Early social isolation disrupts adult personality expression in group-living mites

Animal personalities are characterized by intra-individual consistency and consistent inter-individual variability in behaviour across time and contexts. Personalities abound in animals, ranging from sea anemones to insects, arachnids, birds, fish and primates, yet the pathways mediating personality formation and expression remain elusive. Social conditions during the early postnatal period are known determinants of mean behavioural trait expressions later in life, but their relevance in shaping personality trajectories is unknown. Here, we investigated the consequences of early social isolation on adult personality expression in plant-inhabiting predatory mites Phytoseiulus persimilis. These mites are adapted to live in groups. We hypothesized that transient experience of social isolation early in life, that is, deprivation of any social contact during a sensitive window in the post-hatching phase, has enduring adverse effects on adult personality expression. Newly hatched mites were transiently reared in isolation or in groups and tested as adults for repeatability of various within-group behaviours, such as movement patterns and mutual interactions including sociability, defined as the propensity to associate and interact benignly with conspecifics, and activity patterns when alone. Groups composed of individuals with the same or different early-life experiences were repeatedly videotaped and individual behaviours were automatically analysed using AnimalTA. Social experiences early in life had persistent effects on mean behavioural traits as well as adult personality expression, as measured by intraclass correlation coefficients (indicating repeatability). On average, isolation-reared females moved at higher speeds, meandered less, kept greater distances from others and had fewer immediate neighbours than group-reared females. Group-reared females were highly repeatable in inter-individual distance, moving speed, meandering and area explored, whereas isolation-reared females were repeatable only in the number of immediate neighbours. Activity, quantified as the proportion of time spent moving within groups, was only repeatable in group-reared females, whereas activity, quantified as the proportion of time spent moving when alone, was only repeatable in females reared in isolation. Strikingly, also the early-life experiences of male mates influenced personality expression of mated females, with isolation-reared males boosting the repeatability of behavioural traits of group-reared females. Overall, our study provides evidence that a transient phase of social isolation during a critical period early in life has lasting effects that extend into adulthood, impairing adult personality expression. These effects should cascade upward, changing the phenotypic composition and diversity within populations.

Exploring behavioral traits over different contexts in four species of Australian funnel-web spiders

Australian funnel-web spiders are arguably the most venomous spiders in the world, with much research focusing on this aspect of their biology. However, other aspects related to their life history, ecology and behaviour have been overlooked. For the first time, we assessed repeatability, namely risk-taking behaviour, aggressiveness and activity in the contexts of predation, conspecific tolerance and exploration of a new territory in four species of Australian funnel-web spiders: two are closely related, Hadronyche valida and H. infensa, and two have overlapping distributions but occupy different habitats, H. cerberea and Atrax robustus. We also compared behaviors between species. At the species level, we found that H. valida showed consistency in risk-taking behavior when exposed to a predator stimulus, aggressiveness against conspecifics, and exploration of a new territory. In contrast, in the other species, only A. robustus showed repeatability in the context of exploration of a new territory. These results suggest that some behavioral traits are likely more flexible than others, and that the repeatability of behaviors may be species-specific in funnel-webs. When we compared species, we found differences in risk-taking behavior and defensiveness. This study provides novel insights to understanding variation in behavioral traits within and between species of funnel-web spiders, suggesting that some behavioral traits are likely context and/or species dependent, as a result of their evolutionary history. These findings provide key insights for understanding the ecological role of behavior and venom deployment in venomous animals, and a greater understanding of behavior in these medically significant and iconic spiders that are of conservation concern.

Aquatic and Terrestrial Invertebrate Welfare

Invertebrates are a diverse group of animals that make up the majority of the animal kingdom and encompass a wide array of species with varying adaptations and characteristics. Invertebrates are found in nearly all of the world's habitats, including aquatic, marine, and terrestrial environments. There are many misconceptions about invertebrate sentience, welfare requirements, the need for environmental enrichment, and overall care and husbandry for this amazing group of animals. This review addresses these topics and more for a select group of invertebrates with biomedical, economical, display, and human companionship importance.

