Energy metabolism and personality in wild-caught fall field crickets

Context-dependent effects of thermal acclimation on physiological correlates of animal personality in Asiatic toads

Persistent individual variation in behaviour, or 'personality', is a widespread phenomenon in animals, and understanding the evolution of animal personality is a key task of current biology. Natural selection has been proposed to promote the integration of personality with animal 'intrinsic states', such as metabolic or endocrine traits, and this integration varies with ecological conditions. However, these external ecological modulatory effects have rarely been examined. Here, we investigate the effects of thermal acclimation on between-individual covariations between physiology and behaviour in Asiatic toads (Bufo gargarizans) along an altitudinal gradient. Our results reveal that the thermal modulatory effects on the covariations depend on the altitudinal population. Specifically, at low altitudes, between-individual covariations are highly plastic, with risk-taking behaviour covarying with baseline glucocorticoids (GCs) under warm acclimation, but risk-taking and exploration behaviour covarying with resting metabolic rate (RMR) under cold acclimation. In contrast, between-individual covariations are relatively fixed at high altitudes, with risk-taking behaviour consistently covarying with baseline GCs. Furthermore, at low altitudes, changes in covariations between RMR and personality are associated with adjustment of energy management models. Evidently, animal physiological states that determine or covary with personality can adapt according to the seasonal thermal environment and the thermal evolutionary background of populations. Our findings highlight the importance of a multi-system physiological approach to understand the evolution of animal personality.

Energy allocation is revealed while behavioural performance persists after fire disturbance

Metabolic physiology and animal behaviour are often considered to be linked, positively or negatively, according to either the performance or allocation models. Performance seems to predominate over allocation in natural systems, but the constraining environmental context may reveal allocation limitations to energetically expensive behaviours. Habitat disturbance, such as the large-scale fire that burnt wetlands of Biebrza National Park (NE Poland), degrades natural ecosystems. It arguably reduces food and shelter availability, modifies predator-prey interactions, and poses a direct threat for animal survival, such as that of the wetland specialist root vole Microtus oeconomus. We hypothesized that fire disturbance induces physiology-behaviour co-expression, as a consequence of changed environmental context. We repeatedly measured maintenance and exercise metabolism, and behavioural responses to the open field, in a root voles from post-fire and unburnt locations. Highly repeatable maintenance metabolism and distance moved during behavioural tests correlated positively, but relatively labile exercise metabolism did not covary with behaviour. At the same time, voles from a post-fire habitat had higher maintenance metabolism and moved shorter distances than voles from unburnt areas. We conclude there is a prevalence of the performance mechanism, but simultaneous manifestation of context-dependent allocation constraints of the physiology-behaviour covariation after disturbance. The last occurs at the within-individual level, indicating the significance of behavioural plasticity in the context of environmental disturbance.

Differential metabolic responses in bold and shy sea anemones during a simulated heatwave

As climate change-induced heatwaves become more common, phenotypic plasticity at multiple levels is a key mitigation strategy by which organisms can optimise selective outcomes. In ectotherms, changes to both metabolism and behaviour can help alleviate thermal stress. Nonetheless, no study in any ectotherm has yet empirically investigated how changing temperatures affect among-individual differences in the associations between these traits. Using the beadlet anemone (Actinia equina), an intertidal species from a thermally heterogeneous environment, we investigated how individual metabolic rates, linked to morphotypic differences in A. equina, and boldness were related across changing temperatures. A crossed-over design and a temporal control were used to test the same individuals at a non-stressful temperature, 13°C, and under a simulated heatwave at 21°C. At each temperature, short-term repeated measurements of routine metabolic rate (RMR) and a single measurement of a repeatable boldness-related behaviour, immersion response time (IRT), were made. Individual differences, but not morphotypic differences, were highly predictive of metabolic plasticity, and the plasticity of RMR was associated with IRT. At 13°C, shy animals had the highest metabolic rates, while at 21°C, this relationship was reversed. Individuals that were bold at 13°C also exhibited the highest metabolic rates at 21°C. Additional metabolic challenges during heatwaves could be detrimental to fitness in bold individuals. Equally, lower metabolic rates at non-stressful temperatures could be necessary for optimal survival as heatwaves become more common. These results provide novel insight into the relationship between metabolic and behavioural plasticity, and its adaptive implications in a changing climate.

