Lay Summaries

The below summaries are provided by our authors to help put their research paper into context for the wider scientific community and the general public. Lay summaries for the current issue are here. You can also find all the previous lay summaries by issue, as well as summaries for articles on Early View, in the lay summaries archive.

 

Lay summaries for the current issue

 

You can also find all the previous lay summaries by issue, as well as summaries for articles on Early View, in the lay summaries archive.

 

Is the energy expenditure of free-living animals linked to their metabolic costs at rest?

Jorg Welcker, John R. Speakman, Kyle H. Elliott, Scott A. Hatch and Alexander S. KitayskyKittiwakes breeding at the study site on Middleton Island, Alaska, USA. Photo  by Jorg Welcker.

Share this summary:

 


Google+ Linkedin

Reproduction is energetically costly and the overall rate at which animals expend energy is usually highest when they rear their young. The overall rate of energy expenditure integrates the energy an animal spends to raise its offspring and to keep its own body up and running. The resting metabolic rate, on the other hand, measures the minimal energetic cost to an animal at rest to maintain its body tissues.

A widespread assumption is that an increase in parental energy expenditure requires a concurrent increase of the resting metabolic rate as higher energy intake and expenditure would need to be facilitated by larger or metabolically more active internal organs such as the heart, liver or alimentary tract. Larger or costlier metabolic machinery would, in turn, result in higher resting energetic costs. However, if changes in resting and overall energy expenditures were not inherently linked, it could be beneficial for animals to reduce their resting energetic costs as they could thus increase the amount of energy spent on raising young.

We examined whether this might be the case in free-living kittiwakes. We manipulated the energy demands of parents by increasing the number of chicks in their nests or by removing entire broods. We also manipulated energy supplies by providing some nests with supplemental food.

We found that overall and resting metabolic rates were not inherently linked: birds that raised chicks had higher overall energy expenditure yet lower resting metabolic costs compared to birds that had their broods removed. Overall energy expenditure was constrained as neither parents of enlarged broods nor those provided with unlimited food spent more energy than controls. Thus, our results suggest that reducing resting energetic costs is a strategy to increase the amount of energy allocated to raising young when overall energy expenditure is constrained. The increase in energy allocated to chick rearing caused higher levels of stress incurred by parents, suggesting that such a strategy might be costly to the parental birds.

Image caption: Kittiwakes breeding at the study site on Middleton Island, Alaska, USA. Photo by Jorg Welcker.
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.

 

Less is more: choosy wasps used in biological control show why a diverse diet is not always an asset.

Silvia Rossinelli and Sven Bacher Parasitic wasp searching for its leafminer host.

Share this summary:

 


Google+ Linkedin

The question of why species should specialize, i.e. use only a fraction of all resources available to them, has puzzled scientists and non-scientists alike. The proverbial saying "the Jack of all trades is master of none" provides an intuitive explanation. It implies that there should be a trade-off between the ability to use many different resources and the efficiency of using each single one. Thus, specialists should gain advantages on their resource compared to generalists. However, empirical tests so far have had problems showing such trade-offs and their importance for the evolution of specialization is still debated.

Parasitic wasps are one of the largest insect groups with maybe more than 1 million species. They parasitize other insect species by laying their eggs upon or inside the host’s body, where hatching larvae develop and eventually kill the host. For about 100 years, parasitic wasps have been widely used for the biological control of insect pests worldwide. Within this insect group all degrees of diet breadth are found, however, narrow host ranges prevail.

We analysed the history of parasitic wasps that were released to control pest insects and found that specialised wasps, i.e. those that can only parasitize a few pest species, establish better than generalist species with a wide host range. Thus, this is the most comprehensive test for the hypothesis that specialists are generally better able to use their hosts than generalists. The results provide the first robust support for the general importance of trade-offs in the evolution of specialization in the mega-diverse group of parasitic wasps. However, specialization is not always more advantageous; in environments where the preferred host is not always available, generalists will profit from being able to utilise a variety of different hosts.

Image caption: Parasitic wasp searching for its leafminer host.
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.