Sex-specific life-history strategies among immature jumping spiders: Differences in body parameters and behavior

Selection forces often generate sex-specific differences in various traits closely related to fitness. While in adult spiders (Araneae), sexes often differ in coloration, body size, antipredator, or foraging behavior, such sex-related differences are less pronounced among immatures. However, sex-specific life-history strategies may also be adaptive for immatures. Thus, we hypothesized that among spiders, immature individuals show different life-history strategies that are expressed as sex-specific differences in body parameters and behavioral features, and also in their relationships. We used immature individuals of a protandrous jumping spider, Carrhotus xanthogramma, and examined sex-related differences. The results showed that males have higher mass and larger prosoma than females. Males were more active and more risk tolerant than females. Male activity increased with time, and larger males tended to capture the prey faster than small ones, while females showed no such patterns. However, females reacted to the threatening abiotic stimuli more with the increasing number of test sessions. In both males and females, individuals with better body conditions tended to be more risk averse. Spiders showed no sex-specific differences in interindividual behavioral consistency and in intraindividual behavioral variation in the measured behavioral traits. Finally, we also found evidence for behavioral syndromes (i.e., correlation between different behaviors), where in males, only the activity correlated with the risk-taking behavior, but in females, all the measured behavioral traits were involved. The present study demonstrates that C. xanthogramma sexes follow different life-history strategies even before attaining maturity.

Conditional on the social environment? Roots of repeatability in hormone concentrations of male guinea pigs

Individual differences in behavioral and physiological traits among members of the same species are increasingly being recognized as important in animal research. On the group level, shaping of behavioral and hormonal phenotypes by environmental factors has been reported in different taxa. The extent to which the environment impacts behavior and hormones on the individual level, however, is rather unexplored. Hormonal phenotypes of guinea pigs can be shaped by the social environment on the group level: pair-housed and colony-housed males differ systematically in average testosterone and stressor-induced cortisol levels (i.e. cortisol responsiveness). The aim of the present study was to evaluate whether repeatability and individual variance components (i.e. between- and within-individual variation) of hormonal phenotypes also differ in different social environments. To test this, we determined baseline testosterone, baseline cortisol, and cortisol responsiveness after challenge in same-aged pair-housed and colony-housed guinea pig males over a period of four months. We found comparable repeatability for baseline cortisol and cortisol responsiveness in males from both social conditions. In contrast, baseline testosterone was repeatable only in males from colonies. Interestingly, this result was brought about by significantly larger between-individual variation of testosterone, that was not explained by differences in dominance rank. Individualized social niches differentiated under complex colony, but not pair housing, could be an explanation for this finding.

Complex sexual-social environments produce high boldness and low aggression behavioral syndromes

Introduction

Evidence of animal personality and behavioral syndromes is widespread across animals, yet the development of these traits remains poorly understood. Previous research has shown that exposure to predators, heterospecifics, and urbanized environments can influence personality and behavioral syndromes. Yet, to date, the influence of early social experiences with conspecifics on the development of adult behavioral traits is far less known. We use swordtail fish (Xiphophorus nigrensis), a species with three genetically-determined male mating strategies (courtship display, coercion, or mixed strategy) to assess how different early-life social experiences shape adult behavioral development.

Methods

We raised female swordtails from birth to adulthood in density-controlled sexual-social treatments that varied in the presence of the type of male mating tactics (coercers only, displayers only, coercers and displayers, and mixed-strategists only). At adulthood, we tested females’ boldness, shyness, aggression, sociality, and activity.

Results

We found that the number of different mating strategies females were raised with (social complexity) shaped behavioral development more than any individual mating strategy. Females reared in complex environments with two male mating tactics were bolder, less shy, and less aggressive than females reared with a single male mating tactic (either courtship only or coercion only). Complex sexual-social environments produced females with behavioral syndromes (correlations between aggression and activity, shyness and aggression, and social interaction and activity), whereas simple environments did not.

