Fight-flight or freeze-hide? Personality and metabolic phenotype mediate physiological defence responses in flatfish

Unveil the toxicity induced on early life stages of zebrafish (Danio rerio) exposed to 3,4-methylenedioxymethamphetamine (MDMA) and its enantiomers

The increased detection of the recreational drug 3,4-methylenedioxymethamphetamine (MDMA) in aquatic ecosystems, has raised concern worldwide about its possible negative impacts on wildlife. MDMA is produced as racemate but its enantioselective effects on non-target organisms are poorly understood. Therefore, this study aimed to provide a comprehensive study of the toxicity of MDMA and its enantiomers in the early life stages of zebrafish (Danio rerio). Zebrafish embryos (≈3 h post fertilization) were exposed to different concentrations (0.02, 0.2, 2, 20, and 200 μg/L) of (R,S)-MDMA and both pure enantiomers. Both enantiomers induced effects on embryonic development, DNA integrity, and behaviour and enantioselective effects were noted. (S)-MDMA exhibits higher toxic effects on embryonic development level with increased mortality and severity of teratogenic effects, and behavioural abnormalities in acoustic startle-habituation response. (R)-MDMA affected general activity and avoidance behaviour, showing greater inhibitory effects on behavioural activity. Additionally, (R,S)-MDMA induced higher genotoxic effects than the two isolated enantiomers. These results are of concern at populational levels since effects on mortality, development, and behaviour were observed even at environmentally relevant concentrations, which can cause a reduction of larval viability and in the number of individuals in each generation, and an increase in the risk of predation of the organisms. Yet, the bioaccumulation studies showed that MDMA is not accumulated in zebrafish. Therefore, this work demonstrated for the first time the occurrence of MDMA enantiotoxicity in the early life stages of zebrafish, which should be considered in further environmental risk assessments involving fish species or other non-target aquatic organisms.

Swimming performance, but not metabolism, is related to a boldness-activity syndrome in schoolmaster snapper (Lutjanus apodus)

Commercial overexploitation and climate change can alter the physiology and behavior of marine organisms, although intraspecific phenotypic responses to such changes can vary greatly depending on the environment, species, and severity of the stressor. Under the pace-of-life syndrome (POLS) hypothesis, behavior, physiology, and life-history traits are linked, and thus, affected by selection targeting any aspect of organismal biology. However, these links are understudied in tropical marine fishes, and further work is needed to better understand the impacts of fisheries and climate change on wild stocks. Moreover, tropical regions have a greater reliance on fisheries; thus investigations should focus on species with substantial socioeconomic value to ensure benefits at the local level. This study aimed to address this need by measuring the behavior (boldness and activity), metabolism, and swimming performance (using a critical swim speed [Ucrit] test) of schoolmaster snapper Lutjanus apodus in Eleuthera, the Bahamas. We report a strong positive correlation between boldness and activity, high repeatability of these behavioral metrics, and two groupings that were consistent with "proactive" and "reactive" behavioral types. These behavioral types differed significantly in their swimming performance, with reactive individuals having a 13.1% higher mean Ucrit. In contrast, no significant differences were found in the measured metabolic parameters between behavioral types. This study is the first to investigate the intraspecific links between behavior and physiology in a snapper species, using the novel and ecologically relevant comparison of Ucrit with behavioral syndrome types. These data suggest that additional research is needed to better predict the success of proactive/reactive tropical fish if overexploited and as influenced by climate change.

Differential toxic effects of nano-titanium dioxide on clams (Meretrix meretrix) with various individuality

Nano-TiO2 is inevitably released into aquatic environment with increasing of nanotechnology industries. Study pointed that different individuality showed divergent behavioral and physiological response when facing environmental stress. However, the effects of nano-TiO2 on tolerance of bivalves with different individualities remain unknown. In the study, clams were divided into two types of individuality - proactive and reactive by post-stress recovery method. It turned out that proactive individuals had quicker shell opening level, stronger burrowing behavior, faster feeding recovery, higher standard metabolic rate and more rapid ammonia excretion ability than reactive individuals after exposed to air. Then, the survival rate, hemocytes response and oxidase activity of classified clams were evaluated after nano-TiO2 exposure. Results showed that after 30 d exposure, proactive individuals accelerated burrowing behavior with higher survival rate. Moreover, proactive clams had better adaptability and less hemocytes response and oxidative damage than reactive clams. The study highlights the individualities of marine shell fish determine individual capacity to adapt to environmental changes, play important roles in aquaculture and coastal ecosystem health.

Effects of Personality and Behavioral Syndromes on Competition for Social Hierarchical Status in Anemonefish Amphiprion clarkii

In this study, the behavioral ethogram of Amphiprion clarkii during the growth phase prior to sexual differentiation was summarized based on behavioral observations in three social environments. These behaviors can be classified into four categories: in addition to normal behaviors, the other three categories of behaviors-threatening, agonistic, and appeasing behaviors-represent different intentions in interactions with other individuals. Subsequently, the personalities of each individual were assessed by testing their reactions to intruders. These individuals mainly exhibited two distinct personality types: bold-aggressive and shy-submissive. In pairing experiments, the interactive behaviors of the anemonefish were observed in pairing combinations of different body sizes and personalities. The impact of personality on the establishment of a stable social hierarchy was confirmed by significant differences in the success rates of different pairing combinations, with the frequency of appeasing behaviors being the main factor influencing the success rate. Our results suggested that in natural waters, when juvenile individuals migrate among host anemones, shy-submissive individuals are more likely to be accepted due to their appeasing behaviors towards larger individuals, thus avoiding the risk of being attacked and bitten, and benefiting the survival of the individual. Conversely, bold-aggressive individuals are more likely to be driven away to another host anemone due to their unwillingness to settle for a lower-ranked status, thereby contributing to population dispersal and increasing opportunities for gene exchange between populations.

Switch from fight-flight to freeze-hide: The impacts of severe stress and brain serotonin on behavioral adaptations in flatfish

Animals often experience changes in their environment that can be perceived as stressful. Previous evidence indicates that different individuals may have distinct stress responses. The role of serotonin (5-HT) in stress adaptation is well established, but its relationship with different defense strategies and the persistence of physiological and behavioral responses in different individuals during repeated acute stress remain unclear. In this study, using olive flounder (Paralichthys olivaceus) as a model, we analyzed the relationship between boldness and neurotransmitter 5-HT activity. We found that 5-HT suppression with 5-HT synthesis inhibitor p-chlorophenylalanine (pCPA) and 5-HT receptor subtype 1A (5-HT1A) antagonist WAY-100635 increased their oxygen consumption rates and the boldness of shy individuals. We determined the metabolic and behavioral changes in bold and shy individuals to repeated acute stress. The results suggest that bold individuals switch on passive "energy-saving" personality by changing their defense behavior from "fight-flight" to "freeze-hide" during a threat encounter, which manifests high behavioral plasticity. Both behavioral types decreased their spontaneous activity levels, which were also strengthened by limiting metabolic rate. Interestingly, treatment with pCPA and WAY-100635 before stress procedure attenuated stress and increased the boldness across diverse behavioral types. This study provides the initial empirical evidence of how perception of stress impacts both individual defense behavior and personality in this species. These findings can enhance our comprehension of individual variability and behavioral plasticity in animals, thereby improving our ability to develop effective adaptive management strategies.

