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Public information is widely available at low cost to animals living in social groups. For instance, bystanders may eavesdrop on signaling interactions between conspecifics and use it to adapt their subsequent behavior towards the observed individuals. This social eavesdropping ability is expected to require specialized mechanisms such as social attention, which selects social information available for learning. To begin exploring the genetic basis of social eavesdropping, we used a previously established attention paradigm in the lab to study the brain gene expression profile of male zebrafish (Danio rerio) in relation to the attention they paid towards conspecifics involved or not involved in agonistic interactions. Microarray gene chips were used to characterize their brain transcriptomes based on differential expression of single genes and gene sets. These analyses were complemented by promoter region-based techniques. Using data from both approaches, we further drafted protein interaction networks. Our results suggest that attentiveness towards conspecifics, whether interacting or not, activates pathways linked to neuronal plasticity and memory formation. The network analyses suggested that fos and jun are key players on this response, and that npas4a, nr4a1 and egr4 may also play an important role. Furthermore, specifically observing fighting interactions further triggered pathways associated to a change in the alertness status (dnajb5) and to other genes related to memory formation (btg2, npas4b), which suggests that the acquisition of eavesdropped information about social relationships activates specific processes on top of those already activated just by observing conspecifics. [ABSTRACT FROM AUTHOR]

Animals communicate through the exchange of signals. However, third-party individuals can detect and intercept signals not directly sent to them, a phenomenon known as eavesdropping, and the presence of bystanders can influence the signalling behaviour of interacting conspecifics, a phenomenon named the audience effect. So far, research done on audience effects and eavesdropping has been mainly focused on their function, rather than on their proximate mechanisms. For this reason, we were interested in testing the occurrence of audience effects on male zebrafish, a genetically tractable model organism that is emerging as a major candidate for the study of the neural basis of social behaviour. Here, pairs of males were exposed to a mixed-sex shoal, which was used as an audience, at two different times: (1) during a contest between them, to test for an audience effect and (2) before the contest, to test whether this prior exposure influences subsequent agonistic behaviour (i.e. aggressive priming). We analysed the pairs' aggressive signalling during the contest by measuring variables that characterize both the individuals' behaviour and the interaction, and found that pre-exposure to an audience induced a shorter latency to display, an increase in the time dominants spent chasing subordinates and a shorter time to resolve the agonistic interaction. Also, exposure to the audience during the interaction led to a higher number of interactions in which displays occurred, a higher number of resolved interactions with displays and a decrease in the escalation of aggression for resolved interactions. These results add zebrafish to the literature on the audience effect and, most importantly, open the way for the study of the neural mechanisms involved in the processing of social information in a model organism. [ABSTRACT FROM AUTHOR]

In the peacock blenny (Salaria pavo) the reproductive behaviour is described to vary between two populations that differ in nest availability. At the Gulf of Trieste (GT), Italy, where nest availability is high, conventional sex roles are present and males adopting an alternative parasitic reproductive tactic are rare. Conversely, at Ria Formosa (RF), Portugal, where nest site availability is low, females are the courting sex and a high percentage of parasitic males occur. Laboratory experiments were used to study the degree of plasticity of the reproductive behaviours used by females and by the two male morphs in both populations. Nesting males were sequentially presented with a female and a female-like parasitic male and the reproductive behaviours of all fish were quantified. Under similar laboratory conditions, nesting males from both populations did not differ in sexual or agonistic displays towards females or parasitic males, showing that males from the sex-reversed population are also able to express significant levels of courtship. In contrast, females followed the typical population pattern, with females from RF courting nesting males more and more readily than females from GT. We hypothesised that apparent differences in behavioural plasticity between nesting males and females were a consequence of the perception of the presence of eggs in the nest. Nesting males from both populations received an empty nest during test trials and, thus, had to court females in order to receive a first spawn. On the other hand, females were probably unaware of the presence or absence of eggs when presented to the nesting male and assumed the population typical courtship profile. Interestingly, the parasitic males' behaviour towards the nesting male closely followed the displays of females from their own population; parasitic males from RF courted the nesting male with a high frequency of female-like displays while parasitic males from GT failed to exhibit female-like courtship behaviour. Taken together, the results suggest that S. pavo presents high levels of plasticity in reproductive behaviours and that these may underlie the interpopulation differences in behaviour reported for the species. Additionally, the results also suggest that the parasitic male reproductive tactic at GT is not based on female-mimicry. [ABSTRACT FROM AUTHOR]