Discussion

Importantly, the characteristics of these socially-induced behavioral syndromes differ from those driven by predation, but converge on characteristics emerging from animals found in urban environments. Our findings suggest that complexity of the sexual-social environment shapes the development of personality and behavioral syndromes to facilitate social information gathering. Furthermore, our research highlights the previously overlooked influence of sexual selection as a significant contributing factor to diverse behavioral development.

Effects of developmental environment on animal personality in a tropical skink

Abstract

Developmental environments play a significant role in shaping animal phenotype, including behavior. Within a species, individuals often differ in behavior in a consistent and repeatable way (i.e., demonstrate animal personality). This consistency in behavior can be affected by differences in conditions experienced early in life. It is, however, unclear whether effects of developmental environments on animal personality are driven by changes in within- or between-individual variation. To investigate this, we measured activity, exploration, sociability, and boldness in adult male southern rainforest sunskinks, Lampropholis similis, incubated at either 23 °C or 26 °C, and compared behavioral phenotypes between these incubation treatments. We also compared the behavior of these incubation groups to a cohort of wild-caught skinks to determine whether rearing in captivity also affected the personality of the lizards. Skinks that had been incubated at a higher temperature were more explorative and demonstrated personality in a larger suite of traits compared to lizards incubated at a lower temperature or caught in the wild. These differences among developmental environment were primarily driven by within-individual variation, which tended to be higher among the high incubation treatment. We also found no evidence for a behavioral syndrome in either captive- or wild-reared skinks. Our results suggest the potential for greater behavioral plasticity in skinks incubated at a higher temperature, which may enable them to cope with environmental change, such as climate warming, in the short term. Overall, we show that effects of developmental environment are complex and play a pivotal role in shaping animal personality.

Significance statement

Experiences during development are expected to influence how animals develop, including their behavior. We tested early environment effects on behavior in adult southern rainforest sunskinks by comparing lizards incubated at different temperatures as well as comparing those reared in the wild with those reared in captive environments. We found that lizards incubated at the higher temperature were more exploratory. Furthermore, both incubation temperature and captivity/wild-rearing had pronounced effects on the consistency of behavior—in different directions for different traits—demonstrating developmental environments have strong effects on animal personality. Such changes in behavioral traits likely have flow-on effects for the animal’s fitness and biotic interactions.

Constitutive gene expression differs in three brain regions important for cognition in neophobic and non-neophobic house sparrows (Passer domesticus)

Neophobia (aversion to new objects, food, and environments) is a personality trait that affects the ability of wildlife to adapt to new challenges and opportunities. Despite the ubiquity and importance of this trait, the molecular mechanisms underlying repeatable individual differences in neophobia in wild animals are poorly understood. We evaluated wild-caught house sparrows (Passer domesticus) for neophobia in the lab using novel object tests. We then selected a subset of neophobic and non-neophobic individuals (n = 3 of each, all females) and extracted RNA from four brain regions involved in learning, memory, threat perception, and executive function: striatum, caudal dorsomedial hippocampus, medial ventral arcopallium, and caudolateral nidopallium (NCL). Our analysis of differentially expressed genes (DEGs) used 11,889 gene regions annotated in the house sparrow reference genome for which we had an average of 25.7 million mapped reads/sample. PERMANOVA identified significant effects of brain region, phenotype (neophobic vs. non-neophobic), and a brain region by phenotype interaction. Comparing neophobic and non-neophobic birds revealed constitutive differences in DEGs in three of the four brain regions examined: hippocampus (12% of the transcriptome significantly differentially expressed), striatum (4%) and NCL (3%). DEGs included important known neuroendocrine mediators of learning, memory, executive function, and anxiety behavior, including serotonin receptor 5A, dopamine receptors 1, 2 and 5 (downregulated in neophobic birds), and estrogen receptor beta (upregulated in neophobic birds). These results suggest that some of the behavioral differences between phenotypes may be due to underlying gene expression differences in the brain. The large number of DEGs in neophobic and non-neophobic birds also implies that there are major differences in neural function between the two phenotypes that could affect a wide variety of behavioral traits beyond neophobia.