Boldness suppresses hoarding behavior in food hoarding season and reduces over-wintering survival in a social rodent

The "pace-of-life" syndrome (POLS) framework can encompass multiple personality axes that drive important functional behaviors (e.g., foraging behavior) and that co-vary with multiple life history traits. Food hoarding is an adaptive behavior important for an animal's ability to adapt to seasonal fluctuations in food availability. However, the empirical evidence for the relationships between animal personality and hoarding behavior remains unclear, including its fitness consequences in the POLS framework. In this study, the Mongolian gerbil (Meriones unguiculatus), a social rodent, was used as a model system to investigate how boldness or shyness is associated with food hoarding strategies during the food hoarding season and their impact on over-winter survival and reproduction at both individual and group levels. The results of this study showed that, compared with shy gerbils, bold gerbils had a lower effort foraging strategy during the food hoarding season and exhibited lower over-winter survival rates. However, bold-shy personality differences had no effect on over-winter reproduction. These findings suggest that the personality is a crucial factor influencing the foraging strategy during the food hoarding season in Mongolian gerbils. Personality may be related to energy states or the reaction to environmental changes (e.g., predation risk and food availability) in bold or shy social animals. These results reflect animal life history trade-offs between current versus future reproduction and reproduction versus self-maintenance, thereby helping Mongolian gerbils in adapting to seasonal fluctuations in their habitat.

Differential effects of ocean warming and BDE-47 on mussels with various personalities

Marine warming and polybrominated diphenyl ethers (PBDEs) pollution are two of the most concerning environmental problems in recent years. However, the impact of their co-occurrence on marine bivalves and the tolerance of bivalves with different traits remain unknown. In this study, thick shell mussels Mytilus coruscus were divided into two personalities according to individual feeding and byssus growth. The reliability of the classification was validated by respiration, self-organization, and post-stress behavior. Then, the survival rate, hemolymph immunity, and digestive glands oxidase activity of classified mussels were evaluated after 21 days of compound exposure to warming and BDE-47. The results showed that mussels could be divided into proactive and reactive types consistently. Compared to reactive mussels, proactive mussels exhibited some traits, such as faster food recovery, more byssus growth, higher metabolic rate, and more efficient clustering. Both single or combined warming and BDE-47 exposure impacted the individual survival, hemolymph, and antioxidase of mussels. Notably, the negative impacts of BDE-47 were exacerbated by warming. Moreover, proactive mussels displayed better adaptability with higher survival rates along with less damage to hemolymph immunity and antioxidant ability compared to reactive ones when facing environmental challenges. This study highlights potential risks associated with the coexistence of marine warming and PBDEs pollution while demonstrating differential fitness among individuals with distinct personalities.

Energy allocation is revealed while behavioural performance persists after fire disturbance

Metabolic physiology and animal behaviour are often considered to be linked, positively or negatively, according to either the performance or allocation models. Performance seems to predominate over allocation in natural systems, but the constraining environmental context may reveal allocation limitations to energetically expensive behaviours. Habitat disturbance, such as the large-scale fire that burnt wetlands of Biebrza National Park (NE Poland), degrades natural ecosystems. It arguably reduces food and shelter availability, modifies predator-prey interactions, and poses a direct threat for animal survival, such as that of the wetland specialist root vole Microtus oeconomus. We hypothesized that fire disturbance induces physiology-behaviour co-expression, as a consequence of changed environmental context. We repeatedly measured maintenance and exercise metabolism, and behavioural responses to the open field, in a root voles from post-fire and unburnt locations. Highly repeatable maintenance metabolism and distance moved during behavioural tests correlated positively, but relatively labile exercise metabolism did not covary with behaviour. At the same time, voles from a post-fire habitat had higher maintenance metabolism and moved shorter distances than voles from unburnt areas. We conclude there is a prevalence of the performance mechanism, but simultaneous manifestation of context-dependent allocation constraints of the physiology-behaviour covariation after disturbance. The last occurs at the within-individual level, indicating the significance of behavioural plasticity in the context of environmental disturbance.

Revisiting the role of behavior-mediated structuring in the survival of populations in hostile environments

Increasing the population density of target species is a major goal of ecosystem and agricultural management. This task is especially challenging in hazardous environments with a high abundance of natural enemies such as parasites and predators. Safe locations with lower mortality have been long considered a beneficial factor in enhancing population survival, being a promising tool in commercial fish farming and restoration of threatened species. Here we challenge this opinion and revisit the role of behavior structuring in a hostile environment in shaping the population density. We build a mathematical model, where individuals are structured according to their defensive tactics against natural enemies. The model predicts that although each safe zone enhances the survival of an individual, for an insufficient number of such zones, the entire population experiences a greater overall mortality. This is a result of the interplay of emergent dynamical behavioral structuring and strong intraspecific competition for safe zones. Non-plastic structuring in individuals' boldness reduces the mentioned negative effects. We demonstrate emergence of non-plastic behavioral structuring: the evolutionary branching of a monomorphic population into a dimorphic one with bold/shy strains. We apply our modelling approach to explore fish farming of salmonids in an environment infected by trematode parasites.

Resilience of research capacity strengthening initiatives in Africa during crises: the case of CARTA during COVID

Background: Several research capacity strengthening (RCS) initiatives have been established in Africa over the past decade. One such initiative is the Consortium for Advanced Research Training in Africa (CARTA) that has gained traction over the years and has been proven as an effective multidisciplinary approach to strengthen research capacity to address public and population health in Africa. Objectives: In this article, we document the experiences and management-related interventions that cushioned the CARTA programme and enabled it to remain resilient during the COVID pandemic. We further make recommendations on the enablers of resilience and optimal performance of such RCS initiatives during crises and beyond. Methods: We used routine information gathered by the CARTA secretariat from consortium correspondence, meeting minutes, reports and other related documents produced in the year 2020 in order to consolidate the experiences and interventions taken by the programme at programmatic, institutional and fellowship levels. Results: We identified a series of management-related cyclic phases that CARTA went through during the pandemic period, which included immobilisation, reflection, brainstorming, decision-making, intervening and recovery. We further identified strategic management-related interventions that contributed to the resilience of the programme during the pandemic including assessment and monitoring, communication management, policy and resource management, making investments and execution. Moreover, we observed that the strength of the leadership and management of CARTA, coupled with the consortium´s culture of collaboration, mutual trust, respect, openness, transparency, equitability, ownership, commitment and accountability, all contributed to its success during the pandemic period. Conclusion: We conclude that RCS initiatives undergo a series of phases during crises and that they need to promptly adopt and adapt appropriate management-related strategic interventions in order to remain resilient during such periods. This can be significantly realised if RCS initiatives build a culture of trust, commitment and joint ownership, and if they invest in strong management capacity.

