droughts Richards et al
- Nectar Seekers Sneak Insect Snacks! Clare et al
- Herbivores in a small world: long-term movement patterns of herbivorous coral reef fishes are defined by small-world network dynamics Fox & Bellwood
- Adaptive maternal plasticity in yellow dung flies Buser et al
- Heterogeneity of reproductive age increases the viability of semelparous populations Acker et al
- Niche overlap in relation to resource availability and heterogeneity Price et al
- The costs and benefits of cooperation among plants Schöb et al
- Cues from a specialist herbivore increase tolerance to defoliation in tomato Korpita et al
- Increased atmospheric carbon dioxide concentrations increase ecosystem carbon flow Staddon et al
- Aphid honeydew alters plant defence responses Schwartzberg & Tumlinson
- Mycorrhizal fungi and aphids affect each other via their common host plant Babikova et al
- Sex-dependent evolution of life-history traits following adaptation to climate warming Rogell et al
- The forces driving tropical trees co-occurrence in communities Yang et al
- Learned recognition of introduced predators determines survival of tadpole prey. Polo-Cavia and Gomez-Mestre
- Sexual size dimorphism requires a corresponding sex difference in development time: a meta-analysis in insects Teder
- The impact of thermal fluctuations on reaction norms in specialist and generalist parasitic wasps. Foray et al
- Does reproduction increase free-radical damage? It depends on what you measure! Xu et al
- Better living through chemistry: the importance of chemical-producing symbionts to marine invertebrates Lopanik
- How do alien dandelions exclude their native congeners? Nishida et al
- Microbes hidden battles may determine disease in their hosts May and Nelson
- Defensive symbiosis in the real world—advancing ecological studies of heritable protective bacteria in aphids and beyond Oliver at al
- Ants, bees, and wasps team up with microbial symbionts for defense Kaltenpoth and Engl
- Symbiotic fungi are the source of important chemicals in some plants Panaccione et al
Structural, compositional and trait differences between native and non-native dominated grassland patches.
Nicole A. Molinari and Carla M. D'Antonio
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.
Alexandria C. Brown, Heather M. Leonard, Kevin J. McGraw and Ethan D. Clotfelter
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.
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 Criscuolo
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.
Mihail Garbuzov and Francis L. W. Ratnieks
Bees and other pollinating insects are declining in many countries. Many people are concerned and want to help reverse this decline, but do not know how. One way that the general public can help is via their gardens, by growing ornamental plants that are also attractive to flower-visiting insects. Although individual gardens are relatively small, collectively they comprise a substantial area. City parks also contain ornamental flower beds.
Which plant varieties are attractive to flower-visiting insects? Given the great public interest, many lists of recommended plants have recently been produced. For example, in 2011, the UK’s Royal Horticultural Society produced a “Perfect for Pollinators” list and logo. Many plants now sold in UK garden centres now bear this logo. But where did this information come from? On a closer look, it appears that these lists are based largely on personal experiences, opinions and anecdotes.
This study is an attempt to put these recommendations on a firmer scientific footing. We planted an experimental garden of summer-flowering garden plants on the University of Sussex campus. Thirty-two varieties were compared, each in two patches of 1×1m, in 2011 and 2012. All varieties were easy to purchase and considered attractive to humans. Throughout both summers we made repeated counts of the numbers of insects on each patch. As they were counted the insects were also identified into nine categories (honey bee, 4 sub-categories of bumblebees, other bees, hoverflies, butterflies & moths, other insects).
The most simple and striking result was that garden plants vary enormously, approximately 100-fold, in their attractiveness to insect flower-visitors. The most numerous insects by far were bees which comprised over 84% of all insects seen. Bumblebees 47-62% and honey bees 26-32% were the most numerous, with all other bees only 3-5%. After the bees, the next most abundant were hoverflies, 7-10%. Butterflies and moths were only 1-3%. Sixteen species of butterflies were seen.
Our results also compared different varieties of the same plant type. In the case of Dahlia, varieties with open flowers were much more attractive than those with “cactus” or “pom-pom” flowers, in which the pollen and nectar producing areas were reduced and inaccessible. In the case of lavenders, the traditional blue colour was not better than white or pink. However, the hybrid Lavandula × intermedia varieties attracted more insects than the species L. angustifolia, possibly because they were larger and had more blooms.
Flowers attractive to bees and other insects are attractive from a human perspective and are no harder to grow or more expensive. Therefore, choosing insect-attractive varieties over less attractive varieties is a zero cost option, and is a practical and simple way of helping bees and other flower-visiting insects in gardens and parks.
Image caption: Popular garden plants. Photo provided by authors.
You can find the Early View Article free online here: Garbuzov, M., Ratnieks, F. L. W. (2013), Quantifying variation among garden plants in attractiveness to bees and other flower-visiting insects. Functional Ecology. doi: 10.1111/1365-2435.12178.
Roberto F. Nespolo, José Luis Bartheld, Avia González, Andrea Bruning, Derek A. Roff, Leonardo D. Bacigalup & Juan Diego Gaitán-Espitia
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
Jennifer A. Schweitzer, Ivan Juric, Tess F. J. van de Voorde, Keith Clay, Wim H. van der Putten and Joseph K. Bailey
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.
Fredrik Christiansen, Gisli A. Víkingsson, Marianne H. Rasmussen and David Lusseau
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.
