Tank size alters mean behaviours and individual rank orders in personality traits of fish depending on their life stage

Effects of Cheliped Amputation on the Personality of Crayfish

Animal personality, which describes inter-individual differences and intra-individual consistency in behaviors across time and contexts, has been widely observed and has significance for both ecology and evolution. Morphological modifications, particularly during early life stages, may highly influence animal behavior in adulthood; thus, exploring this relationship can elucidate personality development throughout ontogeny. In this study, we reared juvenile crayfish (Procambarus clarkii) with different degrees of cheliped mutilation and explored their personality patterns, including exploration and aggression, when they reached sexual maturity. Male crayfish showed repeatability in exploration, and both sexes showed repeatability in aggression. We observed no significant correlation between the two behavioral traits, indicating the absence of behavioral syndromes. Moreover, exploration did not differ according to the type of mutilation, but crayfish with more intact chelipeds were more aggressive, and males were more aggressive than females. These results indicate that cheliped mutilation may modify the average levels of personality traits associated with competition or self-defense. Our study provides insights into how morphological modifications may shape animal personalities in adulthood.

How to measure exploration: A combined estimation method

The personality axis 'exploration-avoidance' is often measured using an open field test (OFT) from which measurements such as mobility level (e.g. distance travelled) and space use (e.g. area covered) in an unknown environment are extracted. Recently developed tracking software surprisingly includes only a measure of mobility level in their output summary. Consequently, recent articles using these software programs started to ignore a measure of space use in their determination of exploration. In this short communication, we show briefly why it is important to not overlook a measure of space use, provide an easy way to calculate such a measure, with adjustable resolution, from the available position data provided by the software and a method to determine a proxy for exploration.

Beyond compliance: harmonising research and husbandry practices to improve experimental reproducibility using fish models

Reproducibility in animal research is impacted by the environment, by husbandry practices in the laboratory and by the animals' provenance. These factors, however, are often not adequately considered by researchers. A disconnect between researchers and animal care staff can result in inappropriate housing and husbandry decisions for scientific studies with those animals. This is especially the case for the research in neuro-behaviour, epigenetics, and the impact of climate change, as heritable phenotypic, behavioural or physiological changes are known to result from the animals' environmental housing, husbandry, provenance and prior experience. This can lead to greater variation (even major differences) in data outcomes among studies, driving scientific uncertainties. Herein, we illustrate some of the endpoints measured in fish studies known to be intrinsically linked to the environment and husbandry conditions and assess the significance of housing and husbandry practice decisions for research adopting these endpoints for different fish species. We highlight the different priorities and challenges faced by researchers and animal care staff and how harmonising their activities and building greater understanding of how husbandry practices affect the fish will improve reproducibility in research outcomes. We furthermore illustrate how improving engagement between stakeholders, including regulatory bodies, can better underpin fish husbandry decisions and where researchers could help to drive best husbandry practices through their own research with fish models.

Maze design: size and number of choices impact fish performance in cognitive assays

Although studies on fish cognition are increasing, consideration of how methodological details influence the ability to detect and measure performance is lagging. Here, in two separate experiments the authors compared latency to leave the start position, latency to make a decision, levels of participation and success rates (whether fish entered the rewarded chamber as first choice) across different physical designs. Experiments compared fish performance across (a) two sizes of T-mazes, large and standard, and a plus-maze, and (b) open choice arenas with either two or four doors. Fish in T-mazes with longer arms took longer to leave the start chamber and were less likely to participate in a trial than fish in T-mazes with shorter arms. The number of options, or complexity, in a maze significantly impacted success but did not necessarily impact behavioural measures, and did not impact the number of fish that reached a chamber. Fish in the plus-maze had similar latencies to leave the start box and time to reach any chamber as fish in the same-sized T-maze but exhibited lower overall success. Similarly, in an open choice arena, increasing the number of options - doors to potential reward chambers - resulted in lower probability of success. There was an influence of reward position in the choice arena, with rewarded chambers closest to the sides of the arena resulting in lower latencies to enter and higher probability of decision success. Together the results allow the authors to offer practical suggestions towards optimal maze design for studies of fish cognition.