 

Food jumpstarts feather moult.

Raymond M. Danner, Russell S. Greenberg, Julie E. Danner and Jeffrey R. WaltersA swamp sparrow moulting throat, face, and crown feathers in eastern North Carolina.  Photo by Jeff Lewis, used with permission.

Share this summary:

 


Google+Linkedin

Moulting (periodic loss of old feathers and growth of new ones) is critical for many bird species, but it costs both time and energy. Moulting may interfere with other important activities, such as breeding, migration, and maintaining body heat. Therefore, the timing of moult is essential for ensuring a successful year. In birds, the prebreeding moult is especially important because it may delay breeding. The prebreeding moult is also when males of many species acquire colourful plumage that is important for attracting mates and competing with other males.

The end of the winter is a lean time for many birds because food resources have been depleted since the previous fall. We hypothesized that the scarcity of food in late winter inhibits the initiation of prebreeding moult. We experimentally tested, for the first time, if food abundance influences the timing of moult in the wild. We conducted a controlled food supplementation experiment on free-living swamp sparrows (Melospiza georgiana) preceding and during the time of natural prebreeding moult (January–March 2009, 2010).

Supplemented birds began moulting the body, face, and crown earlier than control birds (11, 14, and 8 days earlier, respectively) indicating that food abundance limits the initiation of moult. Along with interannual variation in moult timing, these results indicate that day length is not the sole cue for moult initiation. Both control and supplemented birds moulted in sequence, starting with the body, followed by the crown 9 days later, and the face 11 days later. The presence of a sequence further suggests energetic limitation of moult or possibly a strategy to moult specific regions first to ensure completion at an optimal time.

This study provides novel experimental evidence that food abundance can limit moult timing in the wild. Food limitation of moult timing could affect the timing of breeding or feather quality, and thus cascade through other life history stages in the annual cycle and ultimately affect reproductive success. These results indicate that food availability is a cue for moult initiation, possibly acting secondarily to photostimulation.

Image caption: A swamp sparrow moulting throat, face, and crown feathers in eastern North Carolina. Photo by Jeff Lewis, used with permission.
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.

 

Stress hormones regulate how the past can affect the future in wild banded mongooses.

Jennifer L. Sanderson, Andrew J. Young, Sarah J. Hodge, Solomon Kyabulima, Susan L. Walker & Michael A. Cant A banded mongoose (Mungos mungo) pup on the Mweya Peninsular, Western Uganda. Photo credit: Jennifer Sanderson.

Share this summary: Google+Linkedin

Virtually every decision that you make will affect your later life. For example, a decision to work hard can leave you tired and less likely to work hard the following day. In ecology this is called a ‘carry-over effect’. Such carry-over effects are widespread in animal populations and may explain why individuals with high parental investment in one breeding attempt often invest relatively little in a second breeding attempt.

Evidence suggests that carry-over effects arise when the energetic losses from previous parental investment persist into the next breeding attempt. However, little is known about the physiological mechanisms that regulate these effects. Here, we test the hypothesis that carry-over effects arise because working hard to raise offspring causes increased concentrations of stress hormones (glucocorticoids; GCs), which inhibit future parental investment. Our field study of wild banded mongooses provided strong support for this hypothesis, and suggests that factors known to influence an individual’s stress physiology can have lifelong impacts on reproductive behaviour and fitness.

The banded mongoose is a close relative of the meerkat and is found living in stable social groups across Central and Eastern Africa. Banded mongooses breed cooperatively; all individuals assist in offspring care even if they do not breed themselves. We collected faecal samples and behavioural observations from banded mongooses living on the Mweya Peninsular in Western Uganda to investigate if GCs mediate a carry-over effect whereby individuals that invest heavily in cooperative offspring care in one breeding attempt invest little in the next.

Banded mongooses that entered a breeding attempt with low GCs fed pups more often than individuals with high GCs, suggesting that elevated GCs inhibit offspring care. High investment in offspring care led to an increase in GCs during the breeding attempt, and this elevation persisted after the care period. Furthermore, supplementary feeding of carers led to a decrease in GCs, confirming that this GC increase is due to energetic losses. Our results provide new insight into the physiological regulatory mechanism behind carry-over effects and a better understanding of how stress associated with the past can affect behaviours in the present.

