Equal performance but distinct behaviors: sex differences in a novel object recognition task and spatial maze in a highly social cichlid fish

Does visual or mechanosensory disruption influence risk assessment in coral reef fishes: a preliminary study

Interpreting and responding to environmental cues from different modalities has survival value. In fish, the role of multimodal perception has been studied in regard to both foraging and risk assessment, with modalities including vision, olfaction, and mechanoreception via lateral lines. We studied reef fish boldness by placing novel objects that obstructed vision, lateral line use, or both into a coral reef environment with native algal samples inside, and then quantifying exploration as a function of obstruction type and as a function of functional diet groups (herbivores, omnivores, carnivores). Fish were more neophobic with more sensory obstructions, displaying longer latencies to visitation across all novel objects. Fish were also less likely to pass by objects that blocked multiple perceptual modalities. Across diets, there is early evidence that different functional groups respond differently to novelty. However, this conclusion requires further study. Overall, our findings provide key insights into perceptual ecology. In turn, this knowledge can be applied to understanding the effects of novel anthropogenic modifications in the marine environment. Such modifications may include positive activities like the construction of substrates to restore coral reefs, coral transplantation to restore reefs, as well as the negative consequences of construction and pollution.

From land to water: "Sunken" T-maze for associated learning in cichlid fish

The study introduced and evaluated learning paradigms for Maylandia callainos cichlids using a modified version of the rodent T-maze, filled with tank water (the "sunken" modification). Both male and female fish underwent training in two distinct conditioning paradigms. Firstly, simple operant conditioning involved placing a food reward in either the right or left compartment. Cichlids demonstrated the ability to purposefully find the bait within 6 days of training, with a persistent place preference lasting up to 6 days. Additionally, the learning dynamics varied with sex: female cichlids exhibited reduction in latency to visit the target compartment and consume the bait, along with a decrease in the number of errors 3 and 4 days earlier than males, respectively. Secondly, visually-cued operant conditioning was conducted, with a food reward exclusively placed in the yellow compartment, randomly positioned on the left or right side of the maze during each training session. Visual learning persisted for 10 days until reaction time improvement plateaued. Color preference disappeared after 4 consecutive check-ups, with no sex-related interference. For further validation of visually-cued operant conditioning paradigm, drugs MK-801 (dizocilpine) and caffeine, known to affect performance in learning tasks, were administered intraperitoneally. Chronic MK-801 (0.17 mg/kg) impaired maze learning, resulting in no color preference development. Conversely, caffeine administration enhanced test performance, increasing precision in fish. This developed paradigm offers a viable approach for studying learning and memory and presents an effective alternative to rodent-based drug screening tools, exhibiting good face and predictive validity.

Cognitive-exercise dual-task intervention ameliorates cognitive decline in natural aging rats via inhibiting the promotion of LncRNA NEAT1/miR-124-3p on caveolin-1-PI3K/Akt/GSK3β Pathway

Aging-related cognitive impairment (ARCI) is rapidly becoming a healthcare priority. However, there is currently no excellent cure for it. Cognitive-exercise dual-task intervention (CEDI) is a promising method to improve ARCI, while the underlying mechanisms remain unclear. Long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) are involved in the onset, development, and rehabilitation of ARCI. This study aimed to investigate the effects of CEDI and the role of regulation of the lncRNA NEAT1/miR-124-3p on the caveolin-1-PI3K/Akt/GSK3β pathway in CEDI improving cognitive function. Forty 18-month-old natural aging rats were randomly assigned to four groups: exercise training group, cognitive training group, CEDI group, and aging control group, and underwent 12 weeks of intervention. A novel object recognition test was performed to determine the cognitive function, and the hippocampus was separated three days after the behavioral tests for further molecular detection. In an in vitro study, the mouse hippocampal neuronal cell line HT22 was cultured. MiR-124-3p and lncRNA NEAT1 were over-expressed or down-expressed, respectively. The expressions of related proteins, lncRNA, and miRNA were examined by WB and/or qRT-PCR. The results showed that compared with the aging control group, the CEDI group had a higher discrimination index, and significantly decreased the expressions of lncRNA NEAT1, and the protein expressions of caveolin-1 and p-GSK3β, while significantly increased the expressions of miR-124-3p, and the protein expressions of p-PI3K and p-Akt. Inhibition of the lncRNA NEAT1 could significantly increase the protein expressions of p-PI3K and p-Akt in HT22 cells. Upregulation of miR-124-3p decreased the protein expressions of caveolin-1 and p-GSK3β, and increased the protein expressions of p-PI3K and p-Akt significantly. Inhibition of miR-124-3p had the opposite effects. Our study demonstrated that CEDI improved cognitive function in aging rats better than a single intervention. The mechanisms of cognitive improvement could be related to the regulation of the lncRNA NEAT1/miR-124-3p on the caveolin-1-PI3K/Akt/GSK3β pathway.