John P. DeLong, Torrance C. Hanley, and David A. Vasseur
Body size is among the most distinctive features of an organism. From bacteria to redwood trees, size clearly plays a role in how living things get along in the world, but understanding why organisms have a particular body size and how to predict the evolution of size in a changing world is still very difficult. Why, for example, do animals tend to be larger at northern latitudes, have some humans gotten taller over the 20th century, and are many ectotherms (cold-blooded animals) getting smaller as the climate warms? Answering these and many similar questions depends on a satisfactory linking of the fitness consequences of particular body sizes to the environmental signals that vary in space and time.
In our study, we developed a simple model to predict changes in body size in response to a changing ecological context. We paired a simple optimality criterion for body size with the dynamics of population abundance that occur in predator-prey relationships. The optimality concept is that the ‘best’ size to be is the size which matches the bodily demand for resources with the environmental supply. Since both the demand for resources and the supply of those resources are tightly linked to the factors that govern population dynamics, the model allows us to predict how the body size of a predator will change as the abundance of the predator and its prey change through time.
We tested our model against data for the single-celled protist predator Didinium nasutum consuming the protist Paramecium aurelia. We tracked changes in the abundance of the prey and the predator as well as the predator’s body size over several generations and found strong agreement between the data and the model. Interestingly, the predator’s size ranged ten-fold over the course of the experiment due to environmental rather than genetic signals (the predators were all clonal descendants of a single individual).
Image caption: photo provided by authors.
Elektra L. E. Sinclair, Carolina R. Noronha de Souza, Ashley J. W. Ward & Frank Seebacher
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
Jennie S. Garbutt, Jennifer A. Scholefield, Pedro F. Vale and Tom J. Little
All organisms face being attacked by pathogens and predators. The ability to protect oneself depends on quite a few things, including your genetic makeup, but also for example how much you have been able to eat, and therefore how much energy you have. Previously, we have shown that how much your mother has had to eat also influences the ability to mount a defence against a parasite. This is an example of a trans-generational (or maternal) effect. Here we show that the ability to defend against parasites is also influenced by the temperature experienced by your mother. To do this, we examined a crustacean waterflea known as Daphnia. We placed the waterfleas at 15°C, 20°C & 25°C and tested the ability of their babies to resist infection by a bacterial parasite called Pasteuria ramosa. We found that Daphnia mothers held at a higher temperature were more resistant to P. ramosa infection, and that this was especially true if we also restricted their food. In other words, warm mothers kept on a strict diet gave birth to babies with the best immunity. We think this makes sense for a waterflea, because in the small ponds where they usually live, the greatest threat from parasites happens to be when food gets low and temperatures rise in the hottest months of the year. Responding to these environments by giving birth to babies with improved immunity is likely to give these babies an advantage when there are lots of parasites about.
Image caption: Daphnia. Photo provided by authors.
Santiago Soliveres and David J. Eldridge
An increase in shrub cover or density in semiarid ecosystems, known as shrub encroachment, is a worldwide phenomenon that affects the diversity of plants and animals, and a number of services that such ecosystems provide to human beings, such as carbon sequestration or forage production for livestock grazing, a major land use in most semiarid systems across the Earth. However, the general perception of shrub encroachment as a process leading to land degradation is at odds with the generally positive effects of individual shrubs registered worldwide. We attempted to understand what factors lay behind the contrasting positive effects of individual shrubs vs. the general view of dense shrub stands as degraded systems. Thus, we compared the effect of individual shrubs across contrasting levels of shrub cover or grazing pressure, because both increasing shrub cover and grazing are likely to reduce the positive effect that individual shrubs have on their understorey. We found that the positive effect of shrubs on plant diversity, biomass and soil fertility did not decline with shrub covers in the landscape as high as 50%, which are among the maximum registered for the study area.
Thus, our first result is that the encroachment of woody species is not necessarily bad for the provision of services by ecosystems, but rather it might depend on which species are increasing in cover. For example, negative effects of shrub encroachment on diversity and ecosystem services seem more likely to occur for trees than for shrubs, or for plants able to fix nitrogen rather than those that cannot. Our second result was that increases in the number of herbivores had a big influence on how shrubs affect the ecosystem. Generally, grazing reduces the number and biomass of plant species, and alters the distribution of nutrients in the soil; these effects of grazing reduced the ability of shrubs to improve the environment beneath them when occurring at high densities. Overall, our results help us to understand the consequences of shrub encroachment on semiarid environments, especially how the effects on biodiversity and ecosystem services depend on land use, which species is encroaching and how dense are the stands.
Image caption: This picture shows how the landscape changes as shrubs get denser (known as shrub encroachment). Images taken by the authors from Google Earth.
Natasha Jensen, Richard M. Allen, & Dustin J. Marshall
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
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.
Anna E. Richards, Ian J. Wright, Tanja I. Lenz and Amy E. Zanne
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.
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
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. Bellwood
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) .
Claudia C. Buser, Paul I. Ward, Luc F. Bussière
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.
Paul Acker, Alexandre Robert, Romain Bourget and Bruno Colas
The size of any population in a natural environment is necessarily limited by intraspecific competition because no resource is unlimited. The temporal variation of resource availability (food, reproductive sites…) and of other environmental factors (temperature, parasite density…) results in an unpredictable variation of demographic rates, such as survival or fecundity, called environmental stochasticity. Both intraspecific competition and environmental stochasticity are major processes affecting population size. Previous research has shown that, all else being equal in a given habitat, smaller carrying capacity and higher environmental stochasticity tend to decrease population size and to increase extinction risk.
