Aggression and sex differences in lateralization in the zebrafish

Sex differences in aggression and its neural substrate in a cichlid fish

Aggression is ubiquitous among social species and can function to maintain social dominance hierarchies. The African cichlid fish Astatotilapia burtoni is an ideal study species for studying aggression due to their dominance hierarchy and robust behavioral repertoire. To further understand the potential sex differences in aggression in this species, we characterized aggression in male and female A. burtoni in a mirror assay. We then quantified neural activation patterns in brain regions of the social behavior network (SBN) to investigate if differences in behavior are reflected in the brain with immunohistochemistry by detecting the phosphorylated ribosome marker phospho-S6 ribosomal protein (pS6), a marker for neural activation. We found that A. burtoni perform both identical and sex-specific aggressive behaviors in response to a mirror assay. Females had greater pS6 immunoreactivity than males in the Vv (ventral part of the ventral telencephalon), a homolog of the lateral septum in mammals. Males but not females had higher pS6 immunoreactivity in the ATn after the aggression assay. The ATn (anterior tuberal nucleus) is a homolog of the ventromedial hypothalamus in mammals, which is strongly implicated in the regulation of aggression in males. Several regions also have higher pS6 immunoreactivity in negative controls than fish exposed to a mirror, implicating a role for inhibitory neural processes in suppressing aggression until a relevant stimulus is present. Male and female A. burtoni display both similar and different behavioral patterns in aggression in response to a mirror assay. There are also sex differences in the corresponding neural activation patterns in the SBN. In mirror males but not females, the ATn clusters with the POA, revealing a functional connectivity of these regions that is triggered in an aggressive context in males. These findings suggest that distinct neural circuitry underlie aggressive behavior in male and female A. burtoni, serving as a foundation for future work investigating the molecular and neural underpinnings of sex differences in behavior in this species to reveal fundamental insights into understanding aggression.

Observation of Agonistic Behavior in Pacific White Shrimp (Litopenaeus vannamei) and Transcriptome Analysis

Agonistic behavior has been identified as a limiting factor in the development of intensive L. vannamei aquaculture. However, the characteristics and molecular mechanisms underlying agonistic behavior in L. vannamei remain unclear. In this study, we quantified agonistic behavior through a behavioral observation system and generated a comprehensive database of eyestalk and brain ganglion tissues obtained from both aggressive and nonaggressive L. vannamei employing transcriptome analysis. The results showed that there were nine behavior patterns in L. vannamei which were correlated, and the fighting followed a specific process. Transcriptome analysis revealed 5083 differentially expressed genes (DEGs) in eyestalk and 1239 DEGs in brain ganglion between aggressive and nonaggressive L. vannamei. Moreover, these DEGs were primarily enriched in the pathways related to the energy metabolism process and signal transduction. Specifically, the phototransduction (dme04745) signaling pathway emerges as a potential key pathway for the adjustment of the L. vannamei agonistic behavior. The G protein-coupled receptor kinase 1-like (LOC113809193) was screened out as a significant candidate gene within the phototransduction pathway. Therefore, these findings contribute to an enhanced comprehension of crustacean agonistic behavior and provide a theoretical basis for the selection and breeding of L. vannamei varieties suitable for high-density aquaculture environments.

Sex differences in aggression and its neural substrate in a cichlid fish

Aggression is ubiquitous among social species and functions to maintains social dominance hierarchies. The African cichlid fish Astatotilapia burtoni is an ideal study species for studying aggression due to their unique and flexible dominance hierarchy. However, female aggression in this species and the neural mechanisms of aggression in both sexes is not well understood. To further understand the potential sex differences in aggression in this species, we characterized aggression in male and female A. burtoni in a mirror assay. We then quantified neural activation patterns in brain regions of the social behavior network (SBN) to investigate if differences in behavior are reflected in the brain with immunohistochemistry by detecting the phosphorylated ribosome marker phospho-S6 ribosomal protein (pS6), a marker for neural activation. We found that A. burtoni perform both identical and sex-specific aggressive behaviors in response to a mirror assay. We observed sex differences in pS6 immunoreactivity in the Vv, a homolog of the lateral septum in mammals. Males but not females had higher ps6 immunoreactivity in the ATn after the aggression assay. The ATn is a homolog of the ventromedial hypothalamus in mammals, which is strongly implicated in the regulation of aggression in males. Several regions also have higher pS6 immunoreactivity in negative controls than fish exposed to a mirror, implicating a role for inhibitory neurons in suppressing aggression until a relevant stimulus is present. Male and female A. burtoni display both similar and sexually dimorphic behavioral patterns in aggression in response to a mirror assay. There are also sex differences in the corresponding neural activation patterns in the SBN. In mirror males but not females, the ATn clusters with the POA, revealing a functional connectivity of these regions that is triggered in an aggressive context in males. These findings suggest that distinct neural circuitry underlie aggressive behavior in male and female A. burtoni, serving as a foundation for future work investigating the molecular and neural underpinnings of sexually dimorphic behaviors in this species to reveal fundamental insights into understanding aggression.

