Sex differences in discrimination reversal learning in the guppy

Coercive mating has no impact on spatial learning, cognitive flexibility, and fecundity in female porthole livebearers (Poeciliopsis gracilis)

Coercive mating is a sexual selection strategy that is likely to influence female cognition. Female harassment levels have been linked to altered brain gene expression patterns and brain size evolution, suggesting females may respond to coercive mating by investing energy into "outsmarting" males. However, females exposed to coercive males have decreased foraging efficiency and likely increased stress levels, suggesting their brain function might instead be impaired. While it is therefore likely that coercive mating impacts female cognitive abilities, a direct test of this idea is currently lacking. In this study, we investigate the impact of coercive mating on female spatial memory and cognitive flexibility in a species with prevalent coercive mating. We compared the performance of female porthole livebearers (Poeciliopsis gracilis), which had been previously housed alone or with a coercive male, in both a spatial food localization task and a reversal learning task. While we found that both single and paired fish exhibited high proficiency in learning both tasks, we found no differences in learning ability between females that had or had not experienced coercive mating. In addition, our study found that the presence of a coercive male had no impact on female fecundity, but did influence female mass and standard length. Several studies have assumed that the presence of males, particularly coercive males, may affect the cognitive performance of female fish. However, our study shows that for some species females adapted to coercive mating regimes may be unaffected by male presence with regards to some cognitive tasks.

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.

Individual differences and knockout in zebrafish reveal similar cognitive effects of BDNF between teleosts and mammals

The remarkable similarities in cognitive performance between teleosts and mammals suggest that the underlying cognitive mechanisms might also be similar in these two groups. We tested this hypothesis by assessing the effects of the brain-derived neurotrophic factor (BDNF), which is critical for mammalian cognitive functioning, on fish's cognitive abilities. We found that individual differences in zebrafish's learning abilities were positively correlated with bdnf expression. Moreover, a CRISPR/Cas9 mutant zebrafish line that lacks the BDNF gene (bdnf-/-) showed remarkable learning deficits. Half of the mutants failed a colour discrimination task, whereas the remaining mutants learned the task slowly, taking three times longer than control bdnf+/+ zebrafish. The mutants also took twice as long to acquire a T-maze task compared to control zebrafish and showed difficulties exerting inhibitory control. An analysis of habituation learning revealed that cognitive impairment in mutants emerges early during development, but could be rescued with a synthetic BDNF agonist. Overall, our study indicates that BDNF has a similar activational effect on cognitive performance in zebrafish and in mammals, supporting the idea that its function is conserved in vertebrates.

Assessing cognitive flexibility in humans and rhesus macaques with visual motion and neutral distractors

Introduction

Cognitive flexibility is the ability of an individual to make behavioral adjustments in response to internal and/or external changes. While it has been reported in a wide variety of species, established paradigms to assess cognitive flexibility vary between humans and non-human animals, making systematic comparisons difficult to interpret.

Methods

We developed a computer-based paradigm to assess cognitive flexibility in humans and non-human primates. Our paradigm (1) uses a classical reversal learning structure in combination with a set-shifting approach (4 stimuli and 3 rules) to assess flexibility at various levels; (2) it employs the use of motion as one of three possible contextual rules; (3) it comprises elements that allow a foraging-like and random interaction, i.e., instances where the animals operate the task without following a strategy, to potentially minimize frustration in favor of a more positive engagement.

Results and Discussion

We show that motion can be used as a feature dimension (in addition to commonly used shape and color) to assess cognitive flexibility. Due to the way motion is processed in the primate brain, we argue that this dimension is an ideal candidate in situations where a non-binary rule set is needed and where participants might not be able to fully grasp other visual information of the stimulus (e.g., quantity in Wisconsin Card Sorting Test). All participants in our experiment flexibly shifted to and from motion-based rules as well as color- and shape-based rules, but did so with different proficiencies. Overall, we believe that with such approach it is possible to better characterize the evolution of cognitive flexibility in primates, as well as to develop more efficient tools to diagnose and treat various executive function deficits.