Individuals are more likely to compete for the same resource or to be affected similarly by a fluctuation of the environment when they are of the same age class or life history stage, e.g. adult birds competing for nesting sites, or seedlings affected by drought. Then, in this context, a population consisting of individuals of various ages or stages at any time would fluctuate less and have lower extinction risk than a population where all individuals are fully synchronized. Such desynchronization can be favored in populations where demographic rates vary among individuals of the same cohort due to genetic variation or a spatially heterogeneous environment.
We examined these simple ideas by modeling the dynamics of populations with various levels of demographic heterogeneity in the age at reproduction among individuals that reproduce only once (semelparous). Heterogeneity among individuals was generated by allowing individuals to take one of several life paths in the life cycle, simulating spatially heterogeneous environmental conditions, generally not considered in population models.
We observed that heterogeneity substantially reduces the level of demographic synchrony and the extinction risk of populations where intraspecific competition or environmental stochasticity (or both) were implemented. Although we calibrated the models with realistic distributions of demographic parameters from a rare cliff-dwelling plant, Centaurea corymbosa, we used a life cycle that could easily be adapted to other semelparous organisms such as annual plants, many arthropods, salmon, octopuses… In such species, neglecting heterogeneity leads to overestimation of the level of synchronization among individuals, which may in turn strongly bias viability assessments in realistic environments.
Image caption: Flowering plant of Centaurea corymbosa. Heterogeneity of reproductive age among individuals can strongly affect the dynamics and viability of semelparous populations.
Jodi N. Price, Antonio Gazol, Riin Tamme, Inga Hiiesalu and Meelis Pärtel
The idea that heterogeneity should promote species richness through niche partitioning (niche theory) has a long history in ecology. It follows that heterogeneity should not only increase species diversity, but species should also be different in traits as they occupy different ‘niches’, although to our knowledge this has never been tested. Recently, it has become apparent that the effect of heterogeneity depends on the scale of observation – with a number of studies on plants finding that small-scale heterogeneity can actually decrease diversity compared to homogenous conditions. The mechanisms for this reduction are related to plant root extent and the size of the resource patches, as well as root foraging and behaviour. Specifically, if resource patches are smaller than the root extent of most species, then faster growing species, or those with greater precision in root foraging, can access resource-rich patches depleting them of nutrients and potentially excluding smaller species. In this case, we expect species to be more similar as traits associated with resource acquisition and competitive ability are favoured. We experimentally tested the effect of nutrient heterogeneity at two scales (large and small patches) on species dissimilarity using plant traits compared to homogenous conditions.
We conducted a greenhouse experiment with 5 treatments, with 3 levels of homogenous soil nutrient availability (low, medium, high) and scale of resource heterogeneity (at medium fertility, large-scale and small-scale). We measured community weighted means and niche overlap for 3 functional traits (specific leaf area, leaf area and plant height) to determine if species are more different than expected in relation to the experimental treatments.
For all traits, we found the heterogeneity treatments had similar mean traits and overlap (similarity) as the high fertility homogenous treatment and differed significantly from the homogeneous treatment of the same overall fertility level. Hence, if high fertility patches are available, faster growing species are able to access soil resources, affecting niche overlap in the same way as if nutrients were enriched homogenously.
Image caption: Photo of greenhouse experiment. Picture provided by authors.
Christian Schöb, Iván Prieto, Cristina Arma and Francisco I. Pugnaire
p>Plants often grow in association with other plants. Such close association implies that species interact with each other, either negatively competing for space and resources or positively improving soil conditions or attracting pollinators. Consequently, co-occurrence of plants generally goes along with both positive and negative effects on each other.
The high-elevation ecosystems of the Sierra Nevada Mountains in southeastern Spain are particularly stressful for plants, since water and soil are scarce and temperatures are low. In such environments, plant associations have been shown to be drivers of species survival and increased biodiversity. Consequently, cooperation among plants can be very important for ecosystem services on which we humans rely.
With this study we looked more into the details of cooperation between the alpine cushion plant Arenaria tetraquetra ('lion skin' or 'chubby cheeks' in Spanish) and three herbaceous plants that frequently grow inside the cushion. As expected from previous work on alpine cushion plants, the three plants profit from this association, and we show that this is a consequence of the positive influence cushion plants have on water availability. Cushion plants accrue organic material that works like a sponge in holding water. This water is then available not only for the cushion itself but also to other plants associated with the cushion.
By contrast, the cushion plant suffered from the association and showed diminished reproduction. The hosted plants likely reduced the amount of water available for the cushion, accounting for the negative effect observed. Interestingly, whereas cushion plants without associated plants generally showed increased reproduction with increasing well-being, cushion plants with a high number of associated plants did not show such a direct relationship, which suggest that reproduction of cushions with associated species is not only reduced, but also largely independent of the available resources. We argue that plants suffering from the association with other plants invest their resources into either growth or defence to fend off competing species and increase survival, rather than investing into reproduction.
Cooperation of plants in stressful environments may often be someone’s benefit at another one’s cost, similar to parasitism, and those plants paying the cost for being cooperative may have developed adaptations to this cost in order to survive and reproduce.