Boldness, activity, and aggression: Insights from a large-scale study in Baltic salmon (Salmo salar L)

Atlantic salmon (Salmo salar) display high levels of agonistic behavior in aquaculture farms, resulting in fin damage and chronic stress. Aggression affects fish growth and performance negatively, and presents a serious welfare problem. Indeed, it would be beneficial to identify, separate or exclude overly aggressive individuals. Research on behavioral syndromes suggests that aggressive behavior may correlate with other behavioral traits, such as boldness and locomotory activity. We aimed to develop a high-throughput method to quantify and predict aggressive behavior of individual parr in hatchery-reared Baltic salmon (Salmo salar L.). We screened approximately 2000 parr in open field (OF) and mirror image stimulation (MIS) tests. We extracted seven variables from video tracking software for each minute of the tests; distance moved and duration moving (activity), the duration in and number of entries to the center of the arena (boldness), the distance moved in and duration spent in the area adjacent to the mirror during the MIS test (aggressiveness) and head direction (lateralization). To investigate the relationship between activity, boldness and aggression we first correlated the first six variables to one another. Second, we assigned individuals to high, medium, low or zero aggression groups based on the MIS test and quantified activity and boldness in each group. Third, we analyzed whether the fish viewed the mirror with the left or right eye. Our results show that medium and low aggressive fish were the most active, while highly aggressive fish showed average activity. Aggressive groups did not differ in boldness. Activity and boldness were positively correlated. Finally, we detected a preference for fish to view the mirror with the left eye. We conclude that aggressiveness cannot be predicted from the results of the OF test alone but that the MIS test can be used for large-scale individual aggression profiling of juvenile salmon.

Sex differences in social buffering and social contagion of alarm responses in zebrafish

The alarm substance in fish is a pheromone released by injured individuals after a predator attack. When detected by other fish, it triggers fear/defensive responses, such as freezing and erratic movement behaviours. Such responses can also help other fish in the shoal to modulate their own behaviours: decreasing a fear response if conspecifics have not detected the alarm substance (social buffering) or triggering a fear response if conspecifics detected the alarm substance (social contagion). Response variation to these social phenomena is likely to depend on sex. Because males have higher-risk life-history strategies than females, they may respond more to social buffering where they risk not responding to a real predator attack, while females should respond more to social contagion because they only risk responding to a false alarm. Using zebrafish, we explored how the response of males and females to the presence/absence of the alarm substance is modified by the alarmed/unalarmed behaviour of an adjacent shoal of conspecifics. We found that, in social buffering, males decreased freezing more than females as expected, but in social contagion males also responded more than females by freezing at a higher intensity. Males were, therefore, more sensitive to visual information, while females responded more to the alarm substance itself. Because visual information updates faster than chemical information, males took more risks but potentially more benefits as well, because a quicker adjustment of a fear response allows to save energy to other activities. These sex differences provide insight into the modifying effect of life-history strategies on the use of social information.

Laterality in the Damaraland Mole-Rat: Insights from a Eusocial Mammal

Lateralization is the functional control of certain behaviors in the brain being processed by either the left or right hemisphere. Behavioral asymmetries can occur at an individual and population level, although population-level lateralization is less common amongst solitary species, whereas social species can benefit more from aligning and coordinating their activities. We assessed laterality (individual and population) through turning biases in the eusocial Damaraland mole rat, Fukomys damarensis. We considered factors such as breeding status (queen or subordinate), environment (wild-caught or captive), sex (male or female), colony and body mass. All individuals together demonstrated significant left-turning biases, which was also significant at the population level. Wild-caught animals were more strongly lateralized, had a wider spread over a laterality index and lacked the population-level left-turning bias as compared to captive mole rats. Subordinate animals were more lateralized than queens, demonstrating social status differences in turning biases for social mole rats. This emphasizes the importance of animal handling and context when measuring and interpreting behavioral asymmetries.

