The joy of being frightened: Fear experience in psychopathy

OBJECTIVE

Psychopathic traits are associated with abnormalities in fear processing. While traditional theories focus on a lack of fear, Hosker-Field et al. (2016) provided a new perspective. They suggested that individuals with elevated psychopathic traits may experience threatening situations with appreciation or positivity, resulting in reduced negative fear responses and heightened positive responses (fear enjoyment hypothesis, FEH).

METHOD

Our study aimed to refine Hosker-Field et al.'s (2016) study design, addressing methodological limitations and improving the inconsistent operationalization of fear experience in the literature. In an online sample of 353 participants from the general population, we examined the relationship between the FEH and relevant psychopathic traits, specifically those derived from the PCL-R framework (i.e., SRP 4 Factor 1), and from a more trait-based approach to psychopathy with assumed links to fearlessness (i.e., TriPM Boldness).

RESULTS

By employing linear mixed effect models, we extended Hosker-Field et al.'s correlational analysis and provided further evidence for the FEH, particularly in relation to psychopathic traits measured using the PCL-R framework. The results regarding Boldness, however, are somewhat inconclusive.

CONCLUSION

The present study enhances existing research on fear deficits in psychopathy by assessing the subjective experience of individuals facing threat.

Among-individual behavioural variation in the ornamental red cherry shrimp, Neocaridina heteropoda

Personality variation, defined as among-individual differences in behaviour that are repeatable across time and context, is widely reported across animal taxa. From an evolutionary perspective, characterising the amount and structure of this variation is useful since differences among individuals are the raw material for adaptive behavioural evolution. However, behavioural variation among individuals also has implications for more applied areas of evolution and ecology-from invasion biology to ecotoxicology and selective breeding in captive systems. Here, we investigate the structure of personality variation in the red cherry shrimp, Neocaridina heteropoda, a popular ornamental species that is readily kept and bred under laboratory conditions and is emerging as a decapod crustacean model across these fields, but for which basic biological, ecological and behavioural data are limited. Using two assays and a repeated measures approach, we quantify behaviours putatively indicative of shy-bold variation and test for sexual dimorphism and/or size-dependent behaviours (as predicted by some state-dependent models of personality). We find moderate-to-high behavioural repeatabilities in most traits. Although strong individual-level correlations across behaviours are consistent with a major personality axis underlying these observed traits, the multivariate structure of personality variation does not fully match a priori expectations of a shy-bold axis. This may reflect our ecological naivety with respect to what really constitutes bolder, more risk-prone, behaviour in this species. We find no evidence for sexual dimorphism and only weak support for size-dependent behaviour. Our study contributes to the growing literature describing behavioural variation in aquatic invertebrates. Furthermore, it lays a foundation for further studies harnessing the potential of this emerging model system. In particular, this existing behavioural variation could be functionally linked to life-history traits and invasive success and serve as a target of artificial selection or bioassays. It thus holds significant promise in applied research across ecotoxicology, aquaculture and invasion biology.

Unravelling the origins of boldness behaviour: a common garden experiment with cavefish (Barbatula barbatula)

Many animals show an aversion to bright, open spaces, with significant variability seen across species, populations and individuals within populations. Although there is much interest in the underlying causes of this behaviour, few studies have been able to systematically isolate the role of heritable and environmental effects. Here, we addressed this gap using a common garden experiment with cavefish. Specifically, we bred and cross-bred cave loaches (Barbatula barbatula), Europe's only known cavefish, in the laboratory, raised the offspring in complete darkness or normal light conditions, and studied their light avoidance behaviour. Cavefish spent much more time in a light area and ventured further out, while surface fish spent considerable time in risk-assessment behaviour between the light and dark areas. Hybrids behaved most similarly to cavefish. Light treatment and eye quality and lens size only had a modest effect. Our results suggest light avoidance behaviour of cavefish has a heritable basis and is fundamentally linked to increased boldness rather than reduced vision, which is likely adaptive given the complete lack of macropredators in the cave environment. Our study provides novel experimental insights into the behavioural divergence of cavefish and contributes to our broader understanding of the evolution of boldness and behavioural adaptation.

Olfaction and reaction: The role of olfactory and hypothalamic investment in the antipredator responses to chemical alarm cues by northern redbelly dace

Neuroplasticity enables teleosts to promote or downregulate the growth of their brains regionally. To compensate for the effects of predation pressure, teleosts may alter their brain morphology and behavioral responses to mitigate its impact on individual fitness. High-predation environments often promote specific patterns of brain growth and produce bolder and more proactive populations. Owing to the expense of maintaining neural tissue, relative size indicates the regions most relied upon. In northern redbelly dace Chrosomus eos, as little as 2 weeks of elevated predation pressure, resulted in increased investment in their olfactory bulbs and optic tecta, while the imposition of captivity produced smaller, less symmetric hypothalami. Taken together, these results suggest that an individual could potentially become better able to detect a threat, and simultaneously less inclined to react to it, making the impact of either change in isolation is difficult to discern. Here, we compared interindividual variation in gross brain morphology, risk-taking tactics in a novel arena (shy-bold personality), and responding to olfactory cues (proactive/reactive stress-coping style). We hypothesized that olfactory investment would positively correlate with response intensity to predator cue concentration and respond across a wider range of cue concentrations, while hypothalamus size would correlate with shyness and reactivity. Exposure to heightened risk produced more bold/proactive individuals, with larger olfactory bulbs and smaller hypothalami. However, the direction of the correlation between hypothalamus size and behavior varied by treatment, and olfactory investment only corresponded with response intensity amongst proactive individuals. Our findings illustrate the potential pitfalls of relating gross brain morphology to complex behavior and suggest that stress-coping style is a relevant consideration in future studies.

Bioacoustic monitoring to determine addiction levels of primates to the human sphere: A feasibility study on Japanese macaques

Some nonhuman primate species, whose original habitats have been reclaimed by artificial activities, have acquired boldness toward humans which is evident based on the diminished frequency of escape behaviors. Eventually, such species have become regular users of human settlements, and are referred to as "urban primates." Considering this, we developed a noninvasive technique based on bioacoustics to provide a transparent assessment of troop addiction levels in anthropogenic environments, which are determined by the dependence on agricultural crops and human living sphere for their diets and daily ranging, respectively. We attempted to quantify the addiction levels based on the boldness of troops when raiding settlements, characterized by a "landscape of fear" because of the presence of humans as predators. We hypothesized that the boldness of troops could be measured using two indices: the frequency of raiding events on settlements and the amount of time spent there. For hypothesis testing, we devised an efficient method to measure these two indices using sound cues (i.e., spontaneous calls) for tracing troop movements that are obtainable throughout the day from most primate species (e.g., contact calls). We conducted a feasibility study of this assessment procedure, targeting troops of Japanese macaques (Macaca fuscata). For this study, we collected 346 recording weeks of data using autonomous recorders from 24 troops with different addiction levels during the nonsnowy seasons. The results demonstrated that troops that reached the threshold level, at which radical interventions including mass culling of troop members is officially permitted, could be readily identified based on the following behavioral characteristics: troop members raiding settlements two or three times per week and mean time spent in settlements per raiding event exceeding 0.4 h. Thus, bioacoustic monitoring could become a valid option to ensure the objectivity of policy judgment in urban primate management.

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.

Individual differences in response to alcohol and nicotine in zebrafish: Gene expression and behavior

Alcohol and nicotine are psychoactive substances responsible for serious health consequences. Although the biological mechanisms of alcohol and nicotine have been studied extensively, individual differences in the response to these drugs have received little attention. Here we evaluated gene expression and behavior of bold and shy individuals after acute exposure to alcohol and nicotine. For this, zebrafish were classified as bold and shy individuals based on emergence tests, and then fish were exposed to 0.00, 0.10, and 0.50% alcohol or 0.00, 1.00, and 5.00 mg/L nicotine and their anxiety-like and locomotor behavior was observed. After behavioral assessment, brain mRNA expression (ache, bdnf, gaba1, gad1b, th1, and tph1) was evaluated. Locomotion patterns differed between profiles depending on alcohol and nicotine concentration. Anxiety increased in shy fish and decreased in bold fish after exposure to both drugs. Alcohol exposure induced an increase in tph1 mRNA expression in bold fish, while bdnf mRNA expression was increased in shy fish. Nicotine increased ache, bdnf, and tph1 mRNA levels in both profiles, but at higher levels in bold fish. Based on our research, we found that alcohol induces anxiogenic effects in both bold and shy zebrafish. Additionally, shy individuals exposed to a low concentration of nicotine exhibited stronger anxiety-like responses than their bold counterparts. These findings further support the validity of using zebrafish as a dependable tool for studying the effects of drugs and uncovering the underlying mechanisms associated with individual variations.

