Too young to be bold: Lack of personality in juvenile goby

Consistent individual differences (CIDs) in animal behavior, also known as personality or temperament, are measured in a variety of assays and are presumed to represent relatively stable traits of individual animals. Because these behaviors are presumed to represent stable traits, repetition of assays over short and long-term time frames and contexts is crucial; such repetitions are not commonly achieved in literature regarding the topic of CIDs, especially not in a singular study. In beef cattle, CIDs are often related to feeding and social preferences, which is relevant for extensively managed herds of ruminants. This study investigated the consistency of behavior among 50 breeding Angus x Hereford cows across repetitions within one year and over one year during three distinct contexts: handling and isolation in a chute corral system, choice in a social-feed tradeoff test, and response in a novel bucket approach test. We found that cows were consistent across short-term (assessed with repeatabilities [R]) and long-term (assessed with correlations across multivariate models [r]) timeframes in durations of behaviors exhibited in the management context (e.g. while handled [R = 0.60, r = 0.39], while traversing a cement chute [R = 0.69, r = 0.67] and an open squeeze stall [R = 0.76, r = 0.85]). Repeatable behaviors from the handling and isolation in chute system context were input into PCA with varimax rotation. Behaviors loaded onto three principal components that explained 66 % of the variance in the data and distinguished cows along axes of activity, fearfulness and excitability. Cows that were deemed less active (p = 0.010) and less excitable (p = 0.039) chose to approach the supplement bucket over gaining proximity to conspecifics in a social-feed tradeoff test. Even though the cows were not restrained in a squeeze stall, consistent individual differences in behavior across short (within year) and long-term (between years) timeframes were found. This suggests that future research can use unrestrained methods to evaluate cattle temperament, which could improve animal welfare and safety of handlers during experiments. Passive and less excitable beef cattle were more feed-centric, indicating that CIDs in behavior assays could potentially be used to predict feeding behavior because of an underlying stable trait in cows that ties response to handling and management with feed choice in a social-feed tradeoff task.

Animal personality

Resting metabolic rate (RMR) is highly variable between individuals within a single species and the relationship between body mass and RMR does not wholly explain this variability. One factor that could account for a portion of the residual variation is animal personality or consistent individual differences (CIDs) in behaviour, but no study has examined this relationship in a free-living population of mammals. In this paper, we test for a relationship between RMR and CIDs in activity in live-trapped meadow voles Microtus pennsylvanicus after controlling for the effect of body mass. We quantified the activity levels of voles both in an unfamiliar environment and for the first 2 min in the metabolic apparatus, and then measured RMR using open-flow respirometry. As expected, there was a linear relationship between RMR and body mass, and we found strong evidence for repeatable differences in activity levels between individuals. However, contrary to the hypothesis, we did not identify a significant correlation between CIDs in behaviour and RMR after controlling for body mass. Our results suggest that, at least within species, higher activity levels may not require a greater investment in energetically demanding tissues or increased capacity for processing of energy. Alternatively, if a relationship exists, our inability to detect it may reflect a weak behavioural signal in noisy RMR data that are influenced by many factors. Our results could also reflect an artefact of individual responses to stress or a sampling bias towards more exploratory individuals in animals captured by live-trapping.

Strong personalities, not social niches, drive individual differences in social behaviours in sticklebacks

Consistent individual differences in parenting are widespread; however, we know little about why there is variation in parenting behavior among individuals within species. One possible explanation for consistent individual differences in parenting is that individuals invest in different aspects of parental care, such as provisioning or defense. In this field study we measured consistent individual differences in parenting behavior and evaluated correlations between parenting and other behaviors in threespine stickleback (Gasterosteus aculeatus). We repeatedly measured male parenting behavior and male behavior in the presence of three different types of live intruders: a female, a conspecific male, and a predator, meant to provoke courtship, aggressive and antipredator behavior, respectively. While males plastically adjusted their reactions to different types of intruders, we found consistent individual differences in behavior (behavioral types) both within and across contexts, even after accounting for variation in body size and nest characteristics. Males that performed more parenting behavior responded faster to all types of intruders. These results suggest that in nature, individual male stickleback exhibit robust parental behavioral types, and highly parental males are more attentive to their surroundings. Future studies are needed to examine the potential causes of individual variation in parental behavior in the field.

