Quantifying personality in the terrestrial hermit crab: Different measures, different inferences

There is much interest in studying animal personalities but considerable debate as to how to define and evaluate them. We assessed the utility of one proposed framework while studying personality in terrestrial hermit crabs (Coenobita clypeatus). We recorded the latency of individuals to emerge from their shells over multiple trials in four unique manipulations. We used the specific testing situations within these manipulations to define two temperament categories (shyness-boldness and exploration-avoidance). Our results identified individual behavioral consistency (i.e., personality) across repeated trials of the same situations, within both categories. Additionally, we found correlations between behaviors across contexts (traits) that suggested that the crabs had behavioral syndromes. While we found some correlations between behaviors that are supposed to measure the same temperament trait, these correlations were not inevitable. Furthermore, a principal component analysis (PCA) of our data revealed new relationships between behaviors and provided the foundation for an alternate interpretation: measured behaviors may be situation-specific, and may not reflect general personality traits at all. These results suggest that more attention must be placed on how we infer personalities from standardized methods, and that we must be careful to not force our data to fit our frameworks.     

Within‐Individual Correlations Reveal Link Between a Behavioral Syndrome,Condition, and Cortisol in Free‐Ranging Belding's Ground Squirrels

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.     

Testing for personality consistency across naturally occurring behavioral contexts in sanctuary chimpanzees (Pan troglodytes)

Personality is both a reflection of the bio-behavioral profile of individuals and a summary of how they typically interact with their physical and social world. Personality is usually defined as having distinct behavioral characteristics, which are assumed to be consistent over time and across contexts. Like other mammals, primates have individual differences in personality. Although temporal consistency is sometimes measured in primates, and contextual consistency is sometimes measured across experimental contexts, it is rare to measure both in the same individuals and outside of experimental settings. Here, we aim to measure both temporal and contextual consistency in chimpanzees, assessing their personality with behavioral observations from naturally occurring contexts (i.e., real-life settings). We measured personality-based behaviors in 22 sanctuary chimpanzees, in the contexts of feeding, affiliation, resting, and solitude, across two time periods, spanning 4 years. Of the 22 behaviors recorded, about 64% were consistent across two to four contexts and 50% were consistent over time. Ten behaviors loaded significantly onto three trait components: explorativeness, boldness-sociability, and anxiety-sociability, as revealed by factor analysis. Like others, we documented individual differences in the personality of chimpanzees based on reliably measured observations in real-life contexts. Furthermore, we demonstrated relatively strong, but not absolute, temporal, and contextual consistency in personality-based behaviors. We also found another aspect of individual differences in personality, specifically, the extent to which individual chimpanzees show consistency. Some individuals showed contextual and temporal consistency, whereas others show significant variation across behaviors, contexts, and/or time. We speculate that the relative degree of consistency in personality may vary within chimpanzees. It may be that different primate species vary in the extent to which individuals show consistency of personality traits. Our behavioral-based assessment can be used with wild populations, increasing the validity of personality studies, facilitating comparative studies and potentially being applicable to conservation efforts.     

A Continuum of Behavioral Plasticity in Urban and Desert Black Widows

Behavioral plasticity marks an individual's ability to modulate behavior across functional contexts. Behavioral syndromes, on the other hand, appear as consistent individual variation in behavior that is both repeatable for individuals within a functional context (e.g., consistent voracity toward prey) and correlated across contexts (e.g., high voracity toward prey and high levels of boldness toward enemies). Thus, adaptive plasticity and syndromes represent two extremes of a behavioral plasticity continuum upon which most behavioral phenotypes fall. We tested for both adaptive plasticity and behavioral syndromes in the western black widow spider, Latrodectus hesperus. We measured behavior in three contexts: startle, startle + prey, and startle + mate, and found (1) classic behaviorally plastic responses to predation risk, (2) high repeatability of behavior within contexts, and (3) evidence of a correlation between startle + prey and startle + mate contexts, indicative of a behavioral syndrome. As relative behavioral plasticity may vary across populations, we also compared urban and desert populations to test whether spiders from these habitats exhibit different behaviors and/or behavioral syndromes. While we found that urban males used in mating trials courted urban females significantly more than desert females, we found no other differences in the behavior of urban and desert black widows. Thus, black widows, regardless of habitat, are characterized by both context‐specific behavioral plasticity and across‐context correlations, presenting a phenotypic complexity that is likely exhibited, to varying degrees, by most organisms.     