Female zebrafish (Danio rerio) demonstrate stronger preference for established shoals over newly-formed shoals in the three-tank open-swim preference test

Zebrafish (Danio rerio) share a considerable amount of biological similarity with mammals, including identical or homologous gene expression pathways, neurotransmitters, hormones, and cellular receptors. Zebrafish also display complex social behaviors like shoaling and schooling, making them an attractive model for investigating normal social behavior as well as exploring impaired social function conditions such as autism spectrum disorders. Newly-formed and established shoals exhibit distinct behavior patterns and inter-member interactions that can convey the group's social stability. We used a three-chamber open-swim preference test to determine whether individual zebrafish show a preference for an established shoal over a newly-formed shoal. Results indicated that both sexes maintained greater proximity to arena zones nearest to the established shoal stimulus. In addition, we report the novel application of Shannon entropy to discover sex differences in systematicity of responses not revealed by unit-based measurements; male subjects spent more time investigating between the two shoals than female subjects. This novel technique using established versus newly-formed shoals can be used in future studies testing transgenics and pharmacological treatments that mimic autism spectrum disorder and other disorders that affect social interaction.

A meta-analysis of sex differences in animal personality: no evidence for the greater male variability hypothesis

The notion that men are more variable than women has become embedded into scientific thinking. For mental traits like personality, greater male variability has been partly attributed to biology, underpinned by claims that there is generally greater variation among males than females in non-human animals due to stronger sexual selection on males. However, evidence for greater male variability is limited to morphological traits, and there is little information regarding sex differences in personality-like behaviours for non-human animals. Here, we meta-analysed sex differences in means and variances for over 2100 effects (204 studies) from 220 species (covering five broad taxonomic groups) across five personality traits: boldness, aggression, activity, sociality and exploration. We also tested if sexual size dimorphism, a proxy for sex-specific sexual selection, explains variation in the magnitude of sex differences in personality. We found no significant differences in personality between the sexes. In addition, sexual size dimorphism did not explain variation in the magnitude of the observed sex differences in the mean or variance in personality for any taxonomic group. In sum, we find no evidence for widespread sex differences in variability in non-human animal personality.

Predation shapes behavioral lateralization: insights from an adaptive radiation of livebearing fish

Hemispheric brain lateralization can drive the expression of behavioral asymmetry, or laterality, which varies notably both within and among species. To explain these left–right behavioral asymmetries in animals, predator-mediated selection is often invoked. Recent studies have revealed that a relatively high degree of lateralization correlates positively with traits known to confer survival benefits against predators, including escape performance, multitasking abilities, and group coordination. Yet, we still know comparatively little about 1) how consistently predators shape behavioral lateralization, 2) the importance of sex-specific variation, and 3) the degree to which behavioral lateralization is heritable. Here, we take advantage of the model system of the radiation of Bahamas mosquitofish (Gambusia hubbsi) and measure behavioral lateralization in hundreds of wild fish originating from multiple blue holes that differ in natural predation pressure. Moreover, we estimated the heritability of this trait using laboratory-born fish from one focal population. We found that the degree of lateralization but not the particular direction of lateralization (left or right) differed significantly across high and low predation risk environments. Fish originating from high-predation environments were more strongly lateralized, especially females. We further confirmed a genetic basis to behavioral lateralization in this species, with significant additive genetic variation in the population examined. Our results reveal that predation risk represents one key ecological factor that has likely shaped the origin and maintenance of this widespread behavioral phenomenon, even potentially explaining some of the sex-specific patterns of laterality recently described in some animals.

Hunger Potentiates the Habenular Winner Pathway for Social Conflict by Orexin-Promoted Biased Alternative Splicing of the AMPA Receptor Gene

Many animals fight for dominance between conspecifics. Because winners could obtain more resources than losers, fighting outcomes are important for the animal's survival, especially in a situation with insufficient resources, such as hunger. However, it remains unclear whether and how hunger affects fighting outcomes. Herein, we investigate the effects of food deprivation on brain activity and fighting behaviors in zebrafish. We report that starvation induces winning in social conflicts. Before the fights, starved fish show potentiation of the lateral subregion of the dorsal habenula (dHbL)-dorsal/intermediate interpeduncular nucleus (d/iIPN) pathway, which is known to be essential for and potentiated after winning fights. Circuit potentiation is mediated by hypothalamic orexin/hypocretin neuropeptides, which prolong AMPA-type glutamate receptor (AMPAR) activity by increasing the expression of a flip type of alternative splicing variant of the AMPAR subunit. This mechanism may underlie how hungry vertebrates win fights and may be commonly shared across animal phylogeny.

