Evaluating cognition and thermal physiology as components of the pace-of-life syndrome

Integrating behavioural thermoregulatory strategy into the animal personality framework using the common lizard, Zootoca vivipara as a model

The study of consistent between-individual behavioural variation in single (animal personality) and across two or more behavioural traits (behavioural syndrome) is a central topic of behavioural ecology. Besides behavioural type (individual mean behaviour), behavioural predictability (environment-independent within-individual behavioural variation) is now also seen as an important component of individual behavioural strategy. Research focus is still on the 'Big Five' traits (activity, exploration, risk-taking, sociability and aggression), but another prime candidate to integrate to the personality framework is behavioural thermoregulation in small-bodied poikilotherms. Here, we found animal personality in thermoregulatory strategy (selected body temperature, voluntary thermal maximum, setpoint range) and 'classic' behavioural traits (activity, sheltering, risk-taking) in common lizards (Zootoca vivipara). Individual state did not explain the between-individual variation. There was a positive behavioural type-behavioural predictability correlation in selected body temperature. Besides an activity-risk-taking syndrome, we also found a risk-taking-selected body temperature syndrome. Our results suggest that animal personality and behavioural syndrome are present in common lizards, both including thermoregulatory and 'classic' behavioural traits, and selecting high body temperature with high predictability is part of the risk-prone behavioural strategy. We propose that thermoregulatory behaviour should be considered with equal weight to the 'classic' traits in animal personality studies of poikilotherms employing active behavioural thermoregulation.

Learning with lacertids: Studying the link between ecology and cognition within a comparative framework

Cognition is an essential tool for animals to deal with environmental challenges. Nonetheless, the ecological forces driving the evolution of cognition throughout the animal kingdom remain enigmatic. Large-scale comparative studies on multiple species and cognitive traits have been advanced as the best way to facilitate our understanding of cognitive evolution, but such studies are rare. Here, we tested 13 species of lacertid lizards (Reptilia: Lacertidae) using a battery of cognitive tests measuring inhibitory control, problem-solving, and spatial and reversal learning. Next, we tested the relationship between species' performance and (a) resource availability (temperature and precipitation), habitat complexity (Normalized Difference Vegetation Index), and habitat variability (seasonality) in their natural habitat and (b) their life history (size at hatching and maturity, clutch size, and frequency). Although species differed markedly in their cognitive abilities, such variation was mostly unrelated to their ecology and life history. Yet, species living in more variable environments exhibited lower behavioral flexibility, likely due to energetic constrains in such habitats. Our standardized protocols provide opportunities for collaborative research, allowing increased sample sizes and replication, essential for moving forward in the field of comparative cognition. Follow-up studies could include more detailed measures of habitat structure and look at other potential selective drivers such as predation.

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.

How to behave when marooned: the behavioural component of the island syndrome remains underexplored

Animals on islands typically depart from their mainland relatives in assorted aspects of their biology. Because they seem to occur in concert, and to some extent evolve convergently in disparate taxa, these changes are referred to as the 'island syndrome'. While morphological, physiological and life-history components of the island syndrome have received considerable attention, much less is known about how insularity affects behaviour. In this paper, we argue why changes in personality traits and cognitive abilities can be expected to form part of the island syndrome. We provide an overview of studies that have compared personality traits and cognitive abilities between island and mainland populations, or among islands. Overall, the pickings are remarkably slim. There is evidence that animals on islands tend to be bolder than on the mainland, but effects on other personality traits go either way. The evidence for effects of insularity on cognitive abilities or style is highly circumstantial and very mixed. Finally, we consider the ecological drivers that may induce such changes, and the mechanisms through which they might occur. We conclude that our knowledge of the behavioural and cognitive responses to island environments remains limited, and we encourage behavioural biologists to make more use of these 'natural laboratories for evolution'.

Two stressors are worse than one: combined heatwave and drought affect hydration state and glucocorticoid levels in a temperate ectotherm

Heatwaves and droughts are becoming more intense and frequent with climate change. These extreme weather events often occur simultaneously and may alter organismal physiology, yet their combined impacts remain largely unknown. Here, we experimentally investigated physiological responses of a temperate ectotherm, the asp viper (Vipera aspis), to a simulated heatwave and drought. We applied a two-by-two factorial design by manipulating the daily temperature cycle (control vs. heatwave) and the water availability (water available vs. water-deprived) over a month followed by exposure to standard thermal conditions with ad libium access to water. Simulated heatwave and water deprivation additively increased mass loss, while water deprivation led to greater plasma osmolality (dehydration). Mass gain from drinking after the treatment period was higher in vipers from the heatwave and water-deprived group suggesting that thirst was synergistically influenced by thermal and water constraints. Heatwave conditions and water deprivation also additively increased baseline corticosterone levels but did not influence basal metabolic rates and plasma markers of oxidative stress. Our results demonstrate that a short-term exposure to combined heatwave and drought can exacerbate physiological stress through additive effects, and interactively impact behavioral responses to dehydration. Considering combined effects of temperature and water availability is thus crucial to assess organismal responses to climate change.