On the evolution of personalities via frequency-dependent selection

Personality differences can be found in a wide range of species across the animal kingdom, but why natural selection gave rise to such differences remains an open question. Frequency-dependent selection is a potent mechanism explaining variation; it does not explain, however, the other two key features associated with personalities, consistency and correlations. Using the hawk-dove game and a frequency-dependent foraging game as examples, we here show that this changes fundamentally whenever one takes into account the physiological architecture underlying behavior (e.g., metabolism). We find that the inclusion of physiology changes the evolutionary predictions concerning consistency and correlations: while selection gives rise to inconsistent individuals and stochastically fluctuating behavioral correlations in scenarios that neglect physiology, we find high levels of behavioral consistency and tight and stable trait correlations in scenarios that incorporate physiology. The coevolution of behavioral and physiological traits also gives rise to adaptive physiological differences that are systematically associated with behavioral differences. As well as providing a framework for understanding behavioral consistency and behavioral correlations, our work thus also provides an explanation for systematic physiological differences within populations, a phenomenon that appears to exist in a wide range of species but that, up to now, has been poorly understood.     

Individual Variation in Male Size and Behavioral Repertoire in the Sailfin Molly Poecilia latipinna

Variation among individuals in the expression of behaviors and associations of behaviors in different contexts can lead to the maintenance of behavioral polymorphisms. Individual variation in morphology is often associated with behavioral polymorphism, yet the degree to which morphology predicts behavioral phenotype is not well understood. We measured individual variation in size and behaviors in the sailfin molly, Poecilia latipinna, by comparing the behavior of individual males of different sizes across four different contexts (mating, exploratory tendency, sociability, and predator inspection). We also investigated the degree to which male size, a fixed genetic trait, influenced the expression of each behavior and associations between behaviors. We found that male mollies show strong associations between certain behaviors and only some of these are predicted by male size. For example, size has a strong influence on the courtship‐boldness axis with larger males showing higher rates of courtship displays and being bolder in predator inspection. A positive association was found between exploratory tendency, sociability, and gonopodial thrusting rates, yet the expression of these behaviors was independent of male size. Thus, sailfin mollies, like many fish species, show associations of behaviors that contribute to differences among males in personality type. The fixed genetic effect of male size at maturity influences courtship and boldness, but individual variation in exploratory tendency, sociability, and sneak copulation attempts through gonopodial thrusts is independent of male size. Such variation among males in behavioral associations within and between different contexts may slow the rate at which populations of P. latipinna can diverge in individual behaviors.     

Behavioral syndromes: an intergrative overiew

A behavioral syndrome is a suite of correlated behaviors expressed either within a given behavioral context (e.g., correlations between foraging behaviors in different habitats) or across different contexts (e.g., correlations among feeding, antipredator, mating, aggressive, and dispersal behaviors). For example, some individuals (and genotypes) might be generally more aggressive, more active or bold, while others are generally less aggressive, active or bold. This phenomenon has been studied in detail in humans, some primates, laboratory rodents, and some domesticated animals, but has rarely been studied in other organisms, and rarely examined from an evolutionary or ecological perspective. Here, we present an integrative overview on the potential importance of behavioral syndromes in evolution and ecology. A central idea is that behavioral correlations generate tradeoffs; for example, an aggressive genotype might do well in situations where high aggression is favored, but might be inappropriately aggressive in situations where low aggression is favored (and vice versa for a low aggression genotype). Behavioral syndromes can thereby result in maladaptive behavior in some contexts, and potentially maintain individual variation in behavior in a variable environment. We suggest terminology and methods for studying behavioral syndromes, review examples, discuss evolutionary and proximate approaches for understanding behavioral syndromes, note insights from human personality research, and outline some potentially important ecological implications. Overall, we suggest that behavioral syndromes could play a useful role as an integrative bridge between genetics, experience, neuroendocrine mechanisms, evolution, and ecology.     