Personality traits differentially affect components of reproductive success in a Neotropical poison frog

Individual reproductive success has several components, including the acquisition of mating partners, offspring production, and offspring survival until adulthood. While the effects of certain personality traits-such as boldness or aggressiveness-on single components of reproductive success are well studied, we know little about the composite and multifaceted effects behavioural traits can have on all the aspects of reproductive success. Behavioural traits positively linked to one component of reproductive success might not be beneficial for other components, and these effects may differ between sexes. We investigated the influence of boldness, aggressiveness, and exploration on the number of mating partners, mating events, and offspring surviving until adulthood in males and females of the Neotropical poison frog Allobates femoralis. Behavioural traits had different-even opposite-effects on distinct components of reproductive success in both males and females. For example, males who displayed high levels of aggressiveness and exploration (or low levels of aggressiveness and exploration) managed to attract high number of mating partners, while males with low levels of boldness, low levels of aggressiveness, and high levels of exploration had the most offspring surviving until adulthood. Our results therefore suggest correlational selection favouring particular combinations of behavioural traits.

Foraging valor linked with aggression: selection against completely abandoning aggression in the high-elevation ant Tetramorium alpestre?

Aggression has multiple benefits and is often coupled with other behaviors ("behavioral syndromes"). The level of aggressiveness is influenced by an adaptive benefit-cost ratio suggesting that benefits should outweigh the costs of aggression. Here, we assess if several behaviors are coupled in two behaviorally different populations (aggressive, peaceful) of the high-elevation ant Tetramorium alpestre. For three weeks, we collected colony fragments and analyzed boldness, exploring, foraging, and risk-taking behaviors. We hypothesized that the aggressive population is bolder, more explorative and risk-prone, and forages more food than the peaceful population. To test whether (a) the combination of experiments and parameters used yields a good setup, (b) populations differ behaviorally, and (c) populations display behavioral syndromes, we assessed (a) the frequency of repeatable behaviors of each experiment, (b) the behavioral means among populations, and (c) the behavioral repeatability, respectively. We found that (a) boldness and exploring were most repeatable and represent a good experimental setup, (b) the aggressive population was bolder and more explorative and risk-prone than the peaceful population, (c) boldness and exploring behaviors were highly repeatable in both populations, thus corroborating our hypothesis. The results suggest that boldness, exploring, and risk-taking but not foraging are presumably coupled with aggression and indicate the presence of behavioral syndromes in this ant. Under specific ecological conditions, aggression may be coupled with other behaviors and important for finding food. Aggression is probably adaptive in T. alpestre, possibly indicating that selection favors aggression at least partially, which may counteract the complete loss of intraspecific aggression.

Dietary tannins alter growth, behavior, and the gut microbiome of larval amphibians

Research has shown that leached plant toxins negatively impact the growth and development of larval amphibians. However, tadpoles may encounter these same toxins in food material, and differential exposure routes and distribution of toxic chemicals can yield variable downstream effects on animals. To date, most research understanding the interactions between dietary plant toxins and herbivores has been conducted in terrestrial systems. Despite the abundance of plant toxins in food and water sources, the effects of dietary plant toxins on larval amphibians have not been studied, and tannins could negatively affect these species. Here, green frog tadpoles (Lithobates clamitans) were fed diets with or without 2% tannic acid to test how their growth, development, behavior, and gut microbiome respond to dietary tannins. At the end of the trial, we conducted a behavioral assay to measure tadpole activity and boldness and inventoried the gut microbiome using 16S rRNA sequencing. Dietary tannins significantly decreased body mass by 66% and length by 28%, without influencing tadpole developmental stage. We found significant differences in exploratory behavior and boldness during the first minute of our behavioral assay, demonstrating that tannins have the potential to influence behavior during novel or stressful events. Finally, tannins significantly sculpted the gut microbiome, with an increase in the measurement of Shannon entropy. We observed 7 microbial phyla and 153 microbial genera that exhibited significantly differential abundances differences between control and tannic acid-fed tadpoles. Collectively, our results demonstrate that dietary tannins have the potential to alter amphibian growth, behavior, and microbiome.

Boldness is not associated with dynamic performance capacity in hermit crabs

Boldness, the way an individual reacts to risk, is a commonly studied personality trait in animals. Consistent among-individual differences in startle response durations (latency to recover from a startling stimulus) are frequently assumed to reflect variation in boldness. An alternative explanation is that these latencies are not directly driven by variation in responses to information on risk, but by underlying differences in dynamic performance capacities. Here we investigate this possibility by analysing relationships between locomotory speed, a measure of whole-body dynamic performance capacity in hermit crabs, and startle response duration, a repeatable latency measure used as an index of boldness. Individuals differed in mean startle response duration, in the consistency of their startle responses, in their reaction norms across repeated observations, and mean startle responses increased with crab mass. However, there were no relationships between startle responses and locomotory speed. This indicates that startle responses do not reflect underlying performance capacities and suggests that they provide insight into differences in how individuals respond to risky situations. Since similar latencies are used as measures of boldness in other animals, we suggest that potential relationships between apparent boldness and performance capacity should be tested.

Size specific boldness associated with differences in resource requirements and habitat use: a cross-sectional study in hermit crabs

Animal personality is often studied within compressed periods of observation that represent narrow windows in comparison to animal lifespans. Although much is known about the relations between repeatable personality traits and cross-situational behavioral plasticity, less is known about how such traits might differ across age classes or life history transitions. We conducted a cross-sectional study of startle response duration in 3 size classes of Pagurus bernhardus, the common European hermit crab. We defined size classes using transitions in the preferred species of gastropod shells that accompany growth, and this change in preference is in turn associated with a transition from intertidal to subtidal habitats. Compared with small- and medium-sized intertidal individuals the larger subtidal hermit crabs behaved cautiously by showing startle responses of greater duration following disturbance. Startle responses were also repeatable within all 3 size classes, confirming the presence of animal personality in intertidal hermit crabs and demonstrating that this pattern is retained within the largest size classes, which have undergone the transition from intertidal to subtidal habitat. Interestingly, there was a trend for the pattern of repeatable startle response durations to increase with size class, with the highest value for repeatability and the greatest range of startle response durations being present within the large subtidal population. The greater range of startle responses indicates that the longer startle response durations in some larger individuals are more likely due to developmental changes with age and habitat use than reflecting selection against the boldest individuals during earlier stages of life.

Coping styles vary with species' sociality and life history: A systematic review and meta-regression analysis

Despite a long history of animal studies investigating coping styles, the causal connections between behavior and stress physiology remain unclear. Consistency across taxa in effect sizes would support the idea of a direct causal link maintained by either functional or developmental dependencies. Alternatively, lack of consistency would suggest coping styles are evolutionarily labile. Here, we investigated correlations between personality traits and baseline and stress-induced glucocorticoid levels using a systematic review and meta-analysis. Most personality traits did not consistently vary with either baseline or stress-induced glucocorticoids. Only aggression and sociability showed a consistent negative correlation with baseline glucocorticoids. We found that life history variation affected the relationship between stress-induced glucocorticoid levels and personality traits, especially anxiety and aggression. The relationship between anxiety and baseline glucocorticoids depended on species' sociality with solitary species showing more positive effect sizes. Thus, integration between behavioral and physiological traits depends on species' sociality and life history and suggests high evolutionary lability of coping styles.