Laterality in the Cape mole-rat, Georychus capensis

Behavioural lateralization, the differential use one side of the body, and/or the bilateral use of sensory organs or limbs, is common in many vertebrates. One way in which behavioural lateralization can be detected in animals is through turning biases, which is an inherent preference to either turn left or right. Mole-rats are a unique group of mammals that demonstrate a wide range of social organizations ranging from solitary to eusociality. Behavioural asymmetry has not previously been investigated in mole-rats. In this study, captive and wild solitary Cape-mole rats (Georychus capensis) were investigated for individual (relative laterality (L_R)) and population-level (absolute laterality (L_A)) laterality. Mole-rats in the captive group were in the laboratory for at least one year, whereas the wild group were captured and experimented on within 2 weeks of capture. Animals were placed in a Y-maze facing away from the centre of the maze, and the turn towards the centre of the maze was evaluated to determine individual turning biases. Lateralized individual turning biases were more apparent in wild (7/9), compared to captive (3/10) individuals. Both captive and wild populations demonstrated a left bias, which was higher in wild animals, but not significantly so. Cape mole-rats are extremely xenophobic and aggressive, and this aggressive behaviour may underlie the turning biases in these animals, as aggression is primarily a right hemisphere dominant process. The reduced lateralization observed in captive animals may be due to a reduced need for these behaviours as a result of different environments in captivity.

Zebrafish models of impulsivity and impulse control disorders

Impulse control disorders (ICDs) are characterized by generalized difficulty controlling emotions and behaviors. ICDs are a broad group of the central nervous system (CNS) disorders including conduct disorder, intermittent explosive, oppositional-defiant disorder, antisocial personality disorder, kleptomania, pyromania and other illnesses. Although they all share a common feature (aberrant impulsivity), their pathobiology is complex and poorly understood. There are also currently no ICD-specific therapies to treat these illnesses. Animal models are a valuable tool for studying ICD pathobiology and potential therapies. The zebrafish (Danio rerio) has become a useful model organism to study CNS disorders due to high genetic and physiological homology to mammals, and sensitivity to various pharmacological and genetic manipulations. Here, we summarize experimental models of impulsivity and ICD in zebrafish and highlight their growing translational significance. We also emphasize the need for further development of zebrafish ICD models to improve our understanding of their pathogenesis and to search for novel therapeutic treatments.

Ecotype differences in aggression, neural activity and behaviorally relevant gene expression in cichlid fish

In Lake Malawi, two ecologically distinct lineages of cichlid fishes (rock- vs sand-dwelling ecotypes, each comprised of over 200 species) evolved within the last million years. The rock-dwelling species (Mbuna) are aggressively territorial year-round and males court and spawn with females over rocky substrate. In contrast, males of sand-dwelling species are not territorial and instead aggregate on seasonal breeding leks in which males construct courtship "bowers" in the sand. However, little is known about how phenotypic variation in aggression is produced by the genome. In this study, we first quantify and compare behavior in seven cichlid species, demonstrating substantial ecotype and species differences in unconditioned mirror-elicited aggression. Second, we compare neural activity in mirror-elicited aggression in two representative species, Mchenga conophoros (sand-dwelling) and Petrotilapia chitimba (rock-dwelling). Finally, we compare gene expression patterns between these two species, specifically within neurons activated during mirror aggression. We identified a large number of genes showing differential expression in mirror-elicited aggression, as well as many genes that differ between ecotypes. These genes, which may underly species differences in behavior, include several neuropeptides, genes involved in the synthesis of steroid hormones and neurotransmitter activity. This work lays the foundation for future experiments using this emerging genetic model system to investigate the genomic basis of evolved species differences in both brain and behavior.