Syndromes or Flexibility: Behavior during a Life History Transition of a Coral Reef Fish

The theory of behavioral syndromes focuses on quantifying variation in behavior within and among individual organisms and attempts to account for the maintenance of differences in behavior that occur in a consistent manner among individuals. Behavioral syndromes have potentially important ecological consequences (e.g. survivorship tradeoffs) and can be shaped by population dynamics through selective mortality. Here, we search for any evidence for consistency of behavior across situations in juveniles of a common damselfish, Pomacentrus amboinensis (Pomacentridae) at the transition between larval habitats in the plankton and juvenile habitats on the reef. Naïve fish leaving the pelagic phase to settle on reefs were caught by light traps and their behaviors observed using similar methods across three different situations (small aquaria, large aquaria, field setting); all of which represent low risk and well-sheltered environments. Seven behavioral traits were compared within and among individuals across situations to determine if consistent behavioral syndromes existed. No consistency was found in any single or combination of behavioral traits for individuals across all situations. We suggest that high behavioral flexibility is likely beneficial for newly-settled fish at this ontogenetic transition and it is possible that consistent behavioral syndromes are unlikely to emerge in juveniles until environmental experience is gained or certain combinations of behaviors are favored by selective mortality.     

You eat what you are: personality‐dependent filial cannibalism in a fish with paternal care

Many animal parents invest heavily to ensure offspring survival, yet some eventually consume some or all of their very own young. This so‐called filial cannibalism is known from a wide range of taxa, but its adaptive benefit remains largely unclear. The extent to which parents cannibalize their broods varies substantially not only between species, but also between individuals, indicating that intrinsic behavioral differences, or animal personalities, might constitute a relevant proximate trigger for filial cannibalism. Using a marine fish with extensive paternal care, the common goby (Pomatoschistus microps), we investigated the influence of animal personality on filial cannibalism by assessing (1) behavioral consistency across a breeding and a nonbreeding context; (2) correlations between different breeding (egg fanning; filial cannibalism) and nonbreeding (activity) behaviors, and, in a separate experiment; (3) whether previously established personality scores affect filial cannibalism levels. We found consistent individual differences in activity across contexts. Partial filial cannibalism was independent of egg fanning but correlated strongly with activity, where active males cannibalized more eggs than less active males. This pattern was strong initially but vanished as the breeding season progressed. The incidence of whole clutch filial cannibalism increased with activity and clutch size. Our findings indicate that filial cannibalism cannot generally be adjusted independently of male personality and is thus phenotypically less plastic than typically assumed. The present work stresses the multidimensional interaction between animal personality, individual plasticity and the environment in shaping filial cannibalism.     

Repeatable nest defense behavior in a wild population of Eastern bluebirds (Sialia sialis) as evidence of personality

Consistent individual differences in behavior, or personality, have been demonstrated in a variety of species other than humans, including mammals, birds, and invertebrates. Behavioral consistency has been shown to affect dispersal, foraging, exploration, and antipredator responses, which may have an impact on parental and offspring survival. Despite increasing research in behavioral consistency, the repeatability of nest defense behavior has rarely been assessed in wild bird populations. Furthermore, previous studies investigating nest defense behavior have utilized laboratory studies or mounted predators to elicit defensive behavior. It is important to assess personality in wild populations to fully understand the fitness consequences of behavioral consistency across natural contexts and to utilize live predators or competitors for accurate assessment of defensive behavior. We used an ecologically relevant, live, invasive, nest site competitor, the house sparrow (Passer domesticus), to elicit nest defense behavior in a wild population of Eastern bluebirds (Sialia sialis) to determine if nest defense behavior is repeatable within and between years for males and females (males: 2009, N?=?17; 2010, N?=?18; both years, N?=?9. Females: 2009, N?=?22; 2010, N?=?15; both years, N?=?11). We also determined if individual behavior changes as a function of season, parental age, brood size, or the number of house sparrows around the nest site. We found that females demonstrated repeatable behavior both within and between years. Male nest defense behavior was only repeatable in 1 year and was influenced by season in the other year. Parental age, brood size, and the number of house sparrows around the nest site did not affect nest defense behavior. We conclude that Eastern bluebirds demonstrate consistent nest defense behavior, or personality, although males are more plastic than females.     

Social familiarity modulates personality trait in a cichlid fish

Personality traits, such as exploration–avoidance, are expected to be adaptive in a given context (e.g. low-risk environment) but to be maladaptive in others (e.g. high-risk environment). Therefore, it is expected that personality traits are flexible and respond to environmental fluctuations, given that consistency across different contexts is maintained, so that the relative individual responses in relation to others remains the same (i.e. although the magnitude of the response varies the differences between high and low responders are kept). Here, we tested the response of male cichlid fish (Oreochromis mossambicus) to a novel object (NO) in three different social contexts: (i) social isolation, (ii) in the presence of an unfamiliar conspecific, and (iii) in the presence of a familiar conspecific. Males in the familiar treatment exhibited more exploratory behaviour and less neophobia than males in either the unfamiliar or the social isolation treatments. However, there were no overall correlations in individual behaviour across the three treatments, suggesting a lack of consistency in exploration–avoidance as measured by the NO test in this species. Moreover, there were no differences in cortisol responsiveness to an acute stressor between the three treatments. Together, these results illustrate how behavioural traits usually taken as measures of personality may exhibit significant flexibility and lack the expected consistency across different social contexts.     