Jumping out of trouble: evidence for a cognitive map in guppies (Poecilia reticulata)

Spatial cognitive abilities allow individuals to remember the location of resources such as food patches, predator hide-outs, or shelters. Animals typically incorporate learned spatial information or use external environmental cues to navigate their surroundings. A spectacular example of how some fishes move is through aerial jumping. For instance, fish that are trapped within isolated pools, cut off from the main body of water during dry periods, may jump over obstacles and direct their jumps to return to safe locations. However, what information such re-orientation behavior during jumping is based on remains enigmatic. Here we combine a lab and field experiment to test if guppies (Poecilia reticulata) incorporate learned spatial information and external environmental cues (visual and auditory) to determine where to jump. In a spatial memory assay we found that guppies were more likely to jump towards deeper areas, hence incorporating past spatial information to jump to safety. In a matched versus mismatched spatial cue experiment in the field, we found that animals only showed directed jumping when visual and auditory cues matched. We show that in unfamiliar entrapments guppies direct their jumps by combining visual and auditory cues, whereas in familiar entrapments they use a cognitive map. We hence conclude that jumping behavior is a goal-directed behavior, guided by different sources of information and involving important spatial cognitive skills.

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.

Male mate choice in mosquitofish: personality outweighs body size

Background

Despite its important implications in behavioural and evolutionary ecology, male mate choice has been poorly studied, and the relative contribution of personality and morphological traits remains largely unknown. We used standard two-choice mating trials to explore whether two personality traits (i.e., shyness and activity) and/or body size of both sexes affect mate choice in male mosquitofish Gambusia affinis. In the first set of trials involving 40 males, we tested whether males would prefer larger females and whether the preference would be affected by males’ body length and personality traits, and females’ activity level. In the second set of trials (using another 40 males), we tested whether males would prefer more active females and whether the preference would be affected by males’ body length and personality traits.

Results

Both shyness and activity in males were significantly repeatable and constituted a behavioural syndrome. No overall directional preference for large (or small) females with the same activity levels was detected because larger males preferred larger females and smaller males chose smaller females. Males’ strength of preference for larger females was also positively correlated with the activity level of larger females but negatively with the activity level of smaller females. Males spent more time associating with active females regardless of their body lengths, indicating males’ selection was more influenced by female activity level than body size. Males’ preference for inactive females was enhanced when females became active. There was no convincing evidence for the effect of males’ personality traits or body length on their preferences for females’ activity level.

Conclusions

Our study supports the importance of body size in male mate choice but highlights that personality traits may outweigh body size preferences when males choose mating partners.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12983-022-00450-3.

Cognitive Phenotypic Plasticity: Environmental Enrichment Affects Learning but Not Executive Functions in a Teleost Fish, Poecilia reticulata

Many aspects of animal cognition are plastically adjusted in response to the environment through individual experience. A remarkable example of this cognitive phenotypic plasticity is often observed when comparing individuals raised in a barren environment to individuals raised in an enriched environment. Evidence of enrichment-driven cognitive plasticity in teleost fish continues to grow, but it remains restricted to a few cognitive traits. The purpose of this study was to investigate how environmental enrichment affects multiple cognitive traits (learning, cognitive flexibility, and inhibitory control) in the guppy, Poecilia reticulata. To reach this goal, we exposed new-born guppies to different treatments: an enrichment environment with social companions, natural substrate, vegetation, and live prey or a barren environment with none of the above. After a month of treatment, we tested the subjects in a battery of three cognitive tasks. Guppies from the enriched environment learned a color discrimination faster compared to guppies from the environment with no enrichments. We observed no difference between guppies of the two treatments in the cognitive flexibility task, requiring selection of a previously unrewarded stimulus, nor in the inhibitory control task, requiring the inhibition of the attack response toward live prey. Overall, the results indicated that environmental enrichment had an influence on guppies' learning ability, but not on the remaining cognitive functions investigated.

