Ventilation rates indicate stress-coping styles in Nile tilapia

Behavioural responses to stress can form distinct profiles in a wide range of animals: proactive and reactive profiles or coping styles. Stress responsiveness can also differentiate between the behavioural profiles. The tendency to regain feed intake following transfer to a novel social-isolation tank (the speed of acclimation) can discriminate between proactive or reactive profiles. Consequently, differential stress responsiveness can be linked to this feeding behaviour trait. This study shows that ventilation rates of Nile tilapia, Oreochromis niloticus (L.), correlate with the rate of feeding resumption, following transfer to a novel social-isolation aquarium. Therefore, ventilation rate (VR) indicates coping styles; consequently, VR is a proxy for the way fish will deal with environmental challenges.     

How integrated are behavioral and endocrine stress response traits? A repeated measures approach to testing the stress-coping style model

It is widely expected that physiological and behavioral stress responses will be integrated within divergent stress‐coping styles (SCS) and that these may represent opposite ends of a continuously varying reactive–proactive axis. If such a model is valid, then stress response traits should be repeatable and physiological and behavioral responses should also change in an integrated manner along a major axis of among‐individual variation. While there is some evidence of association between endocrine and behavioral stress response traits, few studies incorporate repeated observations of both. To test this model, we use a multivariate, repeated measures approach in a captive‐bred population of Xiphophorus birchmanni. We quantify among‐individual variation in behavioral stress response to an open field trial (OFT) with simulated predator attack (SPA) and measure waterborne steroid hormone levels (cortisol, 11‐ketotestosterone) before and after exposure. Under the mild stress stimulus (OFT), (multivariate) behavioral variation among individuals was consistent with a strong axis of personality (shy–bold) or coping style (reactive–proactive) variation. However, behavioral responses to a moderate stressor (SPA) were less repeatable, and robust statistical support for repeatable endocrine state over the full sampling period was limited to 11‐ketotestosterone. Although post hoc analysis suggested cortisol expression was repeatable over short time periods, qualitative relationships between behavior and glucocorticoid levels were counter to our a priori expectations. Thus, while our results clearly show among‐individual differences in behavioral and endocrine traits associated with stress response, the correlation structure between these is not consistent with a simple proactive–reactive axis of integrated stress‐coping style. Additionally, the low repeatability of cortisol suggests caution is warranted if single observations (or indeed repeat measures over short sampling periods) of glucocorticoid traits are used in ecological or evolutionary studies focussed at the individual level.     

Behaviour,physiology and carotenoid pigmentation in Arctic charr Salvelinus alpinus

The behaviour during an exploration task and the response to a confinement stress of Arctic charr Salvelinus alpinus were evaluated. Behaviour of individuals during 90 min of exploration was classified into high and low activity. High‐activity individuals had higher plasma cortisol levels following stress compared to low‐activity individuals. This indicates that high‐ and low‐activity individuals correspond to reactive and proactive stress‐coping styles. Further, a pigmentation analysis showed that high‐activity individuals had a higher number of carotenoid spots cm^?2 than low‐activity individuals. Thus, carotenoid pigmentation, as melanin pigmentation in other salmonids, could be linked to stress‐coping style in S. alpinus.     

Individual personality differences in Port Jackson sharks Heterodontus portusjacksoni

This study examined interindividual personality differences between Port Jackson sharks Heterodontus portusjacksoni utilizing a standard boldness assay. Additionally, the correlation between differences in individual boldness and stress reactivity was examined, exploring indications of individual coping styles. Heterodontus portusjacksoni demonstrated highly repeatable individual differences in boldness and stress reactivity. Individual boldness scores were highly repeatable across four trials such that individuals that were the fastest to emerge in the first trial were also the fastest to emerge in subsequent trials. Additionally, individuals that were the most reactive to a handling stressor in the first trial were also the most reactive in a second trial. The strong link between boldness and stress response commonly found in teleosts was also evident in this study, providing evidence of proactive‐reactive coping styles in H. portusjacksoni. These results demonstrate the presence of individual personality differences in sharks for the first time. Understanding how personality influences variation in elasmobranch behaviour such as prey choice, habitat use and activity levels is critical to better managing these top predators which play important ecological roles in marine ecosystems.     