Fear generalization and behavioral responses to multiple dangers

Animals often exhibit consistent-individual differences (CIDs) in boldness/fearfulness, typically studied in the context of predation risk. We focus here on fear generalization, where fear of one danger (e.g., predators) is correlated with fear of other dangers (e.g., humans, pathogens, moving vehicles, or fire). We discuss why fear generalization should be ecologically important, and why we expect fear to correlate across disparate dangers. CIDs in fear are well studied for some dangers in some taxa (e.g., human fear of pathogens), but not well studied for most dangers. Fear of some dangers has been found to correlate with general fearfulness, but some cases where we might expect correlated fears (e.g., between fear of humans, familiar predators, and exotic predators) are surprisingly understudied.

Genetic associations between human-directed behavior and intraspecific social aggression in growing pigs

This study estimated the genetic parameters for human-directed behavior and intraspecific social aggression traits in growing pigs, and explored the phenotypic correlations among them. Data on 2,413 growing pigs were available. Pigs were mixed into new social groups of 18 animals, at 69 ± 5.2 d of age and skin lesions (SL) were counted 24 h (SL24h) post-mixing. Individual behavioral responses to isolation in a weighing crate (CRATE) or when alone in an arena while a human directly approached them (IHAT) were assessed within 48 h post-mixing. Additionally, pigs were tested for behavioral responses to the presence of a single human observer walking in their home pen in a circular motion (WTP) within one (T1) and 4 wk post-mixing (T2) noting pigs that followed, nosed or bit the observer. Animal models were used to estimate genetic and phenotypic parameters for all studied traits. Heritabilities (h2) for SL, CRATE and IHAT responses were low to moderate (0.07 to 0.29), with the highest h2 estimated for speed of moving away from the approaching observer. Low but significant h2 were estimated for nosing (0.09) and biting (0.11) the observer at T2. Positive high genetic correlations (rg) were observed between CRATE and IHAT responses (0.52 to 0.93), and within SL traits (0.79 to 0.91) while positive low to high correlations between the estimated breeding values (rEBV) were estimated within the WTP test (0.24 to 0.59) traits. Positive moderate rg were observed between CRATE and central and posterior SL24h. The rEBV of CRATE and IHAT test responses and WTP test traits were low, mostly negative (-0.21 to 0.05) and not significant. Low positive rEBV (0.06 to 0.24) were observed between SL and the WTP test traits. Phenotypic correlations between CRATE and IHAT responses and SL or WTP test traits were mostly low and not significant. Under the conditions of this study, h2 estimates for all studied traits suggest they could be suitable as a method of phenotyping aggression and fear/boldness for genetic selection purposes. Additionally, genetic correlations between aggression and fear indicators were observed. These findings suggest selection to reduce the accumulation of lesions is likely to make pigs more relaxed in a crate environment, but to alter the engagement with humans in other contexts that depends on the location of the lesions under selection.

Urbanization increases fluctuating asymmetry and affects behavioral traits of a common grasshopper

Urbanization has a major impact on biodiversity. For many organisms, the urbanization process means environmental stress caused by fragmentation and increased temperatures in cities and atmospheric, soil, light, and noise pollution. Such environmental stress can influence both the morphology and behavior of animals. Hence, individuals might be selected for survival-facilitating traits under high pressures in urban areas. The specific impact of urbanization on insect behavior is still largely unexplored. We studied the impact of urbanization on one of the most common grasshopper species in Germany, Chorthippus biguttulus, by comparing morphological and behavioral traits of individuals sampled from grasslands with low, medium, and high urbanization levels. We first investigated whether urbanization as a stressor affected body size and fluctuating asymmetry in the locomotor organs. Next, we examined whether urbanization induced changes in the individuals' boldness and activity. Our results showed that fluctuating asymmetry of grasshoppers' locomotory organs increased more than twofold with urbanization level. Further, individuals' boldness and walking activity increased from areas with low to high urbanization levels. Our results indicate strong responses of grasshoppers in terms of morphology and behavior to the urban environment. To compensate for urbanization effects on arthropod populations, management strategies need to be developed that maintain ecological processes and reduce environmental stress in urban areas.

Western Hognose Snakes (Heterodon nasicus) Prefer Environmental Enrichment

The environmental enrichment needs of snakes are often disregarded. Using preference testing, we aimed to shed light on the enrichment preferences of a popular pet species, the western hognose snake (Heterodon nasicus). Snakes' enclosures were divided into enriched and standard sides. The enriched half had substrate for burrowing, interactive stimuli, and a large water dish. The standard half had paper towel substrate and a small water dish. Each side also contained a single shelter. We provided belly heat to create a thermal gradient on one side of the cage. Snakes were observed for 6 days, four times daily. We predicted a preference for enriched conditions and, as snakes are ectothermic, a preference for the warmer side. Snakes were additionally given an exploration assay, to explore whether differences in preference for environmental enrichment interact with boldness levels. We found that hognose snakes preferred enrichment, and the strength of this preference increased over time. Preference for enrichment was stronger when the enriched side was cooler. This may be due to the burrowing tendencies of these snakes. We found no relationship between preference and boldness. These findings emphasise the importance of preference testing in establishing research-informed enrichment opportunities for reptiles.

Pain processing and antisocial behavior: A multimodal investigation of the roles of boldness and meanness

Antisocial behavior has been linked to an increased tolerance of painful stimuli; however, there is evidence that pain behavior is multidetermined. The current study used pain measures from 3 different modalities (pain tolerance, pain ratings, electrocortical reactivity) and assessed triarchic traits of boldness and meanness to clarify the dispositional basis of associations between pain processing and antisocial behavior. High boldness was significantly associated with blunted early neural response to painful and nonpainful stimuli as well as increased pain tolerance. High meanness was associated with blunted elaborative processing of painful images, lower ratings of perceived pain for self and others, and increased pain tolerance. Meanness also accounted for variance shared between pain processing and antisocial behavior. Findings demonstrate that boldness and meanness contribute to pain processing in different ways and suggest that meanness may uniquely account for the association between blunted pain processing and antisocial behavior. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

The Good, the Bad, and the Ugly? A Triarchic Perspective on Psychopathy at Work

Does psychopathy have an upside in vocational contexts? Applying the triarchic model of psychopathy, we propose that the dimensions of boldness, disinhibition, and meanness have different relations to workplace outcomes. Focusing on boldness and in line with socioanalytic personality theory, we propose that political skill moderates the relation between boldness and job performance. Using a sample of 477 target-coworker pairings, we found interaction effects of boldness and political skill on contextual and task performance, and the buffering of counterproductive work behavior. Furthermore, political skill moderated the relation between boldness and adaptive performance. Disinhibition and meanness were positively correlated with counterproductive work behaviors, thereby reflecting the dark core of psychopathy. In sum, boldness is a trait linked to career success in the absence of the other traits that make up psychopathy as a whole. Furthermore, we encourage the use of the triarchic model as an overarching framework in vocational contexts.

Concurrent, Convergent, and Discriminant Validity of the DSM-5 Section III Psychopathy Specifier

Section III of the fifth iteration of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) includes an alternative model of personality disorder diagnosis that conceptualizes antisocial personality disorder as an interpersonal, rather than behavioral, construct. However, the diagnostic specifier for psychopathy has been met with recent controversy due to its conceptual and empirical overlap with triarchic boldness, which has been debated as a necessary and sufficient domain of psychopathy. This study examined the concurrent, convergent, and discriminant validity of the specifier using canonical correlation analysis in samples of undergraduate students (N = 224) and community adults with prior criminal involvement (N = 306). Findings highlight the specifier as a multidimensional construct with divergent associations across its three facets. There was limited validity evidence for two of the three facets, raising concerns regarding the clinical utility of the psychopathy specifier.

Boldness predicts divorce rates in wandering albatrosses (Diomedea exulans)

Personality predicts divorce rates in humans, yet how personality traits affect divorce in wild animals remains largely unknown. In a male-skewed population of wandering albatross (Diomedea exulans), we showed that personality predicts divorce; shyer males exhibited higher divorce rates than bolder males but no such relationship was found in females. We propose that divorce may be caused by the intrusion of male competitors and shyer males divorce more often because of their avoidance of territorial aggression, while females have easier access to mates regardless of their personality. Thus, personality may have important implications for the dynamics of social relationships.