Innate visual discrimination abilities of zebrafish larvae

The ability to discriminate between objects visually plays a key role in animals' interactions with their environment because it enables them to recognise companions, prey, and predators. In the zebrafish, Danio rerio, hatching occurs early on during development (48-72 h post fertilisation), and the larvae must forage and evade predators despite their immature sensory and cognitive systems. Using a preference paradigm, we investigated whether larval zebrafish are nonetheless capable of discriminating between visual stimuli. We found that larvae discriminated not only between figures with different colours or different shapes, but also between two identical figures with different orientations and between sets of figures with different numerosities. By manipulating larvae's exposure to objects before the test, we demonstrated that their discrimination abilities are innate and do not depend upon experience. This study highlighted that zebrafish possess relatively sophisticated visual discrimination abilities even at the larval stage. These abilities likely improve larval survival via the recognition of biologically relevant stimuli.

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.

Heterogeneity of performances in several inhibitory control tasks: male rhesus macaques are more easily distracted than females

Inhibitory control, the ability to override a dominant response, is crucial in many aspects of everyday life. In animal studies, striking individual variations are often largely ignored and their causes rarely considered. Hence, our aims were to systematically investigate individual variability in inhibitory control, to replicate the most common causes of individual variation (age, sex and rank) and to determine if these factors had a consistent effect on three main components of inhibitory control (inhibition of a distraction, inhibition of an action, inhibition of a cognitive set). We tested 21 rhesus macaques (Macaca mulatta) in a battery of validated touchscreen tasks. We first found individual variations in all inhibitory control performances. We then demonstrated that males had poorer performances to inhibit a distraction and that middle-aged individuals exhibited poorer performance in the inhibition of a cognitive set. Hence, the factors of age and sex were not consistently associated with the main components of inhibitory control, suggesting a multi-faceted structure. The rank of the subjects did not influence any inhibitory control performances. This study adopts a novel approach for animal behaviour studies and gives new insight into the individual variability of inhibitory control which is crucial to understand its evolutionary underpinnings.

Fish Behavior for the Exotic Pet Practitioner

Interpreting fish behavior is an important component of providing veterinary care. There are over 28,000 species of fish and while only a handful are commonly encountered by exotic pet and public display veterinarians, there are still hundreds of species to consider. Three models-natural history (species typical modal action patterns), medical (disease state), and learning experience (classical and operant conditioning)-are useful for taking an actionable, holistic approach to interpreting behavior. Models help clinicians formulate appropriate differentials, ensuring they do not exclusively consider disease, particularly in unfamiliar species.

Variation in reversal learning by three generalist mesocarnivores

Urbanization imposes novel challenges for wildlife, but also provides new opportunities for exploitation. Generalist species are commonly found in urban habitats, but the cognitive mechanisms facilitating their successful behavioral adaptations and exploitations are largely under-investigated. Cognitive flexibility is thought to enable generalists to be more plastic in their behavior, thereby increasing their adaptability to a variety of environments, including urban habitats. Yet direct measures of cognitive flexibility across urban wildlife are lacking. We used a classic reversal-learning paradigm to investigate the cognitive flexibility of three generalist mesocarnivores commonly found in urban habitats: striped skunks (Mephitis mephitis), raccoons (Procyon lotor), and coyotes (Canis latrans). We developed an automated device and testing protocol that allowed us to administer tests of reversal learning in captivity without extensive training or experimenter involvement. Although most subjects were able to rapidly form and reverse learned associations, we found moderate variation in performance and behavior during trials. Most notably, we observed heightened neophobia and a lack of habituation expressed by coyotes. We discuss the implications of such differences among generalists with regard to urban adaptation and we identify goals for future research. This study is an important step in investigating the relationships between cognition, generalism, and urban adaptation.

Behavioral flexibility: A review, a model, and some exploratory tests

This paper aimed to explore and clarify the concept of behavioral flexibility. A selective literature review explored how the concept of behavioral flexibility has been used in ways that range from acknowledging the fact that animals’ behavior is not always bounded by instinctual constraints, to describing the variation between species in their capacity for innovative foraging, a capacity that has repeatedly been linked to having a brain larger than would be predicted from body size. This wide range of usages of a single term has led to some conceptual confusion. We sought to find a more precise meaning for behavioral flexibility by representing it within a simple formal model of problem solving. The key to our model is to distinguish between an animal’s state of knowledge about the world and its observable behavior, using a construct of response strength to represent that underlying knowledge. We modelled behavioral flexibility as a parameter in the function that transforms response strengths into observable response probabilities. We tested this model in simulations based on some recent experimental work on animal problem solving. Initial results showed that parametric manipulation can mimic some of the behavioral effects that have been attributed to flexibility.