Image caption: A banded mongoose (Mungos mungo) pup on the Mweya Peninsular, Western Uganda. Photo credit: Jennifer Sanderson.
This article can be found here.

 

Nutritional geometry of the giant panda.

Yonggang Nie, Zejun Zhang, David Raubenheimer, James J. Elser, Wei Wei and Fuwen WeiPhotograph caption: Giant panda feeding on wood bamboo shoot. Photo credited to Fuwen Wei.

Share this summary: Google+Linkedin

Many studies have shown that herbivores face nutritional challenges, including plant-produced toxins and nutritionally imbalanced foods. These challenges, which can have significant influences on critical aspects of animals’ life cycles including longevity and reproduction, may become more acute under ongoing climate change. This is especially true for species that live in seasonal environments. In response to such challenges, animals have evolved behavioral, developmental, and physiological adaptations to meet their demands for various nutrients and maintain performance.

The giant panda (Ailuropoda melanoleuca) is a unique species in the order Carnivora that evolved to specialize on various species of bamboo, which are generally thought to be of poor nutritional quality due to low protein and high fiber and lignin contents. The giant panda may thus face particularly acute nutritional challenges. Previous studies have highlighted many ecological and life history characteristics that might be associated with the ability of panda populations to survive as bamboo specialists. For example, pandas have a seasonal reproductive pattern with mating in spring and birth in fall which is believed to be an ecological adaptation to different seasonal nutritional environments.

We combined behavioral observations of food selection with analysis of the calcium, phosphorus, and nitrogen (as a proxy for protein) composition of foods and matched feces, to determine how the panda's distinctive seasonal habitat choice and food selection relate to its nutritional balance. Our results showed that pandas displayed marked foraging changes, with four primary foraging periods corresponding to the annual life cycles of the two bamboo species that make up most of its diet. These foraging changes are also coupled to its seasonal migration between low and high elevations. Analysis suggests that the pattern of migration coupled with seasonal diet switches were necessary to obtain a diet balanced in calcium, phosphorus and protein, and likely play an important role in the life cycle and reproduction of giant pandas. These results have potentially important implications for habitat conservation for giant pandas, suggesting that the summer and winter habitats of giant pandas are not nutritionally interchangeable, but provide complementary nutrition required to complete the life cycle.

Image caption: Photograph caption: Giant panda feeding on wood bamboo shoot. Photo credited to Fuwen Wei.
You can find the article here.

 

Ageing gracefully: physiology but not behaviour changes with age in a diving bird.

Kyle H. Elliott, James F. Hare, Maryline Le Vaillant, Anthony J. Gaston, Yan Ropert-Coudert and W. Gary AndersonMurres in flight. Photo provided by authors.

Share this summary: Google+Linkedin

How can long-lived wild birds both work hard and live long? We examined this question by studying murres (also known as guillemots) aged 3-30 years. Murres have the highest flight costs, for their body size, of any flying animal. They dive exceptionally deep for their body size (over 150 m for five minutes). Yet they also have exceptionally long lives for their body size; they live decades longer than rabbits, which weigh roughly the same. To examine how metabolism changes with age in wild murres, and how that affects dive performance, we measured oxygen consumption, oxygen stores and dive behaviour. Both oxygen stores and oxygen consumption rate declined with age, which we suggest reduces the effect of high metabolism on ageing. In contrast, there was no change in dive performance with age; old murres dove as deep, for as long and spent as much time recovering at the surface as young murres. Thus, multiple physiological systems changed in tandem with advancing age in murres, and offset each other such that there was no detectable decline in behavioural performance. Murres were able to maintain their ‘healthspan’ into old age.

Image caption: Murres in flight. Photo provided by authors.
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.

 

Pesticide chronically affects bee foraging.