Teleosts as behaviour test models for social stress

Stress is an important aspect of our everyday life and exposure to it is an unavoidable occurrence. In humans, this can come in the form of social stress or physical stress from an injury. Studies in animal models have helped researchers to understand the body's adaptive response to stress in human. Notably, the use of behavioural tests in animal models plays a pivotal role in understanding the neural, endocrine and behavioural changes induced by social stress. Under socially stressed conditions, behavioural parameters are often measured physiological and molecular parameters as changes in behaviour are direct responses to stress and are easily assessed by behavioural tests. Throughout the past few decades, the rodent model has been used as a well-established animal model for stress and behavioural changes. Recently, more attention has been drawn towards using fish as an animal model. Common fish models such as zebrafish, medaka, and African cichlids have the advantage of a higher rate of reproduction, easier handling techniques, sociability and most importantly, share evolutionary conserved genetic make-up, neural circuitry, neuropeptide molecular structure and function with mammalian species. In fact, some fish species exhibit a clear diurnal or seasonal rhythmicity in their stress response, similar to humans, as opposed to rodents. Various social stress models have been established in fish including but not limited to chronic social defeat stress, social stress avoidance, and social stress-related decision-making. The huge variety of behavioural patterns in teleost also aids in the study of more behavioural phenotypes than the mammalian species. In this review, we focus on the use of fish models as alternative models to study the effects of stress on different types of behaviours. Finally, fish behavioural tests against the typical mammalian model-based behavioural test are compared and discussed for their viability.

Assessing sex differences in behavioural flexibility in an endangered bird species: the Southern ground-hornbill (Bucorvus leadbeateri)

Since ecology influences the expression of cognitive traits, intra-specific variation in ecological demands can drive differences in cognition. This is often the case, for instance, when sexes face different ecological challenges. However, so far, most studies have focused on few cognitive domains (i.e., spatial cognition), which limits our understanding of the evolution of sexually dimorphic cognition in animals. Endangered Southern ground-hornbills (Bucorvus leadbeateri), for example, show sex-specific ecological differences in age at dispersal, where females disperse from their natal group earlier than males. Based on this potential sex-specific source of selection, females and males may differ in their capacity to behave flexibly. Here, we used the reversal-learning paradigm in ten Southern ground-hornbills in two conditions: spatial and colour. During the pre-test (learning phase), regardless the sex, all subjects were faster at associating the food reward with spatial rather than with colour cues. Similarly, during the test (reversal-learning phase), both sexes learned the new association quicker with spatial cues. There were no sex differences in learning or reversal learning during both experimental phases. This possibility, however, requires further observation and experimentation. We hope our study will provide the impetus to assess further the cognitive capacities of this still overlooked species.