Are bold-shy personalities of European perch (Perca fluviatilis) linked to stress tolerance and immunity? A scope of harnessing fish behavior in aquaculture

The sensitivity to stress and its impact on immunity are supposedly related to a fish's personality. In the present study, European perch (Perca fluviatilis) were exposed to an open-field and a novel-object test to identify distinctive shy and bold individuals. This series of cognitive tests revealed clear differences between proactive individuals with pronounced exploration behavior (bold personality) and reactive individuals that took a freeze-hide position (shy personality). A cohort of shy and bold perch was then exposed to elevated stocking density. Frozen activity and lower explorative behavior were related to higher basal and stocking-induced cortisol levels compared to proactive individuals. Since cortisol is a well-known modulator of immune-gene expression, we used multiplex real-time PCR to profile the differential immune responses to the intraperitoneal injection of Aeromonas hydrophila in the head kidney and peritoneal cells of bold and shy perch individuals. These expression differences between stimulated bold and shy perch were generally modest, except for the genes encoding the complement component c3 and the matrix metallopeptidase mmp9. The strong differential expression of these two bactericidal and inflammatory genes in the context of the modestly regulated features suggests that a fish's personality is linked to a particular immune-defense strategy. In conclusion, our approach, based on behavioral video observations, phagocytosis and enzyme assays, immunogene-expression profiling, and quantification of stress-relevant metabolites, revealed indications for divergent coping styles in cohorts of bold or shy European perch. This divergence could be exploited in future selective breeding programs.

Genetic polymorphisms in the serotonin, dopamine and opioid pathways influence social attention in rhesus macaques (Macaca mulatta)

Behaviour has a significant heritable component; however, unpicking the variants of interest in the neural circuits and molecular pathways that underpin these has proven difficult. Here, we present a comprehensive analysis of the relationship between known and new candidate genes from identified pathways and key behaviours for survival in 109 adult rhesus macaques (Macaca mulatta). Eight genes involved in emotion were analysed for variation at a total of nine loci. Genetic data were then correlated with cognitive and observational measures of behaviour associated with wellbeing and survival using MCMC-based Bayesian GLMM in R, to account for relatedness within the macaque population. For four loci the variants genotyped were length polymorphisms (SLC6A4 5-hydroxytryptamine transporter length-polymorphic repeat (5-HTTLPR), SLC6A4 STin polymorphism, Tryptophan 5-hydroxylase 2 (TPH2) and Monoamine oxidase A (MAOA)) whilst for the other five (5-hydroxytryptamine receptor 2A (HTR2A), Dopamine Receptor D4 (DRD4), Oxytocin receptor (OXTR), Arginine vasopressin receptor 1A (AVPR1a), Opioid receptor mu(μ) 1 (OPRM1)) SNPs were analysed. STin genotype, DRD4 haplotype and OXTR haplotype were significantly associated with the cognitive and observational measures of behaviour associated with wellbeing and survival. Genotype for 5-HTTLPR, STin and AVPR1a, and haplotype for HTR2A, DRD4 and OXTR were significantly associated with the duration of behaviours including fear and anxiety. Understanding the biological underpinnings of individual variation in negative emotion (e.g., fear and anxiety), together with their impact on social behaviour (e.g., social attention including vigilance for threat) has application for managing primate populations in the wild and captivity, as well as potential translational application for understanding of the genetic basis of emotions in humans.

Relationship between boldness and exploratory behavior in adult zebrafish

Behavioral responses vary between individuals and may be repeated in different contexts over time. When a behavioral response set is linked and present regardless of the context, it characterizes a behavioral syndrome. By evaluating how bold and shy (profiles related to risk-taking) individuals perform about exploration and anxiety, we can predict relationships of behavioral syndromes and better understand how different axis of personality is formed. Here we classified the profiles by risk-taking and evaluated their exploration behavior in the open field test. In this context, the two groups showed significant differences in thigmotaxis behavior: bold individuals habituate faster and show decreased thigmotaxis (less anxiety), while shy ones are less prone to leave the security of the side areas of the open tank and present higher anxiety. We emphasized the importance of further investigating the behavior of these profiles in other contexts and the importance of each one for the evolution and fitness of the species, in addition to a better understanding of which behaviors are involved in the behavioral syndromes in zebrafish.

Exploiting animal personality to reduce chronic stress in captive fish populations

Chronic stress is a major source of welfare problems in many captive populations, including fishes. While we have long known that chronic stress effects arise from maladaptive expression of acute stress response pathways, predicting where and when problems will arise is difficult. Here we highlight how insights from animal personality research could be useful in this regard. Since behavior is the first line of organismal defense when challenged by a stressor, assays of shy-bold type personality variation can provide information about individual stress response that is expected to predict susceptibility to chronic stress. Moreover, recent demonstrations that among-individual differences in stress-related physiology and behaviors are underpinned by genetic factors means that selection on behavioral biomarkers could offer a route to genetic improvement of welfare outcomes in captive fish stocks. Here we review the evidence in support of this proposition, identify remaining empirical gaps in our understanding, and set out appropriate criteria to guide development of biomarkers. The article is largely prospective: fundamental research into fish personality shows how behavioral biomarkers could be used to achieve welfare gains in captive fish populations. However, translating potential to actual gains will require an interdisciplinary approach that integrates the expertise and viewpoints of researchers working across animal behavior, genetics, and welfare science.

Predation and parasitism as determinants of animal personalities

Within the same population, proactive (i.e. bolder, more exploratory, active and aggressive) and reactive (i.e. more timid, less exploratory, less active and more passive) individuals could be hypothetically maintained due a trade-off between foraging and vigilance behaviours, provided that both phenotypes differ in their state (e.g. metabolic rates, body condition or energetic needs). Yet, recent findings indicate that among-individual variation in intrinsic state can explain only a small proportion of variation in behaviour, meaning that other mechanisms, such as the presence of trophically transmitted parasites, might contribute to maintaining inter-individual behavioural differences. Empirical evidence, indeed, suggests strong relationships between certain animal personality traits and parasitic load within host populations. However, the direction of causation between these traits remains unclear: are different behaviours in infected hosts in contrast to uninfected ones the result of manipulation by parasites to increase host predation, or are some personalities inherently more susceptible to infection than others? To better understand the role of parasites in shaping behavioural differences within host populations and examine to what extent parasite manipulation and/or intrinsic differences in parasite susceptibility contribute to maintaining behavioural differences, we used a simulation approach and analyzed the change in the frequencies of proactive and reactive individuals over time under different predation and starvation scenarios, when individual phenotype either affected a host's risk of infection or not. We found that in the absence of parasites, predation pressure strongly affected the expression of host personality, but the trade-off between foraging and vigilance behaviours alone could not explain the maintenance of inter-individual behavioural differences without temporal variation in predation pressure. By contrast, in the presence of parasites, the two host phenotypes could coexist within populations even when individuals experienced no temporal variations in predation risk, but only when proactive and reactive hosts were equally susceptible to parasitism. Our findings thus indicate that parasites can play an important role in maintaining genetic diversity in their host populations in addition to generating behavioural differences though manipulation.