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'.

Effects of Wolf Spiders’ Captive Environment on Their Locomotor and Exploratory Behaviours

Simple Summary

Since the 1960s, abuses of domestic and of wild animals that have been tamed or are held in captivity have been legally prohibited and laws ensure their well-being. Many scientific investigations carried out in this context recommend ways to adapt farming and thus to avoid physical and/or psychological suffering. Evaluations of animals’ welfare in captivity entail the need to understand in detail the fundamental behaviours of the focus species and to know the degree of their variation to be able to establish objective bases that can ensure breeding conditions that respect the animals’ welfare. Current laws do not apply to invertebrate animals (such as insects or spiders) and consideration of the welfare of these animals in captivity is neglected. Here, I compared the behaviour of wild adult spiders just after collection and that of adult spiders hatched and bred in the laboratory. My results show that captivity induced rapid changes of wild spiders’ behaviour once in captivity. Therefore, it is important to establish the best breeding conditions for the needs of both invertebrate and vertebrate animals in order to promote their well-being.

Abstract

Here I detail the effects of the abiotic/captive environment of an adult wandering spider, Pardosa saltans (Lycosidae) on its behaviour. These studies focused on spiders collected as adults in their natural environment and spiders developed in the laboratory under controlled conditions. Wild-caught spiders were tested either immediately after capture or after being housed for 15 days post-collection. Laboratory reared spiders were kept in different environments: small or large space combined with the presence or absence of litter. Two tests evaluated by sex show the influence of these rearing conditions: an open-field test and a radial-arm maze test. The results show that wild caught spiders of both sexes tested immediately after capture weighed significantly less and were significantly more active than spiders housed in the laboratory for 15 days and spiders reared in the laboratory. Laboratory conditions induced a positive impact on body mass and negative impact on behaviour activities. The locomotor and exploratory activities of spiders of both sexes kept in container without substrate showed lower. My results suggest that the physical enrichment of the environment can reduce these negative effects for females, but not for males that seem to be more affected by being reared under controlled conditions.

Changes in the anxiety-like and fearful behavior of shrimp following daily threatening experiences

Behavioral variation in animals is often influenced by experience. Previous studies have found that daily threatening experiences can enhance fear- and anxiety-like behaviors in some vertebrates. However, it is unclear whether the change in fear/anxiety behavior occurs in invertebrates. The present study investigated whether fear/anxiety behavior could be affected by a net-chasing treatment in two shrimp species (Neocaridina denticulata ssp. and Palaemon pacificus). The net-chasing treatment was repeated for 8 days to simulate daily predator experiences, and behavioral tests (open-field, shelter-seeking, and escape-response tests) were conducted on the day following the last day of treatment. Net-chased N. denticulata ssp. displayed a tendency to remain near a wall compared with the control in the open-field test, whereas net-chased P. pacificus shrimps demonstrated greater escape behavior compared with the control in the escape-response test. These results suggest that fear/anxiety behavior for both shrimp species can be affected by the net-chasing treatment, although the pattern of behavioral change differed between the two species. The findings suggest that daily threatening experiences change the behavior of shrimp and cause them to select a regular avoidance strategy when they encounter risks and unknown situations.

Beyond spider personality: The relationships between behavioral, physiological, and environmental factors

Spiders are useful models for testing different hypotheses and methodologies relating to animal personality and behavioral syndromes because they show a range of behavioral types and unique physiological traits (e.g., silk and venom) that are not observed in many other animals. These characteristics allow for a unique understanding of how physiology, behavioral plasticity, and personality interact across different contexts to affect spider's individual fitness and survival. However, the relative effect of extrinsic factors on physiological traits (silk, venom, and neurohormones) that play an important role in spider survival, and which may impact personality, has received less attention. The goal of this review is to explore how the environment, experience, ontogeny, and physiology interact to affect spider personality types across different contexts. We highlight physiological traits, such as neurohormones, and unique spider biochemical weapons, namely silks and venoms, to explore how the use of these traits might, or might not, be constrained or limited by particular behavioral types. We argue that, to develop a comprehensive understanding of the flexibility and persistence of specific behavioral types in spiders, it is necessary to incorporate these underlying mechanisms into a synthesized whole, alongside other extrinsic and intrinsic factors.