Behaviorally penetrant, anomalous dopamine efflux exposes sex and circuit dependent regulation of dopamine transporters

Virtually all neuropsychiatric disorders display sex differences in prevalence, age of onset, and/or clinical symptomology. Although altered dopamine (DA) signaling is a feature of many of these disorders, sex-dependent mechanisms uniquely responsive to DA that drive sex-dependent behaviors remain unelucidated. Previously, we established that anomalous DA efflux (ADE) is a prominent feature of the DA transporter (DAT) variant Val559, a coding substitution identified in two male-biased disorders: attention-deficit/hyperactivity disorder and autism spectrum disorder. In vivo, Val559 ADE induces activation of nigrostriatal D2-type DA autoreceptors (D2ARs) that magnifies inappropriate, nonvesicular DA release by elevating phosphorylation and surface trafficking of ADE-prone DAT proteins. Here we demonstrate that DAT Val559 mice exhibit sex-dependent alterations in psychostimulant responses, social behavior, and cognitive performance. In a search for underlying mechanisms, we discovered that the ability of ADE to elicit D2AR regulation of DAT is both sex and circuit-dependent, with dorsal striatum D2AR/DAT coupling evident only in males, whereas D2AR/DAT coupling in the ventral striatum is exclusive to females. Moreover, systemic administration of the D2R antagonist sulpiride, which precludes ADE-driven DAT trafficking, can normalize DAT Val559 behavioral changes unique to each sex and without effects on the opposite sex or wildtype mice. Our studies support the sex- and circuit dependent capacity of D2ARs to regulate DAT as a critical determinant of the sex-biased effects of perturbed DA signaling in neurobehavioral disorders. Moreover, our work provides a cogent example of how a shared biological insult drives alternative physiological and behavioral trajectories as opposed to resilience.

Contrasting parental roles shape sex differences in poison frog space use but not navigational performance

Sex differences in vertebrate spatial abilities are typically interpreted under the adaptive specialization hypothesis, which posits that male reproductive success is linked to larger home ranges and better navigational skills. The androgen spillover hypothesis counters that enhanced male spatial performance may be a byproduct of higher androgen levels. Animal groups that include species where females are expected to outperform males based on life-history traits are key for disentangling these hypotheses. We investigated the association between sex differences in reproductive strategies, spatial behavior, and androgen levels in three species of poison frogs. We tracked individuals in natural environments to show that contrasting parental sex roles shape sex differences in space use, where the sex performing parental duties shows wider-ranging movements. We then translocated frogs from their home areas to test their navigational performance and found that the caring sex outperformed the non-caring sex only in one out of three species. In addition, males across species displayed more explorative behavior than females and androgen levels correlated with explorative behavior and homing accuracy. Overall, we reveal that poison frog reproductive strategies shape movement patterns but not necessarily navigational performance. Together this work suggests that prevailing adaptive hypotheses provide an incomplete explanation of sex differences in spatial abilities.

The contribution of executive functions to sex differences in animal cognition

Cognitive sex differences have been reported in several vertebrate species, mostly in spatial abilities. Here, I review evidence of sex differences in a family of general cognitive functions that control behaviour and cognition, i.e., executive functions such as cognitive flexibility and inhibitory control. Most of this evidence derives from studies in teleost fish. However, analysis of literature from other fields (e.g., biomedicine, genetic, ecology) concerning mammals and birds reveals that more than 40% of species investigated exhibit sex differences in executive functions. Among species, the direction and magnitude of these sex differences vary greatly, even within the same family, suggesting sex-specific selection due to species' reproductive systems and reproductive roles of males and females. Evidence also suggests that sex differences in executive functions might provide males and females highly differentiated cognitive phenotypes. To understand the evolution of cognitive sex differences in vertebrates, future research should consider executive functions.