CO2 scrubbing, zero gases, Keeling plots, and a mathematical approach to ameliorate the deleterious effects of ambient CO2 during 13 C breath testing in humans and animals

13 C breath testing is increasingly used in physiology and ecology research because of what it reveals about the different fuels that animals oxidize to meet their energetic demands. Here I review the practice of 13 C breath testing in humans and other animals and describe the impact that contamination by ambient/background CO2 in the air can have on the accuracy of 13 C breath measurements. I briefly discuss physical methods to avoid sample contamination as well as the Keeling plot approach that researchers have been using for the past two decades to estimate δ13 C from breath samples mixed with ambient CO2 . Unfortunately, Keeling plots are not suited for 13 C breath testing in common situations where (1) a subject's VCO2 is dynamic, (2) ambient [CO2 ] may change, (3) a subject is sensitive to hypercapnia, or (4) in any flow-through indirect calorimetry system. As such, I present a mathematical solution that addresses these issues by using information about the instantaneous [CO2 ] and the δ13 CO2 of ambient air as well as the diluted breath sample to back-calculate the δ13 CO2 in the CO2 exhaled by the animal. I validate this approach by titrating a sample of 13 C-enriched gas into an air stream and demonstrate its ability to provide accurate values across a wide range of breath and air mixtures. This approach allows researchers to instantaneously calculate the δ13 C of exhaled gas of humans or other animals in real time without having to scrub ambient CO2 or rely on estimated values.

The Role of Metabolic Phenotype in the Capacity to Balance Competing Energetic Demands

AbstractGiven the critical role of metabolism in the life history of all organisms, there is particular interest in understanding the relationship between individual metabolic phenotypes and the capacity to partition energy into competing life history traits. Such relationships could be predictive of individual phenotypic performances throughout life. Here, we were specifically interested in whether an individual fish's metabolic phenotype can shape its propensity to feed following a significant stressor (2-min exhaustive exercise challenge). Such a relationship would provide insight into previous intraspecific observations linking high metabolism with faster growth. Using a teleost fish, the barramundi (Lates calcarifer), we predicted that individuals with high standard metabolic rates (SMRs) and maximal metabolic rates (MMRs) would be faster to recover and resume feeding after exercise. Contrary to our prediction, neither SMR nor MMR was correlated with latency to feed after exercise (food was offered at 0.5, 1.5, 3, and 18 h after exercise). Only time after exercise and individual fish ID were significant predictors of latency to feed. Measurements of MMR from the same individuals (three measurements spaced 8-12 d apart) revealed a moderate degree of repeatability (R=0.319). We propose that interindividual differences in biochemical and endocrine processes may be more influential than whole-organism metabolic phenotype in mediating feeding latency after exercise.

Light/dark phase influences intra-individual plasticity in maintenance metabolic rate and exploratory behavior independently in the Asiatic toad

Background

It is well-known that light/dark phase can affect energy expenditure and behaviors of most organisms; however, its influences on individuality (inter-individual variance) and plasticity (intra-individual variance), as well as their associations remain unclear. To approach this question, we repeatedly measured maintenance metabolic rate (MR), exploratory and risk-taking behaviors across light/dark phase four times using wild-caught female Asiatic toads (Bufo gargarizans), and partitioned their variance components with univariate and bivariate mixed-effects models.

Results

The group means of maintenance MR and risk-taking behavior increased at night, while the group mean of exploratory behavior remained constant throughout the day. At night, the intra-individual variances were elevated in maintenance MR but reduced in exploration, suggesting that phenotypic plasticity was enhanced in the former but constrained in the latter. In addition, maintenance MR was not coupled with exploratory or risk-taking behaviors in daytime or at night, neither at the inter-individual nor intra-individual levels.

Conclusions

Our findings suggest that these traits are independently modulated by the light/dark phase, and an allocation energy management model may be applicable in this species. This study sheds new insights into how amphibians adapt nocturnal lifestyle across multiple hierarchy levels via metabolic and behavioral adjustments.

Effect of chronic traffic noise on behavior and physiology of plateau pikas (Ochotona curzoniae)

During the last two decades, numerous studies have shown the effects of traffic noise on animal vocal communication. However, studies on the influences of traffic noise on wildlife behavior and physiology are scarce. In the present study, we experimentally manipulated the traffic noise exposure of plateau pika, a native small mammal widely distributed in the alpine meadow of Qinghai-Tibet Plateau, to explore the effects of traffic noise exposure on its behavior and physiology. We showed that noise exposure increased the pika’s exploration and cortisol concentration (CORT) but decreased the resting metabolic rate (RMR). In addition, the relationships between RMR and exploration or CORT appeared under traffic noise treatment. This study suggests that traffic noise plays a large role in the behavior and physiology of plateau pikas and may have a long-term negative effect on the fitness of rodent populations. Generalizing these non-lethal effects to different taxa is crucial for the conservation and management of biodiversity in this increasingly noisy world.