Effects of maternal stress coping style on offspring characteristics in rainbow trout (Oncorhynchus mykiss)

Maternal size, age, and allostatic load influence offspring size, development, and survival. Some of these effects have been attributed to the release of glucocorticoids, and individual variation in these stress hormones is related to a number of traits. Correlated traits are often clustered and used to define the proactive and reactive stress coping styles. Although stress coping styles have been identified in a number of animal groups, little is known about the coupling between stress coping style and offspring characteristics. In the present study, plasma cortisol levels in ovulated mothers and cortisol levels in non-fertilized eggs from two rainbow trout (Oncorhynchus mykiss) strains selected for high (HR) and low (LR) post-stress plasma cortisol levels were compared. Offspring characteristics such as egg size, larval growth, and energy reserves also were compared between the two strains. Maternal plasma and egg cortisol levels were correlated, but no difference between the HR and LR strains was detected in either parameter. LR females produced larger eggs, and larvae with larger yolk sacs compared to HR females, however no differences in larval body size (excluding the yolk) was detected between strains. Considering that the HR and LR strains have a number of correlated behavioral and physiological traits that resemble the reactive and proactive stress coping styles, respectively, the results suggest that proactive mothers invest more energy into their offspring, producing larvae with larger energy reserves. It is possible that larger energy reserves in proactive larvae support the energy requirement for establishing and defending territory in salmonid fish. Furthermore, in the present study we found a positive relationship between mother plasma cortisol and egg cortisol; however neither mother plasma cortisol nor egg cortisol differed between strains. These results indicate that cortisol endowment from the mother to the offspring plays a minor role in the transfer of the behavioral and physiological traits which separates these strains.     

Three different coping styles in police dogs exposed to a short-term challenge

According to some researchers, animals show different coping styles to deal with stressful situations. In the case of social carnivores, social stress is a substantial part of the overall stress load. Previous research has established two extreme (proactive and reactive) coping styles in several animal species, but means of coping with social stress has not yet been investigated in the case of dogs. The aim of this current study was to examine whether (1) experienced working police dogs adopt different coping strategies during a short-term unexpected social challenge presented by a threatening human, (2) whether this affects post-encounter cortisol levels, and (3) whether there is an association between the cortisol response and the behavior (coping strategy) displayed during the threatening approach. Using factor analysis, we have identified three different group of dogs which were characterized by either fearfulness, aggressiveness, or ambivalence and in parallel showed specific differences in their reaction norm when threatened by an approaching stranger. This grouping also allowed to draw possible parallels between aggressiveness and the proactive behavior style and fearfulness and reactive coping style, respectively. In addition, we have revealed a third group of animals which show ambivalent behavior in a social threatening situation.     

Three different coping styles in police dogs exposed to a short-term challenge

According to some researchers, animals show different coping styles to deal with stressful situations. In the case of social carnivores, social stress is a substantial part of the overall stress load. Previous research has established two extreme (proactive and reactive) coping styles in several animal species, but means of coping with social stress has not yet been investigated in the case of dogs. The aim of this current study was to examine whether (1) experienced working police dogs adopt different coping strategies during a short-term unexpected social challenge presented by a threatening human, (2) whether this affects post-encounter cortisol levels, and (3) whether there is an association between the cortisol response and the behavior (coping strategy) displayed during the threatening approach. Using factor analysis, we have identified three different group of dogs which were characterized by either fearfulness, aggressiveness, or ambivalence and in parallel showed specific differences in their reaction norm when threatened by an approaching stranger. This grouping also allowed to draw possible parallels between aggressiveness and the proactive behavior style and fearfulness and reactive coping style, respectively. In addition, we have revealed a third group of animals which show ambivalent behavior in a social threatening situation.     

Coping strategies in a strongly schooling fish,the common carp Cyprinus carpio

Individual common carp Cyprinus carpio were screened repeatedly for risk taking (rate of exploration of a novel, potentially dangerous environment) and for competitive ability (success in gaining access to a spatially restricted food source). Marked differences in behaviour were evident, and significant consistency in individual responses across trials was found for both risk taking and competitive ability. In addition, there was a significant positive relationship between individual performance in these two contexts, with fish that explored more quickly in the novel environment tending to be among the first to gain access to restricted food. In two follow‐up studies, resting metabolic rate, blood lactate and glucose and the expression of the cortisol receptor gene in the head kidney and brain were compared in fish from the two extremes of the risk‐taking spectrum. Mass‐specific metabolic rate was significantly higher in risk‐taking than in risk‐avoiding fish, while plasma lactate and glucose concentrations and expression of the cortisol receptor gene were lower. It was concluded that a behavioural syndrome based on boldness and aggression exists in C. carpio, as it does in many other animals, and that this is associated with differences in metabolic and stress physiology (down to the genomic level) similar to those described in animals with different coping strategies.     