Spatial Learning of Individual Cichlid Fish and Its Effect on Group Decision Making

Learning and memory abilities and their roles in group decision-making have important ecological relevance in routine activities such as foraging and anti-predator behaviors in fish species. The aims of the present study were to explore individual spatial learning abilities of juvenile cichlids (Chindongo demasoni) in a foraging context, and to explore the influence of heterogeneity of memory information among group members on group performance in a six-arm radiation maze. In the context of an association between landmarks and food, learning ability was evaluated by the speed and accuracy of reaching the arm with food during seven days of reinforcement, and memory retention was tested at intervals of 2, 5, 8 and 11 days of detraining. Then, the speed and accuracy of an eight-member group with different proportions of memory-trained fish were measured. Both speed and accuracy of individual fish improved significantly and linearly in the first five days of training and leveled off between five and seven days, with values 60% shorter (in speed) and 50% higher (in accuracy) compared to those of the first day. Neither speed nor accuracy showed any decrease after 11 days of detraining, suggesting memory retention of the spatial task. When measured in a group, the speed and accuracy of the majority of the group (more than half) in reaching the arm with food changed linearly with an increasing ratio of trained members. This shows that cichlids can acquire associative learning information through a training process, and group behavior of cichlids seems not likely be determined by a minority of group members under a foraging context.

Endocrine and neuroendocrine regulation of social status in cichlid fishes

Position in a dominance hierarchy profoundly impacts group members' survival, health, and reproductive success. Thus, understanding the mechanisms that regulate or are associated with an individuals' social position is important. Across taxa, various endocrine and neuroendocrine signaling systems are implicated in the control of social rank. Cichlid fishes, with their often-limited resources of food, shelter, and mates that leads to competition, have provided important insights on the proximate and ultimate mechanisms related to establishment and maintenance of dominance hierarchies. Here we review the existing information on the relationships between endocrine (e.g., circulating hormones, gonadal and other tissue measures) and neuroendocrine (e.g., central neuropeptides, biogenic amines, steroids) systems and dominant and subordinate social rank in male cichlids. Much of the current literature is focused on only a few representative cichlids, particularly the African Astatotilapia burtoni, and several other African and Neotropical species. Many hormonal regulators show distinct differences at multiple biological levels between dominant and subordinate males, but generalizations are complicated by variations in experimental paradigms, methodological approaches, and in the reproductive and parental care strategies of the study species. Future studies that capitalize on the diversity of hierarchical structures among cichlids should provide insights towards better understanding the endocrine and neuroendocrine mechanisms contributing to social rank. Further, examination of this topic in cichlids will help reveal the selective pressures driving the evolution of endocrine-related phenotypic traits that may facilitate an individual's ability to acquire and maintain a specific social rank to improve survival and reproductive success.

Social ascent changes cognition, behaviour and physiology in a highly social cichlid fish

When an individual ascends in dominance status within their social community, they often undergo a suite of behavioural, physiological and neuromolecular changes. While these changes have been extensively characterized across a number of species, we know much less about the degree to which these changes in turn influence cognitive processes like associative learning, memory and spatial navigation. Here, we assessed male Astatotilapia burtoni, an African cichlid fish known for its dynamic social dominance hierarchies, in a set of cognitive tasks both before and after a community perturbation in which some individuals ascended in dominance status. We assayed steroid hormone (cortisol, testosterone) levels before and after the community experienced a social perturbation. We found that ascending males changed their physiology and novel object recognition preference during the perturbation, and they subsequently differed in social competence from non-ascenders. Additionally, using a principal component analysis we were able to identify specific cognitive and physiological attributes that appear to predispose certain individuals to ascend in social status once a perturbation occurs. These previously undiscovered relationships between social ascent and cognition further emphasize the broad influence of social dominance on animal decision-making. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