Zebrafish (Danio rerio) behavioral laterality predicts increased short-term avoidance memory but not stress-reactivity responses

Once considered a uniquely human attribute, behavioral laterality has proven to be ubiquitous among non-human animals, and is associated with several neurophenotypes in rodents and fishes. Zebrafish (Danio rerio) is a versatile vertebrate model system widely used in translational neuropsychiatric research owing to their highly conserved genetic homology, well-characterized physiological responses, and extensive behavioral repertoire. Although spontaneous left- and right-biased responses, and associated behavioral domains (e.g., stress reactivity, aggression, and learning), have previously been observed in other teleost species, no information relating to whether spontaneous motor left–right-bias responses of zebrafish predicts other behavioral domains has been described. Thus, we aimed to investigate the existence and incidence of natural left–right bias in adult zebrafish, exploiting an unconditioned continuous free movement pattern (FMP) Y-maze task, and to explore the relationship of biasedness on performance within different behavioral domains. This included learning about threat cues in a Pavlovian fear conditioning test, and locomotion and anxiety-related behavior in the novel tank diving test. Although laterality did not change locomotion or anxiety-related behaviors, we found that biased animals displayed a different search strategy in the Y-maze, making them easily discernable from their unbiased counterparts, and increased learning associated to fear cues. In conclusion, we showed, for the first time, that zebrafish exhibit a natural manifestation of motor behavioral lateralization which can influence aversive learning responses.

It's in the eye of the beholder: visual lateralisation in response to the social environment in poeciliids

The social environment offers fish complex information about the quality, performance, personality and other cues of potential mates and competitors simultaneously. It is likely, therefore, that the environmental information regarding the context of mate choice is perceived and processed differently in species and sexes in respect to lateralisation. The present study comparatively assessed visual lateralisation behaviour in response to different social or sexual stimuli in three closely related poeciliid species (P. latipinna, P. mexicana, P. formosa) in comparison to a more distantly related species (P. reticulata). Individuals were presented with four different social or sexual stimuli that were tested against a control stimulus; (a) a conspecific male, (b) a conspecific female, (c) a heterosexual conspecific pair, (d) three conspecific females (shoal). In order to approach a target stimulus, focal fish had to perform detours to the right or left of a vertically straight-shaped barrier. The three closely related poeciliid species, P. latipinna, P. mexicana, P. formosa, appeared to have a general tendency to turn right (i.e., left-eye preference), whereas the more distantly related P. reticulata males and females showed an overall bias to the left (i.e., right-eye preference) in response to various social-sexual incitements. Moreover, body size seemed to significantly influence especially the males' detour behaviour, with smaller males acting in opposition to their larger conspecifics in response to certain social stimuli. In this case, smaller and larger Poecilia spp. males responded in the same way as smaller and larger males of the other three poeciliid species. Therefore, results possibly point to differences in the degree of general social behaviour between closely and more distantly related species and mating motivation amongst larger and smaller individuals when placed in a novel social environment. Hence, present results possibly suggest a sex-specific functional lateralisation for the analysis of visual information and seem to support the closer ancestral relationships between the Poecilia spp. tested in this study and the more distantly related guppies in terms of their left-right lateralisation. Generally, present results suggest that functional asymmetries in behaviour could be widespread among vertebrates, thus supporting the hypothesis of an early evolution of lateralisation in brain and behaviour.

Real or fake? Natural and artificial social stimuli elicit divergent behavioural and neural responses in mangrove rivulus, Kryptolebias marmoratus

Understanding how the brain processes social information and generates adaptive behavioural responses is a major goal in neuroscience. We examined behaviour and neural activity patterns in socially relevant brain nuclei of hermaphroditic mangrove rivulus fish (Kryptolebias marmoratus) provided with different types of social stimuli: stationary model opponent, regular mirror, non-reversing mirror and live opponent. We found that: (i) individuals faced with a regular mirror were less willing to interact with, delivered fewer attacks towards and switched their orientation relative to the opponent more frequently than fish exposed to a non-reversing mirror image or live opponent; (ii) fighting with a regular mirror image caused higher expression of immediate-early genes (IEGs: egr-1 and c-Fos) in the teleost homologues of the basolateral amygdala and hippocampus, but lower IEG expression in the preoptic area, than fighting with a non-reversing mirror image or live opponent; (iii) stationary models elicited the least behavioural and IEG responses among the four stimuli; and (iv) the non-reversing mirror image and live opponent drove similar behavioural and neurobiological responses. These results suggest that the various stimuli provide different types of information related to conspecific recognition in the context of aggressive contests, which ultimately drive different neurobiological responses.