Stress coping styles and singing behavior in the short-tailed singing mouse (Scotinomys teguina)

Stress coping styles have been characterized as a proactive/reactive dichotomy in laboratory and domesticated animals. In this study, we examined the prevalence of proactive/reactive stress coping styles in wild-caught short-tailed singing mice (Scotinomys teguina). We compared stress responses to spontaneous singing, a social and reproductive behavior that characterizes this species. To establish proactive/reactive profiles for singing mice, we measured exploratory and anxiety behavior using an open-field behavioral test. We examined correlations between open-field behaviors and fecal corticosterone (CORT) metabolites, baseline plasma CORT, and stress-induced CORT. Mice with proactive behavioral responses in the open-field had higher fecal CORT titers than reactive males, but did not differ in baseline or stress-induced plasma CORT. We suggest that individual differences in CORT metabolism may contribute to this surprising pattern. Males that sang in the open-field were behaviorally proactive and had lower stress-induced CORT, indicating a link between stress responses and singing in this species. Overall, the data demonstrate that singing mice offer an interesting model for exploring how stress reactivity can shape social behaviors.     

Behavioral plasticity in rainbow trout (Oncorhynchus mykiss) with divergent coping styles: when doves become hawks

Consistent and heritable individual differences in reaction to challenges, often referred to as stress coping styles, have been extensively documented in vertebrates. In fish, selection for divergent post-stress plasma cortisol levels in rainbow trout (Oncorhynchus mykiss) has yielded a low (LR) and a high responsive (HR) strain. A suite of behavioural traits is associated with this physiological difference, with LR (proactive) fish feeding more rapidly after transfer to a new environment and being socially dominant over HR (reactive) fish. Following transport from the UK to Norway, a switch in behavioural profile occurred in trout from the 3rd generation; HR fish regained feeding sooner than LR fish in a novel environment and became dominant in size-matched HR–LR pairs. One year after transport, HR fish still fed sooner, but no difference in social dominance was found. Among offspring of transported fish, no differences in feeding were observed, but as in pre-transported 3rd generation fish, HR fish lost fights for social dominance against size-matched LR opponents. Transported fish and their offspring retained their distinctive physiological profile throughout the study; HR fish showed consistently higher post-stress cortisol levels at all sampling points. Altered risk-taking and social dominance immediately after transport may be explained by the fact that HR fish lost more body mass during transport than did LR fish. These data demonstrate that some behavioural components of stress coping styles can be modified by experience, whereas behavioural plasticity is limited by genetic effects determining social position early in life story.     

Biological clock function is linked to proactive and reactive personality types

Background

Many physiological processes in our body are controlled by the biological clock and show circadian rhythmicity. It is generally accepted that a robust rhythm is a prerequisite for optimal functioning and that a lack of rhythmicity can contribute to the pathogenesis of various diseases. Here, we tested in a heterogeneous laboratory zebrafish population whether and how variation in the rhythmicity of the biological clock is associated with the coping styles of individual animals, as assessed in a behavioural assay to reliably measure this along a continuum between proactive and reactive extremes.

Results

Using RNA sequencing on brain samples, we demonstrated a prominent difference in the expression level of genes involved in the biological clock between proactive and reactive individuals. Subsequently, we tested whether this correlation between gene expression and coping style was due to a consistent change in the level of clock gene expression or to a phase shift or to altered amplitude of the circadian rhythm of gene expression. Our data show a remarkable individual variation in amplitude of the clock gene expression rhythms, which was also reflected in the fluctuating concentrations of melatonin and cortisol, and locomotor activity. This variation in rhythmicity showed a strong correlation with the coping style of the individual, ranging from robust rhythms with large amplitudes in proactive fish to a complete absence of rhythmicity in reactive fish. The rhythmicity of the proactive fish decreased when challenged with constant light conditions whereas the rhythmicity of reactive individuals was not altered.

Conclusion

These results shed new light on the role of the biological clock by demonstrating that large variation in circadian rhythmicity of individuals may occur within populations. The observed correlation between coping style and circadian rhythmicity suggests that the level of rhythmicity forms an integral part of proactive or reactive coping styles.