Differential Branchial Response of Low Salinity Challenge Induced Prolactin in Active and Passive Coping Style Olive Flounder

Stress coping styles are very common in fish, and investigations into this area can greatly improve fish welfare and promote the sustainable development of aquaculture. Although most studies have focused on the behavioral and physiological differences of these fishes, the endocrine response of different coping styles fish when undergoing salinity challenge is still unclear. We examined the physiological response in olive flounder with active coping (AC) style and passive coping (PC) style after transferred from seawater (SW) to freshwater for 0, 2, 5, 8, and 14 days. The results showed that: 1) the plasma prolactin level of FW-acclimated AC flounder was substantially higher than that of FW-acclimated PC flounder at 5, 8, and 14 days, and the branchial gene expression of prolactin receptor (PRLR) in AC flounder was slightly higher than PC flounder after transfer. While there was no remarkable difference observed in cortisol (COR) levels between AC and PC flounder. After transfer, glucocorticoid receptor (GR) expression in AC flounder was significantly higher compared with PC flounder at 8 days. 2) Branchial NKA-IR ionocytes numbers were reduced in PC flounder after transfer, while ionocytes number remain stable in AC flounder. 3) The branchial stem cell transcription factor foxi1 gene expression of AC flounder was significantly higher than PC flounder at 2, 5, and 14 days after transfer, while branchial stem cell transcription factor p63 gene expression of FW-acclimated AC flounder was only substantially higher than that of PC flounder at 5 days. 4) As an apoptosis upstream initiator, the branchial gene expression of caspase-9 in PC flounder was considerably higher than in AC flounder after transfer at 8 days. This study revealed that olive flounder with active and passive coping styles have different endocrine coping strategies after facing the low-salinity challenge. AC flounder adopt an active endocrine strategy by increasing ionocyte differentiation and prolactin secretion significantly. In contrast, PC flounder employ a passive strategy of reducing ionocytes differentiation and retaining prolactin content at a low level to reduce branchial ionocytes number.

Wolf Responses to Experimental Human Approaches Using High-Resolution Positioning Data

Humans pose a major mortality risk to wolves. Hence, similar to how prey respond to predators, wolves can be expected to show anti-predator responses to humans. When exposed to a threat, animals may show a fight, flight, freeze or hide response. The type of response and the circumstances (e.g., distance and speed) at which the animal flees are useful parameters to describe the responses of wild animals to approaching humans. Increasing knowledge about behavioral responses of wolves toward humans might improve appropriate management and decrease conflicts related to fear of wolves. We did a pilot study by conducting 21 approach trials on seven GPS-collared wolves in four territories to investigate their responses to experimental human approaches. We found that wolves predominantly showed a flight response (N = 18), in a few cases the wolf did not flee (N = 3), but no wolves were seen or heard during trials. When wolves were downwind of the observer the flight initiation distance was significantly larger than when upwind, consistent with the hypothesis that conditions facilitating early detection would result in an earlier flight. Our hypothesis that early detection would result in less intense flights was not supported, as we found no correlation between flight initiation distances and speed, distance or straightness of the flight. Wolves in more concealed habitat had a shorter flight initiation distance or did not flee at all, suggesting that perceived risk might have been affected by horizontal visibility. Contrary to our expectation, resettling positions were less concealed (larger horizontal visibility) than the wolves’ initial site. Although our small number of study animals and trials does not allow for generalizations, this pilot study illustrates how standardized human approach trials with high-resolution GPS-data can be used to describe wolf responses at a local scale. In continuation, this method can be applied at larger spatial scales to compare wolf flight responses within and between populations and across anthropogenic gradients, thus increasing the knowledge of wolf behavior toward humans, and potentially improving coexistence with wolves across their range.

Cohabitation With Atlantic Salmon (Salmo salar) Affects Brain Neuromodulators But Not Welfare Indicators in Lumpfish (Cyclopterus lumpus)

Lumpfish are utilized to combat ectoparasitic epidemics in salmon farming. Research gaps on both cleaning behavior and client preferences in a natural environment, emphasizes the need to investigate the physiological impacts on lumpfish during cohabitation with piscivorous Atlantic salmon. Lumpfish (39.9 g, S.D ± 8.98) were arranged in duplicate tanks (n = 40 per treatment) and exposed to Live Atlantic salmon (245.7 g, S.D ± 25.05), salmon Olfaction or lifelike salmon Models for 6 weeks. Growth and health scores were measured every second week. In addition, the final sampling included measurements of neuromodulators, body color, and plasma cortisol. A stimulation and suppression test of the hypothalamic-pituitary-interrenal (HPI) axis was used for chronic stress assessment. Results showed that growth, health scores, and body color remained unaffected by treatments. Significant reductions in levels of brain dopamine and norepinephrine were observed in Live compared to Control. Plasma cortisol was low in all treatments, while the stimulation and suppression test of the HPI axis revealed no indications of chronic stress. This study presents novel findings on the impact on neuromodulators from Atlantic salmon interaction in the lumpfish brain. We argue that the downregulation of dopamine and norepinephrine indicate plastic adjustments to cohabitation with no negative effect on the species. This is in accordance with no observed deviations in welfare measurements, including growth, health scores, body color, and stress. We conclude that exposure to salmon or salmon cues did not impact the welfare of the species in our laboratory setup, and that neuromodulators are affected by heterospecific interaction.

Personality, density and habitat drive the dispersal of invasive crayfish

There is increasing evidence that personality traits may drive dispersal patterns of animals, including invasive species. We investigated, using the widespread signal crayfish Pacifastacus leniusculus as a model invasive species, whether effects of personality traits on dispersal were independent of, or affected by, other factors including population density, habitat, crayfish size, sex and limb loss, along an invasion gradient. Behavioural traits (boldness, activity, exploration, willingness to climb) of 310 individually marked signal crayfish were measured at fully-established, newly-established and invasion front sites of two upland streams. After a period at liberty, recaptured crayfish were reassessed for behavioural traits (newly-established, invasion front). Dispersal distance and direction of crayfish movement, local population density, fine-scale habitat characteristics and crayfish size, sex and limb loss were also measured. Individual crayfish exhibited consistency in behavioural traits over time which formed a behavioural syndrome. Dispersal was both positively and negatively affected by personality traits, positively by local population density and negatively by refuge availability. No effect of size, sex and limb loss was recorded. Personality played a role in promoting dispersal but population density and local habitat complexity were also important determinants. Predicting biological invasion in animals is likely to require better integration of these processes.