Behavioral and Perceptual Differences between Sexes in Dogs: An Overview

In this paper, we review the scientific reports of sex-related differences in dogs as compared to the outcomes described for wild animals. Our aim was to explore whether the differences in male and female dogs were affected by the domestication process, in which artificial selection is the main driver. For this purpose, we used information regarding personality traits, cognitive processes, and perception, for which there is a wide theoretical framework in behavioral ecology. Aggressiveness and boldness, described as a behavioral syndrome, were reported as being higher in males than females. Females also seemed more inclined to interspecific social interactions with humans in tasks that require cooperative skills, whereas males appeared more inclined to social play, thus implying different levels of social engagement between the sexes, depending on the context. Studies on cognitive processes underlined a greater flexibility in resorting to a particular navigation strategy in males. Most lateralization studies seem to support the view that males are preferentially left-handed and females are preferentially right-handed. Reports on visual focusing coherently rank females as superior in focusing on single social and physical stimuli. Only male dogs are able to discriminate kin; however, the timing of the olfactory recording in sexes is related to the stimulus relevance. Dogs are largely in line with life-history theories, which indicate that sex differences in dogs are mainly rooted in their biological and evolutionary heritage, remaining unchanged despite artificial selection. In contrast, the higher intraspecific sociability in wild male animals was not replicated in dogs.

Effects of elevated carbon dioxide on male and female behavioural lateralization in a temperate goby

Behavioural abnormality in fishes has been proposed as a significant consequence of the increasing levels of carbon dioxide occurring in the oceans. Negative effects of elevated CO₂ have been reported for behaviours such as predator-prey interactions, foraging, hearing and behavioural lateralization. Importantly, the effects vary greatly both within and between species, and some recent studies have shown minimal effects of CO₂ on behaviour. Whether the effect of CO₂ also varies between males and females is, however, virtually unexplored. According to resource allocation theory, females are expected to be more sensitive to elevated CO₂, meaning that non-sex-specific studies may overlook ecologically important differences between the sexes. In this study, we investigated the possible differences between males and females in their response to elevated CO₂ by performing behavioural lateralization tests in adult temperate two-spotted gobies, Gobiusculus flavescens. We found that the strength of the side bias (absolute lateralization) was unaffected by the CO₂ treatment, and there was no difference between males and females. The control fish were slightly right-biased in their behavioural asymmetry (mean relative lateralization of 14). Exposure to high CO₂ affected this pattern, such that treated fish were slightly left-biased (mean relative lateralization of -10), regardless of their sex. The same results were obtained yet again when the study was repeated during a second year. We discuss our results in light of the great variation in lateralization that has been reported to depend on variables such as species, ecological settings and environmental factors.

Developmental exposure to the SSRI citalopram causes long-lasting behavioural effects in the three-spined stickleback (Gasterosteus aculeatus)

Selective Serotonin re-uptake inhibitors (SSRIs) are a class of psychotropic drugs used to treat depression in both adolescents and pregnant or breast-feeding mothers as well as in the general population. Recent research on rodents points to long-lasting behavioural effects of pre- and perinatal exposure to SSRIs which last into adulthood. In fish however, studies on effects of developmental exposure to SSRIs appears to be non-existent. In order to study effects of developmental SSRI exposure in fish, three-spine sticklebacks were exposed to 1.5 µg/l of the SSRI citalopram in the ambient water for 30 days, starting two days post-fertilisation. After approximately 100 days of remediation in clean water the fish were put through an extensive battery of behavioural tests. Feeding behaviour was tested as the number of bites against a piece of food and found to be increased in the exposed fish. Aggression levels were measured as the number of bites against a mirror image during 10 min and was also found to be significantly increased in the exposed fish. Novel tank behaviour and locomotor activity was tested in an aquarium that had a horizontal line drawn half-way between the bottom and the surface. Neither the latency to the first transition to the upper half, nor the number of transitions or the total time spent in the upper half was affected by treatment. Locomotor activity was significantly reduced in the exposed fish. The light/dark preference was tested in an aquarium where the bottom and walls were black on one side and white on the other. The number of transitions to the white side was significantly reduced in the exposed fish but there was no effect on the latency to the first transition or the total time spent in the white half. The results in the current study indicate that developmental SSRI exposure causes long-lasting behavioural effects in fish and contribute to the existing knowledge about SSRIs as environmental pollutants.