Foraging aggressiveness determines trophic niche in a generalist biological control species

There is a growing evidence that consistent interindividual differences in behavior, that is, behavioral types, can play an important role in key ecological processes such as predator–prey interactions, which in turn can have direct implications on biological control. Behavioral types of generalist predators may affect these interactions through individual differences in predators’ prey preferences and the breadth of predators’ trophic niches. This study examined how the multivariate nature of behavior, namely foraging aggressiveness, activity level, and risk-taking behavior, determines prey selection and trophic niche of the generalist agrobiont spider Philodromus cespitum. In laboratory experiments, we determined the repeatability of these behaviors and the preference between crickets, moths, fruit flies, and collembolans. We found that all three behaviors were moderately to strongly repeatable but there were no correlations between them, thus they did not form a behavioral syndrome. Only foraging aggressiveness influenced the prey selection of philodromid spiders and the more aggressive individuals had wider trophic niches because they incorporated prey that were more difficult to capture in their diet. In addition, more aggressive individuals killed a greater quantity of particular prey types while other prey types were killed at a similar rate by both aggressive and nonaggressive individuals. The differences in philodromids’ foraging aggressiveness, therefore, affected not only the overall prey density but also resulted in different prey community composition. As pest density and composition can both affect crop performance, further research needs to investigate how the interindividual behavioral differences of generalist natural enemies cascade down on the crops.

Jumping spiders: An exceptional group for comparative cognition studies

Several non-mutually exclusive hypotheses have been proposed to explain the evolution of cognition in animals. Broadly, these hypotheses fall under two categories: those that pertain to the selective pressures exerted either by sociality or by the ecological niche in which animals live. We review these ideas and then discuss why the highly visual jumping spiders (Salticidae) are excellent models for investigating how cognitive ability evolves. With few exceptions, these behaviorally complex spiders are non-social, making them ideal candidates to explore ideas pertaining to selection based on habitat complexity and selection based on predatory behavior (foraging niche hypotheses). With the exception of Antarctica, salticids are found in all habitats on Earth, ranging from very complex to barren and simple. While many species are generalist predators, a minority also have specialized predatory behavior and prey specialization on dangerous prey, which has been proposed as an explanation for advanced cognitive ability. As this large group has a diversity of habitats in which it lives, diverse predatory behavior, as well as some "social" species, we argue that salticids are ideal candidates for comparative studies to explore the myriad selection factors acting upon a group well known for their cognitive prowess, despite having miniature brains.

Environmental complexity during early life shapes average behavior in adulthood

Personality has been identified in a range of animal taxa during the last few decades, with important ecological and evolutionary implications. Investigating the effects of environmental factors during early life can provide important insights into the ontogeny of animal personality. We reared newborn mosquitofish, Gambusia affinis, in tanks of different structural complexities, and measured their behavioral traits (i.e., shyness, exploration, and sociability) when they reached sexual maturity. Univariate linear mixed-effects models were fitted to test the effects of environmental complexity and sex on population-average behavior, whereas multivariate models were fitted to quantify behavioral repeatability (i.e., personality) and among-individual correlations (i.e., behavioral syndromes). On average, females were shyer and more social than males, and the fish reared in complex environments were shyer, less explorative, and more social than those reared in open environments. Among-individual differences were consistently large across trials for all behaviors, indicating that personality variation was present in mosquitofish of both sexes reared in different environments. Repeatability did not differ among behaviors, and there were no differences in repeatability in any behavior between sexes or among environments. A negative correlation between shyness and exploration was found in mosquitofish from all treatments at both phenotypic and among-individual levels, with the latter indicating a strong shyness–exploration behavioral syndrome. Our study provides robust evidence that average levels of personality might vary when mosquitofish are raised in different levels of structural complexity during early life.