Covariation among behavioral traits and hatching time in zebrafish

Individuals of the same population differ in several ways. For instance, in fish populations, individuals who hatch earlier show more active behavior and are more explorative than those that hatch later, which is a characteristic of the behavioral personality type. One of the aspects relevant to this theory is the consistency of behavioral differences between contexts and over time. Thus, the present study evaluated the relationship between hatching time and behavioral consistency in two ontogenetic stages: juvenile and adult, and different contexts in zebrafish (Danio rerio). For this, the animals were separated according to hatching time into early-hatching (EH) and late-hatching (LH) fish and tested in an anxiety-like context (black-white paradigm) at the 30th-day post fertilization (dpf) and the 120th dpf. The animals were also tested in a novel tank paradigm and novel object paradigm to access explorativeness and boldness, respectively. In the black-white test, EH animals presented shorter latency to enter the white area and stayed longer in the black area than LH animals. The EH individuals were more explorative and bold in the novel tank and novel object tests and showed less anxiety-like behavior than the LH. In general, the results obtained suggest that hatching time may indicate consistent differences for zebrafish behavioral profiles.

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.

Diel rhythm of urotensin I mRNA expression and its involvement in the locomotor activity and appetite regulation in olive flounder Paralichthys olivaceus

Urotensin I (UI), a member of the corticotropin-releasing hormone family of peptides, regulates a diverse array of physiological functions, including appetite regulation, defensive behavior and stress response. In this study, firstly, the tissue-specific distribution of UI mRNA in olive flounder (Paralichthys olivaceus) was characterized and we found that UI mRNA was highly expressed in caudal neurosecretory system (CNSS) tissue. Secondly, alignment analysis found that a conserved cAMP response binding (CREB) site and a TATA element were located in the proximal promoter of UI gene. In addition, treatment of forskolin activatated cAMP-CREB pathway and induced the up-regulation of UI mRNA in cultured CNSS, suggesting the role of CREB in regulating the UI mRNA expression. Furthermore, plasma UI concentration and UI mRNA in CNSS showed obvious daily rhythm, with higher values in the daytime while lower values in the nighttime. Thirdly, using bold personality (BP) and shy personality (SP) flounder as an animal model, we found that flounder exhibited significantly higher locomotor activity in the nighttime than in the daytime (P < 0.001), and BP flounder showed significantly higher locomotor activity (P < 0.001) compared with SP flounder both in the daytime and nighttime. Analysis of feeding behavior revealed that BP flounder showed a shorter latency to feed and more attacks to prey. Furthermore, the qPCR and immunohistochemistry results showed that BP flounder expressed significantly lower level of UI mRNA and protein in CNSS tissue. Collectively, our study suggested that the UI plays an important role in locomotor activity and appetite regulation, which provides a basis for understanding the mechanism of defensive behavior and animal personality in flounder.

Comparative transcriptome and methylome analysis of the hindbrain in olive flounder (Paralichthys olivaceus) considering individual behavior-type and oxygen metabolism

In previous studies we employed multiple behavior assays, including propensity to feed, simulated trawl capture and escape response, to prove the presence of bold and shy personality (BP,SP) in olive flounder (Paralichthys olivaceus). However, the molecular mechanism of the different personality has not been elucidated. In this study, firstly, we found that the SP flounder had lower red blood cell count (RBC) and haemoglobin concentration (HBG) than BP flounder. Secondly, the transcriptomic profiles of the hindbrain in flounder with distinct personality were compared. A total of 144 differently expressed genes (DEGs) were identified, including 70 up-regulated and 74 down-regulated genes in SP flounder compared with BP flounder. Genes involved in hypoxia stress were detected in SP flounder, accompanied with down-regulation of ribosomal RNA synthesis. In addition, genes related with calcium signaling pathway, including endothelin, b-Fos, c-Fos and c-Jun were up-regulated in SP flounder. Furthermore, personality-related genes including UI, CCK, c-Fos showed significantly higher level in SP flounder than in BP flounder. GO enrichment analysis indicated that the GO categories "the tight junction pathway" and "lipid transport or localization pathway" were enriched in SP flounder, suggesting that the central nervous system homeostasis would be compromised. Thirdly, using a simple and scalable DNA methylation profiling method (MethylRAD), which allows for methylation analysis for DEGs in RNA-seq, we found that only part of gene expression was negatively associated with promoter methylation. Altogether, our study will not only lay a foundation for further studies on animal personality but also facilitate the selective breeding of olive flounder in aquaculture.

Repeatability of behavior and physiology: No impact of reproductive investment

Animals have well-documented individual differences in their behaviour, including in their response to stressful stimuli. The physiological bases for the repeatability of these traits has been the focus of much research in recent years, in an attempt to explain the mechanistic drivers for behavioral syndromes. Whilst a range of studies have demonstrated repeatable individual differences in physiological traits, little is known about potential trade-offs between reproductive investment and the physiological responses to subsequent stressors. We therefore sought to test the behavioral and physiological responses of male zebra finches (Taeniopygia guttata) to a novel environment, quantifying a series of repeated "temporal reaction norms" before and after reproduction. Given that reproductive investment is costly both in time and energy, it is likely to affect expression of behavioral and physiological traits. We hypothesised that reproductive investment would impact the consistency of these temporal reaction norms. Specifically, we predicted that individuals which invested more in reproduction would show altered rates of habituation to a stressful stimulus. Therefore, we quantified temporal reaction norm components (i.e., intercept and slope) of two behaviours and metabolic rate (MR) within and among individuals before and after a breeding season. We found that individuals consistently differed in how their locomotor and feeding activity increased upon introduction into a novel environment and also how their MR decreased after being handled and confined within the metabolic chamber. We also found that the slope of the feeding activity reaction norm was negatively correlated with stress-induced corticosterone levels at the within-individual level. Finally, in contrast to our prediction, we found that neither the intercept nor slope of the reaction norms were influenced by the reproductive effort (the number of fledglings produced) displayed by individual males. This suggests that the substantial individual variation in the expression of physiological and behavioural traits is not plastic with respect to the immediate consequences of reproductive investment. This study is the first quantification of metabolic rate reaction norms and their relationships with fitness, which represents an important first step towards understanding the evolutionary significance of instantaneous habituation to stressful and novel situations.