Temporal repeatability of behaviour in a lizard: implications for behavioural syndrome studies

It is well established that, across taxa, individuals within populations exhibit consistent differences in their behaviour across time and/or contexts. Further, the functional coupling of traits may result in the formation of a behavioural syndrome. Despite extensive evidence on the existence of consistent among-individual differences in behaviour and behavioural syndromes in the animal realm, these findings are predominately based upon short-term assessments, leading to questions regarding their stability over longer periods. Understanding if these estimates are temporally stable would allow predictions of individual behaviour to be made using short-term repeated measures. Here, we used 57 adult male delicate skinks (Lampropholis delicata) to evaluate the stability of behavioural variation observed both among (animal personality and behavioural plasticity) and within individuals (behavioural predictability), as well as behavioural syndromes, across short (four weeks) and long (five months) timeframes. To do so, we repeatedly assayed activity, exploration, and boldness five times per each individual. Overall, our study revealed complex patterns of behavioural variation and trait (co)variation over time. Activity was always repeatable across time intervals, whereas behavioural differences among individuals in exploration and boldness were not consistent. Yet a behavioural syndrome between activity and exploration was detected at both shorter and longer temporal scales, suggesting that syndrome structure in these traits does not vary as a function of time. Our findings indicate that, at least for some traits (e.g. activity) and studies, short-term measures may be adequate in serving as a proxy for long-term variation in individual behaviour, and to reveal the existence of behavioural syndromes at the population level.

Comparison of anxiety-like and social behaviour in medaka and zebrafish

The medaka, Oryzias latipes, is rapidly growing in importance as a model in behavioural research. However, our knowledge of its behaviour is still incomplete. In this study, we analysed the performance of medaka in 3 tests for anxiety-like behaviour (open-field test, scototaxis test, and diving test) and in 3 sociability tests (shoaling test with live stimuli, octagonal mirror test, and a modified shoaling test with mirror stimulus). The behavioural response of medaka was qualitatively similar to that observed in other teleosts in the open-field test (thigmotaxis), and in 2 sociability tests, the shoaling test and in the octagonal mirror test (attraction towards the social stimulus). In the remaining tests, medaka did not show typical anxiety (i.e., avoidance of light environments and preference for swimming at the bottom of the aquarium) and social responses (attraction towards the social stimulus). As a reference, we compared the behaviour of the medaka to that of a teleost species with well-studied behaviour, the zebrafish, tested under the same conditions. This interspecies comparison indicates several quantitative and qualitative differences across all tests, providing further evidence that the medaka responds differently to the experimental settings compared to other fish models.

Ecology of fear in highly invasive fish revealed by robots

Invasive species threaten biodiversity and ecosystem functioning. We develop an innovative experimental approach, integrating biologically inspired robotics, time-series analysis, and computer vision, to build a detailed profile of the effects of non-lethal stress on the ecology and evolution of mosquitofish (Gambusia holbrooki)—a global pest. We reveal that brief exposures to a robotic predator alter mosquitofish behavior, increasing fear and stress responses, and mitigate the impact of mosquitofish on native tadpoles (Litoria moorei) in a cause-and-effect fashion. Effects of predation risk from the robot carry over to routine activity and feeding rate of mosquitofish weeks after exposure, resulting in weight loss, variation in body shape, and reduction in the fertility of both sexes—impairing survival, reproduction, and ecological success. We capitalize on evolved responses of mosquitofish to reduce predation risk—neglected in biological control practices—and provide scientific foundations for widespread use of state-of-the-art robotics in ecology and evolution research.

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Can robotic predators reveal the vulnerabilities of invasive and pest species?

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Our predator selectively targets invasive fish to protect native amphibians

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Stress from the robot compromises behavior, health, and reproduction of invaders

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We open new frontiers for robotics in ecology, evolution, and biocontrol research

Behavioural plasticity in a native species may be related to foraging resilience in the presence of an aggressive invader

Competition between invasive and native species can result in the exploitation of resources by the invader, reducing foraging rates of natives. However, it is increasingly recognized that multiple factors can enhance the resilience of native species competing for limiting resources with invaders. Although extensively studied in terrestrial species, little research has focused on behavioural plasticity in aquatic ecosystems and how this influences native species resilience. Here, we examined the role of behavioural plasticity in interactions between a native Australian fish, Pseudomugil signifer, and a widespread invasive fish, Gambusia holbrooki. To determine whether P. signifer displays behavioural plasticity that may mitigate competition with G. holbrooki, we first quantified social behaviours (aggression, submission and affiliation) and shoal cohesion for each species in single- and mixed-species groups. Second, we compared the feeding rates of both species in these groups to ascertain if any modulation of social behaviours and cohesion related to foraging success. We found that aggressive and submissive behaviours of G. holbrooki and P. signifer showed plasticity in the presence of heterospecifics, but social affiliation, shoaling and, most importantly, foraging, remained inflexible. This variation in the degree of plasticity highlights the complexity of the behavioural response of a native species and suggests that both behavioural modulation and consistency may be related to sustaining foraging efficiency in the presence of an invader.