The impact of learning opportunities on the development of learning and decision-making: an experiment with passerine birds

Developmental context has been shown to influence learning abilities later in life, namely through experiments with nutritional and/or environmental constraints (i.e. lack of enrichment). However, little is known about the extent to which opportunities for learning affect the development of animal cognition, even though such opportunities are known to influence human cognitive development. We exposed young zebra finches (Taenopygia guttata) (n = 26) to one of three experimental conditions, i.e. an environment where (i) colour cues reliably predicted the presence of food (associative learning), (ii) a combination of two-colour cues reliably predicted the presence of food (conditional learning), or (iii) colour cues were non-informative (control). After conducting two different discrimination tasks, our results showed that experience with predictive cues can cause increased choice accuracy and decision-making speed. Our first learning task showed that individuals in the associative learning treatment outperformed the control treatment, while task 2 showed that individuals in the conditional learning treatment had shorter latencies when making choices compared with the control treatment. We found no support for a speed-accuracy trade-off. This dataset provides a rare longitudinal and experimental examination of the effect of predictive versus non-predictive cues during development on the cognition of adult animals. This article is part of the theme issue 'Life history and learning: how childhood, caregiving and old age shape cognition and culture in humans and other animals'.

What lies beneath? Population dynamics conceal pace-of-life and sex ratio variation, with implications for resilience to environmental change

Life-history and pace-of-life syndrome theory predict that populations are comprised of individuals exhibiting different reproductive schedules and associated behavioural and physiological traits, optimized to prevailing social and environmental factors. Changing weather and social conditions provide in situ cues altering this life-history optimality; nevertheless, few studies have considered how tactical, sex-specific plasticity over an individual's lifespan varies in wild populations and influences population resilience. We examined the drivers of individual life-history schedules using 31 years of trapping data and 28 years of pedigree for the European badger (Meles meles L.), a long-lived, iteroparous, polygynandrous mammal that exhibits heterochrony in the timing of endocrinological puberty in male cubs. Our top model for the effects of environmental (social and weather) conditions during a badger's first year on pace-of-life explained <10% of variance in the ratio of fertility to age at first reproduction (F/α) and lifetime reproductive success. Conversely, sex ratio (SR) and sex-specific density explained 52.8% (males) and 91.0% (females) of variance in adult F/α ratios relative to the long-term population median F/α. Weather primarily affected the sexes at different life-history stages, with energy constraints limiting the onset of male reproduction but playing a large role in female strategic energy allocation, particularly in relation to ongoing mean temperature increases. Furthermore, the effects of social factors on age of first reproduction and year-to-year reproductive success covaried differently with sex, likely due to sex-specific responses to potential mate availability. For females, low same-sex densities favoured early primiparity; for males, instead, up to 10% of yearlings successfully mated at high same-sex densities. We observed substantial SR dynamism relating to differential mortality of life-history strategists within the population, and propose that shifting ratios of 'fast' and 'slow' life-history strategists contribute substantially to population dynamics and resilience to changing conditions.

Within-Family Environment and Cross-Fostering Stress Affect Behavior and Physiology in Wild Cavies (Cavia aperea)