Sex chromosome complement affects multiple aspects of reversal-learning task performance in mice

Determining the mechanisms by which the sex-chromosome complement (SCC) affects learning, attention, and impulsivity has implications for observed sex differences in prevalence, severity, and prognosis of psychiatric/neurodevelopmental disorders and syndromes associated with sex-chromosome aneuploidy. Here, Four Core Genotypes (FCG) mice were evaluated in order to assess the separable and/or interacting effects of gonads (testes vs. ovaries) and their secretions and/or SCC (XX vs. XY) acting via non-gonadal mechanisms on behavior. We tested FCG mice on a reversal-learning task that enables the quantification of aspects of learning, attention and impulsivity. Across testing phases (involving the initial acquisition of a spatial discrimination and subsequent reversal learning), overall error rate was larger in XY compared with XX mice. Although XX and XY groups did not differ in the total number of trials required in order to reach a preset performance criterion, analyses of reversal error types showed more perseverative errors in XY than XX mice, with no difference in regressive errors. Additionally, prepotent-response latencies during the reversal phase were shorter in XY males, as compared with both XX gonadal males and females of either SCC, and failures to sustain the observing response were more frequent in XY mice than XX mice during the acquisition phase. These results indicate that SCC affects the characteristic pattern of response selection during acquisition and reversal performance without affecting the overall learning rate. More broadly, these results show direct effects of the SCC on cognitive processes that are relevant to psychiatric/neurodevelopmental disorders and syndromes associated with sex-chromosome aneuploidies.

Sex differences in cognitive performance and style across domains in mosquitofish (Gambusia affinis)

Given that the sexes often differ in their ecological and sexual selection pressures, sex differences in cognitive properties are likely. While research on sexually dimorphic cognition often focuses on performance, it commonly overlooks how sexes diverge across cognitive domains and in behaviors exhibited during a cognitive task (cognitive style). We tested male and female western mosquitofish (Gambusia affinis) in three cognitive tasks: associative learning (numerical discrimination), cognitive flexibility (detour task), and spatio-temporal learning (shuttlebox). We characterized statistical relationships between cognitive performances and cognitive style during the associative learning task with measures of anxiety, boldness, exploration, reaction time, and activity. We found sex differences in performance, cognitive style, and the relationships between cognitive domains. Females outperformed males in the spatio-temporal learning task, while the sexes performed equally in associate learning and cognitive flexibility assays. Females (but not males) exhibited a 'fast-exploratory' cognitive style during associative learning trials. Meanwhile, only males showed a significant positive relationship between domains (associative learning and cognitive flexibility). We propose that these sexually dimorphic cognitive traits result from strong sexual conflict in this taxon; and emphasize the need to explore suites of sex-specific cognitive traits and broader comparative work examining sexual selection and cognition.

Guppies show sex and individual differences in the ability to inhibit behaviour

In humans, individual and sex differences have been long reported for several cognitive tasks and are at least in part due to variability in the function that inhibits behaviour (i.e. inhibitory control). Similar evidence of individual and sex differences in inhibitory abilities is also present in other vertebrates, but is scarce outside primates. Experiments on reversal learning, which requires inhibiting behaviours, suggest that this variability may exist in a teleost fish, the guppy, Poecilia reticulata. We tested this hypothesis by observing guppies in an inhibitory task. Guppies were exposed to unreachable prey inside a transparent tube for six trials. Guppies showed a marked reduction in the number of attempts to catch the prey within the first trial and also over repeated trials. We found a striking sex difference in the capacity to inhibit foraging behaviour. Males attempted to attack the prey twice as often as females and showed negligible improvement over trials. Irrespective of sex, individuals remarkably differed in their performance, with some guppies being systematically more skilled than others across the repeated trials. These results confirm that individual and sex differences in the ability to inhibit behaviour are not restricted to humans and other primates, suggesting that they might be widespread among vertebrates. Variability in inhibitory ability provides an explanation for emerging records of variability in other cognitive tasks in fish.