Image caption: The cushion plant Arenaria tetraquetra ssp. amabilis and the two beneficiary species Plantago nivalis and Lotus corniculatus ssp. glacialis in the Sierra Nevada Mountains, southeastern Spain. Photo credit: Christian Schöb.
Timothy Korpita, Sara Gómez and Colin M. Orians
In agricultural and natural settings plants are often attacked by herbivores that have the capacity to cause extensive defoliation. While it is well known that plants respond to damage by inducing the production of chemicals that deter herbivores, more recent evidence indicates that plants undergo a shift in resource allocation that results in the accumulation of carbon and nitrogen resources in stem and root tissue (tissues inaccessible to herbivores). Could this mean plants use herbivore cues to alter their growth and reproduction in ways that increase their tolerance to damage? Here we investigated whether prior herbivore damage confers a subsequent growth advantage on tomato following defoliation. To test this we mechanically wounded and also treated plants with either regurgitant of caterpillars of the specialist moth Manduca sexta (=herbivore cue) or deionized water (=damage control) and compared their response to undamaged controls. After five days of treatment we found that plants treated with regurgitant had less chlorophyll in the remaining leaves and grew the least (but had thicker stems). However, regurgitant treated plants recovered more quickly from the defoliation treatment, producing more new leaves and flowers compared to undamaged and mechanically damaged treatments. While these results support the hypothesis that changes in resource allocation induced by a specialist herbivore increase regrowth ability in a domesticated plant, future studies should compare these results to wild relatives in an ecologically relevant context..
Image caption: Photo of regrowth in a defoliated tomato.
Philip L. Staddon, Sabine Reinsch, Pål Axel Olsson, Per Ambus, Andreas Lüscher and Iver Jakobsen
Current changes in climate are widely noticed as hotter summers, colder winters, extreme rain events or drier summers. Furthermore, especially since the industrial revolution, the atmospheric carbon dioxide concentration has been constantly rising. Even though carbon dioxide is invisible to our eyes, increased concentrations in the atmosphere affect natural processes considerably through plant uptake of carbon dioxide from the air. A change in this uptake might further influence processes involved in carbon transport within plants as well as into and within the soil. We investigated if and how increased atmospheric carbon dioxide concentrations change the distribution of carbon in an ecosystem. We used a specific label of the carbon to trace its fate in the plant-soil system.
Our experiment was conducted in a Swiss grassland where plants have been exposed to increased atmospheric carbon dioxide concentrations for ten years. We examined how this increased concentration affected the uptake of carbon dioxide by plants and how this carbon was utilized by soil bacteria and fungi. We observed that more atmospheric carbon dioxide was taken up by plants and pushed through soil bacteria and fungi. However, the distribution of carbon in the soil microbial community remained unchanged, and our results therefore suggest that processes involved in carbon transport and utilization are not or only little changed when atmospheric carbon dioxide concentrations increase. This result has implications for theories on the mitigation of increasing carbon dioxide concentrations by carbon storage in the soil.
Image caption: Experimental ring in the grassland vegetation in the Swiss grassland of ETH Zurich: The black poles of the ring release carbon dioxide to increase the atmospheric carbon dioxide concentration of the grassland within the ring. The diameter of the ring is 23 m. Photo credit: Manuel Schneider.
Ezra G. Schwartzberg and James H. Tumlinson
When plants are attacked by herbivorous insects they react by ramping up the production of chemical defences. These defences include chemical toxins as well as the release of airborne volatiles that can attract natural enemies of the attacking herbivore. Many of these chemical defences are orchestrated by the plant hormone jasmonic acid (JA). Naturally, of course, herbivores have evolved countermeasures to combat these plant defences.
The research presented here demonstrates the ability of pea aphids, Acyrthosiphon pisum, to feed on broad bean plants, Vicia faba, without eliciting the JA response that would normally lead to an increase in chemical defence. Furthermore, we show how honeydew excreted by aphids onto plant tissue inhibits the induction of JA and induces production of the plant hormone salicylic acid, which has been shown to interfere with JA-related defences. We tested this by applying honeydew collected from aphids onto plants prior to artificial wounding. While the wounding simulated herbivore damage and resulted in JA accumulation, the addition of honeydew inhibited the plant’s defence response. Hence, aphid honeydew acted to limit the plant’s defences towards herbivores. We conclude that aphids may be able to protect themselves from plant defences by excreting honeydew onto plants as they feed.
Image caption: Pea aphids feeding on broad bean plants.
Zdenka Babikova, David Johnson, Lucy Gilbert, Toby Bruce, John A Pickett and Sarah Y Dewhirst
Most plants interact with both arbuscular mycorrhizal (AM) fungi, which increase nutrient acquisition, and herbivores such as aphids, which drain nutrients from plants. Both AM fungi and aphids can affect plant metabolic pathways and may influence each other by altering the condition of the shared host plant. Here we test simultaneous effects of AM fungi on aphids (bottom-up effects), and of aphids on AM fungi (top-down effects). We hypothesised that: (i) attractiveness of plants to aphids is regulated by induced changes in production of plant volatile organic compounds (VOCs) triggered by AM fungi or aphids; (ii) aphids reduce AM fungal colonisation; and (iii) AM fungal colonisation affects aphid development. To test for the strength of bottom-up and top-down effects, separate treatments enabled establishment of mycorrhizas either before or after aphids were added to plants. VOCs produced by plants were used to (i) test their attractiveness to aphids, and (ii) identify the compounds causing attraction. We also measured plant growth and nutrition, AM fungal colonisation and aphid reproduction. AM fungi increased the attractiveness of plants to aphids, and this effect tended to prevail even for aphid-infested plants. However, both attractiveness, production of plant VOCs and aphid population growth depended on the timing of AM fungal inoculation. Aphids had a negative effect on mycorrhizal colonisation, plant biomass and nutrition. Our data show that below- and above-ground organisms can interact by altering the quality of their shared host plant even though there is no direct contact between them. Plant interactions with herbivores and AM fungi operate in both directions: AM fungi have a key bottom-up role in insect host location by increasing the attractiveness of plant VOCs to aphids, whereas aphids inhibit formation of AM symbioses.