Cryptic effects of biological invasions: Reduction of the aggressive behaviour of a native fish under the influence of an "invasive" biomolecule

The invasive green alga Caulerpa cylindracea has become an important component of the diet of the Mediterranean white seabream Diplodus sargus. As a consequence of this “exotic diet”, the algal bisindolic alkaloid caulerpin accumulates in the fish tissues. Although the compound shows structural similarity to endogenous indolamines that modulate animal behaviour, the potential impact of caulerpin on fish behaviour still remains unexplored. In this report, behavioural experiments both on groups and on single fish responding towards a mirror were performed under different doses of dietary caulerpin. Differences between treated and control groups for each behaviour and for the overall aggressive pattern during the different experimental phases showed that the aggressiveness of D. sargus decreased with the administration of caulerpin. These results call the attention to a still unexplored potential ability of bioactive metabolites from marine invasive species, to alter the behaviour on native species, with putative negative effects on patterns of fish growth and population dynamics.

Prozac impacts lateralization of aggression in male Siamese fighting fish

Previous studies have shown that Siamese fighting fish, Betta splendens, preferentially use right-eye during the aggressive displays. However, administration of antidepressant drugs may disrupt eye-use preference in association with a reduction in aggression; a phenomena that has not been explored in fish. The objective of the current study was to examine the effects of exposure to the antidepressant drug, fluoxetine, on lateralization in eye-use during aggressive displays in male Siamese fighting fish. Baseline aggression and lateralization in eye use of thirty fish were assessed toward live conspecifics, following which experimental subjects (n=15) were then exposed to fluoxetine (540ng/L) in a static renewal water system. Behavior was quantified again after 9 days of exposure. All of the subjects preferentially used the right-eye during aggressive responses before the exposure experiments. Fluoxetine exposed subjects showed a reduction in the time spent gill flaring as has previously been reported, indicative of a reduction in the level of aggression. Fluoxetine also had a significant effect on the lateralization in preferred eye-use while looking at their opponent. Fish exposed to fluoxetine switched from a preferential use of the right-eye during aggressive encounters prior to exposure to using their left-eye after exposure to fluoxetine. The results are discussed with regard to asymmetrical distribution of serotonin between the two brain hemispheres.

Lateralisation in agonistic encounters: do mirror tests reflect aggressive behaviour? A study on a West African cichlid

In this study, population level lateralisation and the suitability of mirror tests as a test of natural aggressive behaviour in male rainbow kribs Pelvicachromis pulcher was investigated. Aggressive behaviour in live agonistic trials correlated positively with behaviours towards a mirror image and no visual lateralisation was detected.

Waterborne citalopram has anxiolytic effects and increases locomotor activity in the three-spine stickleback (Gasterosteus aculeatus)

Citalopram is an antidepressant drug, which acts by inhibiting the re-uptake of serotonin from the synaptic cleft into the pre-synaptic nerve ending. It is one of the most common drugs used in treatment of depression, it is highly lipophilic and frequently found in sewage treatment plant effluents and surface waters around the world. Citalopram and other selective serotonin re-uptake inhibitors have, at concentrations that occur in nature, been shown to have behavioural as well as physiological effects on fish and other animals. This study is the result of several different experiments, intended to analyse different aspects of behavioural effects of chronic citalopram exposure in fish. Our model species the three-spine stickleback is common in the entire northern hemisphere and is considered to be a good environmental sentinel species. Female three-spine sticklebacks were exposed to 0, 1.5 and 15μg/l nominal concentrations of citalopram for 21 days and subjected to the novel tank (NT) diving test. In the NT test, the fish exposed to 1.5μg/l, but not the 15μg/l fish made a significantly higher number of transitions to the upper half and stayed there for significantly longer time than the fish exposed to 0μg/l. The 15μg/l group, however, displayed a significantly lower number of freeze bouts and a shorter total freezing time. The test for locomotor activity included in the NT test showed that fish treated with 1.5 and 15μg/l displayed a significantly higher swimming activity than control fish both 5-7 and 15-17min after the start of the experiment. In the next experiment we compared fish exposed to 1.5μg/l and 0.15μg/l to pure water controls with regard to shoaling intensity and found no effect of treatment. In the final experiment the propensity of fish treated with 1.5μg/l to approach an unknown object and aggressive behaviour was investigated using the Novel Object test and a mirror test, respectively. The exposed fish ventured close to the unknown object significantly more often and stayed there for significantly longer time than unexposed fish. The aggression test yielded no statistically significant effects. It is concluded that citalopram changes the behaviour of the three-spine stickleback in a way that is likely to have ecological consequences and that it must not be considered an environmentally safe pharmaceutical.