Ecological differences in the facultative Caribbean cleaning goby Elacatinus prochilos do not predict learning performance in discriminatory two-choice tasks

The ecological approach to comparative cognition emphasizes that the ecological and social environment are important predictors of cognitive performance. We used this approach to test whether differences in habitat use and social behavior in the facultative Caribbean cleaning goby Elacatinus prochilos predict differences in learning performance in two discriminatory two-choice tasks. This species has two behavioral ecotypes: one that frequently engages in cleaning interactions and inhabits corals in male-female pairs (cleaning gobies) and another that rarely engages in cleaning interactions and inhabits barrel sponges in large groups (sponge-dwellers). We predicted that cleaning gobies would outperform sponge-dwellers in a pattern-cued task, which consisted of identifying the pattern on a plate that consistently provided food, while sponge-dwellers would outperform cleaning gobies in a spatial task, which consisted of identifying the location of the plate. Contrary to our predictions, there was no difference in performance between the two ecotypes. Most of the gobies performed poorly in the pattern-cued task and well in the spatial task. A possible explanation for these results is that the association of a pattern with positive and negative reinforcement may not be a pre-requisite for engaging in cleaning interactions, while spatial skills might be equally required in both ecotypes. Alternatively, the two ecotypes can flexibly adjust to new feeding conditions, which would explain their similar performance in the spatial task. Further research should investigate which aspects of E. prochilos' social and ecological environment might impose challenges that require spatial cognition and whether individuals can flexibly adjust to new habitats and feeding conditions.

Sex differences in color discrimination and serial reversal learning in mollies and guppies

Behavioral flexibility provides an individual with the ability to adapt its behavior in response to environmental changes. Studies on mammals, birds, and teleosts indicate greater behavioral flexibility in females. Conversely, males appear to exhibit greater behavioral persistence. We, therefore, investigated sex differences in behavioral flexibility in 2 closely related molly species (Poecilia latipinna, P. mexicana) and their more distant relative, the guppy P. reticulata by comparing male and female individuals in a serial, visual reversal learning task. Fish were first trained in color discrimination, which was quickly learned by all females (guppies and mollies) and all molly males alike. Despite continued training over more than 72 sessions, male guppies did not learn the general test procedure and were, therefore, excluded from further testing. Once the reward contingency was reversed serially, molly males of both species performed considerably better by inhibiting their previous response and reached the learning criterion significantly faster than their respective conspecific females. Moreover, Atlantic molly males clearly outperformed all other individuals (males and females) and some of them even reached the level of 1-trial learning. Thus, the apparently universal pattern of higher female behavioral flexibility seems to be inverted in the 2 examined molly species, although the evolutionary account of this pattern remains highly speculative. These findings were complemented by the observed lower neophobia of female sailfin mollies compared with their male conspecifics. This sex difference was not observed in Atlantic mollies that were observed to be significantly less distressed in a novel situation than their consexuals. Hypothetically, sex differences in behavioral flexibility can possibly be explained in terms of the different roles that males and females play in mating competition, mate choice, and reproduction or, more generally, in complex social interactions. Each of these characteristics clearly differed between the closely related mollies and the more distantly related guppies.

Male and female guppies differ in problem-solving abilities

In a number of species, males and females have different ecological roles and therefore might be required to solve different problems. Studies on humans have suggested that the 2 sexes often show different efficiencies in problem-solving tasks; similarly, evidence of sex differences has been found in 2 other mammalian species. Here, we assessed whether a teleost fish species, the guppy, Poecilia reticulata, displays sex differences in the ability to solve problems. In Experiment 1, guppies had to learn to dislodge a disc that occluded a feeder from which they had been previously accustomed to feed. In Experiment 2, guppies had to solve a version of the detour task that required them to learn to enter a transparent cylinder from the open sides to reach a food reward previously freely available. We found evidence of sex differences in both problem-solving tasks. In Experiment 1, females clearly outperformed males, and in Experiment 2, guppies showed a reversed but smaller sex difference. This study indicates that sex differences may play an important role in fish’s problem-solving similar to what has previously been observed in some mammalian species.