Exploration Behavior and Morphology are Correlated in Captive Gray Mouse Lemurs (<Emphasis Type="Italic">Microcebus murinus</Emphasis>)

Behavior varies among individuals and is flexible within individuals. However, studies of behavioral syndromes and animal personality have demonstrated that animals can show consistency in their behavior and as such may be restricted in their behavioral responses. Like any other trait, including morphology, performance, or physiology, personality is now considered an important component of ecology and may have fitness consequences. Moreover, in some species personality correlates with other traits, as predicted in the context of a recent theoretical framework postulating that individual differences in growth and body size can affect behavior through effects on growth–mortality tradeoffs. This “pace of life” hypothesis predicts that animals that explore more should be larger and have higher growth rates than those that explore less. We tested for associations between morphology and a behavioral trait in a captive colony of gray mouse lemurs (Microcebus murinus). We used open-field tests to evaluate exploration behavior and measured a series of morphological traits in 72 individuals (32 males and 40 females). Our results show that the latency to start exploring correlates positively with adult body size and body weight at birth. These data provide evidence for a link between morphology and behavior in this species, thus supporting predictions of dispersal models but diverging from the predictions of the “pace of life” model.     

Two Sides of the Same Coin? Consistency in Aggression to Conspecifics and Predators in a Female Songbird

Different forms of aggression have traditionally been treated separately according to function or context (e.g. aggression towards a conspecific versus a predator). However, recent work on individual consistency in behavior predicts that different forms of aggression may be correlated across contexts, suggesting a lack of independence. For nesting birds, aggression towards both conspecifics and nest predators can affect reproductive success, yet the relationship between these behaviors, especially in females, is not known. Here we examine free-living female dark-eyed juncos (Junco hyemalis) and compare their aggressive responses towards three types of simulated intruders near the nest: a same-sex conspecific, an opposite-sex conspecific, and a nest predator. We also examine differences in the strength of response that might relate to the immediacy of the perceived threat the intruder poses for the female or her offspring. We found greater aggression directed towards a predator than a same-sex intruder, and towards a same-sex than an opposite-sex intruder, consistent with a predator being a more immediate threat than a same-sex intruder, followed by an opposite-sex intruder. We also found positive relationships across individuals between responses to a same-sex intruder and a simulated predator, and between responses to a same-sex and an opposite-sex intruder, indicating that individual females are consistent in their relative level of aggression across contexts. If correlated behaviors are mediated by related mechanisms, then different forms of aggression may be expressions of the same behavioral tendency and constrained from evolving independently.     

High Repeatability of Anti-Predator Responses and Resting Metabolic Rate in a Beetle

Measures of repeatability are essential for understanding behavioral consistency and individual differences in behavior, i.e. animal personalities. We studied anti-predator responses of the yellow mealworm beetle (Tenebrio molitor) and performed behavioral tests in plastic containers representing a typical laboratory environment of T. molitor. Behavioral tests were repeated in Eppendorf test tubes where we also measured resting metabolic rate (RMR). Results show that the response latency to a threatening/startling stimulus, and the total time spent in the state of tonic immobility, correlated across the tests. The behavioral responses were repeatable and RMR covaried phenotypically with personality: we found a negative correlation between response latency time and time spent immobile, a positive correlation between response latency and RMR, and a negative correlation between RMR and total time spent immobile. These correlations were also similar across trials performed in the Eppendorf test tubes and the plastic containers.     