The Gut Microbiota May Affect Personality in Mongolian Gerbils

The "gut-microbiota-brain axis" reveals that gut microbiota plays a critical role in the orchestrating behavior of the host. However, the correlation between the host personalities and the gut microbiota is still rarely known. To investigate whether the gut microbiota of Mongolian gerbils (Meriones unguiculatus) differs between bold and shy personalities, we compared the gut microbiota of bold and shy gerbils, and then we transplanted the gut microbiota of bold and shy gerbils into middle group gerbils (individuals with less bold and shy personalities). We found a significant overall correlation between host boldness and gut microbiota. Even though there were no significant differences in alpha diversity and beta diversity of gut microbiota between bold and shy gerbils, the Firmicutes/Bacteroidetes phyla and Odoribacter and Blautia genus were higher in bold gerbils, and Escherichia_shigella genus was lower. Furthermore, the fecal microbiota transplantation showed that changes in gut microbiota could not evidently cause the increase or decrease in the gerbil's boldness score, but it increased the part of boldness behaviors by gavaging the "bold fecal microbiota". Overall, these data demonstrated that gut microbiota were significantly correlated with the personalities of the hosts, and alteration of microbiota could alter host boldness to a certain extent.

Coral-reef fishes can become more risk-averse at their poleward range limits

As climate warms, tropical species are expanding their distribution to temperate ecosystems where they are confronted with novel predators and habitats. Predation strongly regulates ecological communities, and range-extending species that adopt an effective antipredator strategy have a higher likelihood to persist in non-native environments. Here, we test this hypothesis by comparing various proxies of antipredator and other fitness-related behaviours between range-extending tropical fishes and native-temperate fishes at multiple sites across a 730 km latitudinal range. Although some behavioural proxies of risk aversion remained unaltered for individual tropical fish species, in general they became more risk-averse (increased sheltering and/or flight initiation distance), and their activity level decreased poleward. Nevertheless, they did not experience a decline in body condition or feeding rate in their temperate ranges. Temperate fishes did not show a consistently altered pattern in their behaviours across range locations, even though one species increased its flight initiation distance at the warm-temperate location and another one had lowest activity levels at the coldest range location. The maintenance of feeding and bite rate combined with a decreased activity level and increased sheltering may be behavioural strategies adopted by range-extending tropical fishes, to preserve energy and maintain fitness in their novel temperate ecosystems.

Capture vulnerability of sea turtles on recreational fishing piers

Capture vulnerability of commercial and recreational fishes has been associated with behavioral, morphological, and life-history traits; however, relationships with non-target species, such as sea turtles, have not been adequately studied. We examined species composition, timing of captures, morphological variables including body size and head width, and body condition of sea turtles captured from a recreational fishing pier in the northern Gulf of Mexico and of sea turtles captured in the waters adjacent to the pier. From 2014 to 2019, 148 net captures and 112 pier captures of three sea turtle species were documented. Green turtles were captured most frequently in the net and on the pier. Turtles captured from the pier were larger than those captured in the net. There was no difference in head width between net-caught and pier-caught turtles; however, small sample sizes limited those comparisons. The body condition index was lower for pier-caught than net-caught Kemp';s ridleys but did not differ with green turtles or loggerheads. Differences were also observed in the timing of capture on the pier as compared to in the net. Finally, the relationship between size, body condition, and pier-capture vulnerability suggests these are complex interactions. Mortality of sea turtles captured from fishing piers could be selecting against bolder individuals, which may result in changes in sea turtle population demographics over a long time period.

Environmental temperature during early life affects the personality of mosquitofish in adulthood

Personality has been observed in a variety of animal taxa with important implications in ecology and evolution. Exploring the influence of environmental temperature during early life on personality could help to understand the ontogeny of this phenotypic trait in animals. In this study, we reared newborn mosquitofish Gambusia affinis at high (30°C) and low (25°C) water temperatures and measured their shyness and exploration upon sexual maturity. We tested the repeatability of each behavioral trait; the correlation between them; and the effects of rearing temperature, sex, and body length on the behaviors. When growing up at low temperatures, female fish exhibited repeatability in shyness and exploration, and males exhibited marginal repeatability in shyness. However, neither of the 2 behaviors were repeatable when the fish were reared at high temperatures. There was a negative correlation between shyness and exploration, indicating that the 2 behaviors comprise a behavioral syndrome in this species. Mosquitofish reared at high temperatures were more explorative than those reared at low temperatures, while there was no difference in shyness between the 2 treatments. Body length and sex had no significant effects on the average values of the 2 behaviors. The results indicate that environmental temperature during early life could shape the personality of mosquitofish and modify the average of the behavioral traits. These findings might provide insights to understand the ontogeny of animal personality and how changes in environmental temperature influence animal dispersal by shaping their personality.

Evaluating the validity of brief prototype-based informant ratings of triarchic psychopathy traits in prisoners

The validity of self-report psychopathy assessment has been questioned, especially in forensic settings where clinical evaluations influence critical decision-making (e.g., institutional placement, parole eligibility). Informant-based assessment offers a potentially valuable supplement to self-report but is challenging to acquire in under-resourced forensic contexts. The current study evaluated, within an incarcerated sample (n = 322), the extent to which brief prototype-based informant ratings of psychopathic traits as described by the triarchic model (boldness, meanness, disinhibition; Patrick et al., 2009) converge with self-report trait scores and show incremental validity in predicting criterion measures. Self/informant convergence was robust for traits of boldness and disinhibition, but weaker for meanness. Informant-rated traits showed incremental predictive validity over self-report traits, both within and across assessment domains. These findings indicate that simple prototype-based informant ratings of the triarchic traits can provide a useful supplement to self-report in assessing psychopathy within forensic-clinical settings.

Do human infrastructures shape nest distribution in the landscape depending on individual personality in a farmland bird of prey?

Individuals' distribution across habitats may depend on their personality. Human activities and infrastructures are critical elements of the landscape that may impact the habitat selection process. However, depending on their personality, individuals may respond differently to these unnatural elements. In the present study, we first investigated whether some human infrastructures (buildings, roads and paths) shaped Montagu's harrier nest spatial distribution in the landscape according to female personality (boldness). Second, we tested if the reproductive success of females depended on their boldness and nest location regarding infrastructures. Using a long-term (19 years) dataset, we calculated, for each infrastructure type, the distance from each nest to the nearest infrastructure and the infrastructure density around the nest. We tested the effects of female boldness (bold vs. shy) and its interaction with egg-laying date on these six metrics. Nest location in the landscape depended on female personality and on some human infrastructures: the building density was smaller around nests from shy females than from bold ones. Nest distribution related to other infrastructure metrics did not depend on female boldness. The pattern related to building density is consistent with some habitat choice hypotheses, which are discussed. Path density around nests negatively affected reproductive success regardless of female boldness, and late breeders nested further away from paths than early breeders. Human activities on paths (more common later in the season) could lead to disturbance and a decrease in parental care, reducing reproductive success. Increasing human presence in farmlands implies a need to better understand its impact on population composition, in terms of personality. Our results suggest that individual behavioural differences should be taken into account in studies assessing the effects of human disturbance on animal populations, to propose more appropriate conservation measures.