Guppies show rapid and lasting inhibition of foraging behaviour

To cope with the variable environment, animals are continuously required to learn novel behaviours or, in certain cases, to inhibit automatic and previously learned behaviours. Traditionally, inhibition has been regarded as cognitively demanding and studied mostly in primates, other mammals and birds, using laboratory tasks, such as the cylinder task. Recent studies have also revealed that fish show high levels of inhibition in the cylinder task. However, conclusions on such results are undermined by evidence that the cylinder task may be inappropriate to compare such phylogenetically distant species. Here, we studied whether a fish, the guppy, Poecilia reticulata, could learn to inhibit behaviour using a different paradigm, which exploited spontaneous foraging behaviour and overcame some drawbacks that characterised the cylinder task. We exposed guppies to live brine shrimp nauplii, Artemia salina, enclosed within a transparent tube. Initially, the guppies attempted to attack the prey but over time showed a rapid decrease of the attacks. Control tests seemed to exclude the possibility that this behavioural trend was due to response to novelty or habituation, and suggested that the guppies were learning to inhibit the foraging behaviour. Memory tests indicated that guppies retained the inhibition of foraging behaviour for at least 24 h. Our study seems to indicate that teleost fish display rapid and durable inhibition of spontaneous foraging behaviour; this may be related to previous evidence, from the cylinder task, supporting efficient behavioural inhibition in this taxon.

Male mate choice in livebearing fishes: an overview

Although the majority of studies on mate choice focus on female mate choice, there is growing recognition of the role of male mate choice too. Male mate choice is tightly linked to 2 other phenomena: female competition for males and ornamentation in females. In the current article, I review the existing literature on this in a group of fishes, Poeciliidae. In this group, male mate choice appears to be based on differences in female quality, especially female size, which is a proxy for fecundity. Some males also have to choose between heterospecific and conspecific females in the unusual mating system of the Amazon molly. In this case, they typically show a preference for conspecific females. Whereas male mate choice is relatively well documented for this family, female ornamentation and female competition are not.

Sex differences in obesity and cognitive function in a cognitively normal aging Chinese Han population

BACKGROUND

Sex differences in Alzheimer's disease and mild cognitive impairment have been well recognized. However, sex differences in cognitive function and obesity in cognitively normal aging Chinese Han population have not attracted much attention.

OBJECTIVE

The aim of this study was to investigate the relationship between sex, obesity, and cognitive function in an elderly Chinese population with normal cognitive function.

SUBJECTS AND METHODS

A total of 228 cognitively normal aging participants (males/females =93/135) entered this study. Their general demographic information (sex, age, and education) was collected by standardized questionnaire. Apolipoprotein E (APOE) genotype and serum lipid levels were measured. The Montreal Cognitive Assessment (MoCA) was used to assess participants' cognitive function.

RESULTS

The prevalence of obesity in elderly women (18/133, 13.5%) was significantly higher than that in men (5/92, 5.4%, P=0.009). Regression analyses showed that obesity was associated with drinking alcohol (OR =13.695, P=0.045) and triglyceride (OR =1.436, P=0.048) in women and limited to low-density lipoprotein (OR =11.829, P=0.023) in men. Women performed worse on the naming score for MoCA than men (P<0.01). Stepwise linear regression analysis showed that education (t=3.689, P<0.001) and smoking (t=2.031, P=0.045) were related to the score of naming in female, while high-density lipoprotein (t=-2.077, P=0.041) was related to the score of naming in male; however, no correlation was found between body mass index and cognitive function in both male and female (P>0.05).

CONCLUSION

Our finding suggests that there are significant sex differences in obesity and specific cognitive domains in aging Chinese Han population with normal cognitive function.