State and physiology behind personality in arthropods: a review

In the endeavour to understand the causes and consequences of the variation in animal personality, a wide range of studies were carried out, utilising various aspects to make sense of this biological phenomenon. One such aspect integrated the study of physiological traits, investigating hypothesised physiological correlates of personality. Although many of such studies were carried out on vertebrates (predominantly on birds and mammals), studies using arthropods (mainly insects) as model organisms were also at the forefront of this area of research. In order to review the current state of knowledge on the relationship between personality and the most frequently studied physiological parameters in arthropods, we searched for scientific articles that investigated this relationship. In our review, we only included papers utilising a repeated-measures methodology to be conceptually and formally concordant with the study of animal personality. Based on our literature survey, metabolic rate, thermal physiology, immunophysiology, and endocrine regulation, as well as exogenous agents (such as toxins) were often identified as significant affectors shaping animal personality in arthropods. We found only weak support for state-dependence of personality when the state is approximated by singular elements (or effectors) of condition. We conclude that a more comprehensive integration of physiological parameters with condition may be required for a better understanding of state’s importance in animal personality. Also, a notable knowledge gap persists in arthropods regarding the association between metabolic rate and hormonal regulation, and their combined effects on personality. We discuss the findings published on the physiological correlates of animal personality in arthropods with the aim to summarise current knowledge, putting it into the context of current theory on the origin of animal personality.

Integrating humans into pace-of-life studies: The Big Five personality traits and metabolic rate in young adults

The pace-of-life syndrome (POLS) predicts that personality and metabolism should be correlated if they function as an integrated unit along a slow-fast continuum. Over the last decade, this conceptual framework has been tested in several empirical studies over a wide array of non-human animal taxa, across multiple personality traits and using standardized measures of metabolism. However, studies associating metabolic rate and personality in humans have been surprisingly scarce. Here, we tested whether there was covariation among personality scores, measured using the Big Five Inventory test, resting metabolic rate (RMR) and preferred walking speed (PWS) in a cohort of young human adults aged between 18 and 27 years old. We found a significant, negative relationship between RMR and Extraversion; less extraverted individuals had a 30% higher RMR than the most extraverted ones. No other personality traits correlated with RMR and none correlated with PWS. The negative correlation between Extraversion and RMR may suggest an allocation energy trade-off between personality and basal metabolism. Our results yielded equivocal support for the POLS and emphasized the need for more research on human to test the generality of this conceptual framework and further assess its validity.

Territoriality in Drosophila: indirect effects and covariance with body mass and metabolic rate

Territoriality (i.e., defense of a resource) is the outcome of behavioral interactions that can result in selective advantages in many vertebrates and invertebrates. Since territoriality is expressed in a social context, an individuals’ territoriality may change according to the phenotype of the opponents that they are confronted with (termed “indirect effects”). Defending a territory may also confer energetic costs to individuals, which could be reflected in their standard metabolic rate (SMR), a key component of an ectotherms’ energy budget. Here, we measured territoriality using dyadic contests, body mass, and SMR using flow-through respirometry, twice in each of 192 adult male Drosophila melanogaster. Territoriality, body mass, and (whole-animal) SMR were all significantly repeatable. However, essentially all the among-individual variation in SMR was shared with body mass, as indicated by a very strong among-individual correlation (rind) between body mass and SMR. The among-individual correlation between territoriality and SMR also tended to be positive, suggesting the presence of underlying metabolic costs to territoriality. Although indirect effects on territoriality were present but weak (accounting for 8.4% of phenotypic variance), indirect effects on territoriality were negatively and significantly correlated with body mass. This indicates that larger individuals tended to suppress their opponents territoriality. Variation among individuals in their ability to suppress territoriality in others was not associated with their own territoriality or SMR.

High-Stakes Decision-Making by Female Crickets (Gryllus texensis): When to Trade In Wing Muscles for Eggs

AbstractResource-intensive traits, such as dispersal and reproduction, can be difficult to express simultaneously because of resource limitations. One solution is to switch between resource-intensive behaviors. Such phenotypic plasticity is one strategy that organisms use to funnel resources from one expensive trait to another. In crickets (Gryllus texensis), the development and maintenance of flight muscles reduce resource availability for reproduction, leading to physiological trade-offs between the two traits. Long-winged female G. texensis can histolyze their wing muscles, resulting in increased egg production, but they can then no longer fly. Using a diet that mimics food availability in the field, we found that long-winged females adopted one of the three following strategies: early reproduction, intermediate reproduction, and late reproduction. Some late reproducers maintained their flight capability until the end of their natural life span and laid few eggs. If females lost the ability to fly (i.e., their hind wings are removed), they laid eggs earlier, leading to increased reproductive output. However, other environmental cues (e.g., an increased number of mates, increased oviposition substrate quality, or a bout of dispersal flight) had no effect. Late-reproducing females laid 96% fewer eggs than early reproducers, suggesting that late reproduction exacts a huge fitness cost. Nevertheless, some females maintain their flight muscles to the end of their natural life span in both the lab and the field. We suggest that the ability to fly allows for bet hedging against an environmental catastrophe (e.g., drought or flood). This benefit may help explain the persistence of late-reproducing long-winged females, despite the cost of this choice. As climate change increases drought and flood in Texas, late dispersal may be one factor that helps this species survive in the future. An increased understanding of factors that maintain seemingly low fitness strategies can help us predict the resilience of species under climate change.