Image caption: Pea aphids feedign on broad bean (top). Arbuscular mycorrhizal fungi colonising roots of broad bean (bottom).
Björn Rogell, William Widegren, Lára R. Hallsson, David Berger, Mats Björklund and Alexei A. Maklakov
There is tremendous variation in lifespan across the animal kingdom, and in almost all species, the sexes differ in their lifespan. How and why do these differences in lifespan evolve? Many studies have shown that long lifespan is associated with the ability to withstand harsh environments. Change in environmental conditions are often stressful because animals are out of sync with the new environments. It implies that animals striving in novel stressful environments may evolve longer lifespan. It is tempting to think of such animals as “super organisms” as they both live longer and are better at withstanding harsh conditions. However, this is generally far from being the case as such animals are likely to experience some kind of trade-off, such as having fewer offspring or growing slower than their short-lived and less robust relatives. Current increase in global temperature is thus expected to affect animal lives and prompt rapid evolutionary change in how long animals are able to live, how they grow and reproduce. We studied the effects of slowly increasing temperature on how lifespan, fecundity and growth evolve in a very wide-spread small insect, a seed beetle. We found that beetles living in high temperature evolved a longer lifespan in males, but not in females. Surprisingly, populations from novel thermal environment also had higher fecundity than their counterparts living in unchanged conditions. It is possible that the reason why both sexes did not live longer when evolving under novel conditions is that the females are paying a price for increased fecundity. We suggest that differences in lifespan between the sexes may evolve indirectly when changes in the environment exert selection on other traits.
Image caption: Seed beetles. Photo provided by Lena Rönn.
Jie Yang, Guocheng Zhang, Xiuqin Ci, Nathan G. Swenson, Min Cao, Liqing Sha, Jie Li, Carol C. Baskin, J. W. Ferry Slik and Luxiang Lin
Historically, ecologists are interested in the forces that permit species to co-occur in communities. Increasingly, methods based on plant traits and evolutionary information are popular in this research area. That is, are plants more likely to co-occur if they are functionally similar, or if they are related (not always the same thing)? However, there remains the challenge of successfully applying this method across plant sizes, spatial scales and habitats in a single analysis.We performed this analysis using 10 plant traits and evolutionary information at the molecular level for more than 400 tree species found in a 20-ha tropical forest plot in southwest China. In this analysis, we used six spatial scales (subplot sizes) (e.g. 5 m × 5 m, 20 m × 20 m, 50 m × 50 m) , three size classes (the range of diameters at tree breast height) (1-5 cm, 5-15 cm, and 15 cm and above) and six distinct habitat types (e.g. valley, slope, plateau) described in the plot.
The relative importance of species competition and environmental effects is expected to vary across size classes, spatial scales and habitats. Specifically, we expect species competition should be more pronounced than environmental effects at finer spatial scales within habitats and at larger size classes, due to local thinning of similar individuals or an accumulation of this effect through time. Our results demonstrate that functionally similar species co-occur across size classes, spatial scales and habitats in this plot, indicating the importance of the environment in governing the co-occurrence of tree species in communities. There was also evidence that species competition may play a dominant role in structuring tree communities in less stressful habitats, while environment effects are more prevalent in stressful habitats. Our results support the hypothesis that environmental effects are more important at larger scales while species competition is more important on smaller scales.
Image caption: View of overlooking the research plot from the near mountain top. Photo credit: Xiaoxue Mo.
Nuria Polo-Cavia and Ivan Gomez-Mestre
The introduction of alien species outside their original range is one of the greatest threats to biodiversity. In particular, alien predators are considered to be one of the major causes of decline and extinction of prey species. Amphibians –the most vulnerable group of vertebrates with ~41% of species endangered– are especially vulnerable to the introduction of new predators because they often present complex life cycles with aquatic eggs and larvae that are consumed in large amounts by aquatic alien predators. Tadpoles of many amphibian species are capable of innately responding to the presence of chemical cues from native predators through changes in morphology and behaviour. In contrast, tadpoles are generally incapable of recognising cues from introduced predators with which they have not shared a long evolutionary past. This lack of adaptive responses to alien predators is considered a major cause of global amphibian declines.