Quantifying Aggressive Behavior in Zebrafish

Aggression is a complex behavior that influences social relationships and can be seen as adaptive or maladaptive depending on the context and intensity of expression. A model organism suitable for genetic dissection of the underlying neural mechanisms of aggressive behavior is still needed. Zebrafish has already proven to be a powerful vertebrate model organism for the study of normal and pathological brain function. Despite the fact that zebrafish is a gregarious species that forms shoals, when allowed to interact in pairs, both males and females express aggressive behavior and establish dominance hierarchies. Here, we describe two protocols that can be used to quantify aggressive behavior in zebrafish, using two different paradigms: (1) staged fights between real opponents and (2) mirror-elicited fights. We also discuss the methodology for the behavior analysis, the expected results for both paradigms, and the advantages and disadvantages of each paradigm in face of the specific goals of the study.

Population-level lateralized aggressive and courtship displays make better fighters not lovers: evidence from a fly

Lateralization (i.e., left-right asymmetries in the brain and behavior) of aggressive and courtship displays has been examined in many vertebrate species, while evidence for invertebrates is limited. We investigated lateralization of aggressive and courtship displays in a lekking tephritid species, the olive fruit fly, Bactrocera oleae. Results showed a left-biased population-level lateralization of aggressive displays, with no differences between the sexes. In both male-male and female-female contests, aggressive behaviors performed with left body parts led to greater fighting success than those performed with right body parts, while no differences in fighting duration were found. Olive fruit fly males also showed a side bias during courtship and mating behavior, courting females more frequently from the left than the right, front, or back sides. No differences were detected between courtship duration and copulation duration following the different male directional approaches. Male mating success was comparable whether females were approached from the left, right, front, or back side. Lateralized aggressive and courtship displays at the population-level may be connected to the prolonged social interactions occurring among lekking flies. Further research is needed on possible benefits arising from lateralization of courtship traits in insects.

Do right-biased boxers do it better? Population-level asymmetry of aggressive displays enhances fighting success in blowflies

Lateralisation (i.e. left-right asymmetries in brain and behaviour) of aggressive traits has been deeply studied in a number of vertebrates, while evidence for invertebrates is scarce. We investigated lateralisation of boxing behaviour in the blowfly Calliphora vomitoria (Diptera: Calliphoridae), where males fight for non-resource based spaces. We found a population-level lateralisation of aggressive displays: three repeated testing phases confirmed the preferential use of right legs over left ones. Duration of contests and number of boxing acts per fighting event were not different between males using left and right legs. The use of right legs for boxing acts lead to higher fighting success over males using left legs. Lateralised aggressive displays at population-level may be connected to the prolonged social interactions occurring among males searching for food and mates.

First report of behavioural lateralisation in mosquitoes: right-biased kicking behaviour against males in females of the Asian tiger mosquito, Aedes albopictus

Lateralisation (i.e. functional and/or structural specialisations of left and right sides of the brain) of aggressive traits has been studied in a number of vertebrates, while evidence for invertebrates is scarce. Mosquito females display aggressive responses against undesired males, performing rejection kicks with the hind legs. In this research, we examined lateralisation of kicking behaviour in females of the Asian tiger mosquito, Aedes albopictus. We found a right-biased population-level lateralisation of kicking behaviour. Four repeated testing phases on mosquito females confirmed the preferential use of right legs. However, when left legs were used, the mean number of kicks per rejection event was not different to that performed with right legs. Both left and right kicking behaviour lead to successful displacement of undesired partners. This is the first report about behavioural lateralisation in mosquitoes.

Dominance and stress signalling of carotenoid pigmentation in Arctic charr (Salvelinus alpinus): lateralization effects?

Social conflicts are usually solved by agonistic interactions where animals use cues to signal dominance or subordinance. Pigmentation change is a common cue used for signalling. In our study, the involvement of carotenoid-based pigmentation in signalling was investigated in juvenile Arctic charr (Salvelinus alpinus). Size-matched pairs were analysed for pigmentation both before and after being tested for competitive ability. We found that dominant individuals had fewer carotenoid-based spots on the right and left sides as well as lower plasma cortisol levels compared to subordinate individuals. Further, the number of spots on both sides was positively associated with plasma cortisol levels. These results indicate that carotenoid-based pigmentation in Arctic charr signals dominance and stress coping style. Further, it also appears as if carotenoid-based pigmentation is lateralized in Arctic charr, and that the right side signals aggression and dominance whereas the left side signals stress responsiveness.