Specific dynamic action of mussels exposed to TiO2 nanoparticles and seawater acidification

Both nanoparticles (NPs) and ocean acidification (OA) pose threats to marine animals as well as marine ecosystems. The present study aims to evaluate the combined effects of NPs and OA on specific dynamic action (SDA) of mussels. The thick shell mussels Mytilus coruscus were exposed to two levels of pH (7.3 and 8.1) and three concentrations of TiO₂ NPs (0, 2.5, and 10 mg L^-1) for 14 days followed by a 7-day recovery period. The SDA parameters, including standard metabolic rate, peak metabolic rate, aerobic metabolic scope, SDA slope, time to peak, SDA duration and SDA, were measured. The results showed that TiO₂ NPs and low pH significantly affected all parameters throughout the experiment. When the mussels were exposed to seawater acidification or TiO₂ NPs conditions, standard metabolic rate, aerobic metabolic scope, SDA slope and SDA significantly decreased, whereas peak metabolic rate, time to peak and SDA duration significantly increased. In addition, interactive effects between TiO₂ NPs and pH were observed in SDA parameters except time to peak and SDA. Therefore, the synergistic effect of TiO₂ NPs and low pH can adversely affect the feeding metabolism of mussels.

Differential Coping Strategies in Response to Salinity Challenge in Olive Flounder

To examine how different fish coping strategies respond to salinity challenge, olive flounder (Paralichthys olivaceus) with active coping style (AC) and passive coping style (PC) were transferred from seawater (SW) to freshwater (FW) and their behavior and physiology were analyzed. Different behavioral coping strategies, in terms of escape and feeding tendencies, were confirmed in AC and PC fish without FW exposure. Differences in swimming distance between AC and PC flounder were then assessed after 1 and 2 days of FW transfer. Plasma parameters and branchial gene expression were also determined 2, 5, 8, and 14 days after transfer, with comparisons between AC and PC fish and against a SW-acclimated control group. The results showed that: (1) PC flounder exhibited a significant reduction in swimming activity, while AC flounder significantly increased locomotion 2 days after transfer. (2) The plasma osmolality and plasma ionic (Na⁺ and Cl⁻) concentration of FW-acclimated PC flounder declined in a continuous fashion over time but this contrasted against the plasma parameters of AC flounder which fluctuated below the baseline level of a SW-acclimated control group. (3) The expression of NKA-α1 and NHE-3-like mRNA in PC flounder gill increased significantly from 5 days, but the expression of these two genes in AC flounder only increased after 8 days of transfer. (4) There were no remarkable differences observed in Rhcg expressions between AC and PC flounder. This study indicates for the first time that PC flounder adopt a “freeze-passive tolerance” strategy while AC flounder adopt a “flight-active resistance” defense strategy in response to salinity challenge.

Exploitation may influence the climate resilience of fish populations through removing high performance metabolic phenotypes

Physiological rates and processes underpin the relationships between ectothermic organisms, such as fish, and their environment. The response and persistence of fish populations in an increasingly variable ocean is dependent on the distribution and diversity of physiological phenotypes. Growing evidence suggests that fisheries exploitation can selectively target certain physiological and behavioural phenotypes, which may shift exploited populations to altered physiological states. Here we test if commercial fisheries have the potential to do this in a “natural laboratory” along the South African coast. We compare metabolic traits of exploited and protected populations of the fish species, Chrysoblephus laticeps, which is a major component of the South African hook and line fishery. We find that high-performance aerobic scope phenotypes are reduced in the fished population. The most likely mechanism for this finding is a positive relationship between aerobic scope and capture vulnerability in passive-gear fisheries. Our results further highlight the selective nature of capture-fisheries and suggest that exploitation has the capacity to alter climate responses of fish populations on a physiological level. Our finding also implicates how Marine Protected Areas, through harbouring individuals with a greater diversity of physiological traits, may provide greater fish response diversity to environmental variability.

Winter corticosterone and body condition predict breeding investment in a nonmigratory bird

Reproduction is an energetically demanding life history stage that requires costly physiological and behavioral changes, yet some individuals will invest more into reproduction and breed more successfully than others. To understand variation in reproductive investment, previous studies have evaluated factors during breeding, but conditions outside of this life history stage may also play a role. Using a free-ranging population of black-capped chickadees (Poecile atricapillus), we assessed the repeatability of plastic traits relating to energetic condition (circulating initial corticosterone concentrations and body condition) during the nonbreeding season and evaluated whether these traits predicted reproductive investment in the subsequent breeding season. We found that initial corticosterone concentrations and an index of body condition, but not fat score, were moderately repeatable over a 1-week period in winter. This trait repeatability supports the interpretation that among-individual variation in these phenotypic traits could reflect an intrinsic strategy to cope with challenging conditions across life history stages. We found that females with larger fat reserves during winter laid eggs sooner and tended to spend more time incubating their eggs and feeding their offspring. In contrast, we found that females with higher residual body mass delayed breeding, after controlling for the relationship between fat score and timing of breeding. Additionally, females with higher initial corticosterone in winter laid lighter eggs. Our findings suggest that conditions experienced outside of the breeding season may be important factors explaining variation in reproductive investment.

Gene expression and hormone secretion profile of urotensin I associated with osmotic challenge in caudal neurosecretory system of the euryhaline flounder, Platichthys flesus

The caudal neurosecretory system (CNSS) is a part of stress response system, a neuroendocrine structure unique to fish. To gain a better understanding of the physiological roles of CNSS in fluid homeostasis, we characterized the tissue distribution of urotensin I (UI) expression in European flounder (Platichthys flesus), analyzed the effect chronic exposure to seawater (SW) or freshwater (FW), transfer from SW to FW, and reverse transfer on mRNA levels of UI, L-type Ca²⁺ channels and Ca-activated K⁺ channels transcripts in CNSS. The tissue distribution demonstrated that the CNSS is dominant sites of UI expression, and UI mRNA level in fore brain appeared greater than other non-CNSS tissues. There were no consistent differences in CNSS UI expression or urophysis UI content between SW- and FW-adapted fish in July and September. After transfer from SW to FW, at 8 h CNSS UI expression was significantly increased, but urophysis UI content was no significantly changes. At 24 h transfer from SW to FW, expression of CNSS UI was no apparent change and urophysis UI content was reduced. At 8 h and 24 h after transfer from FW to SW UI expression and urophysis UI content was no significantly effect. The expression of bursting dependent L-type Ca²⁺ channels and Ca-activated K⁺ channels in SW-adapted fish significantly decreased compared to those in FW-adapted. However, there were no differences in transfer from SW to FW or from FW to SW at 8 h and 24 h. Thus, these results suggest CNSS UI acts as a modulator in response to osmotic stress and plays important roles in the body fluid homeostasis.

The role of intraspecies variation in fish neurobehavioral and neuropharmacological phenotypes in aquatic models

Intraspecies variation is common in both clinical and animal research of various brain disorders. Relatively well-studied in mammals, intraspecies variation in aquatic fish models and its role in their behavioral and pharmacological responses remain poorly understood. Like humans and mammals, fishes show high variance of behavioral and drug-evoked responses, modulated both genetically and environmentally. The zebrafish (Danio rerio) has emerged as a particularly useful model organism tool to access neurobehavioral and drug-evoked responses. Here, we discuss recent findings and the role of the intraspecies variance in neurobehavioral, pharmacological and toxicological studies utilizing zebrafish and other fish models. We also critically evaluate common sources of intraspecies variation and outline potential strategies to improve data reproducibility and translatability.