The red swamp crayfish, Procambarus clarkii, is one of the most harmful invasive species in aquatic systems worldwide, with major ecological impacts on native amphibian populations through intense predation of eggs and tadpoles. Here we investigated in a series of behavioural experiments the potential for learned predator recognition to reduce the impact of this invasive crayfish. We first showed that naïve tadpoles of the western spadefoot toad, Pelobates cultripes, are not capable of innately recognising water-borne predator cues from the red swamp crayfish, whereas they readily reduce their activity rate when facing a common native predator (dragonfly nymphs). Then we show that tadpoles can learn to recognise novel cues from the invasive predator as a threat through experience, and that this acquired predator recognition makes a difference to tadpoles’ survival. Our results show for the first time a quantifiable effect of learned predator recognition on survival rates of amphibian larvae against an exotic, globally introduced predator. Moreover, this learning-mediated behavioural plasticity might lead the way for native amphibians towards adaptation to novel predators.
Image caption: Procambarus clarkii extracted from a pond where native amphibians commonly breed. Photo by Ivan Gomez-Mestre.
Sexual size dimorphism requires a corresponding sex difference in development time: a meta-analysis in insects
Sex differences in body size (= sexual size dimorphism; SSD) are ubiquitous in animals. Females are the larger sex in most insects, spiders, and cold-blooded vertebrates while males tend to be larger in birds and mammals. According to the prevailing view, size differences between males and females primarily reflect the adaptation of males and females to their different reproductive roles. Nevertheless, the evolution of sexual size dimorphism cannot be fully understood without knowledge of how females and males diverge in body size during development from egg to adult.
In principle, sex differences in body size may arise in just three non-exclusive ways: through sex differences in birth size, growth rate or development time, or any combination of these three factors. In insects, there is little evidence for sex differences in the egg or hatchling size, whereas sex differences in growth rate and development time have repeatedly been reported. Nevertheless, in spite of the small number of alternatives the relative role of these options is far from clear.
In this study, I used a comprehensive literature-derived database on 169 insect species to examine the importance of sex differences in larval development time as a determinant of sexual size dimorphism. The results indicate that sex differences in larval development time are crucial in the development of sexual size dimorphism. First, in most species, the larger sex takes longer to complete its larval development. In strongly size-dimorphic species, this correspondence is nearly universal. Second, within a diverse array of insect families, sex differences in larval development times are largest in the most size-dimorphic species. The reported evidence thus suggests that the evolution of any considerable level of sexual size dimorphism is rarely possible without a more-prolonged development of the larger sex.
Image caption: Photo taken by Anu Tiitsaar.
Vincent Foray, Emmanuel Desouhant, Patricia Gibert
Climate changes affect both the mean and the variability of thermal conditions. The impacts of these two components on organisms have to be understood to predict the consequences of climate changes on biodiversity. This is particularly true for cold-blooded animals, including insects, as they are highly sensitive to temperature. Sensitivity of insects to temperature is classically described by nonlinear functions, named thermal reaction norms, obtained by measuring various performance traits like fecundity and survival at different constant temperatures. These performance traits increase from low to intermediate temperatures, reach a maximum at their optimal temperature, and then decrease rapidly under warm conditions. This pattern tends to vary among species, populations and also according to the trait. The impact of fluctuating temperatures on thermal reaction norms is largely unclear with studies finding a beneficial, detrimental or no effect of thermal fluctuations.
Here we compare the effects of constant and fluctuating thermal regimes having the same mean temperature on an insect, the parasitoid Venturia canescens. Further, we ask whether the effect of thermal fluctuations can be predicted by a mathematical property of nonlinear functions, Jensen’s Inequality. This property suggests that the effect of thermal fluctuations depends on the curvature of the reaction norm. The effects of thermal regimes were tested on the wasp during its development in its host, the Mediterranean Flour Moth Ephestia kuehniella. We studied two populations of V. canescens that express contrasted sensitivity to temperature (a generalist and a specialist strategy), and analyzed both performance traits and energetic reserves of the wasps.
We show that thermal fluctuations decrease the performance traits, and that this effect changes according to the mean temperature and the population. As predicted by the Jensen’s inequality, the curvature of the reaction norm defines the phenotypic change induced by development under fluctuating thermal conditions. An experiment in the field confirms that the two populations respond differently to thermal fluctuations, but that energetic reserves are not affected by thermal fluctuations.
Image caption: A female parasitoid wasp, Venturia canescens, probing the substrate with its ovipositor to find hosts. The female parasitoid lays its eggs in Lepidopteran larvae, like the Mediterranean Flour Moth, Ephestia kuehniella, a pest of stored products. Photo by François Débias, CNRS.
Yan-Chao Xu, Deng-Bao Yang, John R. Speakman, De-Hua Wang
Having more babies is advantageous because it makes your genes more common in the future, so more babies should be selected by natural selection. Why then do some animal species have only a very few offspring? The main reason is that having babies is costly and makes it more likely that the parent animal will die. If animals have lots of babies they die quicker and hence their lifetime production of offspring may actually be lower. It is better therefore for an animal to optimise its reproduction so as to maximise total produced over a whole lifespan. Ecologists have known about this for a long time and the study of these trade-offs and how the optimal solutions are found is called life history theory.
But why exactly does having more offspring make you die quicker? It is important to find this out because our ability to predict how the trade-off might change in response to things like climate change depend on knowing why the trade-off is there.
One idea is that if reproductive individuals put all their energy into reproducing, they may have less energy to spend on other things, such as protecting themselves from harmful compounds that are produced as a by-product of metabolism. In fact reproduction may deliver a double-whammy by increasing production of the harmful by-products while diminishing the ability to defend against them.
