Parental and personal experience drive personality formation and individual niche diversification in group-living mites

The idea of individual niche specialization suggests that individuals should diversify in their realized niches to mitigate inter-individual conflict. We tested the hypothesis that parental and early-life diet experiences drive individual foraging specialization and animal personality formation in plant-inhabiting predatory mites Phytoseiulus persimilis and Phytoseiulus macropilis. Both species are specialized predators of herbivorous spider mites. Adult females and males, whose parents had been exposed to either prey eggs or mobile prey, and/or who themselves had experienced either eggs or mobile prey during juvenile development, were tested for their prey life stage preference, and exploration and activity patterns. Parental and/or personal experience of a given prey life stage exerted species- and sex-dependent effects on the adult predators' mean and individual foraging phenotypes, with parental plus early-life effects being the strongest. Repeatability in activity and exploration was linked to prey life stage preference, pointing at co-variation of personality formation and individualized foraging niches.

Prey or protection? Access to food alters individual responses to competition in black widow spiders

Animals influence the phenotype and reproductive success of their conspecifics through competitive interactions. Such effects of competition can alter the intensity of selection and ultimately change the rate of evolution. However, the magnitude of the effects of competition, and their evolutionary impact, should vary depending on environmental conditions and individual responses among competitors. We tested whether a key environmental variable, resource availability, affects the response to competition in black widow spiders by manipulating access to prey and the level of competition. We examined if focal spiders modify their web structure and aggressiveness towards prey stimuli when a competitor is present, and whether these responses depend on prior prey access. We also tested if any effects of competition vary with individual differences among competitors. Access to resources changed how individuals respond to competition. Spiders with limited access to prey were less likely to attack prey stimuli in the presence of a conspecific competitor than spiders with greater access to prey, suggesting that limiting resources hinders competitive responses. In contrast, all spiders built better-protected webs in the presence of competitors, regardless of prior access to prey. Crucially, these responses differed among focal spiders and depended on individual competitors. Our findings highlight the importance of environmental conditions and individual differences in mediating the impact of social interactions on phenotypes and eventually on their evolution.

Is the speed of adjusting to environmental change condition dependent? An experiment with house mice (Mus musculus)

Environmental conditions change constantly either by anthropogenic perturbation or naturally across space and time. Often, a change in behavior is the first response to changing conditions. Behavioral flexibility can potentially improve an organism's chances to survive and reproduce. Currently, we lack an understanding on the time-scale such behavioral adjustments need, how they actually affect reproduction and survival and whether behavioral adjustments are sufficient in keeping up with changing conditions. We used house mice (Mus musculus) to test whether personality and life-history traits can adjust to an experimentally induced food-switch flexibly in adulthood or by intergenerational plasticity, that is, adjustments only becoming visible in the offspring generation. Mice lived in 6 experimental populations of semi-natural environments either on high or standard quality food for 4 generations. We showed previously that high-quality food induced better conditions and a less risk-prone personality. Here, we tested whether the speed and/ or magnitude of adjustment shows condition-dependency and whether adjustments incur fitness effects. Life-history but not personality traits reacted flexibly to a food-switch, primarily by a direct reduction of reproduction and slowed-down growth. Offspring whose parents received a food-switch developed a more active stress-coping personality and gained weight at a slower rate compared with their respective controls. Furthermore, the modulation of most traits was condition-dependent, with animals previously fed with high-quality food showing stronger responses. Our study highlights that life-history and personality traits adjust at different speed toward environmental change, thus, highlighting the importance of the environment and the mode of response for evolutionary models.

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.

Effects of resource availability on the web structure of female western black widows: is the web structure constrained by physiological trade-offs?

A major challenge of biological research is to understand what generates and maintains consistent behavioral variation among animals. Time and energy trade-offs, where expressing one behavior is achieved at the expense of another, are often suggested to favor the maintenance of behavioral differences between individuals. However, few studies have investigated how individuals adjust their allocation to different functions over time and depending on resource abundance. Black widow spiders of the genus Latrodectus build persistent webs that include structural threads which protect against predators and sticky trap threads to capture prey. Web structure consistently differs among individuals in the number of trap and structural threads. To quantify the intensity of a trade-off, we assessed the relationship between the number of structural and trap threads and tested whether varying food abundance affected individual differences in web structure. We further quantified how these individual differences change over time and with food abundance. We subjected spiders to three different levels of prey abundance and monitored the structure of their webs every twelve hours. We found no evidence for a trade-off between trap and structural threads. Instead, spiders that produced more structural threads also produced more trap threads, showing that spiders invested equally in both types of threads. Interestingly, the magnitude of individual differences in web structure was greatest when spiders were fed ad libitum and at the beginning of web construction. We suggest that variation in web structure between spiders could be the result of stable developmental differences in morphology or genetic differences.