Effect of Tank Size on Zebrafish Behavior and Physiology

Simple Summary

Living space is an important aspect of animal welfare. Understanding the effects of welfare on experimental animals would help in drawing a precise conclusion. In this work, zebrafish in different tank sizes were studied through behavioral and physiology tests. Results showed that changes in the tank size affected zebrafish behavior; those that lived in small tanks behaved less boldly, had poor stamina, and spent much time on movement. Therefore, researchers should focus on zebrafish’s living space to generate valid data from laboratory studies.

Abstract

Environmental conditions strongly affect experimental animals. As a model organism, zebrafish has become important in life science studies. However, the potential effect of living environment on their behavior and physiology is often overlooked. This work aimed to determine whether tank size affects zebrafish behavior and physiology. Tests on shelter leaving, shelter seeking, shoaling, stamina, and pepsin and cortisol levels were conducted. Results showed that zebrafish behavior is easily affected by changes on the tank size. Fish that lived in small tanks behaved less boldly, had poor stamina, and spent much time on movement. Sex differences in behavior were only evident in the shelter seeking tests. Tank size had no effect on pepsin and cortisol, but cortisol concentrations in males were lower than those in females. This study suggests that zebrafish behavior is easily influenced by their living environment, and future related studies should consider their living space.

Environmental complexity during early life shapes average behavior in adulthood

Personality has been identified in a range of animal taxa during the last few decades, with important ecological and evolutionary implications. Investigating the effects of environmental factors during early life can provide important insights into the ontogeny of animal personality. We reared newborn mosquitofish, Gambusia affinis, in tanks of different structural complexities, and measured their behavioral traits (i.e., shyness, exploration, and sociability) when they reached sexual maturity. Univariate linear mixed-effects models were fitted to test the effects of environmental complexity and sex on population-average behavior, whereas multivariate models were fitted to quantify behavioral repeatability (i.e., personality) and among-individual correlations (i.e., behavioral syndromes). On average, females were shyer and more social than males, and the fish reared in complex environments were shyer, less explorative, and more social than those reared in open environments. Among-individual differences were consistently large across trials for all behaviors, indicating that personality variation was present in mosquitofish of both sexes reared in different environments. Repeatability did not differ among behaviors, and there were no differences in repeatability in any behavior between sexes or among environments. A negative correlation between shyness and exploration was found in mosquitofish from all treatments at both phenotypic and among-individual levels, with the latter indicating a strong shyness–exploration behavioral syndrome. Our study provides robust evidence that average levels of personality might vary when mosquitofish are raised in different levels of structural complexity during early life.

VHSV Single Amino Acid Polymorphisms (SAPs) Associated With Virulence in Rainbow Trout

The Viral Hemorrhagic Septicemia Virus (VHSV) is an OIE notifiable pathogen widespread in the Northern Hemisphere that encompasses four genotypes and nine subtypes. In Europe, subtype Ia impairs predominantly the rainbow trout industry causing severe rates of mortality, while other VHSV genotypes and subtypes affect a number of marine and freshwater species, both farmed and wild. VHSV has repeatedly proved to be able to jump to rainbow trout from the marine reservoir, causing mortality episodes. The molecular mechanisms regulating VHSV virulence and host tropism are not fully understood, mainly due to the scarce availability of complete genome sequences and information on the virulence phenotype. With the scope of identifying in silico molecular markers for VHSV virulence, we generated an extensive dataset of 55 viral genomes and related mortality data obtained from rainbow trout experimental challenges. Using statistical association analyses that combined genetic and mortality data, we found 38 single amino acid polymorphisms scattered throughout the complete coding regions of the viral genome that were putatively involved in virulence of VHSV in trout. Specific amino acid signatures were recognized as being associated with either low or high virulence phenotypes. The phylogenetic analysis of VHSV coding regions supported the evolution toward greater virulence in rainbow trout within subtype Ia, and identified several other subtypes which may be prone to be virulent for this species. This study sheds light on the molecular basis for VHSV virulence, and provides an extensive list of putative virulence markers for their subsequent validation.