Do consistent individual differences in metabolic rate promote consistent individual differences in behavior?

Personality and artificial light at night in a semi-urban songbird population: No evidence for personality-dependent sampling bias, avoidance or disruptive effects on sleep behaviour

Animals often exhibit consistent individual differences in behavior (i.e. animal personality) and correlations between behaviors (i.e. behavioral syndromes), yet the causes of those patterns of behavioral variation remain insufficiently understood. Many authors hypothesize that state-dependent behavior produces animal personality and behavioral syndromes. However, empirical studies assessing patterns of covariation among behavioral traits and state variables have produced mixed results. New statistical methods that partition correlations into between-individual and residual within-individual correlations offer an opportunity to more sufficiently quantify relationships among behaviors and state variables to assess hypotheses of animal personality and behavioral syndromes. In a population of wild Belding's ground squirrels (Urocitellus beldingi) we repeatedly measured activity, exploration, and response to restraint behaviors alongside glucocorticoids and nutritional condition. We used multivariate mixed models to determine whether between-individual or within-individual correlations drive phenotypic relationships among traits. Squirrels had consistent individual differences for all five traits. At the between-individual level, activity and exploration were positively correlated whereas both traits negatively correlated with response to restraint, demonstrating a behavioral syndrome. At the within-individual level, condition negatively correlated with cortisol, activity and exploration. Importantly, this indicates that although behavior is state-dependent, which may play a role in animal personality and behavioral syndromes, feedback mechanisms between condition and behavior appear not to produce consistent individual differences in behavior and correlations between them.

Animal personality due to social niche specialisation

The evolutionary causes of consistent individual differences in behaviour are currently a source of debate. A recent hypothesis suggests that consistent individual differences in life-history productivity (growth and/or fecundity) may covary with behavioural traits that contribute to growth-mortality trade-offs, such as risk-proneness (boldness) and foraging activity (voraciousness). It remains unclear, however, to what extent individual behavioural and life-history profiles are set early in life, or are a more flexible result of specific environmental or developmental contexts that allow bold and active individuals to acquire more resources. Longitudinal studies of individually housed animals under controlled conditions can shed light on this question. Since growth and behaviour can both vary within individuals (they are labile), studying between-individual correlations in behaviour and growth rate requires repeated scoring for both variables over an extended period of time. However, such a study has not yet been done. Here, we repeatedly measured individual mass seven times each, boldness 40 times each and voracity eight times each during the first 4months of life on 90 individually housed crayfish (Cherax destructor). Animals were fed ad libitum, generating a context where individuals can express their intrinsic growth rate (i.e. growth capacity), but in which bold and voracious behaviour is not necessary for high resource acquisition (crayfish can and do hoard food back to their burrow). We show that individuals that were consistently bold over time during the day were also bolder at night, were more voracious and maintained higher growth rates over time than shy individuals. Independent of individual differences, we also observed that males were faster-growing, bolder and more voracious than females. Our findings imply that associations between bold behaviour and fast growth can occur in unlimited food contexts where there is no necessary link between bold behaviour and resource acquisition - offering support for the 'personality-productivity' hypothesis. We suggest future research should study links between consistent individual differences in behaviour and life history under a wider range of contexts, in order to shed light on the role of biotic and abiotic conditions in the strength, direction and stability of their covariance.

Social insect colonies and the workers comprising them, each exhibit consistent individual differences in behavior, also known as ‘personalities’. Because the behavior of social insect colonies emerges from the actions of their workers, individual variation among workers’ personality may be important in determining the variation we observe among colonies. The reproductive unit of social insects, on which natural selection acts, is the colony, not individual workers. Therefore, it is important to understand what mechanisms govern the observed variation among colonies. Here I propose three hypotheses that address how consistent individual differences in the behavior of workers may lead to consistent individual differences in the behavior of colonies: 1. Colonies differ consistently in their average of worker personality; 2. The distribution but not the average of worker personalities varies consistently among colonies; and 3. Colony personality does not emerge from its worker personality composition but from consistent external constraints. I review evidence supporting each of these hypotheses and suggest methods to further investigate them. The study of how colony personality emerges from the personalities of the workers comprising them may shed light on the mechanisms underlying consistent individual differences in the behavior of other animals.