Does Living in Human-Altered Environments Affect Life-History and Personality of Wild Mice?

In urban habitats, animals are faced with different and often challenging environmental conditions compared to their native habitats. Behavior is the fastest response to environmental change and therefore a very important component to adjust to human-altered environments. Behaviors such as novelty responses and innovativeness which allow animals to cope with novel stimuli are often altered in urban populations. The mechanisms producing such adaptations are currently not well understood. In this study, we investigate whether urban living has an impact on the microevolution of mouse behavioral and life-history traits including boldness, stress-coping, growth, longevity, and emphasis on reproduction. We hypothesized that animals living together with humans for longer show increased novelty-seeking and boldness characteristics at the species and subspecies level. We, therefore, compared behavior and life history characteristics among Mus musculus, a commensal rodent, Mus spicilegus as a synanthropic but not commensal, and Apodemus uralensis as a strictly rural species. In addition, we compared three subspecies of M. musculus (in total six populations) that differ in the time living together with humans. Behavioral and life history differences are stronger between populations even of the same subspecies rather than showing a structural trend with the time animals have spent with humans. In addition, species differ in behavior and life history, albeit not in a pattern that suggests an evolutionary adaptation to living in human-altered habitats. We, therefore, suggest that behavioral adaptations of wild mice are geared toward environmental differences such as geographic origin or habitat specifics but not necessarily directly evolve by living together with humans.

Phylogenetic conservation of behavioural variation and behavioural syndromes

Individuals frequently differ consistently from one another in their average behaviours (i.e. 'animal personality') and in correlated suites of consistent behavioural responses (i.e. 'behavioural syndromes'). However, understanding the evolutionary basis of this (co)variation has lagged behind demonstrations of its presence. This lag partially stems from comparative methods rarely being used in the field. Consequently, much of the research on animal personality has relied on 'adaptive stories' focused on single species and populations. Here, we used a comparative approach to examine the role of phylogeny in shaping patterns of average behaviours, behavioural variation and behavioural correlations. In comparing the behaviours and behavioural variation for five species of Gryllid crickets, we found that phylogeny shaped average behaviours and behavioural (co)variation. Despite differences among species, behavioural responses and variation were most similar among more closely related species. These results suggest that phylogenetic constraints play an important role in the expression of animal personalities and behavioural syndromes and emphasize the importance of examining evolutionary explanations within a comparative framework.

Responses of intended and unintended receivers to a novel sexual signal suggest clandestine communication

Inadvertent cues can be refined into signals through coevolution between signalers and receivers, yet the earliest steps in this process remain elusive. In Hawaiian populations of the Pacific field cricket, a new morph producing a novel and incredibly variable song (purring) has spread across islands. Here we characterize the current sexual and natural selection landscape acting on the novel signal by (1) determining fitness advantages of purring through attraction to mates and protection from a prominent deadly natural enemy, and (2) testing alternative hypotheses about the strength and form of selection acting on the novel signal. In field studies, female crickets respond positively to purrs, but eavesdropping parasitoid flies do not, suggesting purring may allow private communication among crickets. Contrary to the sensory bias and preference for novelty hypotheses, preference functions (selective pressure) are nearly flat, driven by extreme inter-individual variation in function shape. Our study offers a rare empirical test of the roles of natural and sexual selection in the earliest stages of signal evolution.

How do developmental and parental exposures to predation affect personality and immediate behavioural plasticity in the snail Physa acuta?

Individuals differ in personality and immediate behavioural plasticity. While developmental environment may explain this group diversity, the effect of parental environment is still unexplored-a surprising observation since parental environment influences mean behaviour. We tested whether developmental and parental environments impacted personality and immediate plasticity. We raised two generations of Physa acuta snails in the laboratory with or without developmental exposure to predator cues. Escape behaviour was repeatedly assessed on adult snails with or without predator cues in the immediate environment. On average, snails were slower to escape if they or their parents had been exposed to predator cues during development. Snails were also less plastic in response to immediate predation risk on average if they or their parents had been exposed to predator cues. Group diversity in personality was greater in predator-exposed snails than unexposed snails, while parental environment did not influence it. Group diversity in immediate plasticity was not significant. Our results suggest that only developmental environment plays a key role in the emergence of group diversity in personality, but that parental environment influences mean behavioural responses to the environmental change. Consequently, although different, both developmental and parental cues may have evolutionary implications on behavioural responses.