Personality traits covary with individual differences in inhibitory abilities in 2 species of fish

In a number of animal species, individuals differ in their ability to solve cognitive tasks. However, the mechanisms underlying this variability remain unclear. It has been proposed that individual differences in cognition may be related to individual differences in behavior (i.e., personality); a hypothesis that has received mixed support. In this study, we investigated whether personality correlates with the cognitive ability that allows inhibiting behavior in 2 teleost fish species, the zebrafish Danio rerio and the guppy Poecilia reticulata. In both species, individuals that were bolder in a standard personality assay, the open-field test, showed greater inhibitory abilities in the tube task, which required them to inhibit foraging behavior toward live prey sealed into a transparent tube. This finding reveals a relationship between boldness and inhibitory abilities in fish and lends support to the hypothesis of a link between personality and cognition. Moreover, this study suggests that species separated by a relatively large phylogenetic distance may show the same link between personality and cognition, when tested on the same tasks.

Short-Term Interactive Effects of Experimental Heat Waves and Turbidity Pulses on the Foraging Success of a Subtropical Invertivorous Fish

Sudden increases in temperature and turbidity in aquatic ecosystems are expected for different regions in the future, as a result of the more frequent extreme climatic events that are predicted. The consequences of these abrupt changes in the outcomes of predator–prey interactions are unknown. Here, we tested the effects of a heat wave and a turbidity pulse on the foraging success of a subtropical cichlid fish (Gymnogeophagus terrapurpura) on amphipods (Hyalella curvispina). We carried out a short-term experiment combining treatments of turbidity (3 and 100 nephelometric turbidity units [NTU]) and water temperature (19.2, 22.2, 25.2 and 27.0 °C), considering potential differences given by fish length. Changes in water temperature did not promote significant changes in prey consumption. Higher turbidity, in contrast, decreased prey consumption. Also, we found that fish with different body lengths consumed a similar amount of prey under clear waters, but, in turbid waters, bigger individuals were more efficient than the smaller individuals. This finding is an empirical demonstration that the effect of increased turbidity on predation rate depends upon predator body size, and it suggests that bigger body sizes may help overcome turbidity-associated limitations in finding and capturing prey. Our short-term results suggest that, if turbidity pulses and heat waves become more frequent in the future, the outcome of fish–invertebrate interaction can be affected by local characteristics such as fish population size distribution.

Behavioural and life-history responses of mosquitofish to biologically inspired and interactive robotic predators

Invasive alien species threaten biodiversity worldwide and contribute to biotic homogenization, especially in freshwaters, where the ability of native animals to disperse is limited. Robotics may offer a promising tool to address this compelling problem, but whether and how invasive species can be negatively affected by robotic stimuli is an open question. Here, we explore the possibility of modulating behavioural and life-history responses of mosquitofish by varying the degree of biomimicry of a robotic predator, whose appearance and locomotion are inspired by natural mosquitofish predators. Our results support the prediction that real-time interactions at varying swimming speeds evoke a more robust antipredator response in mosquitofish than simpler movement patterns by the robot, especially in individuals with better body conditions that are less prone to take risks. Through an information-theoretic analysis of animal-robot interactions, we offer evidence in favour of a causal link between the motion of the robotic predator and a fish antipredator response. Remarkably, we observe that even a brief exposure to the robotic predator of 15 min per week is sufficient to erode energy reserves and compromise the body condition of mosquitofish, opening the door for future endeavours to control mosquitofish in the wild.

