Ontogeny and personality affect inhibitory control in guppies, Poecilia reticulata

Sex affects the network of covariances between cognitive, behavioral, and physiological traits in guppies

Cognitive variance has been documented across many species. It may stem from constraints imposed by the covariation among different traits. We hypothesized that sex could contribute to cognitive variance by affecting the traits' covariation. By applying a network analysis in the guppy (Poecilia reticulata), a fish with marked sexual dimorphism, we found that males and females differed along a fast-slow continuum, with males exhibiting higher metabolism, higher activity levels, faster learning, and lower cognitive flexibility. Moreover, we found more covarying traits in males compared to females (12 versus 7). Pairwise associations involving cognitive traits significantly differed in the covariance networks of the two sexes and were stronger in males. Various traits, including learning and cognitive flexibility, had different influences in the covariation network between males and females. Cognitive traits are embedded in a complex, sex-dependent web of covariation, which may be important for the evolution and maintenance of cognitive variance.

Stunned by a Heatwave: Experimental Heatwaves Alter Juvenile Responsiveness to the Threat of Predation

Heatwaves, increasingly prevalent in our rapidly changing climate, significantly impact animals with far-reaching ecological and evolutionary consequences. One of the first responses in animals to stress, including heat stress, is behavioural change, and this can directly influence fitness and survival. Changes in anti-predator behaviour are particularly critical, as they may compromise a prey's ability to evade predators, thus increasing predation risk and jeopardising survival. In the context of climate change, assessing anti-predator reactions under ecologically relevant heat stress is thus crucial, especially during the vulnerable life stage of development. This study investigated the effects of a heatwave on anti-predator responses in juvenile guppies (Poecilia reticulata). One-month-old guppies were subjected to a 5-day experimental heatwave (32°C) or a control temperature (26°C). After the treatment, all individuals were tested at a common temperature (26°C) for anti-predator behavioural responses and swimming performance, the latter serving as a proxy for physical condition. While heatwave exposure did not affect swimming performance, it significantly altered anti-predator responses. Heatwave-exposed juveniles exhibited a reduced freezing response and faster resumption of normal activity compared to control fish. Our findings demonstrate that heatwaves can modify prey's anti-predator behaviours during critical developmental stages. This suggests that heatwaves may increase predation risk, potentially impacting survival rates and reshaping predator-prey interactions in the face of ongoing climate change.

Individual phenotypic variability in the behaviour of an aggregative riverine fish is structured along a reactive-proactive axis

High phenotypic diversity should provide populations with resilience to environmental change by increasing their capacity to respond to changing conditions. The aim of this study was to identify whether there is consistency in individual behaviours on a reactive-proactive axis in European barbel Barbus barbus ("barbel"), a riverine and aggregatory fish that expresses individual differences in its behaviours in nature. This was tested using three sequential experiments in ex-situ conditions that required individuals to leave a shelter and then explore new habitats ('open-field test'), respond to social stimuli ('mirror-image stimulation test') and forage ('foraging behaviour test'; assessing exploratory traits). Each suite of experiments was replicated three times per individual (46 hours minimum time between replicates). There was high variability in behaviours both within and among individuals. The most repeatable behaviours were latency to exit the shelter, active time in the shelter, and the number of food items consumed. Principal component scores did, however, indicate a range of consistent behavioural phenotypes across the individuals, distributing them along a reactive-proactive axis in which most of individuals were more reactive phenotypes (shyer, less exploratory, less social). These results suggest that within controlled conditions, there is considerable phenotypic diversity among individuals in their behaviours, suggesting their populations will have some adaptive capacity to environmental change.

Inbreeding and high developmental temperatures affect cognition and boldness in guppies (Poecilia reticulata)

Inbreeding impairs the cognitive abilities of humans, but its impact on cognition in other animals is poorly studied. For example, environmental stress (e.g. food limitation and extreme temperatures) often amplifies inbreeding depression in morphological traits, but whether cognition is similarly affected is unclear. We, therefore, tested if a higher temperature (30°C versus 26°C) during development exacerbates any difference in inhibitory control between inbred (f = 0.25) and outbred guppies (Poecilia reticulata). Inhibitory control is an aspect of cognition that is often measured in vertebrates using a detour test, in which animals have to navigate around a transparent barrier to reach a reward. We also tested if inbreeding and temperature affect 'boldness', which is a putative personality trait in guppies. Inbreeding lowered inhibitory control of guppies raised at the higher temperature but not those raised at the control temperature. Inbred fish were significantly less bold than outbred fish. In addition, males, but not females, raised at the higher temperature had significantly lower inhibitory control. There was no effect of temperature on the boldness of either sex. Our study is among the first to test if experimentally induced inbreeding impairs cognition in a non-domesticated vertebrate. We show that both inbreeding and higher temperatures during development can affect the behaviour and cognitive abilities of fish. These findings are noteworthy given the twin threats of rising global temperatures and more frequent inbreeding as habitat fragmentation reduces population sizes.