The role of individual behavioral traits on fishway passage attempt behavior

Variations in behavioral traits are widely recognized to drive animal behaviors exhibited within a population. However, information on how behavior traits influence behavior in anthropogenically modified habitats is lacking. Many habitats have become highly fragmented as a result of human processes. To mitigate this and improve habitat connectivity, wildlife passes are increasingly employed, with the aim of enabling animals to move freely between habitats. However, wildlife passes (e.g., fishways) are not always effective in achieving passage and it remains uncertain what factors play a role in an individual's likelihood of passing successfully. This study measured three behavioral traits (boldness, exploration, and activity) in juvenile brown trout (Salmo trutta; n = 78) under field conditions within a river and tested whether these behavior traits influenced both the passage success and the behaviors exhibited during upstream fishway passage attempts. Although behavioral traits were found and collapsed into two behavioral trait dimensions, behavioral traits had low repeatability and so did not contribute to a personality spectrum. Boldness was found to negatively influence the number of passage attempts carried out by an individual and to positively influence passage success, with bolder individuals carrying out fewer attempts and having an increased probability of passage success. No behavioral traits were found to be related to other passage metrics (passage success, Time until First Attempt, and Passage Duration) during the first passage. But all three behavioral traits were significantly negatively related to the changes in passage behaviors at consecutive, successful passage attempts, with bolder, more exploratory and more active individuals passing through a fishway quicker on the second passage than on the first. This study suggests that bolder and more active individuals may perform better during fishway passage attempts, particularly within rivers where multiple barriers to movement exist.

Diet and temperature modify the relationship between energy use and ATP production to influence behavior in zebrafish (Danio rerio)

Food availability and temperature influence energetics of animals and can alter behavioral responses such as foraging and spontaneous activity. Food availability, however, is not necessarily a good indicator of energy (ATP) available for cellular processes. The efficiency of energy transduction from food-derived substrate to ATP in mitochondria can change with environmental context. Our aim was to determine whether the interaction between food availability and temperature affects mitochondrial efficiency and behavior in zebrafish (Danio rerio). We conducted a fully factorial experiment to test the effects of feeding frequency, acclimation temperature (three weeks to 18 or 28°C), and acute test temperature (18 and 28°C) on whole-animal oxygen consumption, mitochondrial bioenergetics and efficiency (ADP consumed per oxygen atom; P:O ratio), and behavior (boldness and exploration). We show that infrequently fed (once per day on four days per week) zebrafish have greater mitochondrial efficiency than frequently fed (three times per day on five days per week) animals, particularly when warm-acclimated. The interaction between temperature and feeding frequency influenced exploration of a novel environment, but not boldness. Both resting rate of producing ATP and scope for increasing it were positively correlated with time spent exploring and distance moved in standardized trials. In contrast, behavior was not associated with whole-animal aerobic (oxygen consumption) scope, but exploration was positively correlated with resting oxygen consumption rates. We highlight the importance of variation in both metabolic (oxygen consumption) rate and efficiency of producing ATP in determining animal performance and behavior. Oxygen consumption represents energy use, and P:O ratio is a variable that determines how much of that energy is allocated to ATP production. Our results emphasize the need to integrate whole-animal responses with subcellular traits to evaluate the impact of environmental conditions on behavior and movement.

Animal Personality and Conservation: Basics for Inspiring New Research

Simple Summary

The study of animal personality is important to conserve animals because it can help in selecting the most appropriate individuals to be released into the wild. Individuals not so bold or aggressive, less stressed, who explore their new environment with greater caution are often more likely to survive after release into the wild. In contrast, bolder and more aggressive animals reproduce more successfully and, therefore, can be released with the aim of rapid repopulation of an area. These and other aspects of how animal personality can help in conservation programs, as well as how to collect personality data are covered in this paper.

Abstract

The number of animal species threatened with extinction are increasing every year, and biologists are conducting animal translocations, as one strategy, to try to mitigate this situation. Furthermore, researchers are evaluating methods to increase translocation success, and one area that shows promise is the study of animal personality. Animal personality can be defined as behavioral and physiological differences between individuals of the same species, which are stable in time and across different contexts. In the present paper, we discuss how animal personality can increase the success of translocation, as well as in the management of animals intended for translocation by evaluating personality characteristics of the individuals. Studies of the influence of birthplace, parental behavior, stress resilience, and risk assessment can be important to select the most appropriate individuals to be released. Finally, we explain the two methods used to gather personality data.

Sexual selection and personality: Individual and group-level effects on mating behaviour in red junglefowl

Despite increasing evidence of the importance of repeatable among-individual differences in behaviour (animal personality) in ecology and evolution, little remains known about the role of animal personalities in sexual selection. Here, we present an investigation of the hypothesis that the personalities of individuals and their sexual partners play a role in different episodes of sexual selection, and the extent to which these effects are modulated by the social environment. We first examined how two repeatable behaviours-exploration and boldness-are associated with pre- and postcopulatory sexual selection in male red junglefowl Gallus gallus, using replicate groups across three experimental sex ratio treatments. We further explored how the social environment modulates relationships between male personality and mating performance, and whether mating is assortative or disassortative with respect to exploration or boldness. Finally, we examined behavioural mechanisms linking personality with mating performance. Across all sex ratios, the fastest and slowest exploring males courted females proportionally less, and faster exploring males associated with females more and received more sexual solicitations. In female-biased groups, the fastest and slowest exploring males experienced the highest mating success and lowest sperm competition intensity. Faster exploring males also obtained more mates in female-biased groups when their competitors were, on average, slower exploring, and the proportion of matings obtained by fast-exploring males decreased with the proportion of fast-exploring males in a group, consistent with negative frequency-dependent sexual selection. While boldness did not predict mating performance, there was a tendency for individuals to mate disassortatively with respect to boldness. Collectively, our results suggest that male exploration can play a role in sexual selection, and that sexual selection on personality is complex and contingent on the social environment.

The battle between harvest and natural selection creates small and shy fish

Harvest of fish and wildlife, both commercial and recreational, is a selective force that can induce evolutionary changes to life history and behavior. Naturally selective forces may create countering selection pressures. Assessing natural fitness represents a considerable challenge in broadcast spawners. Thus, our understanding about the relative strength of natural and fisheries selection is slim. In the field, we compared the strength and shape of harvest selection to natural selection on body size over four years and behavior over one year in a natural population of a freshwater top predator, the northern pike (Esox lucius). Natural selection was approximated by relative reproductive success via parent-offspring genetic assignments over four years. Harvest selection was measured by comparing individuals susceptible to recreational angling with individuals never captured by this gear type. Individual behavior was measured by high-resolution acoustic telemetry. Harvest and natural size selection operated with equal strength but opposing directions, and harvest size selection was consistently negative in all study years. Harvest selection also had a substantial behavioral component independent of body length, while natural behavioral selection was not documented, suggesting the potential for directional harvest selection favoring inactive, timid fish. Simulations of the outcomes of different fishing regulations showed that traditional minimum size-based harvest limits are unlikely to counteract harvest selection without being completely restrictive. Our study suggests harvest selection may be inevitable and recreational fisheries may thus favor small, inactive, shy, and difficult-to-capture fish. Increasing fractions of shy fish in angling-exploited stocks would have consequences for stock assessment and all fisheries operating with hook and line.

State dependence explains individual variation in nest defence behaviour in a long-lived bird

Parental care, such as nest or offspring defence, is crucial for offspring survival in many species. Yet, despite its obvious fitness benefits, the level of defence can consistently vary between individuals of the same species. One prominent adaptive explanation for consistent individual differences in behaviours involves state dependency: relatively stable differences in individual state should lead to the emergence of repeatable behavioural variation whereas changes in state should lead to a readjustment of behaviour. Therefore, empirical testing of adaptive state dependence requires longitudinal data where behaviour and state of individuals of the same population are repeatedly measured.

Here, we test if variation in states predicts nest defence behaviour (a ‘risky’ behaviour) in a long‐lived species, the barnacle goose Branta leucopsis. Adaptive models have predicted that an individual's residual reproductive value or ‘asset’ is an important state variable underlying variation in risk‐taking behaviour. Hence, we investigate how nest defence varies as a function of time of the season and individual age, two state variables that can vary between and within individuals and determine asset.

Repeated measures of nest defence towards a human intruder (flight initiation distance or FID) of females of known age were collected during 15 breeding seasons. Increasing values of FID represent increasing shyness.

We found that females strongly and consistently differed in FID within‐ and between‐years. As predicted by theory, females adjusted their behaviour to state by decreasing their FID with season and age. Decomposing these population patterns into within‐ and between‐individual effects showed that the state‐dependent change in FID was driven by individual plasticity in FID and that bolder females were more plastic than shyer females.