Richard J. Gill & Nigel E. RaineBumblebee foraging on clover. Photo and permission provided by Steve Gill.

Share this summary: Google+Linkedin

Bees provide an essential environmental service by pollinating many wild flowers and key agricultural crops. The importance of these critical pollinators, both economically and for continued food security, make it particularly concerning that bees are suffering global declines. Pesticide exposure has been suggested as one of many possible factors driving bee declines. Although the levels of pesticide to which bees are exposed in the field are typically not lethal to bees, they may still produce sublethal effects, such as changes in behaviour leading to problems with colony function.

In this study we investigated how two commonly used pesticides affect the foraging behaviour of individual workers of bumblebees at approximately field relevant exposure levels. We examined the responses of bees and their colonies following short-term (acute) exposure, and (chronic) exposure over an extended period of time. Bumblebees are social insects, meaning the colony consists of a queen that lays almost all the eggs, accompanied by numerous workers that help to rear the brood, protect the colony and importantly go out to forage by collecting pollen and nectar from flowers. Therefore, understanding whether pesticides impair foraging behaviour is important because this can have detrimental consequences for colony growth and reproductive success. We attached Radio Frequency Identification Tags to automatically record all foraging trips made by each bee. Using this technology we recorded the natural activity patterns of 259 foraging workers from 40 bumblebee colonies over four weeks.

This is the first study to provide data on the impacts of pesticide exposure on the day-to-day dynamics of bee foraging behaviour in the field over a prolonged period of time. Our results showed that a neonicotinoid pesticide (imidacloprid) had both acute and chronic effects on overall foraging activity. Colonies exposed to the neonicotinoid recruited foragers at a higher rate over the four week period than control colonies, an effect that appeared to be a response to impaired individual foraging efficiency. While individual foragers from control colonies improved their pollen foraging performance as they gained experience, the pollen foraging performance of bees exposed to the neonicotinoid became worse. At the colony level, we observed that the proportion of neonicotinoid exposed foragers that successfully collected pollen decreased as the experiment progressed. There was also evidence to suggest forager preferences for particular flower types were affected by neonicotinoid exposure. Our findings highlight the importance of considering prolonged exposure when assessing the risk that pesticides pose to bees.

Image caption: Bumblebee foraging on clover. Photo and permission provided by Steve Gill.
This paper can be found free online here.

 

Maternal effects influence phenotypes and survival during early life stages in an aquatic turtle.

Timothy S. Mitchell, Jessica A. Maciel and Fredric J. JanzenA hatchling painted turtle emerges from the nest after winter.

Share this summary: Google+Linkedin

Many egg-laying animals do not care for their young, but this does not mean that good mothering is not important for offspring. For such animals, there are two maternal effects that are particularly important: nest-site choice and egg size.

We explored the importance of such maternal effects in the painted turtle (Chrysemys picta). By selecting particular microhabitats at the time of nesting, the mother turtle can partially influence the abiotic conditions her eggs will experience during incubation and the hatchlings will experience as they overwinter within the natal nest. This abiotic environment is very important for two reasons: it can shape phenotypes of developing offspring via phenotypic plasticity, and it can act as a selective force. In this field experiment, we compared offspring incubating and hibernating in maternally-selected nests to those in randomly-selected nests. Our results show that mothers selected nests that were relatively open (unshaded), and this resulted in maternal nests being significantly warmer than random nests during incubation. Hatchlings from these maternal nests were longer and developed faster than their counterparts in random nests. However, the ability to modify thermal environments of the nest faded during the overwinter stage. There was a weak correlation between vegetation cover and nest temperature, and maternal and random nests experienced similar thermal environments.

We also tracked individual eggs and hatchlings, and showed that larger eggs produce larger hatchlings. These larger hatchlings had a higher probability of surviving winter, where experiencing lethally cold temperatures was a substantial source of mortality. This novel result provides further support for the “bigger-is-better” hypothesis in early life stages of freshwater turtles.

In the turtle world, three clichés ring true: mother knows best, size matters and location is everything (or at least, it is very important).

Image caption: A hatchling painted turtle emerges from the nest after winter.
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.