Stability of personality traits is well-documented for a wide variety of animals. However, previous results also suggest that behavioral phenotypes are plastic during early ontogeny and can be adaptively shaped to the social environment. In cavies (Cavia aperea), it has already been documented that the size at birth relative to siblings (size rank) greatly influences various behavioral and physiological traits that last at least until independence. The aim of the current study was (1) to investigate if behavioral and physiological differences between pups of the same litter persist until after independence and influence development long-lasting, (2) to determine the potential plasticity in response to changes in the early within-family environment by cross-fostering pups either to the same, a lower, or a higher size rank in a foster-family. We measured three behavioral traits (number of interactions with a novel object, distance moved in an open field, struggle docility) and two physiological traits (resting metabolic rate and basal cortisol levels). We predicted that cross-fostering into a litter where pups occupy the same size rank would not change the expression of traits. Cross-fostering to a different size rank should not influence the expression of traits if repeatability measures indicate low plasticity. Alternatively, if the traits are plastic, animals should adjust trait expression to fit with the size rank occupied in the foster litter. Initial differences in struggle docility, distance moved in an open field and in baseline cortisol concentration between pups of different size-ranks did not remain stable beyond independence. In addition, we found remarkable plasticity of the measured traits in response to cross-fostering to the same, a smaller or larger size-rank, suggesting that differences between pups are more the result of social constraints leading to adaptive shaping of individual phenotypes within a family. We also found a significant influence of the cross-fostering procedure itself. Cross-fostered individuals were less bold, grew slower and showed elevated resting metabolic rates. This finding suggests a cautious interpretation of previous cross-fostering studies and stresses the need for proper control groups to reliably separate the effect of cross-fostering per se from those induced by an experimental treatment.

Personality underground: evidence of behavioral types in the solitary subterranean rodent Ctenomys talarum

BACKGROUND

Animal personalities have been studied in a wide variety of taxa, but among rodents, available studies are relatively scarce and have focused mainly on social species. In this study, we evaluated the existence of personality in the solitary subterranean rodent Ctenomys talarum. Specifically, we aimed to test individual differences in behavior that are stable over time and context in males of C. talarum captured in the wild.

METHODS

Our experimental design included two series of three behavioral tests each, carried out with a 35 day time interval. Each series included an Open Field test, a Social Encounter test, and an Open Field test with a predator stimulus.

RESULTS

Of the total recorded behaviors, 55.55% showed temporal consistency. Principal component analysis of consistent behaviors grouped them into four dimensions that explain inter individual behavioral variability, in order of importance: activity, socioaversion, boldness and exploration. Therefore, our results suggest that the concept of animal personality is applicable to C. talarum and the dimensions found are in accordance with the ecological and behavioral characteristics of this species.

Modelling the evolution of cognitive styles

BACKGROUND

Individuals consistently differ in behaviour, exhibiting so-called personalities. In many species, individuals differ also in their cognitive abilities. When personalities and cognitive abilities occur in distinct combinations, they can be described as 'cognitive styles'. Both empirical and theoretical investigations produced contradicting or mixed results regarding the complex interplay between cognitive styles and environmental conditions.

RESULTS

Here we use individual-based simulations to show that, under just slightly different environmental conditions, different cognitive styles exist and under a variety of conditions, can also co-exist. Co-existences are based on individual specialization on different resources, or, more generally speaking, on individuals adopting different niches or microhabitats.

CONCLUSIONS

The results presented here suggest that in many species, individuals of the same population may adopt different cognitive styles. Thereby the present study may help to explain the variety of styles described in previous studies and why different, sometimes contradicting, results have been found under similar conditions.

Dietary carotenoids affect the development of individual differences and behavioral plasticity

Nutritional conditions experienced during development are expected to play a key role in shaping an individual’s behavioral phenotype. The long term, irreversible effects of nutritional conditions on behavioral variation among and within individuals remains largely unexplored. This study aimed to investigate how long-term carotenoid availability (representing low vs. high quality nutritional conditions) during both larval and adult life stages influences the expression of among-individual variation (animal personality) and within-individual variation (behavioral plasticity). We tested for personality and plasticity along the exploration/avoidance behavioral axis in the Southern Corroboree frog (Pseudophryne corroboree). We predicted that treatment groups receiving carotenoids during early development would be more exploratory and have greater among- and within-individual variation compared with individuals that did not receive carotenoids (i.e., silver spoon hypothesis). Superior nutritional conditions experienced during development are expected to provide individuals with resources needed to develop costly behaviors, giving them an advantage later in life irrespective of prevailing conditions. Unexpectedly, frogs that did not receive carotenoids as larvae expressed greater among-individual variance in exploration behavior. Additionally, frogs that did not receive carotenoids at either life stage displayed greater within-individual variance. Our findings provide no support for the silver spoon hypothesis but suggest that inconsistent nutritional conditions between life stages may adversely affect the development of behavioral phenotypes. Overall, our results indicate that early and late life nutritional conditions affect the development of personality and plasticity. They also highlight that nutritional effects on behavior may be more complex than previously theorized.