Associations between glucocorticoids and sociality across a continuum of vertebrate social behavior

The causes and consequences of individual differences in animal behavior and stress physiology are increasingly studied in wild animals, yet the possibility that stress physiology underlies individual variation in social behavior has received less attention. In this review, we bring together these study areas and focus on understanding how the activity of the vertebrate neuroendocrine stress axis (HPA‐axis) may underlie individual differences in social behavior in wild animals. We first describe a continuum of vertebrate social behaviors spanning from initial social tendencies (proactive behavior) to social behavior occurring in reproductive contexts (parental care, sexual pair‐bonding) and lastly to social behavior occurring in nonreproductive contexts (nonsexual bonding, group‐level cooperation). We then perform a qualitative review of existing literature to address the correlative and causal association between measures of HPA‐axis activity (glucocorticoid levels or GCs) and each of these types of social behavior. As expected, elevated HPA‐axis activity can inhibit social behavior associated with initial social tendencies (approaching conspecifics) and reproduction. However, elevated HPA‐axis activity may also enhance more elaborate social behavior outside of reproductive contexts, such as alloparental care behavior. In addition, the effect of GCs on social behavior can depend upon the sociality of the stressor (cause of increase in GCs) and the severity of stress (extent of increase in GCs). Our review shows that the while the associations between stress responses and sociality are diverse, the role of HPA‐axis activity behind social behavior may shift toward more facilitating and less inhibiting in more social species, providing insight into how stress physiology and social systems may co‐evolve.     

The ontogeny of personality traits in the desert funnel‐web spider,Agelenopsis lisa (Araneae: Agelenidae)

Trait consistency over time is one of the cornerstones of animal personality. Behavioral syndromes are the result of correlations between behaviors. While repeatability in behavior is not a requirement for behavioral syndromes, the two concepts studied together provide a more comprehensive understanding of how behavior can change over ontogeny. The roles of ontogenetic processes in the emergence of personality and behavioral syndromes have received much individual attention. However, the characterization of both individual trait consistency and behavioral syndromes across both sexes, as in our study, has been relatively rare. Ontogeny refers to changes that occur from conception to maturation, and juveniles might be expected to undergo different selection pressures than sexually mature individuals and also will experience profound changes in hormones, morphology, and environment during this period. In this study, we test for behavioral trait consistency and behavioral syndromes across six time points during ontogenetic development in the desert funnel‐web spider (Agelenopsis lisa). Our results indicate behavioral traits generally lack consistency (repeatability) within life stages and across ontogeny. However, penultimate males and mature females do exhibit noticeable mean‐level changes, with greater aggressive responses toward prey, shorter latencies to explore their environment and in the exhibition of risk‐averse responses to predatory cues. These traits also show high repeatability. Some trait correlations do exist as well. In particular, a strong correlation between aggressiveness toward prey and exploration factors is observed in mature males. However, because correlations among these factors are unstable across ontogeny and vary in strength over time, we conclude that behavioral syndromes do not exist in this species. Nevertheless, our results indicate that increased consistency, increasing average trait values, and varying correlations between traits may coincide with developmentally important changes associated with sexual maturation, albeit at different time points in males and females. This period of the life cycle merits systematic examination across taxa.     

Wasteful Killing in Urban Black Widows: Gluttony in Response to Food Abundance

Current work in behavioral ecology contrasts traditional hypotheses of context‐specific adaptation with the suggestion that behaviors are often coupled such that animals exhibit context‐general behavioral syndromes. Wasteful killing, the partial consumption and/or abandonment of prey, is a perplexing phenomenon because the costs of this behavior seem high (e.g. energetic loss, risk of injury). Wasteful killing may be the product of a context‐specific, adaptive foraging strategy restricted spatially and/or temporally to conditions of prey abundance. Alternatively, wasteful killing may represent a context‐general syndrome of high aggression that results in the capture of prey that are not consumed. We investigated the conditions in which a web‐building spider the North American black widow (Latrodectus hesperus) participates in wasteful killing. We employed a powerful repeated‐measures design that reduces error variance by controlling for individual differences. Across the adult life cycle of female spiders collected from urban habitats throughout Phoenix, AZ, we repeatedly measured each spider’s foraging voracity and wastefulness after varied periods of food restriction (2, 7, and 14 d). While food restriction decreased body condition, condition alone was a poor predictor of voracity and wasteful killing. Our results indicate that previous food restriction i) shortens latency to attack, ii) heightens the number of prey killed per trial, and iii) reduces wastefulness. Latency to attack and wasteful killing were neither repeatable within individuals nor correlated with each other and therefore appear unlikely to be components of a behavioral syndrome. We discuss other possible benefits for wasteful killing in the contexts of predation risk and mate attraction.     