By products that may be important are oxygen free radicals which damage the components of our body (oxidative stress), making us more likely to malfunction and die. So if free radicals are an important part of the mechanism, then during reproduction oxidative damage will be increased. Some previous studies carried out in the field have shown that oxidative stress is higher when animals reproduce, but animals studied in the laboratory often show the opposite, i.e. damage is either unchanged or actually goes down when animals reproduce. One big potential factor in this field v lab difference, previously largely ignored, is that people working in the field have measured damage in blood samples (which are easier to collect) while in the lab people have mostly looked at damage in actual tissues. Could it be that the difference between lab and field is just due to different tissues being analysed?
We measured damage during reproduction in blood and the liver in the same individuals . In the blood the damage went up (just like previous field studies based on blood) and in the liver the damage went down (just like in lab studies that previously looked at livers). So our study shows that the result you get depends on the tissue you measure. This has major implications for our interpretations of previous work in this area because we don’t know yet what is more important – tissue damage or blood damage. It also tells us that sampling just one tissue is inadequate to answer the question.
Image caption: Brandt’s vole. Photo by DeHua Wang.
Special Feature: Defensive Symbiosis
Better living through chemistry: the importance of chemical-producing symbionts to marine invertebrates
Nicole B. Lopanik
Symbiosis can play an important role in marine ecosystems: for example, coral reefs depend on the beneficial interaction between corals and symbiotic algae that provide nutrition for the host. High levels of predation in marine habitats like coral reefs have selected for another, but less well-known, type of symbiosis. Many invertebrate animals in the ocean such as sponges, soft corals, bryozoans, and tunicates live in areas where predation pressure is high, but have no apparent physical defenses. In these cases, the animals are often protected from predators by distasteful chemicals. As animals are typically not adept at natural product biosynthesis, microbial symbionts housed within the organism are charged with producing compounds that deter predation on the host in exchange for a stable habitat. Phylogenetically diverse hosts and symbionts can take part in these defensive chemical symbiotic relationships, illustrating their importance in marine systems. In this review, I discuss how researchers discover and study defensive symbiosis in the marine environment, and how new technologies can be utilized to learn more about these relationships. Research has shown that these symbioses can represent a complex coevolutionary history between symbiont, host, and predator. More detailed studies of interactions between the host and symbiont will provide a greater understanding of the intricacies of these mutualisms. Furthermore, these symbiont-produced compounds can sometimes be potential drug candidates, so elucidating how the two partners cooperate may help facilitate large-scale production for pharmaceutical development.
The marine bryozoan, Bugula neritina, has an uncultured symbiont that produces natural products, bryostatins, which protect the host from predators. The reddish-purple B. neritina colony, attached to a solitary tunicate, was collected from a floating dock in Beaufort, North Carolina, USA. Photo credit: Jonathan Linneman.
Sachiko Nishida, Masahiro M. Kanaoka, Keisuke Hashimoto, Koh-Ichi Takakura and Takayoshi Nishida
There are many reports of native plant displacement by closely-related alien species, but the exclusion mechanisms are poorly understood. A candidate mechanism that has attracted recent attention is “reproductive interference”, defined as any kind of negative interaction between species during the reproductive process. Reproductive interference may, for example, reduce seed production by one of the species, and may occur during the transfer of pollen between flowers, while pollen tubes are growing in pistils, or after hybridization. Details of the process are particularly relevant in considerations of ecological impacts of aliens on native species.
We studied the details of reproductive interference in Japanese dandelions through examination of a contrasting pair of species that react differently to the presence of the alien dandelion Taraxacum officinale. The Japanese native species T. japonicum is vulnerable to reproductive interference exerted by T. officinale and has been largely displaced by this alien. A second native species, T. longeappendiculatum, is impervious to alien interference and coexists with T. officinale. We applied a series of hand-pollinations to these two Japanese native dandelions and compared pollen tube behaviors between them. We specifically searched for differences between the native species after application of alien pollen to their flowers.
In the flowers of T. japonicum, the vulnerable species, alien pollen tubes usually grew right down the pistils and reached the ovaries. However, in most of the flowers of T. longeappendiculatum, the impervious species, alien pollen tubes stopped growing part way and did not access the eggs. Producing a viable hybrid between T. japonicum and T. officinale is reportedly rare, and we suggest that T. japonicum suffers from alien reproductive interference by failing to prevent alien pollen tube penetration of their eggs, thus ensuring missed opportunities for fertilization by pollen of the native species.
An increasing number of studies suggest reproductive interference as a mechanism driving the displacement of native plant species by alien relatives. Details of the process and its impact in the wild will contribute to devising means by which reproductive interference can be avoided, thus protecting natives from negative alien impacts.
Image caption: A native Japanese dandelion, Taraxacum longeappendiculatum, is impervious to the alien reproductive interference, but how. Photo credit: Sachiko Nishida.
Special Feature: Defensive Symbiosis
Georgiana May and Paul Nelson
All organisms, include us human beings, harbor many unseen microbes; tiny but diverse organisms. The entire collection of microbes within a host is called the “microbiome”. While microbes are most famous for causing disease, some help their host obtain nutrients and some fight off disease. We call the latter group “defensive mutualists”. In this paper we discuss why evolutionary biologists and ecologists think that microbes help or hurt their host, and why some microbes may switch from preventing to causing disease. We use our work in maize with its pathogen, Ustilago maydis and defensive mutualist, Fusarium verticillioides, to illustrate how these organisms interact with each other to prevent or allow disease. We compare this system to others such as ants that carry protective bacteria with them, insects that pollinate flowers but may also eat seeds, and fungi that protect grasses from animals that eat the plant, but also slow the plant’s growth. We conclude that the “balance of power”, i.e. the extent to which microbes either cause or prevent disease, may depend in large part on the other microbes inside the host. If these microbes are fighting each other for a plant’s resources, they might do so by trying to be the first to kill the plant. If the microbes work together to get what they need from the plant, they are also less likely to kill the plant.