Individual differences in behavior (animal personality) have recently received much attention although less so in young mammals. We tested 74 preweaning-age kittens from 16 litters of domestic cats in five everyday contexts repeated three times each across a 3-week period: a handling test where an experimenter held the kitten, a test where a piece of raw beef was given to the kitten and gradually withdrawn, a test where the kitten was presented with a live mouse in a jar, a test where the kitten was briefly confined in a pet carrier, and an encounter with an unfamiliar human who first remained passive and then attempted to stroke the kitten. We found consistent individual differences in behavior in all tests except with the mouse, although less marked than in equivalent tests with adult cats. Differences in behavior were unrelated to sex, body mass, litter size, or maternal identity. We found only weak correlations in results among the tests (behavioral syndromes), again unlike findings in adult cats. We conclude that weanling kittens show consistent individual differences in behavior but in a different manner to adults. If and how the pattern of such differences changes across development remains to be studied.

Consistent individual differences in behavior imply that individuals act in the same manner every time they encounter a situation while differing from others. While these differences occur in a variety of contexts in a wide range of organisms, how recent experience affects behavioral consistency remains underexplored. Male Siamese fighting fish exhibit consistent individual differences in behavior when both a male and a female are present. However, whether these responses can be shaped by immediate recent aggressive experience is unknown. In this study, males first were presented with paired dummy male and female conspecifics after they had been isolated to obtain a baseline, no-experience measure. Males then won and lost fights and were retested with the dummies after each fight. These three experience types (no, win, loss) occurred both when males did and did not have nests to determine the effects of nest presence, experience, and the interaction between these factors on behavioral consistency. Overall behavior did not change based on experience with the exception of male-directed tail beats. Repeatability values were affected more by having a nest than fight outcome. This study demonstrates that consistent individual differences in behavior to conflicting stimuli are fairly resistant to short-term aggressive experiential effects.

Competition among mammalian carnivores can be particularly intense and can influence population dynamics at lower trophic levels. One strategy employed by carnivores to minimize potentially costly interspecific competition is avoidance of dominant species. Recent research has highlighted the importance of consistent individual differences in behavior (i.e. temperament traits) in understanding behavioral variation during predator–prey interactions and intraspecific interactions. However, the importance of such individual differences to interspecific competition has received little attention. Here, we examined the responses of spotted hyenas (Crocuta crocuta) to their primary competitors, African lions (Panthera leo), to (1) determine whether hyenas avoid lions and (2) evaluate the potential importance of individual differences in behavior during interspecific competition. Spotted hyenas and lions co‐occur throughout much of Africa and are vigorous competitors. Whereas lions sometimes kill hyenas and steal their food, lions also represent a source of food for hyenas via scavenging. Using audio playback experiments, we found that hyenas do not uniformly avoid potential encounters with lions. Indeed, we noted considerable variation among individuals in their responses to lion roars, and this variation reflected consistent individual differences in risk‐taking and vigilance tendencies. Individual differences in vigilance behavior were specific to interactions with lions. We conclude that individual differences in behavior have the potential to play an important role in determining the nature and outcome of interspecific competition.

Temporally consistent individual differences in behavior, also known as animal personality, can have large impacts on individual fitness. Here, we explore the degree to which individual differences in anti-predator response (or boldness) influence survival rates in groups of snails Chlorostoma funebralis when they encounter a predatory sea star Pisaster giganteus. The snail C. funebralis shows consistent individual variation in predator response where some fearful snails actively flee bodies of water occupied by predators whereas bolder snails consistently do not. We show here that bold snails are significantly more likely to survive encounters with a predatory sea star and, somewhat counterintuitively, fearful snails actually suffer higher mortality rates. We also found that smaller snails and those occurring at higher experimental densities experienced higher per capita survival rates. Positive effects of prey boldness on survival are not uncommonly reported in the animal personality literature; however, such results are inconsistent with classic animal personality theory borrowed from the optimal foraging literature. The findings herein add to the growing body of evidence that consistent individual differences in behavior can impact predator–prey interactions and that boldness is potentially under positive predator-driven selection in some systems.