This study shows that nest defence behaviour differs consistently among individuals and is adjusted to individual state in a direction predicted by adaptive personality theory.

Are British urban foxes (Vulpes vulpes) "bold"? The importance of understanding human-wildlife interactions in urban areas

Human-wildlife interactions are believed to be increasing in urban areas. In Britain, numerous media reports have stated that urban foxes (Vulpes vulpes) are becoming "bolder," thereby posing a risk to public safety. However, such claims overlook how an individual's personality might influence urban fox behavior. Personality determines multiple aspects of an animal's interactions with both conspecifics and its environment, and can have a significant impact on how people perceive wildlife. Furthermore, describing urban foxes as "bold" confounds two different but inter-related behaviors, both of which influence an animal's propensity to take risks. Neophobia affects an animal's reaction to novelty, wariness its reaction to potential threats. Since urban wildlife frequently encounters both novel and threatening stimuli, a highly adaptable species such as the red fox might be predicted to exhibit reduced neophobia and wariness. We investigated how social status influenced both behaviors in Bristol's fox population. Dominant foxes were significantly more neophobic and warier than subordinates, which adopt a more exploratory and risk-taking lifestyle to meet their energetic and other needs. We found no seasonal effect on neophobia and wariness, although this may be due to sample size. The presence of conspecifics decreased neophobia for dominants, and wariness for both dominants and subordinates. We highlight the importance of considering animal social status and personality when planning management protocols, since interventions that destabilize fox social groups are likely to increase the number of subordinate foxes in the population, thereby increasing rather than decreasing the number of interactions between humans and urban foxes.

Personality-specific carry-over effects on breeding

Carry-over effects describe the phenomenon whereby an animal's previous conditions influence its subsequent performance. Carry-over effects are unlikely to affect individuals uniformly, but the factors modulating their strength are poorly known. Variation in the strength of carry-over effects may reflect individual differences in pace-of-life: slow-paced, shyly behaved individuals are thought to favour an allocation to self-maintenance over current reproduction, compared to their fast-paced, boldly behaved conspecifics (the pace-of-life syndrome hypothesis). Therefore, detectable carry-over effects on breeding should be weaker in bolder individuals, as they should maintain an allocation to reproduction irrespective of previous conditions, while shy individuals should experience stronger carry-over effects. We tested this prediction in black-legged kittiwakes breeding in Svalbard. Using miniature biologging devices, we measured non-breeding activity of kittiwakes and monitored their subsequent breeding performance. We report a number of negative carry-over effects of non-breeding activity on breeding, which were generally stronger in shyer individuals: more active winters were followed by later breeding phenology and poorer breeding performance in shy birds, but these effects were weaker or undetected in bolder individuals. Our study quantifies individual variability in the strength of carry-over effects on breeding and provides a mechanism explaining widespread differences in individual reproductive success.

Age-Related Changes in the Behaviour of Domestic Horses as Reported by Owners

Simple Summary

Some treatments for common problem behaviours in domestic horses can compromise horse welfare. Such behaviours can be the manifestation of pain, confusion and conflict. In contrast, among the desirable attributes in horses, boldness and independence are two important behavioural traits that affect the fearfulness, assertiveness and sociability of horses when interacting with their environment, objects, conspecifics and humans. Shy and socially dependent horses are generally more difficult to manage and train than their bold and independent counterparts. Previous studies have shown how certain basic temperament traits predict the behavioural output of horses, but few have investigated how the age of the horse and the age it was when started being trained under saddle affect behaviour. Using 1940 responses to the Equine Behaviour Assessment and Research Questionnaire (E-BARQ), the current study explored the behavioural evidence of boldness and independence in horses and how these related to the age of the horse. Results revealed age-related effects on boldness and independence of horses. Older horses were bolder than younger horses, but horses started under saddle at an older age were less bold and independent than those started at a younger age. Additionally, significant differences in boldness and independence relating to specific breeds and primary equestrian disciplines also emerged. Finally, riders with eight or more years of riding experience reported having more independent horses than those who had ridden their whole lives. Understanding how horses’ ages affect behavioural traits can improve horse–rider matching and potentially also optimise welfare.

Abstract

The broad traits of boldness and independence in domestic horses can affect their usefulness and, indirectly, their welfare. The objective of the current study was to explore associations between attributes that reflect equine boldness and independence with both the age of horses and the age at which they were started under saddle, as well as other variables including breed, colour and primary equestrian discipline. All data were sourced from responses (n = 1940) to the 97-question online Equine Behaviour Assessment and Research Questionnaire (E-BARQ). Twenty E-BARQ items from the dataset were selected to reflect boldness and independence and were tested for univariate significance at p < 0.2. Multivariable modelling of the effect of age on remaining traits was assessed by an ordinal logistic regression, using a cumulative log odds model. This revealed that older horses were bolder (p = 0.012). However, horses started under saddle at an older age were less bold and less independent (p = 0.040 and p = 0.010, respectively). Australian Stock Horses were bolder and more independent (p = 0.014 and p = 0.007, respectively) than crossbreed horses. Horses used for breeding conformation (p = 0.039), working equitation (p = 0.045), eventing (p = 0.044) and traditional working horses (p = 0.034) were bolder than those used for other disciplines. Dressage (p = 0.039) and therapy (p = 0.040) horses were less bold than horses used for other disciplines. Stallions were bolder (p = −0.034) than geldings. Brown (p = 0.049) and chestnut (p = 0.027) horses were less bold than bay horses. Compared to crossbreed horses, Thoroughbreds (p = 0.000) and companion horses (p = 0.017) were less bold whilst heavy horses (p = 0.029) and ponies (p = 0.044) were bolder. Compared to pleasure horses, mounted games horses (p = 0.033) were less independent whereas working equitation horses (p = 0.020) were more independent. Riders with more than eight years’ experience reported more independence in their horses (p = 0.015) than those who had ridden their whole lives. The study findings suggest that boldness and independence are separate traits and only boldness was associated with the age of the horse. Factors that relate to desirable boldness and independence are important in ridden horses because they can affect rider safety. Results from this study should improve horse–rider matching and thereby potentially enhance horse welfare.

Urban invaders are not bold risk-takers: a study of 3 invasive lizards in Southern California

Biological invasions threaten biodiversity worldwide, and therefore, understanding the traits of successful invaders could mitigate their spread. Many commonly invasive species do well in disturbed habitats, such as urban environments, and their abilities to effectively respond to disturbances could contribute to their invasiveness. Yet, there are noninvasive species that also do well in disturbed habitats. The question remains whether urban invaders behave differently in urban environments than noninvaders, which could suggest an "urban-exploiting" phenotype. In Southern California, the co-occurrence of invasive Italian wall lizards Podarcis siculus, brown anoles Anolis sagrei, and green anoles A. carolinensis, and native western fence lizards Sceloporus occidentalis offers an opportunity to test whether invasives exhibit consistent differences in risk-taking within human-altered habitats compared with a native species. We predicted that invasive lizards would exhibit more bold behavior by having shorter flight-initiation distances (FIDs) and by being found farther from a refuge (behaviors that would presumably maximize foraging in low-risk environments). Invasive populations had similar or longer FIDs, but were consistently found at distances closer to a refuge. Collectively, invasive lizards in urban habitats were not bolder than a native species. Reliance on nearby refuges might help species successfully invade urban habitats, and if a general pattern, may pose an added challenge in detecting or eliminating them.