Inhibitory control in teleost fish: a methodological and conceptual review

Inhibitory control (IC) plays a central role in behaviour control allowing an individual to resist external lures and internal predispositions. While IC has been consistently investigated in humans, other mammals, and birds, research has only recently begun to explore IC in other vertebrates. This review examines current literature on teleost fish, focusing on both methodological and conceptual aspects. I describe the main paradigms adopted to study IC in fish, identifying well-established tasks that fit various research applications and highlighting their advantages and limitations. In the conceptual analysis, I identify two well-developed lines of research with fish examining IC. The first line focuses on a comparative approach aimed to describe IC at the level of species and to understand the evolution of interspecific differences in relation to ecological specialisation, brain size, and factors affecting cognitive performance. Findings suggest several similarities between fish and previously studied vertebrates. The second line of research focuses on intraspecific variability of IC. Available results indicate substantial variation in fish IC related to sex, personality, genetic, age, and phenotypic plasticity, aligning with what is observed with other vertebrates. Overall, this review suggests that although data on teleosts are still scarce compared to mammals, the contribution of this group to IC research is already substantial and can further increase in various disciplines including comparative psychology, cognitive ecology, and neurosciences, and even in applied fields such as psychiatry research.

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

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

Embryonic exposure to artificial light at night impairs learning abilities and their covariance with behavioural traits in teleost fish

The natural light cycle has profound effects on animals' cognitive systems. Its alteration owing to human activities, such as artificial light at night (ALAN), affects the biodiversity of mammalian and avian species by impairing their cognitive functions. The impact of ALAN on cognition, however, has not been investigated in aquatic species, in spite of the common occurrence of this pollution along water bodies. We exposed eggs of a teleost fish (the zebrafish Danio rerio) to ALAN and, upon hatching, we measured larvae' cognitive abilities with a habituation learning paradigm. Both control and ALAN-exposed larvae showed habituation learning, but the latter learned significantly slower, suggesting that under ALAN conditions, fish require many more events to acquire ecologically relevant information. We also found that individuals' learning performance significantly covaried with two behavioural traits in the control zebrafish, but ALAN disrupted one of these relationships. Additionally, ALAN resulted in an average increase in larval activity. Our results showed that both fish's cognitive abilities and related individual differences are negatively impacted by light pollution, even after a short exposure in the embryonic stage.

Interspecific differences in developmental mode determine early cognitive abilities in teleost fish

Most studies on developmental variation in cognition have suggested that individuals are born with reduced or absent cognitive abilities, and thereafter, cognitive performance increases with age during early development. However, these studies have been mainly performed in altricial species, such as humans, in which offspring are extremely immature at birth. In this work, we tested the hypothesis that species with other developmental modes might show different patterns of cognitive development. To this end, we analysed inhibitory control performance in two teleost species with different developmental modes, the zebrafish Danio rerio and the guppy Poecilia reticulata, exploiting a simple paradigm based on spontaneous behaviour and therefore applicable to subjects of different ages. Zebrafish hatch as larvae 3 days after fertilisation, and have an immature nervous system, a situation that mirrors extreme altriciality. We found that at the early stages of development, zebrafish displayed no evidence of inhibitory control, which only begun to emerge after one month of life. Conversely, guppies, which are born after approximately one month of gestation as fully developed and independent individuals, solved the inhibitory control task since their first days of life, although performance increased with sexual maturation. Our study suggests that the typical progression described during early ontogeny in humans and other species might not be the only developmental trend for animals' cognition and that a species' developmental mode might determine variation in cognition across subjects of different age.

Adaptive phenotypic plasticity induces individual variability along a cognitive trade-off

Animal species, including humans, display patterns of individual variability in cognition that are difficult to explain. For instance, some individuals perform well in certain cognitive tasks but show difficulties in others. We experimentally analysed the contribution of cognitive plasticity to such variability. Theory suggests that diametrically opposed cognitive phenotypes increase individuals' fitness in environments with different conditions such as resource predictability. Therefore, if selection has generated plasticity that matches individuals' cognitive phenotypes to the environment, this might produce remarkable cognitive variability. We found that guppies, Poecilia reticulata, exposed to an environment with high resource predictability (i.e. food available at the same time and in the same location) developed enhanced learning abilities. Conversely, guppies exposed to an environment with low resource predictability (i.e. food available at a random time and location) developed enhanced cognitive flexibility and inhibitory control. These cognitive differences align along a trade-off between functions that favour the acquisition of regularities such as learning and functions that adjust behaviour to changing conditions (cognitive flexibility and inhibitory control). Therefore, adaptive cognitive plasticity in response to resource predictability (and potentially similar factors) is a key determinant of cognitive individual differences.

Correlations begin at home: drivers of co-occurrence patterns in personality and cognitive ability in wild populations of zebrafish

Aquatic habitats are extremely dynamic, with constantly changing ecological factors, which has now been exacerbated due to human-induced rapid environmental change. In such variable environments, it becomes essential to understand how personality and cognition in organisms affect the adaptability of individuals to different habitat conditions. To test this, we studied how personality-related traits as well as cognitive ability differ between populations of wild-caught zebrafish (Danio rerio) from habitats that differed in various environmental factors. We measured emergence into a novel environment as an indicator of boldness, and performance in a spatial task inferred from feeding latencies in a maze over repeated trials to assess learning and memory, as an indicator of cognitive ability. We found that personality affects cognition and although bolder fish are better learners, they show poorer retention of memory across populations. Although personality and cognitive ability varied between habitats, the patterns of their correlations remained similar within each population. However, the individual traits (such as sex and size) that were drivers of personality and cognition differed between the habitats, suggesting that not only do behavioral traits vary between populations, but also the factors that are important in determining them. Personality and cognitive ability and the correlations between these traits determine how well an organism performs in its habitat, as well as how likely it is to find new habitats and adapt to them. Studying these across wild zebrafish populations helps predict performance efficiencies among individuals and also explains how fish adapt to extremely dynamic environments that can lead to variation in behavioral traits and correlations between them. This study not only sheds light on the drivers of interindividual variation and co-occurrence patterns of personality and cognition, but also individual and population factors that might have an effect on them.