     

Melanin-based skin spots reflect stress responsiveness in salmonid fish

Within animal populations, genetic, epigenetic and environmental factors interact to shape individual neuroendocrine and behavioural profiles, conferring variable vulnerability to stress and disease. It remains debated how alternative behavioural syndromes and stress coping styles evolve and are maintained by natural selection. Here we show that individual variation in stress responsiveness is reflected in the visual appearance of two species of teleost fish; rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Salmon and trout skin vary from nearly immaculate to densely spotted, with black spots formed by eumelanin-producing chromatophores. In rainbow trout, selection for divergent hypothalamus–pituitary–interrenal responsiveness has led to a change in dermal pigmentation patterns, with low cortisol-responsive fish being consistently more spotted. In an aquaculture population of Atlantic salmon individuals with more spots showed a reduced physiological and behavioural response to stress. Taken together, these data demonstrate a heritable behavioural–physiological and morphological trait correlation that may be specific to alternative coping styles. This observation may illuminate the evolution of contrasting coping styles and behavioural syndromes, as occurrence of phenotypes in different environments and their response to selective pressures can be precisely and easily recorded.     

Boldness and Stress Responsiveness as Drivers of Nest‐Site Selection in a Ground‐Nesting Bird

Nest‐site selection involves trade‐offs between the probability of nest discovery by egg predators, danger to the incubating parent from predators and provision of an appropriate microclimate for incubation, and all three components are potentially influenced by nest concealment and distance to habitat edge. Personality traits also affect habitat choice, and the trade‐off hypothesis suggests that variable stress‐coping strategies may evolve because individuals prioritize either productivity (proactive coping) or survival (reactive coping), both of which cannot be simultaneously maximized. Applying this hypothesis to understand nest‐site selection by female eider ducks (Somateria mollissima), we predicted that bold individuals with attenuated stress responsiveness should select concealed nests further away from the shore, thereby promoting clutch survival at the potential expense of reduced escape opportunities for themselves. In testing this prediction, we controlled for individual quality (female body condition and breeding experience) and verified that individual stress responses and nest‐site preferences were consistent by analysing their repeatability. Finally, we analysed how the viable proportion of the clutch was related to nest‐site and female characteristics. Our prediction was supported: bold females [short flight initiation distance (FID)] and those with lower handling‐induced body temperature were found in concealed nests, and bold females and those with lower handling‐induced corticosterone concentrations occupied nests farther from the shore. The viable proportion of the clutch peaked at intermediate proportional nest‐cover and increased linearly with increasing nest distance from the shore. Stress coping styles may thus be related to nest‐site selection, but their fitness consequences may be manifested indirectly through the nest‐site characteristics.     

Divergence in behavioural responses to stress in two strains of rainbow trout (Oncorhynchus mykiss) with contrasting stress responsiveness

The aim of this study was to establish whether two lines of rainbow trout divergent for their plasma cortisol response to a standardized stressor would show consistent differences in their behavioural response to a range of challenging situations. Our results show that the high- and low-responding (HR and LR) lines of rainbow trout did not differ in the aggression shown towards an intruder or in their response to the introduction of a novel object to their home environment. However, there was a difference in behaviour between the two selection lines when they were exposed to two unfamiliar environments. These results suggest that the behaviour of the HR and LR fish differs when they are challenged in unfamiliar environments, while their behaviour does not differ when they are challenged in their home environment. These observations are in agreement with studies on mammals that show that individuals with reactive coping styles perform similarly to proactive animals when they are challenged in a familiar environment, while they show different behaviour when they are challenged in unfamiliar environments. Thus, these results provide further evidence that the HR and LR selection lines of rainbow trout exemplify the two different coping styles described in mammals.     

Does individual variation in stress responses and agonistic behavior reflect divergent stress coping strategies in juvenile rainbow trout?

Individual rainbow trout were transferred to visual isolation in experimental aquaria. As a measure of the speed of acclimation, individual food intake was quantified during the first 6 d following transfer. Following acclimation, aggression was quantified by subjecting the fish to three resident-intruder tests, with 30 d of recovery between the tests. Moreover, between the resident-intruder tests (i.e., two times) the fish were exposed to an unfamiliar environment and their cortisol response was measured. The results of this study show that individuals of juvenile rainbow trout differ distinctly in their response to changes in their environment, and that this diversity in behavior is reflected by consistent behavioral traits displayed by individual fish. These traits have proven to be consistent not only over time but also across situations, revealing two distinct behavioral profiles, in the same manner as shown in studies on proactive and reactive mammals. Our results also show that the reactivity of the hypothalamic-pituitary-interrenal (HPI) axis, when exposed to a stressor, is a consistent physiological trait in juvenile rainbow trout. We found that difference in HPI axis reactivity is linked to the different behavioral profiles. However, HPI axis reactivity could not be linked directly to the singular behavioral traits measured. In other words, we did not find that the consistent behavioral traits shown by the fish were associated with a difference in HPI axis reactivity in the same manner as the reactivity of the hypothalamic-pituitary-adrenocortical axis does in mammals. Taken together, our results show that stress coping strategies akin to what has been described as reactive and proactive stress coping in mammals appear to exist in juvenile rainbow trout.     