Polymorphism and multiple correlated characters: Do flatfish asymmetry morphs also differ in swimming performance and metabolic rate?

Phenotypic polymorphisms often differ in multiple correlated traits including morphology, behavior, and physiology, all of which can affect performance. How selection acts on these suites of traits can be complex and difficult to discern. Starry flounder (Platichthys stellatus) is a pleuronectid flatfish that exhibits rare polymorphism for the direction of eye migration and resulting whole-body asymmetry. P. stellatus asymmetry morphs differ subtly in several anatomical traits, foraging behavior, and stable isotope signatures, suggesting they may be ecologically segregated, yet performance and metabolic differences are unknown.Here we tested the hypothesis that sinistral and dextral P. stellatus asymmetry morphs diverge in performance and routine metabolic rate (RMR) by comparing prolonged swimming endurance (time to exhaustion at a constant swimming speed), fast-start swimming velocity and acceleration, and rate of oxygen consumption. Based on subtle morphological differences in caudal tail size, we expected sinistral P. stellatus to have superior prolonged swimming endurance relative to dextral fish, but inferior fast-start performance.Sinistral P. stellatus exhibited both significantly greater prolonged swimming performance and fast-start swimming performance. However, sinistral P. stellatus also exhibited greater RMR, suggesting that their general swimming performance could be enhanced by an elevated metabolic rate.Divergence between P. stellatus asymmetry morphs in swimming performance and metabolic rates contributes to growing evidence of ecological segregation between them, as well as our understanding of possible ecological consequences of asymmetry direction in flatfishes. These data provide an example of the complexity of polymorphisms associated with multiple correlated traits in a rare case of asymmetry polymorphism in a marine flatfish species.

Positive or negative? The shell alters the relationship among behavioral defense strategy, energy metabolic levels and antioxidant capacity in freshwater turtles

Background

The relationships among energy metabolic levels, behavioral and other physiological traits help to determine the trade-off of energy allocation between different traits and the evolution of life-history driven by natural selection. However, these relationships may be distinctive in selected animal taxa because of their unique traits. In the present study, the relationships among energy metabolic levels, behavioral defense strategies, and antioxidant capacity were explored in three freshwater turtle species with different shell morphologies, by assessing responses to attack, righting time, shell morphology, whole-organism metabolic rates, tissue metabolic enzyme activities and antioxidant levels.

Results

The Chinese three-keeled pond turtles, Chinemys reevesii, showed a passive defense strategy, relatively larger shells, a higher resting metabolic rate (RMR) and higher antioxidant levels compared to the snapping turtle, Chelydra serpentina, or the Chinese soft-shelled turtle, Pelodiscus sinensis. These latter two species both showed an active defense strategy, a higher factorial aerobic scope and better muscle anaerobic metabolic capacity but relatively smaller shells, lower RMR and antioxidant capacity.

Conclusion

Our results indicate a negative relationship between RMR and activity levels in behavioral defense strategies along small-big shell continuum among the three turtle species. We also found a positive relationship between antioxidant capacity and energy metabolism but a negative one between antioxidant capacity and activity levels in defense strategies. The present study indicated a role of turtle shell in forming unique relationship between energy metabolic levels and behaviors in freshwater turtle taxa and a possible trade-off between the maintenance of physiological homeostasis and activity levels in energy allocation.

Agonistic behaviour and energy metabolism of bold and shy swimming crabs Portunus trituberculatus

The metabolism and behaviour of crustaceans are highly flexible, and the inter-individual variation in these traits is evolutionarily and ecologically significant. We analysed the relationships among personality traits (boldness, activity and hesitancy), agonistic behaviour and energy status (glycogen, glucose and lactate) in the swimming crab Portunus trituberculatus The main results were as follows. (1) Boldness was significantly correlated with activity and hesitancy. Bold crabs were more likely to initiate and win a fight. In bold individuals, the frequencies of 'move to', 'cheliped display', 'grasp' and 'contact' were significantly higher than those of shy individuals, whereas the frequency of 'move away' was significantly lower than that of shy individuals. (2) Before fighting, the glucose concentrations in the haemolymph of bold individuals were significantly lower than those of shy individuals, whereas the concentrations of lactate showed the opposite trend. There were no significant differences in glycogen and lactate concentrations in the claw muscle between bold and shy individuals. (3) After fighting, the glucose and lactate concentrations in the haemolymph of both bold and shy individuals were significantly higher than those before fighting. The glucose concentrations in the haemolymph were significantly higher in bold individuals than shy individuals. In addition, bold individuals showed a larger increase in glucose in the haemolymph but a smaller increase in lactate compared with shy individuals. (4) After fighting, the glycogen concentrations in the claw muscle were significantly lower than those before fighting; however, there were no significant differences in the concentrations of lactate in the claw muscle. These results indicated that the agonistic behaviour of the swimming crab is related to its behavioural type. Energy reserves may be one of the factors affecting the personality traits and agonistic behaviour in crabs. These results should lay a foundation for in-depth understanding of the relationships among crustacean personality, agonistic behaviour and metabolic physiology.

Bioenergetics-adverse outcome pathway: Linking organismal and suborganismal energetic endpoints to adverse outcomes

Adverse outcome pathways (AOPs) link toxicity across levels of biological organization, and thereby facilitate the development of suborganismal responses predictive of whole-organism toxicity and provide the mechanistic information necessary for science-based extrapolation to population-level effects. Thus far AOPs have characterized various acute and chronic toxicity pathways; however, the potential for AOPs to explicitly characterize indirect, energy-mediated effects from toxicants has yet to be fully explored. Indeed, although exposure to contaminants can alter an organism's energy budget, energetic endpoints are rarely incorporated into ecological risk assessment because there is not an integrative framework for linking energetic effects to organismal endpoints relevant to risk assessment (e.g., survival, reproduction, growth). In the present analysis, we developed a generalized bioenergetics-AOP in an effort to make better use of energetic endpoints in risk assessment, specifically exposure scenarios that generate an energetic burden to organisms. To evaluate empirical support for a bioenergetics-AOP, we analyzed published data for links between energetic endpoints across levels of biological organization. We found correlations between 1) cellular energy allocation and whole-animal growth, and 2) metabolic rate and scope for growth. Moreover, we reviewed literature linking energy availability to nontraditional toxicological endpoints (e.g., locomotor performance), and found evidence that toxicants impair aerobic performance and activity. We conclude by highlighting current knowledge gaps that should be addressed to develop specific bioenergetics-AOPs. Environ Toxicol Chem 2019;38:27-45. © 2018 SETAC.