Size-selective mortality induces evolutionary changes in group risk-taking behaviour and the circadian system in a fish

Intensive and trait-selective mortality of fish and wildlife can cause evolutionary changes in a range of life-history and behavioural traits. These changes might in turn alter the circadian system due to co-evolutionary mechanisms or correlated selection responses both at behavioural and molecular levels, with knock-on effects on daily physiological processes and behavioural outputs. We examined the evolutionary impact of size-selective mortality on group risk-taking behaviour and the circadian system in a model fish species. We exposed zebrafish Danio rerio to either large or small size-selective harvesting relative to a control over five generations, followed by eight generations during which harvesting was halted to remove maternal effects. Size-selective mortality affected fine-scale timing of behaviours. In particular, small size-selective mortality, typical of specialized fisheries and gape-limited predators targeting smaller size classes, increased group risk-taking behaviuor during feeding and after simulated predator attacks. Moreover, small size-selective mortality increased early peaks of daily activity as well as extended self-feeding daily activity to the photophase compared to controls. By contrast large size-selective mortality, typical of most wild capture fisheries, only showed an almost significant effect of decreasing group risk-taking behaviour during the habituation phase and no clear changes in fine-scale timing of daily behavioural rhythms compared to controls. We also found changes in the molecular circadian core clockwork in response to both size-selective mortality treatments. These changes disappeared in the clock output pathway because both size-selected lines showed similar transcription profiles. This switch downstream to the molecular circadian core clockwork also resulted in similar overall behavioural rhythms (diurnal swimming and self-feeding in the last hours of darkness) independent of the underlying molecular clock. To conclude, our experimental harvest left an asymmetrical evolutionary legacy in group risk-taking behaviour and in fine-scale daily behavioural rhythms. Yet, the overall timing of activity showed evolutionary resistance probably maintained by a molecular switch. Our experimental findings suggest that size-selective mortality can have consequences for behaviour and physiological processes.

Scaring Nemo: Contrasting effects of observer presence on two anemonefish species

Behaviours of Clark's anemonefish Amphiprion clarkii and the dusky anemonefish Amphiprion melanopus were studied in Vanuatu. Six anemones and their resident fish were observed for typical behaviours (hiding, watching, roaming, inter-, and intraspecific behaviour) with and without the presence of a snorkelling observer. Observer presence had significant but contrasting effects on hiding behaviour in A. clarkii and A. melanopus. Bolder anemonefish species may be able to outcompete other species in areas with high human presence.

Physiological Stress Integrates Resistance to Rattlesnake Venom and the Onset of Risky Foraging in California Ground Squirrels

Using venom for predation often leads to the evolution of resistance in prey. Understanding individual variation in venom resistance is key to unlocking basic mechanisms by which antagonistic coevolution can sustain variation in traits under selection. For prey, the opposing challenges of predator avoidance and resource acquisition often lead to correlated levels of risk and reward, which in turn can favor suites of integrated morphological, physiological and behavioral traits. We investigate the relationship between risk-sensitive behaviors, physiological resistance to rattlesnake venom, and stress in a population of California ground squirrels. For the same individuals, we quantified foraging decisions in the presence of snake predators, fecal corticosterone metabolites (a measure of “stress”), and blood serum inhibition of venom enzymatic activity (a measure of venom resistance). Individual responses to snakes were repeatable for three measures of risk-sensitive behavior, indicating that some individuals were consistently risk-averse whereas others were risk tolerant. Venom resistance was lower in squirrels with higher glucocorticoid levels and poorer body condition. Whereas resistance failed to predict proximity to and interactions with snake predators, individuals with higher glucocorticoid levels and in lower body condition waited the longest to feed when near a snake. We compared alternative structural equation models to evaluate alternative hypotheses for the relationships among stress, venom resistance, and behavior. We found support for stress as a shared physiological correlate that independently lowers venom resistance and leads to squirrels that wait longer to feed in the presence of a snake, whereas we did not find evidence that resistance directly facilitates latency to forage. Our findings suggest that stress may help less-resistant squirrels avoid a deadly snakebite, but also reduces feeding opportunities. The combined lethal and non-lethal effects of stressors in predator–prey interactions simultaneously impact multiple key traits in this system, making environmental stress a potential contributor to geographic variation in trait expression of toxic predators and resistant prey.

Do Differing Levels of Boldness Influence the Success of Translocation? A Pilot Study on Red Squirrels (Sciurus vulgaris)

Simple Summary

As many species go extinct across the world, conservation initiatives seek to protect and boost wildlife populations, including through translocation programmes that involve the movement or release of captive or wild-caught individuals back into areas they have historically occupied. Captive-bred animals to be released into the wild can undergo behavioural testing to determine if the individuals have skills that would aid survival and increase the establishment of new populations. This research illustrates different levels of boldness in red squirrels and suggests selecting animals for release based on their boldness or timidity. Despite working with a low sample size in this pilot study, we observed trends suggesting that selecting individuals based upon a bold/timid scale of personality may improve future releases of red squirrels. By releasing timid animals first, the establishment of a population may be more successful, and this can be followed by releasing bold animals in later releases to enable faster distribution expansion of the population. This could result in improved success rates of restoration programmes, thus, lowering costs, improving the plight of biodiversity, and reducing early deaths of the released wildlife. Thus, we highlight a need for future research and collaboration within the translocation sector to assess personality.

Abstract

Conservation translocations, including reintroductions, are practices that are vital to restoring biodiversity and ecosystem function within conservation schemes globally. Sadly, population translocations have had a poor success rate historically. At a time where biodiversity is constantly decreasing, improving translocation success is vital for future conservation schemes. Often, to improve success, the selection of individuals is based on genetic characteristics and behaviours linked directly to survival. Further development to improve selection is proposed within this paper using animal personality. The study took place opportunistically to test how personality, in particular an animal’s boldness/timidness, may influence a population restoration of red squirrels into the Ogwen Valley, North Wales. Despite frequent translocations, data on how boldness and timidness may affect the establishment of this species are low. Testing was performed on key survival behaviours and boldness/timidness pre-release. This was performed via video data collection and identification of key behaviours that could be used to identify boldness or behaviours that could be linked to reduced fitness once released. Encounters at different distance intervals were monitored post-release via camera trapping to identify if boldness/timidness may change the furthest encounter distance of focal animals away from their release site. Relationships between the period for an individual to reappear post-threat was significantly linked to boldness, with other behavioural results and the encounter distance also showing trends of a potential relationship. Our results indicate that bolder individuals have a higher chance of expressing behavioural traits that will increase exposure to risks and, therefore, reduce the likelihood of successfully establishing populations. However, the small sample size of this study means that further research is needed. We suggest that during early stages of conservation translocation programmes, personality testing for boldness should become common practice, and we recommend selecting timid individuals for an initial release to improve population establishment, with bolder individuals utilised later to expand population distribution.

Bolder and Brighter? Exploring Correlations Between Personality and Cognitive Abilities Among Individuals Within a Population of Wild Zebrafish, Danio rerio

Within populations, individual differences in behavioral and cognitive traits are dependent on the habitat and specific contexts, such as the presence of a predator or other risks. The ability to show variable responses to changing conditions can be of immense survival advantage to organisms. We studied individual differences in specific personality traits, such as boldness, exploration, and spatial ability, and the effect of these traits on learning ability and memory in the presence of a predatory threat, among wild caught zebrafish (Danio rerio). Under laboratory conditions, individuals were trained to perform a simple navigation task, and their performance, exploration, boldness traits were measured, along with learning and memory abilities under two contexts (i.e., in the presence and absence of a predator). Our results revealed that fish showed a clear decline in emergence time, exploration time, and feeding latency over trials, indicative of learning, and further tests for memory also showed memory retention. While the presence of a predator increased emergence time and latencies for navigating, indicating declines in boldness and exploration, these were found to be correlated to different personalities among the individuals and dependent on their sex. While females tended to be bolder and learned the spatial task faster, they showed lower memory retention abilities than males. Personality traits were also found to affect cognitive abilities among individuals. In general, the presence of a predator decreased performance latencies. However, bolder individuals were less affected and emerged more quickly from the refuge chamber than shy individuals. Our results point to the complex interplay of ecological context along with inherent correlations across personality traits that decide the overall personality and cognitive responses among individuals even within populations. These findings thus highlight the importance of an inclusive approach that combines personality and cognition studies for understanding variations within populations.