Bold and bright: shy and supple? The effect of habitat type on personality-cognition covariance in the Aegean wall lizard (Podarcis erhardii)

Animals exhibit considerable and consistent among-individual variation in cognitive abilities, even within a population. Recent studies have attempted to address this variation using insights from the field of animal personality. Generally, it is predicted that animals with "faster" personalities (bolder, explorative, and neophilic) should exhibit faster but less flexible learning. However, the empirical evidence for a link between cognitive style and personality is mixed. One possible reason for such conflicting results may be that personality-cognition covariance changes along ecological conditions, a hypothesis that has rarely been investigated so far. In this study, we tested the effect of habitat complexity on multiple aspects of animal personality and cognition, and how this influenced their relationship, in five populations of the Aegean wall lizard (Podarcis erhardii). Overall, lizards from both habitat types did not differ in average levels of personality or cognition, with the exception that lizards from more complex habitats performed better on a spatial learning task. Nevertheless, we found an intricate interplay between ecology, cognition, and personality, as behavioral associations were often habitat- but also year-dependent. In general, behavioral covariance was either independent of habitat, or found exclusively in the simple, open environments. Our results highlight that valuable insights may be gained by taking ecological variation into account while studying the link between personality and cognition.

Learning in non-avian reptiles 40 years on: advances and promising new directions

Recently, there has been a surge in cognition research using non-avian reptile systems. As a diverse group of animals, non-avian reptiles [turtles, the tuatara, crocodylians, and squamates (lizards, snakes and amphisbaenids)] are good model systems for answering questions related to cognitive ecology, from the role of the environment on the brain, behaviour and learning, to how social and life-history factors correlate with learning ability. Furthermore, given their variable social structure and degree of sociality, studies on reptiles have shown that group living is not a pre-condition for social learning. Past research has demonstrated that non-avian reptiles are capable of more than just instinctive reactions and basic cognition. Despite their ability to provide answers to fundamental questions in cognitive ecology, and a growing literature, there have been no recent systematic syntheses of research in this group. Here, we systematically, and comprehensively review studies on reptile learning. We identify 92 new studies investigating learning in reptiles not included in previous reviews on this topic - affording a unique opportunity to provide a more in-depth synthesis of existing work, its taxonomic distribution, the types of cognitive domains tested and methodologies that have been used. Our review therefore provides a major update on our current state of knowledge and ties the collective evidence together under nine umbrella research areas: (i) habituation of behaviour, (ii) animal training through conditioning, (iii) avoiding aversive stimuli, (iv) spatial learning and memory, (v) learning during foraging, (vi) quality and quantity discrimination, (vii) responding to change, (viii) solving novel problems, and (ix) social learning. Importantly, we identify knowledge gaps and propose themes which offer important future research opportunities including how cognitive ability might influence fitness and survival, testing cognition in ecologically relevant situations, comparing cognition in invasive and non-invasive populations of species, and social learning. To move the field forward, it will be immensely important to build upon the descriptive approach of testing whether a species can learn a task with experimental studies elucidating causal reasons for cognitive variation within and among species. With the appropriate methodology, this young but rapidly growing field of research should advance greatly in the coming years providing significant opportunities for addressing general questions in cognitive ecology and beyond.

Individual variation in cognitive style reflects foraging and anti-predator strategies in a small mammal

Balancing foraging gain and predation risk is a fundamental trade-off in the life of animals. Individual strategies to acquire, process, store and use information to solve cognitive tasks are likely to affect speed and flexibility of learning, and ecologically relevant decisions regarding foraging and predation risk. Theory suggests a functional link between individual variation in cognitive style and behaviour (animal personality) via speed-accuracy and risk-reward trade-offs. We tested whether cognitive style and personality affect risk-reward trade-off decisions posed by foraging and predation risk. We exposed 21 bank voles (Myodes glareolus) that were bold, fast learning and inflexible and 18 voles that were shy, slow learning and flexible to outdoor enclosures with different risk levels at two food patches. We quantified individual food patch exploitation, foraging and vigilance behaviour. Although both types responded to risk, fast animals increasingly exploited both food patches, gaining access to more food and spending less time searching and exercising vigilance. Slow animals progressively avoided high-risk areas, concentrating foraging effort in the low-risk one, and devoting >50% of visit to vigilance. These patterns indicate that individual differences in cognitive style/personality are reflected in foraging and anti-predator decisions that underlie the individual risk-reward bias.