Behavioural syndromes shape evolutionary trajectories via conserved genetic architecture

Behaviours are often correlated within broader syndromes, creating the potential for evolution in one behaviour to drive evolutionary changes in other behaviours. Despite demonstrations that behavioural syndromes are common, this potential for evolutionary effects has not been demonstrated. Here we show that populations of field crickets (Gryllus integer) exhibit a genetically conserved behavioural syndrome structure, despite differences in average behaviours. We found that the distribution of genetic variation and genetic covariance among behavioural traits was consistent with genes and cellular mechanisms underpinning behavioural syndromes rather than correlated selection. Moreover, divergence among populations' average behaviours was constrained by the genetically conserved behavioural syndrome. Our results demonstrate that a conserved genetic architecture linking behaviours has shaped the evolutionary trajectories of populations in disparate environments-illustrating an important way for behavioural syndromes to result in shared evolutionary fates.

Diet composition and social environment determine food consumption, phenotype and fecundity in an omnivorous insect

Nutrition is the single most important factor for individual's growth and reproduction. Consequently, the inability to reach the nutritional optimum imposes severe consequences for animal fitness. Yet, under natural conditions, organisms may face a mixture of stressors that can modulate the effects of nutritional asymmetry. For instance, stressful environments caused by intense interaction with conspecifics. Here, we subjected the house cricket Acheta domesticus to (i) either of two types of diet that have proved to affect cricket performance and (ii) simultaneously manipulated their social environment throughout their complete life cycle. We aimed to track sex-specific consequences for multiple traits during insect development throughout all life stages. Both factors affected critical life-history traits with potential population-level consequences: diet composition induced strong effects on insect development time, lifespan and fitness, while the social environment affected the number of nymphs that completed development, food consumption and whole-body lipid content. Additionally, both factors interactively determined female body mass. Our results highlight that insects may acquire and invest resources in a different manner when subjected to an intense interaction with conspecifics or when isolated. Furthermore, while only diet composition affected individual reproductive output, the social environment would determine the number of reproductive females, thus indirectly influencing population performance.

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.

Social experiences shape behavioral individuality and within-individual stability

Individual repeatability characterizes many behaviors. Repeatable behavior may result from repeated social interactions among familiar group members, owing to adaptive social niche specialization. In the context of aggression, in species like field crickets, social niche specialization should also occur when individuals repeatedly interact with unfamiliar individuals. This would require the outcome of social interactions to have carry-over effects on fighting ability and aggressiveness in subsequent interactions, leading to long-term among-individual differentiation. To test this hypothesis, we randomly assigned freshly emerged adult males of the southern field cricket Gryllus bimaculatus to either a solitary or social treatment. In social treatment, males interacted with a same-sex partner but experienced a new partner every 3 days. After 3 weeks of treatment, we repeatedly subjected treated males to dyadic interactions to measure aggression. During this time, we also continuously measured the 3-daily rate of carbohydrate and protein consumption. Individual differentiation was considerably higher among males reared in the social versus solitary environment for aggressiveness but not for nutrient intake. Simultaneously, social experience led to lower within-individual stability (i.e., increased within-individual variance) in carbohydrate intake. Past social experiences, thus, shaped both behavioral individuality and stability. While previous research has emphasized behavioral individuality resulting from repeated interactions among familiar individuals, our study implies that behavioral individuality, in the context of aggression, may generally result from social interactions, whether with familiar or unfamiliar individuals. Our findings thus imply that social interactions may have a stronger effect on individual differentiation than previously appreciated.

Developmental and genetic effects on behavioral and life-history traits in a field cricket

A fundamental goal of evolutionary ecology is to identify the sources underlying trait variation on which selection can act. Phenotypic variation will be determined by both genetic and environmental factors, and adaptive phenotypic plasticity is expected when organisms can adjust their phenotypes to match environmental cues. Much recent research interest has focused on the relative importance of environmental and genetic factors on the expression of behavioral traits, in particular, and how they compare with morphological and life-history traits. Little research to date examines the effect of development on the expression of heritable variation in behavioral traits, such as boldness and activity. We tested for genotype, environment, and genotype-by-environment differences in body mass, development time, boldness, and activity, using developmental density treatments combined with a quantitative genetic design in the sand field cricket (Gryllus firmus). Similar to results from previous work, animals reared at high densities were generally smaller and took longer to mature, and body mass and development time were moderately heritable. In contrast, neither boldness nor activity responded to density treatments, and they were not heritable. The only trait that showed significant genotype-by-environment differences was development time. It is possible that adaptive behavioral plasticity is not evident in this species because of the highly variable social environments it naturally experiences. Our results illustrate the importance of validating the assumption that behavioral phenotype reflects genetic patterns and suggest questions about the role of environmental instability in trait variation and heritability.