Juvenile social experience generates differences in behavioral variation but not averages

Developmental plasticity is known to influence the mean behavioral phenotype of a population. Yet, studies on how developmental plasticity shapes patterns of variation within populations are comparatively rare and often focus on a subset of developmental cues (e.g., nutrition). One potentially important but understudied developmental experience is social experience, as it is explicitly hypothesized to increase variation among individuals as a way to promote "social niches." To test this, we exposed juvenile black widow spiders (Latrodectus hesperus) to the silk of conspecifics by transplanting them onto conspecific webs for 48 h once a week until adulthood. We also utilized an untouched control group as well as a disturbed group. This latter group was removed from their web at the same time points as the social treatment, but was immediately placed back on their own web. After repeatedly measuring adult behavior and web structure, we found that social rearing drove higher or significant levels of repeatability relative to the other treatments. Repeatability in the social treatment also decreased in some traits, paralleling the decreases observed in the disturbed treatments. Thus, repeated juvenile disturbance may decrease among-individual differences in adult spiders. Yet, social rearing appeared to override the effect of disturbance in some traits, suggesting a prioritization effect. The resulting individual differences were maintained over at least one-third of the adult lifespan and thus appear to represent stable, canalized developmental effects and not temporal state differences. These results provide proximate insight into how a broader range of developmental experiences shape trait variation.

Adult wheel access interaction with activity and boldness personality in Siberian dwarf hamsters (Phodopus sungorus)

Individual animal personalities interact with environmental conditions to generate differences in behavior, a phenomenon of growing interest for understanding the effects of environmental enrichment on captive animals. Wheels are common environmental enrichment for laboratory rodents, but studies conflict on how this influences behavior, and interaction of wheels with individual personalities has rarely been examined. We examined whether wheel access altered personality profiles in adult Siberian dwarf hamsters. We assayed animals in a tunnel maze twice for baseline personality, then again at two and at seven weeks after the experimental group was provisioned with wheels in their home cages. Linear mixed model selection was used to assess changes in behavior over time and across environmental gradient of wheel exposure. While animals showed consistent inter-individual differences in activity, activity personality did not change upon exposure to a wheel. Boldness also varies among individuals, and there is evidence for female boldness scores converging after wheel exposure, that is, opposite shifts in behavior by high and low boldness individuals, although sample size is too small for the mixed model results to be robust. In general, Siberian dwarf hamsters appear to show low behavioral plasticity, particularly in general activity, in response to running wheels.

Adult bacterial exposure increases behavioral variation and drives higher repeatability in field crickets

Among-individual differences in behavior are now a widely studied research-focus within the field of behavioral ecology. Furthermore, elements of an animal's internal state, such as energy or fat reserves, and infection status can have large impacts on behaviors. Despite this, we still know little regarding how state may affect behavioral variation. Recent exposure to pathogens may have a particularly large impact on behavioral expression given that it likely activates costly immune pathways, potentially forcing organism to make behavioral tradeoffs. In this study we investigate how recent exposure to a common bacterial pathogen, Serratia marcescens, affects both the mean behavioral expression and the among-individual differences (i.e. variation) in boldness behavior in the field cricket, Gryllus integer. We find that recent pathogen exposure does not affect mean behavioral expression of the treatment groups, but instead affects behavioral variation and repeatability. Specifically, bacterial exposure drove large among-individual variation, resulting in high levels of repeatability in some aspects of boldness (willingness to emerge into a novel environment), but not others (latency to become active in novel environment), compared to non-infected crickets. Interestingly, sham injection resulted in a universal lack of among-individual differences. Our results highlight the sensitivity of among-individual variance and repeatability estimates to ecological and environmental factors that individuals face throughout their lives.