 

Do eggshells act like sunscreen?

Golo Maurer, Ivan Mikšík, Steven J Portugal, Mark E Hauber, Douglas Russell, Phillip CasseySong thrush eggs. Photo provided by authors..

Share this summary: Google+Linkedin

The eggs of birds have an amazing array of adaptations to ensure the safety of the embryo developing inside. Such adaptations can include camouflage of the shell to help protect against predation, special pores that allow the correct amount of air into the egg and infection-fighting pigments to help the embryo fight disease. One important aspect the shell of the egg must control is the amount of light that penetrates through to reach the embryo. Too much light penetrating the eggshell will result in lethal levels of radiation from the UV light, but too little light can cause embryo deformities and increase the likelihood of disease. Therefore, the eggshell has to ensure that just the right amount of light is allowed through the shell. Birds nest in a wide range of environments and habitats, including extreme temperatures, altitudes, in burrows, on cliffs; how does the egg of each species in differing environments make sure the right amount of light reaches the embryo? We examined how the eggshells of British breeding birds have adapted to different environments, and how different shells control the amount of light that reaches the embryo. We found that the eggs of species that nest in burrows, holes and other closed environments let more total light pass through the eggshell, compared with species that nest in the open. Specifically, we show that less light passes through thicker eggshells with greater total pigment concentrations. The pigment potentially acts like sun-block. It seems, therefore, that greater light transmission through the shell is required to assist embryonic development under low-light exposure. To make sure enough light gets through to the embryo in these dimly-lit conditions, eggs of birds that nest in burrows and holes are white, allowing more light in as there is less pigment to block the sun. For birds who have a long incubation period (exposing their eggs to the sun for longer), their eggs are often dark with pigment, letting significantly less of the potentially harmful, ultraviolet (UV) light pass through the eggshell.

Image caption: Song thrush eggs. Photo provided by authors..
This paper can be found online in its As Accepted form (not typeset or proofed) here.

 

Daily energy expenditure during lactation is strongly selected in a free-living mammal.

Quinn E. Fletcher, John R. Speakman, Stan Boutin, Jeffrey E. Lane, Andrew G. McAdam, Jamieson C. Gorrell, David W. Coltman and Murray M. Humphries Female red squirrel with one of her pups outside of her grass nest. (Photo credit: Ryan W. Taylor).

Share this summary: Google+Linkedin

Energy is a currency of life because all animals must expend it to survive and reproduce. Despite the importance of energy as a currency, we know very little about the benefits and costs associated with the amount of energy that animals expend. Past research on mammals has demonstrated that lactation is an energetically costly time of the year because females must expend energy to forage for food, and synthesize milk to raise multiple offspring. We found that the female North American red squirrels that expended the most energy during lactation had the most offspring survive to the following year (i.e. they have greater reproductive fitness). At first glance, it makes intuitive sense that there would be reproductive fitness benefits associated with expending large amounts of energy during lactation. However, our results are interesting because they raise a series of mysteries. The first set of mysteries relates to the mechanism by which elevated energy expenditure during lactation is associated with greater reproductive fitness. The most obvious mechanism is that females that raise larger litter sizes or healthier offspring (i.e. faster growing) have more offspring survive to the following year, but also need to expend more energy to do so. However, this mechanism appears not to be true because there is no relationship between a female’s energy expenditure during lactation and either its litter size or the growth rate of its offspring. Moreover, in order for juveniles to survive until the following year, they must first obtain a territory, then hoard enough cones to survive the winter, and then evade a suite predators. Our results are definitely a mystery because they suggest that if pups are raised by females that expend elevated levels of energy, that this somehow helps them to survive these ecological challenges. The second mystery relates to our finding that females that expended the most energy during lactation experienced no negative consequences. Specifically, we found that females with high levels of energy expenditure during lactation had neither reduced survival to the following year, nor a decreased ability to invest in reproduction the following year. These results are interesting because if there are benefits associated with expending energy during lactation, but no costs, why do not all females expend energy at a high rate?