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.

Condition-dependent foraging strategies in a coastal seabird: evidence for the rich get richer hypothesis

The degree to which foraging individuals are able to appropriately modify their behaviors in response to dynamic environmental conditions and associated resource availability can have important fitness consequences. Despite an increasingly refined understanding of differences in foraging behavior between individuals, we still lack detailed characterizations of within-individual variation over space and time, and what factors may drive this variability. From 2014 to 2017, we used GPS transmitters and accelerometers to document foraging movements by breeding adult Brown Pelicans (Pelecanus occidentalis) in the northern Gulf of Mexico, where the prey landscape is patchy and dynamic at various scales. Assessments of traditional foraging metrics such as trip distance, linearity, or duration did not yield significant relationships between individuals. However, we did observe lower site fidelity and less variation in energy expenditure in birds of higher body condition, despite a population-level trend of increased fidelity as the breeding season progressed. These findings suggest that high-quality individuals are both more variable and more efficient in their foraging behaviors during a period of high energetic demand, consistent with a “rich get richer” scenario in which individuals in better condition are able to invest in more costly behaviors that provide higher returns. This work highlights the importance of considering behavioral variation at multiple scales, with particular reference to within-individual variation, to improve our understanding of foraging ecology in wild populations.

Cortisol during adolescence organises personality traits and behavioural syndromes

Despite the growing evidence for the importance of developmental experiences shaping consistent individual differences in behaviour and physiology, the role of endocrine factors underlying the development and maintenance of such differences across multiple traits, remains poorly understood. Here, we investigated how an experimental manipulation of circulating glucocorticoids during early adolescence affects behavioural and physiological variation and covariation later in life in the precocial cavy (Cavia aperea). Plasma cortisol concentrations were experimentally elevated by administering cortisol via food for 3 weeks. Struggle docility, escape latency, boldness, exploration and social behaviour were then tested three times after individuals attained sexual maturity. In addition, blood samples were taken repeatedly to monitor circulating cortisol concentrations. Exogenous cortisol affected mean trait expression of plasma cortisol levels, struggle docility and escape latency. Repeatability of cortisol and escape latency was increased and repeatability of struggle docility tended to be higher (approaching significance) in treated individuals. Increased repeatability was mainly caused by an increase of among-individual variance. Correlations among docility, escape latency and cortisol were stronger in treated animals compared to control animals. These results suggest that exposure to elevated levels of cortisol during adolescence can alter animal personality traits as well as behavioural syndromes. Social and risk-taking traits showed no correlation with cortisol levels and were unaffected by the experimental manipulation, indicating behavioural modularity. Taken together, our data highlight that cortisol can have organising effects during adolescence on the development of personality traits and behavioural syndromes, adding to the increasing evidence that not only early life but also adolescence is an important sensitive period for behavioural development.

You are what you eat: diet shapes body composition, personality and behavioural stability

BACKGROUND

Behavioural phenotypes vary within and among individuals. While early-life experiences have repeatedly been proposed to underpin interactions between these two hierarchical levels, the environmental factors causing such effects remain under-studied. We tested whether an individual's diet affected both its body composition, average behaviour (thereby causing among-individual variation or 'personality') and within-individual variability in behaviour and body weight (thereby causing among-individual differences in residual within-individual variance or 'stability'), using the Southern field cricket Gryllus bimaculatus as a model. We further asked whether effects of diet on the expression of these variance components were sex-specific.

METHODS

Manipulating both juvenile and adult diet in a full factorial design, individuals were put, in each life-stage, on a diet that was either relatively high in carbohydrates or relatively high in protein. We subsequently measured the expression of multiple behavioural (exploration, aggression and mating activity) and morphological traits (body weight and lipid mass) during adulthood.

RESULTS

Dietary history affected both average phenotype and level of within-individual variability: males raised as juveniles on high-protein diets were heavier, more aggressive, more active during mating, and behaviourally less stable, than conspecifics raised on high-carbohydrate diets. Females preferred more protein in their diet compared to males, and dietary history affected average phenotype and within-individual variability in a sex-specific manner: individuals raised on high-protein diets were behaviourally less stable in their aggressiveness but this effect was only present in males. Diet also influenced individual differences in male body weight, but within-individual variance in female body weight.

DISCUSSION

This study thereby provides experimental evidence that dietary history explains both heterogeneous residual within-individual variance (i.e., individual variation in 'behavioural stability') and individual differences in average behaviour (i.e., 'personality'), though dietary effects were notably trait-specific. These findings call for future studies integrating proximate and ultimate perspectives on the role of diet in the evolution of repeatedly expressed traits, such as behaviour and body weight.