The impact of personality, morphotype and shore height on temperature-mediated behavioural responses in the beadlet anemone Actinia equina

Between-individual variation in behavioural phenotype, termed personality, is an important determinant of how populations cope with acute environmental fluctuation related to climate change. Personality in the beadlet sea anemone Actinia equina is linked to genetically distinct morphotypes, which are associated with different heights on the shore. In the intertidal zone, high-shore environments experience more environmental fluctuation due to longer periods of exposure, and animals adapted to live in these environments are predicted to deal more effectively with environmental perturbation than their low-shore counterparts. We collected beadlet anemones of two different morphotypes from three different shore heights. We investigated variation in two behaviours at three different temperatures and in a temporal control treatment where the temperature was not changed: startle response time, the time it took an anemone to re-extend its tentacles after a threatening stimulus, and immersion response time, the time to re-extend tentacles after simulated tidal immersion. These behaviours reflect risk-taking and allow individuals to be categorized as bold, shy or intermediate based upon response times. Both behaviours showed significant changes as the temperature increased. For immersion response, the morphotype associated with the low-shore-lengthened response times at high temperatures. For startle response, all animals lengthened their response times at high temperatures but animals collected from the low-shore lengthened theirs to the greatest degree. At the individual level, although control individuals exhibited temporal changes in their response times, a clear effect of temperature was present in both behaviours. Shy and bold individuals became more intermediate at higher temperatures in immersion response (this effect was present to a lesser degree in control individuals), while intermediate individuals raised their response times at higher temperatures for startle response. Given that prolonged tentacle retraction reduces foraging opportunities and can negatively impact respiratory efficiency, our data suggest that some individuals within a single population of A. equina, particularly those associated with the lower shore, may exhibit less effective behavioural responses to temperature shifts than others. These findings demonstrate that acute temperature changes influence risk-taking, and could have profound short and long-term implications for survival in the face of climate change.

Short-term captivity drives hypothalamic plasticity and asymmetry in wild-caught northern red bellied dace (Chrosomus eos)

Teleost fish are neuroplastic and are known to alter their brain morphology and behaviour in response to environmental change such as an increase in predation pressure. The hypothalamus plays a key role in regulating behavioural responses to predation risk. In this study, wild-caught northern red bellied dace (Chrosomus eos) developed smaller and less symmetric hypothalami when held in captivity for 14 days; both measures correlated with boldness in a latency to emerge test. This study's results highlight the potential impact of short-term holding conditions on brains and behaviour.

Behavioural traits modulate the use of heterospecific social information for nest site selection: experimental evidence from a wild bird population

The use of social information for making decisions is common but can be constrained by behavioural traits via, for example, the ability to gather information. Such constrained information use has been described in foraging habitat selection; yet it remains unexplored in the breeding habitat selection context, despite potentially strong fitness consequences. We experimentally tested whether three behavioural traits (aggressiveness, boldness and neophobia) affected the use of heterospecific social information for nest site selection in wild collared flycatchers Ficedula albicollis. Flycatchers have previously been found to copy or reject an artificial apparent preference of tits (their main competitors) for a nest site feature: they preferred nest-boxes with the same or a different feature, depending on tit early reproductive investment. Here, we confirmed this result and showed that shy individuals and less aggressive old males (i.e. 2 years old or older) copied tit apparent preference, while more aggressive old males rejected the tit preference. Aggressiveness and boldness may allow males to access more information sources or affect males' interactions with dominant tits when selecting a nest site. Our study highlights the links between variation in behaviours and social information use for breeding habitat selection and calls for further work to explore underlying mechanisms.

Towards a comparative approach to the structure of animal personality variation

Latent personality traits underpinning observed behavioral variation have been studied in a great many species. However, a lack of standardized behavioral assays, coupled to a common reliance on inferring personality from a single, observed, behavioral trait makes it difficult to determine if, when, and how conclusions can be directly compared across taxa. Here, we estimate the among-individual (co)variance structure (ID) for a set of four behaviors expressed in an open field trial, putatively indicative of boldness, in seven species of small freshwater fish. We show that the ID matrices differ in terms of the total amount of variation present, and crucially the orientation, and as a consequence, biological interpretation of the first eigenvector. Specifically, loading of observed traits on the main axis of variation in ID matched a priori expectations for a shy-bold continuum in only three of the seven cases. Nonetheless, when the "shape" of the matrices was compared in higher dimensions, there was a high level of similarity among species, and weak evidence of phylogenetic signal. Our study highlights the present difficulty of trying to compare empirical inferences about specific personality traits across studies. However, it also shows how multivariate data collection and analysis allows the structure of behavioral variation to be quantitatively compared across populations or species without reliance on ambiguous verbal labels. This suggests that the field may have much to gain from greater uptake of phylogenetically informed comparative approaches when seeking to test evolutionary hypotheses about the origin and maintenance of personality variation.

Response to underwater laser pointer in the Orange-finned Anemonefish Amphiprion chrysopterus and three-spot damselfish Dascyllus trimaculatus

Response of orange-finned anemonefish Amphiprion chrysopterus and three-spot damselfish Dascyllus trimaculatus to red laser-pointer light was studied in Mo'orea, French Polynesia. Four magnificent anemones Heteractis magnifica and their resident fish were observed for typical behaviours (biting, chasing, hiding, posing, lunging and retreating) with and without exposure to laser-pointer light. Lunging behaviour increased significantly for both fish species upon exposure to laser-pointer light; none of the other behaviours changed significantly. We advance the hypothesis that orange-finned anemonefish and three-spot damselfish interpret laser pointer stimulation as a territorial threat.

Social environment determines the effect of boldness and activity on survival

Populations of animals are composed of individuals that differ in ecologically relevant behaviors. Building evidence also suggests that individuals occupy different social niches. Here, in a mark-recapture experiment, we show evidence of an interacting effect of behavior and social niche on survival in the wild: bold individuals had higher survival if they were initially captured in groups while shy, inactive individuals had higher survival if they were initially captured when alone. These findings provide support for the hypothesis that behavioral type-environment correlations can be favored by natural selection.

Personality predicts foraging site fidelity and trip repeatability in a marine predator

Animal populations are often comprised of both foraging specialists and generalists. For instance, some individuals show higher foraging site fidelity (spatial specialization) than others. Such individual differences in degree of specialization can persist over time‐scales of months or even years in long‐lived animals, but the mechanisms leading to these different individual strategies are not fully understood.

There is accumulating evidence that individual variation in foraging behaviour is shaped by animal personality traits, such as boldness. Despite this, the potential for boldness to drive differences in the degree of specialization is unknown.

In this study, we used novel object tests to measure boldness in black‐legged kittiwakes (Rissa tridactyla) breeding at four colonies in Svalbard and deployed GPS loggers to examine their at‐sea foraging behaviour. We estimated the repeatability of foraging trips and used a hidden Markov model to identify locations of foraging sites in order to quantify individual foraging site fidelity.

Across the breeding season, bolder birds were more repeatable than shy individuals in the distance and range of their foraging trips, and during the incubation period (but not chick rearing), bolder individuals were more site‐faithful. Birds exhibited these differences while showing high spatial similarity in foraging areas, indicating that site selection was not driven by personality‐dependent spatial partitioning.

We instead suggest that a relationship between boldness and site fidelity may be driven by differences in behavioural flexibility between bold and shy individuals. Together, these results provide a potential mechanism by which widely reported individual differences in foraging specialization may emerge.

Does inbreeding affect personality traits?

The question of why variation is maintained in personality traits is an evolutionary puzzle. According to the condition-dependence hypothesis, such traits depend on condition, which limits the behavioral choices available to individuals. Because condition is affected by many genes, it can effectively be manipulated by inbreeding, which exposes the effects of deleterious recessive mutations. Here, I compared two personality traits, boldness and tendency to explore, of male guppies (Poecilia reticulata) from first-generation inbred and outbred treatments. Boldness in guppies is associated with increased sexual attractiveness and is thus expected to affect fitness. Therefore, I hypothesized that the personality traits would be negatively affected by inbreeding. However, the results indicated that inbred guppies did not differ in either personality trait from their outbred counterparts. This finding suggests that mechanisms other than condition dependence are maintaining personality variation in the guppy.