Image caption: Female red squirrel with one of her pups outside of her grass nest. (Photo credit: Ryan W. Taylor).
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.

 

Subdigital adhesive pad morphology varies in relation to structural habitat use in the Namib Day Gecko.

Clint E. Collins, Anthony P. Russell, and Timothy E. Higham Rhoptropus afer pauses before ascending a granite outcrop.

Share this summary: Google+Linkedin

Locomotion is a quintessential aspect of animal life. Effective locomotor performance is crucial for many important tasks such as prey capture, mating, and predator evasion. Gecko locomotion is fascinating because of the specialized adhesive capability that allows them to live on vertical and inverted surfaces. Adhesion is finely controlled by the subdigital toe pad and the millions of microscopic, hair-like structures known as setae that are located on the bottom of each toe pad. However, this specialized behaviour and the adhesive system comes at a cost – running away from predators on level surfaces may be affected owing to the complexity and timing of adhering and detaching to surfaces during locomotion. Quantifying the interplay between escape behaviour and locomotor morphology across habitats that vary in structural composition could reveal how selection acts on locomotion at local levels.

Our study found that in habitats where escape behaviour relies on flatter surfaces, a species of gecko, Rhoptropus afer, the Namib Day Gecko, has exhibited a greatly reduced adhesive morphological system. We investigated the impact of habitat variation and escape behaviour on morphology, including the adhesive system, of Rhoptropus afer, a diurnal and cursorial (adapted to running) gecko from Namibia. Substrate incline and topographical variation are likely important for this pad-bearing gecko due to the trade-off between adhering and sprinting (i.e. using adhesion results in decreased sprint speed) that is triggered by certain inclines. We corroborate the hypothesis that the adhesive system exhibits the greatest degree of reduction in populations that utilize the flattest terrain during an escape. Our findings suggest that the adhesive apparatus is detrimental to rapid locomotion on relatively horizontal surfaces, and may thus be counterproductive to the evasion of predators in such situations.

Image caption: Rhoptropus afer pauses before ascending a granite outcrop.
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.

 

How to best assess the cold tolerance of Drosophila.

Jonas Lembcke Andersen, Tommaso Manenti, Jesper Givskov Sørensen, Heath Andrew MacMillan, Volker Loeschcke and Johannes OvergaardImage supplied by authors.

Share this summary: Google+Linkedin

Insects represent around three quarters of the world’s named species and they often play an important role in human society as pollinators, agricultural pests or carriers of disease. Insects’ distribution across the globe is partially limited by their ability to survive cold. In order to predict changes in the patterns of insect distribution across the world we need to understand how cold affects insects and how some insects survive for hours below 0°C while others die after only short exposures to low temperatures.

Many of the studies done on insect cold tolerance (temperatures that limits insects’ ability to survive, reproduce, or migrate) have been performed with fruit flies (Drosophila) utilizing several different methods to assess cold tolerance. In this study we evaluated the accuracy of cold tolerance estimates obtained using five commonly used methods. We assessed the cold tolerance of 14 Drosophila species using each of the 5 methods. An average natural latitudinal distribution and an expected minimum temperature exposure was determined for each of the species using databases with thousands of observations. These parameters were then correlated to each of the five cold tolerance measurements to investigate which method was best correlated to the actual distribution and minimum temperature exposures of the 14 species in the wild.

We found that the temperature where the flies lost their ability to move (chill coma onset), when ramping down the temperature, had a strong correlation to the environmental variables. So did measurements of survival after 2 hours of low temperature exposure (lethal temperature) as well as survival time at milder low temperatures (lethal time). However, the time it took the flies to recover from cold shock (chill coma recovery time) had a weaker correlation to the environmental variables and supercooling point, the temperature where the flies freezes over, had the weakest correlation to distribution and estimated temperature exposure.

Considering the amount of time involved and the difficulty of making the different measurements, we found that chill coma onset and lethal temperature are superior measurements when estimating cold tolerance in Drosophila.

Image caption: Image supplied by authors.
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.

Search the Site

Search

Site Adverts

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