There is a wealth of game theoretical approaches to the evolution and maintenance of cooperation between unrelated individuals and accumulating empirical tests of these models. This contrasts strongly with our lack of knowledge on proximate causes of cooperative behaviour. Marine cleaning mutualism has been used as a model system to address functional aspects of conflict resolution: client reef fish benefit from cleaning interactions through parasite removal, but cleaner fish Labroides dimidiatus prefer client mucus. Hence, feeding against their preference represents cooperative behaviour in cleaners. Cleaners regularly cheat non-predatory clients while they rarely cheat predatory clients. Here, we asked how precisely cleaners can adjust service quality from one interaction to the next. We found that non-predatory clients receive a better service if the previous client was a predator than if the previous client was a non-predator. In a related laboratory experiment, a hand-net used as a stressor resulted in cleaners feeding more against their preference in subsequent interactions. The combination of the cleaners' behaviour in the two studies shows that the cleaners' service quality for a given client species is not fixed, but it can be manipulated. The results suggest that short-term stress is one factor that causes cleaners to increase their levels of cooperation, a hypothesis that is amenable to further experiments manipulating the endocrine system. [ABSTRACT FROM AUTHOR]

Species with alternative reproductive tactics offer the opportunity to analyse how behavioural and morphological traits are tuned to produce successfully competing phenotypes within one sex. In the teleost fish Salaria pavo, alternative reproductive tactics are sequential. The older ornamented males compete for access to females by guarding a cavity to which they attract females to spawn. Ornamented males that are found without a nest are called ‘floaters’. Younger mature males which are too small to compete with nest-holders attempt to ‘sneak’ as female mimics into successful nests and release their sperm to fertilize freshly spawned eggs. The alternative tactics in S. pavo are associated with different levels of the androgens testosterone and 11-ketotestosterone, which have been found to suppress immune function in several teleost fish. A field study was carried out to analyse the relationship between these reproductive tactics, androgens and blood levels of lymphocytes as a monitoring method of immune function. We expected highest investment in the immune system in sneakers because these have the lowest androgen levels and functionally because investing in self-maintenance increases their future prospect to switch tactic and to reproduce as a nest-holder. Indeed, the relative count of lymphocytes correlated negatively with body size and thus was highest in sneakers and lowest in nest-holders. In concordance, 11-ketotestosterone and testosterone levels were found to be higher in floaters and nest-holders than in sneakers. However, no correlation was found between individual levels of testosterone or 11-ketotestosterone and lymphocytes. Thus, a trade-off between reproductive traits associated with high androgen levels and immunocompetence might exist at the level of alternative tactics but this might not be explained by acute immunosuppressive effects of circulating androgens. [ABSTRACT FROM AUTHOR]

Group living animals may eavesdrop on signalling interactions between conspecifics in order to collect adaptively relevant information obtained from others, without incurring in the costs of first-hand information acquisition. This ability (aka social eavesdropping) is expected to impact Darwinian fitness, and hence predicts the evolution of cognitive processes that enable social animals to use public information available in the environment. These adaptive specializations in cognition may have evolved both at the level of learning and memory mechanisms, and at the level of input mechanisms, such as attention, which select the information that is available for learning. Here we used zebrafish to test if attention in a social species is tuned to the exchange of information between conspecifics. Our results show that zebrafish are more attentive towards interacting (i.e. fighting) than towards non-interacting pairs of conspecifics, with the exposure to fighting not increasing activity or stress levels. Moreover, using video playbacks to manipulate form features of the fighting fish, we show that during the assessment phase of the fight, bystanders' attention is more driven by form features of the interacting opponents; whereas during the post-resolution phase, it is driven by biological movement features of the dominant fish chasing the subordinate fish. [ABSTRACT FROM AUTHOR]

The mechanisms regulating sexual behaviours in female vertebrates are still poorly understood, mainly because in most species sexual displays in females are more subtle and less frequent than displays in males. In a sex-role reversed population of a teleost fish, the peacock blenny Salaria pavo, an external fertilizer, females are the courting sex and their sexual displays are conspicuous and unambiguous. We took advantage of this to investigate the role of ovarian-synthesized hormones in the induction of sexual displays in females. In particular, the effects of the sex steroids oestradiol (E2) and testosterone (T) and of the prostaglandin F2α (PGF2α) were tested. Females were ovariectomized and their sexual behaviour tested 7 days (sex steroids and PGF2α) and 14 days (sex steroids) after ovariectomy by presenting females to an established nesting male. Ovariectomy reduced the expression of sexual behaviours, although a significant proportion of females still courted the male 14 days after the ovary removal. Administration of PGF2α to ovariectomized females recovered the frequency of approaches to the male's nest and of courtship displays towards the nesting male. However, E2 also had a positive effect on sexual behaviour, particularly on the frequency of approaches to the male's nest. T administration failed to recover sexual behaviours in ovariectomized females. These results suggest that the increase in E2 levels postulated to occur during the breeding season facilitates female mate-searching and assessment behaviours, whereas PGF2α acts as a short-latency endogenous signal informing the brain that oocytes are mature and ready to be spawned. In the light of these results, the classical view for female fishes, that sex steroids maintain sexual behaviour in internal fertilizers and that prostaglandins activate spawning behaviours in external fertilizers, needs to be reviewed. [ABSTRACT FROM AUTHOR]