Zebrafish excel in number discrimination under an operant conditioning paradigm

Numerical discrimination is widespread in vertebrates, but this capacity varies enormously between the different species examined. The guppy (Poecilia reticulata), the only teleost examined following procedures that allow a comparison with the other vertebrates, outperforms amphibians, reptiles and many warm-blooded vertebrates, but it is unclear whether this is a feature shared with the other teleosts or represents a peculiarity of this species. We trained zebrafish (Danio rerio) to discriminate between numbers differing by one unit, varying task difficulty from 2 versus 3 to 5 versus 6 items. Non-numerical variables that covary with number, such as density or area, did not affect performance. Most fish reached learning criterion on all tasks up to 4 versus 5 discrimination with no sex difference in accuracy. Although no individual reached learning criterion in the 5 versus 6 task, performance was significant at the group level, suggesting that this may represent the discrimination threshold for zebrafish. Numerosity discrimination abilities of zebrafish compare to those of guppy, being higher than in some warm-blooded vertebrates, such as dogs, horses and domestic fowl, though lower than in parrots, corvids and primates. Learning rate was similar in a control group trained to discriminate between different-sized shapes, but zebrafish were slightly more accurate when discriminating areas than numbers and males were more accurate than females. At the end of the experiment, fish trained on numbers and controls trained on areas generalized to the reciprocal set of stimuli, indicating they had used a relational strategy to solve these tasks.

Mate Choice, Sex Roles and Sexual Cognition in Vertebrates: Mate Choice Turns Cognition or Cognition Turns Mate Choice?

The idea of “smart is sexy,” meaning superior cognition provides competitive benefits in mate choice and, therefore, evolutionary advantages in terms of reproductive fitness, is both exciting and captivating. Cognitively flexible individuals perceive and adapt more dynamically to (unpredictable) environmental changes. The sex roles that females and males adopt within their populations can vary greatly in response to the prevalent mating system. Based on how cognition determines these grossly divergent sex roles, different selection pressures could possibly shape the (progressive) evolution of cognitive abilities, suggesting the potential to induce sexual dimorphisms in superior cognitive abilities. Associations between an individual’s mating success, sexual traits and its cognitive abilities have been found consistently across vertebrate species and taxa, providing evidence that sexual selection may well shape the supporting cognitive prerequisites. Yet, while superior cognitive abilities provide benefits such as higher feeding success, improved antipredator behavior, or more favorable mate choice, they also claim costs such as higher energy levels and metabolic rates, which in turn may reduce fecundity, growth, or immune response. There is compelling evidence in a variety of vertebrate taxa that females appear to prefer skilled problem-solver males, i.e., they prefer those that appear to have better cognitive abilities. Consequently, cognition is also likely to have substantial effects on sexual selection processes. How the choosing sex assesses the cognitive abilities of potential mates has not been explored conclusively yet. Do cognitive skills guide an individual’s mate choice and does learning change an individual’s mate choice decisions? How and to which extent do individuals use their own cognitive skills to assess those of their conspecifics when choosing a mate? How does an individual’s role within a mating system influence the choice of the choosing sex in this context? Drawing on several examples from the vertebrate world, this review aims to elucidate various aspects associated with cognitive sex differences, the different roles of males and females in social and sexual interactions, and the potential influence of cognition on mate choice decisions. Finally, future perspectives aim to identify ways to answer the central question of how the triad of sex, cognition, and mate choice interacts.

Social network dynamics predict hormone levels and behavior in a highly social cichlid fish

Group living confers many benefits while simultaneously exposing group members to intense competition. An individual's rise to prominence within a group may conflict with the overall functioning of the group. There is therefore a complex and dynamic relationship between the behavioral displays that directly benefit an individual, the consequences of these actions for the community, and how they feed back on individual-level fitness. We used a network analysis approach to study the link between behavior, social stability, and steroid hormone levels in replicate communities of the cichlid fish, Astatotilapia burtoni, which live in social groups with a dominance hierarchy. We demonstrate that individual behavior can have direct and indirect effects on the behavior of others while also affecting group characteristics. Our results show that A. burtoni males form stable social networks, where dominant individuals act as hubs for social interactions. However, there was variation in the temporal stability in these networks, and this variation in stability impacted hormone levels. Dominant males had higher testosterone levels, however, the differences in testosterone levels between dominant and subordinate males were greatest in stable communities. In sum, our analyses provide novel insights into the processes by which individual and community properties interact.