Social context affects behavior,preoptic area gene expression,and response to D2 receptor manipulation during territorial defense in a cichlid fish

Social context often has profound effects on behavior, yet the neural and molecular mechanisms which mediate flexible behavioral responses to different social environments are not well understood. We used the African cichlid fish, Astatotilapia burtoni, to examine aggressive defense behavior across three social contexts representing different motivational states: a reproductive opportunity, a familiar male and a neutral context. To elucidate how differences in behavior across contexts may be mediated by neural gene expression, we examined gene expression in the preoptic area, a brain region known to control male aggressive and sexual behavior. We show that social context has broad effects on preoptic gene expression. Specifically, we found that the expression of genes encoding nonapeptides and sex steroid receptors are upregulated in the familiar male context. Furthermore, circulating levels of testosterone and cortisol varied markedly depending on social context. We also manipulated the D2 receptor (D2R) in each social context, given that it has been implicated in mediating context‐dependent behavior. We found that a D2R agonist reduced intruder‐directed aggression in the reproductive opportunity and familiar male contexts, while a D2R antagonist inhibited intruder‐directed aggression in the reproductive opportunity context and increased aggression in the neutral context. Our results demonstrate a critical role for preoptic gene expression, as well as circulating steroid hormone levels, in encoding information from the social environment and in shaping adaptive behavior. In addition, they provide further evidence for a role of D2R in context‐dependent behavior.     

Habitat quality mediates personality through differences in social context

Assessing the stability of animal personalities has become a major goal of behavioral ecologists. Most personality studies have utilized solitary individuals, but little is known on the extent that individuals retain their personality across ecologically relevant group settings. We conducted a field survey which determined that mud crabs, Panopeus herbstii, remain scattered as isolated individuals on degraded oyster reefs while high quality reefs can sustain high crab densities (>10 m^?2). We examined the impact of these differences in social context on personality by quantifying the boldness of the same individual crabs when in isolation and in natural cohorts. Crabs were also exposed to either a treatment of predator cues or a control of no cue throughout the experiment to assess the strength of this behavioral reaction norm. Crabs were significantly bolder when in groups than as solitary individuals with predator cue treatments exhibiting severally reduced crab activity levels in comparison to corresponding treatments with no predator cues. Behavioral plasticity depended on the individual and was strongest in the presence of predator cues. While bold crabs largely maintained their personality in isolation and group settings, shy crabs would become substantially bolder when among conspecifics. These results imply that the shifts in crab boldness were a response to changes in perceived predation risk, and provide a mechanism for explaining variation in behavioral plasticity. Such findings suggest that habitat degradation may produce subpopulations with different behavioral patterns because of differing social interactions between individual animals.     

Molecular keys unlock the mysteries of variable survival responses of blue crabs to hypoxia

Hypoxia is a major stressor in coastal ecosystems, yet generalizing its impacts on fish and shellfish populations across hypoxic events is difficult due to variability among individuals in their history of exposure to hypoxia and related abiotic variables, and subsequent behavioral and survival responses. Although aquatic animals have diverse physiological responses to cope with hypoxia, we know little about how inter-individual variation in physiological state affects survival and behavioral decisions under hypoxic conditions. Laboratory experiments coupled with molecular techniques determined how extrinsic factors (e.g., water body and temperature) and respiratory physiology (hemocyanin concentration and structure) affected survival and behavior of adult blue crabs (Callinectes sapidus) exposed to different levels of hypoxia over a 30-h time period. Nearly 100% of crabs survived the 1.3 mg dissolved oxygen (DO) l^?1 treatment (18.4% air saturation), suggesting that adult blue crabs are tolerant of severe hypoxia. Probability of survival decreased with increasing hypoxic exposure time, lower DO, and increasing temperature. Individual-level differences in survival correlated with water body and crab size. Crabs collected from the oligo/mesohaline and hypoxic Neuse River Estuary (NRE), North Carolina, USA survived hypoxic exposures longer than crabs from the euhaline and normoxic Bogue and Back Sounds, North Carolina. Furthermore, small NRE crabs survived longer than large NRE crabs. Hemocyanin (Hcy) concentration did not explain these individual-level differences, however, hypoxia-tolerant crabs had Hcy structures indicative of a high-O₂-affinity form of Hcy, suggesting Hcy “quality” (i.e., structure) may be more important for hypoxia survival than Hcy “quantity” (i.e., concentration). The geographic differences in survival we observed also highlight the importance of carefully selecting experimental animals when planning to extrapolate results to the population level.