Behavioral and Metabolic Phenotype Indicate Personality in Zebrafish (Danio rerio)

Consistency of individual differences of animal behavior and personality in reactions to various environmental stresses among their life stages could reflect basic divergences in coping style which may affect survival, social rank, and reproductive success in the wild. However, the physiological mechanisms determining personality remain poorly understood. In order to study whether behavior, metabolism and physiological stress responses relate to the personality, we employed post-stress recovery assays to separate zebrafish into two behavioral types (proactive and reactive). The results demonstrated consistent difference among personality, behavior and metabolism in which proactive individuals were more aggressive, had higher standard metabolic rates and showed lower shuttled frequencies between dark and light compartments than the reactive ones. The behavioral variations were also linked to divergent acute salinity stress responses: proactive individuals adopted a swift locomotion behavior in response to acute salinity challenge while reactive individuals remain unchanged. Our results provide useful insight into how personality acts on correlated traits and the importance of a holistic approach to understanding the mechanisms driving persistent inter-individual differences.

Metabolic Scope as a Proximate Constraint on Individual Behavioral Variation: Effects on Personality, Plasticity, and Predictability

Behavioral ecologists have hypothesized that among-individual differences in resting metabolic rate (RMR) may predict consistent individual differences in mean values for costly behaviors or for behaviors that affect energy intake rate. This hypothesis has empirical support and presently attracts considerable attention, but, notably, it does not provide predictions for individual differences in (a) behavioral plasticity or (b) unexplained variation (residual variation from mean individual behavior, here termed predictability). We outline how consideration of aerobic maximum metabolic rate (MMR) and particularly aerobic scope (= MMR - RMR) can be used to simultaneously make predictions about mean and among- and within-individual variation in behavior. We predict that while RMR should be proportional to an individual's mean level of sustained behavioral activity (one aspect of its personality), individuals with greater aerobic scope will also have greater scope to express behavioral plasticity and/or greater unpredictability in behavior (=greater residual variation). As a first step toward testing these predictions, we analyze existing activity data from selectively bred lines of mice that differ in both daily activity and aerobic scope. We find that replicate high-scope mice are more active on average and show greater among-individual variation in activity, greater among-individual variation in plasticity, and greater unpredictability. These data provide some tentative first support for our hypothesis, suggesting that further research on this topic would be valuable.

Repeatability of glucocorticoid hormones in vertebrates: a meta-analysis

We often expect that investigations of the patterns, causes, and consequences of among-individual variation in a trait of interest will reveal how selective pressures or ecological conditions influence that trait. However, many endocrine traits, such as concentrations of glucocorticoid (GC) hormones, exhibit adaptive plasticity and, therefore, do not necessarily respond to these pressures as predicted by among-individual phenotypic correlations. To improve our interpretations of among-individual variation in GC concentrations, we need more information about the repeatability of these traits within individuals. Many studies have already estimated the repeatability of baseline, stress-induced, and integrated GC measures, which provides an opportunity to use meta-analytic techniques to investigate (1) whether GC titers are generally repeatable across taxa, and (2) which biological or methodological factors may impact these estimates. From an intensive search of the literature, we collected 91 GC repeatability estimates from 47 studies. Overall, we found evidence that GC levels are repeatable, with mean repeatability estimates across studies ranging from 0.230 for baseline levels to 0.386 for stress-induced levels. We also noted several factors that predicted the magnitude of these estimates, including taxon, sampling season, and lab technique. Amphibians had significantly higher repeatability in baseline and stress-induced GCs than birds, mammals, reptiles, or bony fish. The repeatability of stress-induced GCs was higher when measured within, rather than across, life history stages. Finally, estimates of repeatability in stress-induced and integrated GC measures tended to be lower when GC concentrations were quantified using commercial kit assays rather than in-house assays. The extent to which among-individual variation in GCs may explain variation in organismal performance or fitness (and thereby inform our understanding of the ecological and evolutionary processes driving that variation) depends on whether measures of GC titers accurately reflect how individuals differ overall. Our findings suggest that while GC titers can reflect some degree of consistent differences among individuals, they frequently may not. We discuss how our findings contribute to interpretations of variation in GCs, and suggest routes for the design and analysis of future research.

Demystifying animal 'personality' (or not): why individual variation matters to experimental biologists

Animal 'personality', defined as repeatable inter-individual differences in behaviour, is a concept in biology that faces intense controversy. Critics argue that the field is riddled with terminological and methodological inconsistencies and lacks a sound theoretical framework. Nevertheless, experimental biologists are increasingly studying individual differences in physiology and relating these to differences in behaviour, which can lead to fascinating insights. We encourage this trend, and in this Commentary we highlight some of the benefits of estimating variation in (and covariation among) phenotypic traits at the inter- and intra-individual levels. We focus on behaviour while drawing parallels with physiological and performance-related traits. First, we outline some of the confusion surrounding the terminology used to describe repeatable inter-individual differences in behaviour. Second, we argue that acknowledging individual behavioural differences can help researchers avoid sampling and experimental bias, increase explanatory power and, ultimately, understand how selection acts on physiological traits. Third, we summarize the latest methods to collect, analyse and present data on individual trait variation. We note that, while measuring the repeatability of phenotypic traits is informative in its own right, it is only the first step towards understanding how natural selection and genetic architecture shape intra-specific variation in complex, labile traits. Thus, understanding how and why behavioural traits evolve requires linking repeatable inter-individual behavioural differences with core aspects of physiology (e.g. neurophysiology, endocrinology, energy metabolism) and evolutionary biology (e.g. selection gradients, heritability).

Thermal preference predicts animal personality in Nile tilapia Oreochromis niloticus

Environmental temperature gradients provide habitat structure in which fish orientate and individual thermal choice may reflect an essential integrated response to the environment. The use of subtle thermal gradients likely impacts upon specific physiological and behavioural processes reflected as a suite of traits described by animal personality. In this study, we examine the relationship between thermal choice, animal personality and the impact of infection upon this interaction. We predicted that thermal choice in Nile tilapia Oreochromis niloticus reflects distinct personality traits and that under a challenge individuals exhibit differential thermal distribution. Nile tilapia were screened following two different protocols: 1) a suite of individual behavioural tests to screen for personality and 2) thermal choice in a custom-built tank with a thermal gradient (TCH tank) ranging from 21 to 33 °C. A first set of fish were screened for behaviour and then thermal preference, and a second set were tested in the opposite fashion: thermal then behaviour. The final thermal distribution of the fish after 48 h was assessed reflecting final thermal preferendum. Additionally, fish were then challenged using a bacterial Streptococcus iniae model infection to assess the behavioural fever response of proactive and reactive fish. Results showed that individuals with preference for higher temperatures were also classified as proactive with behavioural tests and reactive contemporaries chose significantly lower water temperatures. All groups exhibited behavioural fever recovering personality-specific thermal preferences after 5 days. Our results show that thermal preference can be used as a proxy to assess personality traits in Nile tilapia and it is a central factor to understand the adaptive meaning of animal personality within a population. Importantly, response to infection by expressing behavioural fever overrides personality-related thermal choice.