Image caption: Photo of system supplied by author.
Special Feature: Defensive Symbiosis
Defensive symbiosis in the real world—advancing ecological studies of heritable protective bacteria in aphids and beyond
Kerry M. Oliver, Andrew H. Smith and Jacob A. Russell
Nearly all insects are faced with attack by pathogens, parasites and predators, which can kill or harm them if they are unable to deploy effective defenses. Diverse and complex means to avoid or survive enemy attack have thus evolved and are encoded in the would-be-victims’ genomes. A growing body of work, however, shows that infection with particular symbiotic bacteria can also provide protection. In insects, many of these bacterial defenders are heritable –passed from mother to offspring, but occasionally also jump within and among host species, instantly transforming the defensive capabilities of recipients.
Here we review the heritable, protective bacterial symbionts of insects, a hyper-diverse group of medically, agriculturally, and ecologically important animals. Laboratory studies show that diverse bacterial species protect various insect hosts against every major type of natural enemy. While the mechanisms of symbiont-based defense are often unknown, some produce toxins and others ‘prime’ the host immune system, increasing protection against subsequent invaders. Despite these benefits, protective symbionts are often in flux at intermediate levels within insect populations, suggesting changing costs and benefits over time. In general, though, little is known about the effectiveness and ecologies of protective symbionts in natural populations, and we discuss a range of experiments that should help us to understand these interactions. The results of this future work have implications for immunity across many plants and animals and for the control of insect pests whose natural enemies may be often thwarted by covert, defensive microbes.
Image caption: The parasitic wasp Aphidius ervi attacking a pea aphid.
Special Feature: Defensive Symbiosis
Martin Kaltenpoth and Tobias Engl
Insects encounter a multitude of natural enemies, ranging from vertebrate and invertebrate predators to parasites and microbial pathogens. Many species in the insect order Hymenoptera (the ants, bees, and wasps) are especially vulnerable to pathogen infection, because they – like humans – live in large societies that allow detrimental fungi, bacteria and viruses to spread, and/or because they develop in underground nests, surrounded by a plethora of potentially dangerous soil microbes. To counteract these threats, insects have evolved mechanical, chemical and behavioral defenses as well as a complex immune system. In addition to the host‘s own defenses, however, some Hymenoptera team up with protective microbial helpers.
As more and more insect-bacteria symbioses are being discovered, it becomes increasingly clear that such defensive alliances constitute an integral part of insect ecology. In leaf-cutter ants and beewolf wasps, symbiotic bacteria produce mixtures of antibiotics that protect the food resources or the developing offspring against pathogenic fungi. Bumblebees cultivate intestinal microbes that fend off a parasitic protozoan, a close relative to the causative agent of human sleeping sickness. And parasitic wasps that develop in living caterpillars team up with symbiotic viruses to protect themselves against the caterpillar’s immune response. Thus, protective symbioses can be important in a variety of different contexts, and the study of such interactions not only yields insights into an as yet little-understood aspect of insect biology, but may also provide new ideas for sustainable control of increasingly resistant human pathogens. After all, with the help of their symbionts, some insects have successfully combated pathogenic microbes for millions of years.
Image caption: Female beewolf wasp (Philanthus coronatus) with prey. Beewolves team up with symbiotic bacteria that produce antibiotics and thereby protect the wasp offspring against detrimental microbes. Photo: M. Kaltenpoth.
Special Feature: Defensive Symbiosis
Daniel G. Panaccione, Wesley T. Beaulieu and Daniel Cook
Many plants live in mutually beneficial partnerships (symbioses) with fungi that inhabit internal tissues of the plant. These beneficial fungi, known as endophytes, often produce chemicals that protect the plant from insects and grazing animals. The host plant, in turn, provides nutrients and a protected place in which the fungus can live. In some cases of symbioses, the fungus never leaves its host plant; it grows from generation to generation through seeds of the plant. In other cases, fungi may be spread infectiously from one plant to another. In this article we review and summarize the published scientific work on symbiotic fungi that produce noteworthy chemicals in plants. Plants containing these fungi have been known to naturalists or agriculturalists for centuries as being poisonous or as sources of biologically active chemicals; however, research has shown that in the cases that we summarize, symbiotic fungi (as opposed to the plants themselves) are the sources of the important chemicals. Published work indicates that plants and fungi from different families participate in these symbiotic partnerships and that partnerships between plants of different families and their symbiotic fungi arose independently on different occasions. The data also indicate that the ability of the fungus-produced chemicals to protect plants from insects may have been an important factor in the establishment of symbioses between endophytic fungi and plants. We propose that scientists need to further study the possibility that other important chemicals associated with plants may be produced by previously undetected symbiotic fungi in those plants.
Image caption: Leaves of Ipomoea asarifolia lacking (top) or containing (bottom) symbiotic fungus Periglandula ipomoeae.
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