Water warming increases aggression in a tropical fish

Our understanding of how projected climatic warming will influence the world's biota remains largely speculative, owing to the many ways in which it can directly and indirectly affect individual phenotypes. Its impact is expected to be especially severe in the tropics, where organisms have evolved in more physically stable conditions relative to temperate ecosystems. Lake Tanganyika (eastern Africa) is one ecosystem experiencing rapid warming, yet our understanding of how its diverse assemblage of endemic species will respond is incomplete. Herein, we conducted a laboratory experiment to assess how anticipated future warming would affect the mirror-elicited aggressive behaviour of Julidochromis ornatus, a common endemic cichlid in Lake Tanganyika. Given linkages that have been established between temperature and individual behaviour in fish and other animals, we hypothesized that water warming would heighten average individual aggression. Our findings support this hypothesis, suggesting the potential for water warming to mediate behavioural phenotypic expression through negative effects associated with individual health (body condition). We ultimately discuss the implications of our findings for efforts aimed at understanding how continued climate warming will affect the ecology of Lake Tanganyika fishes and other tropical ectotherms.

Metabolic and behavioral adaptations of greater white-toothed shrews to urban conditions

The global trend of urbanization is creating novel challenges for many animal species. Studies investigating behavioral differences between rural and urban populations often report a general increase in risk-taking behaviors in urban populations. According to the most common energy management model (the performance model), behaviors that increase access to resources, such as aggression and boldness, and behaviors that consume net energy, like locomotion and stress responses, are both positively correlated to resting metabolic rate (RMR). Thus, we expect urban populations to not only exhibit a higher level of risk-taking behavior but also a higher RMR. However, these interactions remain poorly investigated. Our main goal was to analyze the relationship between RMR and risk-taking behaviors in the greater white-toothed shrew (Crocidura russula) in rural versus urban populations. Trapped shrews were brought to captivity where we measured RMR, boldness, and exploration rate three times in each individual. Our findings revealed that urban shrews were indeed bolder and more exploratory, but contrary to our expectations, their RMR was lower than that of rural shrews. This is likely explained by differences in the environmental conditions of these two habitats, such as higher ambient temperatures and/or lower prey availability in cities. When looking at each population separately, this relationship remained similar: urban shrews with a higher RMR were less bold, and rural shrews with a higher RMR showed a lower exploration rate. We conclude that the energetic strategy of C. russula is dependent on the environmental and observational context and cannot be explained by the performance model.

Repeatability of behavior and physiology: No impact of reproductive investment

Animals have well-documented individual differences in their behaviour, including in their response to stressful stimuli. The physiological bases for the repeatability of these traits has been the focus of much research in recent years, in an attempt to explain the mechanistic drivers for behavioral syndromes. Whilst a range of studies have demonstrated repeatable individual differences in physiological traits, little is known about potential trade-offs between reproductive investment and the physiological responses to subsequent stressors. We therefore sought to test the behavioral and physiological responses of male zebra finches (Taeniopygia guttata) to a novel environment, quantifying a series of repeated "temporal reaction norms" before and after reproduction. Given that reproductive investment is costly both in time and energy, it is likely to affect expression of behavioral and physiological traits. We hypothesised that reproductive investment would impact the consistency of these temporal reaction norms. Specifically, we predicted that individuals which invested more in reproduction would show altered rates of habituation to a stressful stimulus. Therefore, we quantified temporal reaction norm components (i.e., intercept and slope) of two behaviours and metabolic rate (MR) within and among individuals before and after a breeding season. We found that individuals consistently differed in how their locomotor and feeding activity increased upon introduction into a novel environment and also how their MR decreased after being handled and confined within the metabolic chamber. We also found that the slope of the feeding activity reaction norm was negatively correlated with stress-induced corticosterone levels at the within-individual level. Finally, in contrast to our prediction, we found that neither the intercept nor slope of the reaction norms were influenced by the reproductive effort (the number of fledglings produced) displayed by individual males. This suggests that the substantial individual variation in the expression of physiological and behavioural traits is not plastic with respect to the immediate consequences of reproductive investment. This study is the first quantification of metabolic rate reaction norms and their relationships with fitness, which represents an important first step towards understanding the evolutionary significance of instantaneous habituation to stressful and novel situations.