Ecological conditions drive pace-of-life syndromes by shaping relationships between life history, physiology and behaviour in two populations of Eastern mosquitofish

The pace-of-life syndrome (POLS) hypothesis predicts variation in behaviour and physiology among individuals to be associated with variation in life history. Thus, individuals on the "fast" end of POLS continuum grow faster, exhibit higher metabolism, are more risk prone, but die earlier than ones on the "slow" end. Empirical support is nevertheless mixed and modelling studies suggested POLS to vary along selection gradients. Therefore, including ecological variation when testing POLS is vastly needed to determine whether POLS is a fixed construct or the result of specific selection processes. Here, we tested POLS predictions between and within two fish populations originating from different ecological conditions. We observed opposing life histories between populations, characterized by differential investments into growth, fecundity, and functional morphology under identical laboratory conditions. A slower life history was, on average, associated with boldness (latency to emergence from a refuge), high activity (short freezing time and long distance travelled), and increased standard metabolism. Correlation structures among POLS traits were not consistent between populations, with the expression of POLS observed in the slow-growing but not in the fast-growing population. Our results suggest that POLS traits can evolve independently from one another and that their coevolution depends upon specific ecological processes.

Consistent individual and sex-specific differences in behaviour of common cuckoo chicks: is there a potential impact on host-parasite coevolutionary dynamics?

Research on brood parasitism has focused primarily on specific host anti-parasite behaviours and parasite counter-adaptations, and little is known about other aspects of their behaviours such as consistent behavioural differences between individuals. Therefore, we examined consistency in behaviour of nestlings of common cuckoos (Cuculus canorus) raised by great reed warblers (Acrocephalus arundinaceus). Cuckoo chicks showed high repeatability of both aggressive behaviour and breath rate, and both traits were strongly correlated with each other. This represents the first evidence for consistent differences in behaviour among avian brood parasites. Males were consistently more aggressive and less stressed than females. Nestlings of both sexes that hatched later in the season exhibited higher levels of aggression and lower stress responses than nestlings hatched earlier. This suggests that rearing conditions (e.g., food availability and quality) may modulate stress and aggressive phenotypes of brood parasites. We discuss potential effects of the observed patterns on host-parasite dynamics.

Predation risk and abiotic habitat parameters affect personality traits in extremophile populations of a neotropical fish (Poecilia vivipara)

Understanding whether and how ambient ecological conditions affect the distribution of personality types within and among populations lies at the heart of research on animal personality. Several studies have focussed on only one agent of divergent selection (or driver of plastic changes in behavior), considering either predation risk or a single abiotic ecological factor. Here, we investigated how an array of abiotic and biotic environmental factors simultaneously shape population differences in boldness, activity in an open‐field test, and sociability/shoaling in the livebearing fish Poecilia vivipara from six ecologically different lagoons in southeastern Brazil. We evaluated the relative contributions of variation in predation risk, water transparency/visibility, salinity (ranging from oligo‐ to hypersaline), and dissolved oxygen. We also investigated the role played by environmental factors for the emergence, strength, and direction of behavioral correlations. Water transparency explained most of the behavioral variation, whereby fish from lagoons with low water transparency were significantly shyer, less active, and shoaled less than fish living under clear water conditions. When we tested additional wild‐caught fish from the same lagoons after acclimating them to homogeneous laboratory conditions, population differences were largely absent, pointing toward behavioral plasticity as a mechanism underlying the observed behavioral differences. Furthermore, we found correlations between personality traits (behavioral syndromes) to vary substantially in strength and direction among populations, with no obvious associations with ecological factors (including predation risk). Altogether, our results suggest that various habitat parameters simultaneously shape the distribution of personality types, with abiotic factors playing a vital (as yet underestimated) role. Furthermore, while predation is often thought to lead to the emergence of behavioral syndromes, our data do not support this assumption.

Body length rather than routine metabolic rate and body condition correlates with activity and risk-taking in juvenile zebrafish Danio rerio

In this study, the following hypotheses were explored using zebrafish Danio rerio: (1) individuals from the same cohort differ consistently in activity and risk-taking and (2) variation in activity and risk-taking is linked to individual differences in metabolic rate, body length and body condition. To examine these hypotheses, juvenile D. rerio were tested for routine metabolic rate and subsequently exposed to an open field test. Strong evidence was found for consistent among-individual differences in activity and risk-taking, which were overall negatively correlated with body length, i.e. larger D. rerio were found to be less active in a potentially dangerous open field and a similar trend was found with respect to a more direct measure of their risk-taking tendency. In contrast, routine metabolic rate and body condition were uncorrelated with both activity and risk-taking of juvenile D. rerio. These findings suggest that body length is associated with risk-related behaviours in juvenile D. rerio for which larger, rather than smaller, individuals may have a higher risk of predation, while the role for routine metabolic rate is relatively limited or non-existent, at least under the conditions of the present study.