It has been hypothesized that androgens respond to the social interactions as a way to adjust the behavior of individuals to the challenges of the social environment in an adaptive manner. Therefore, it is expected that transient changes in circulating androgen levels within physiological scope should impact the state of the brain network that regulates social behavior, which should translate into adaptive behavioral changes. Here, we examined the effect that a transient peak in androgen circulating levels, which mimics socially driven changes in androgen levels, has on the forebrain state, which harbors most nuclei of the social decision-making network. For this purpose, we successfully induced transient changes in circulating androgen levels in an African cichlid fish (Mozambique tilapia, Oreochromis mossambicus) commonly used as a model in behavioral neuroendocrinology by injecting 11-ketotestosterone or testosterone, and compared the forebrain transcriptome of these individuals to control fish injected with vehicle. Forebrain samples were collected 30 min and 60 min after injection and analyzed using RNAseq. Our results showed that a transient peak in 11-ketotestosterone drives more accentuated changes in forebrain transcriptome than testosterone, and that transcriptomic impact was greater at the 30 min than at the 60 min post-androgen administration. Several genes involved in the regulation of translation, steroid metabolism, ion channel membrane receptors, and genes involved in epigenetic mechanisms were differentially expressed after 11-ketotestosterone or testosterone injection. In summary, this study identified specific candidate genes that may regulate socially driven changes in behavioral flexibility mediated by androgens. [ABSTRACT FROM AUTHOR]

Proper response to stress and social stimuli depends on orchestrated development of hypothalamic neuronal circuits. Here we address the effects of the developmental transcription factor orthopedia (Otp) on hypothalamic development and function. We show that developmental mutations in the zebrafish paralogous gene otpa but not otpb affect both stress response and social preference. These behavioral phenotypes were associated with developmental alterations in oxytocinergic (OXT) neurons. Thus, otpa and otpb differentially regulate neuropeptide switching in a newly identified subset of OXT neurons that co-express the corticotropin-releasing hormone (CRH). Single-cell analysis revealed that these neurons project mostly to the hindbrain and spinal cord. Ablation of this neuronal subset specifically reduced adult social preference without affecting stress behavior, thereby uncoupling the contribution of a specific OXT cluster to social behavior from the general otpa-/- deficits. Our findings reveal a new role for Otp in controlling developmental neuropeptide balance in a discrete OXT circuit whose disrupted development affects social behavior. [ABSTRACT FROM AUTHOR]

Abstract: Aromatase, the key enzyme in the conversion of androgens to estrogens, regulates the availability of these hormones in tissues and controls many physiological and behavioral processes. In fish and other vertebrates, the regulation of aromatase expression in the brain has been implicated in the modulation of male sexual and aggressive behaviors. Here, the pattern of mRNA expression of the brain aromatase isoform (encoded by the CYP19A2 gene also referred as CYP19b) was quantified at the peak of spawning season in brain macroareas from males and females of the blenny Salaria pavo originated from two populations displaying male alternative reproductive tactics but differing in their mating systems. In Trieste (Adriatic) nesting males aggressively defend nests and take the initiative in courtship and perform sexual displays more often than females while in Ria Formosa (Southern Portugal) the pattern is reversed as a result of shortage of appropriate nesting sites. Nesting males from Ria Formosa had overall higher levels of brain aromatase mRNA expression than nesting males from Trieste, suggesting a higher brain estrogen synthesis in these males. Since in some fish species exogenous estradiol administration has been shown to decrease sexual and agonistic behaviors, the higher levels of brain aromatase in Ria Formosa nesting males may explain their reduced expression of sexual and aggressive displays when compared with nesting males from Trieste. Alternatively, the higher brain aromatase levels in nesting males from Ria Formosa could be a mechanism to decrease the putative androgen-induced activation of aggressive and sexual displays by reducing the local availability of androgens through their metabolization into estrogens. Although females and parasitic female-like males also differ in their displays between populations, the interpopulational pattern of brain aromatase mRNA expression was similar, suggesting that other neuroendocrine agents mediate the expression of female and female-like behaviors. In conclusion, brain aromatase availability seems like a probable mechanism to regulate the effects of steroids on the brain circuits underlying the expression of sexual and agonistic displays in S. pavo. [Copyright &y& Elsevier]