Calorie restriction in the rotifer Brachionus plicatilis enhances hypoxia tolerance in association with the increased mRNA levels of glycolytic enzymes

The rotifer Brachionus plicatilis shows a typical sigmoid growth curve, where calorie restriction (CR) and hypoxia are thought to be introduced at high population density in the stationary phase. CR may induce a shift from aerobic to anaerobic metabolism in this stationary phase, possibly contributing to an increased hypoxia tolerance. This study was undertaken to investigate the effect of CR on hypoxia tolerance at the molecular level. When rotifers were cultured under CR (fed every second day) or fed ad libitum (AL), and subsequently exposed to hypoxia, those in the CR group had a higher survival rate than their AL counterparts. We then cloned cDNAs encoding three glycolytic enzymes, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), enolase (ENO), and phosphoglycerate mutase (PGM) and compared their accumulated mRNA levels between CR and AL rotifers at ages of 1–8 days by quantitative real-time PCR. The CR group showed significantly higher mRNA levels of GAPDH and ENO than their AL counterparts. Furthermore, rotifers in the stationary phase showed higher mRNA levels of these enzymes than those in the exponential growth phase. These results suggest that CR induces anaerobic metabolism, which possibly contributes to population stability under hypoxia in the stationary phase.     

Reproductive success of a marine teleost was correlated with proactive and reactive stress-coping styles

The present study investigated the relationship between reproductive success and stress-coping styles in gilthead seabream Sparus aurata in captivity. To characterise stress-coping styles, a total of 22 breeders were submitted to three different individual-based tests, one group-based test and post-handling glucocorticoid quantification. To assess spawning participation, a microsatellite analysis was performed on a total of 2698 larvae, which allowed each offspring to be assigned unambiguously to a single parental couple. Overall, S. aurata showed defined proactive and reactive behavioural traits. Proactive breeders exhibited higher levels of activity and risk taking and lower glucocorticoid blood levels than reactive breeders. The stress-coping style traits were consistent over time and context (different tests). Breeders that contributed to a higher number of progeny exhibited proactive behaviours, while those showing low progeny contribution exhibited reactive behaviour. Therefore, breeders with a high proportion of progeny (> 20%) had significantly higher activity and risk taking and lower cortisol than breeders with low progeny contribution (< 20%). In addition, males were more proactive than females and males exhibited significantly higher activity, risk taking and lower cortisol than females. This study is the first to establish in S. aurata breeders: (a) a relationship between stress-coping styles and spawning success; (b) a relationship between stress-coping styles and gender; and (c) the existence of proactive and reactive traits at the adult stage.     

Protection of red sea bream Pagrus major against red sea bream iridovirus infection by vaccination with a recombinant viral protein

Megalocytivirus infections cause serious mass mortality in marine fish in East and Southeast Asian countries. In this study the immunogenicity of crude subunit vaccines against infection by the Megalocytivirus RSIV was investigated. Three capsid proteins, 18R, 351R and a major capsid protein, were selected for use as crude subunit vaccines. High homology among Megalocytivirus types was found in the initial sequence examined, the 351R region. Red sea bream (Pagrus major) juveniles were vaccinated by intraperitoneal injection of recombinant formalin‐killed Escherichia coli cells expressing these three capsid proteins. After challenge infection with RSIV, fish vaccinated with the 351R‐recombinant bacteria showed significantly greater survival than those vaccinated with control bacteria. The 351R protein was co‐expressed with GAPDH from the bacterium Edwardsiella tarda in E. coli; this also protected against viral challenge. A remarkable accumulation of RSIV was observed in the blood of vaccinated fish, with less accumulation in the gills and spleen tissues. Thus, the 351R‐GAPDH fusion protein is a potential vaccine against Megalocytivirus infection in red sea bream.