Submissive behaviour is mediated by sex, social status, relative body size and shelter availability in a social fish

Early social complexity influences social behaviour but not social trajectories in a cooperatively breeding cichlid fish

Social competence-defined as the ability to optimize social behaviour according to available social information-can be influenced by the social environment experienced in early life. In cooperatively breeding vertebrates, the current group size influences behavioural phenotypes, but it is not known whether the group size experienced in early life influences behavioural phenotypes generally or social competence specifically. We tested whether being reared in large versus small groups for the first two months of life affects social behaviours, and associated life-history traits, in the cooperatively breeding cichlid Neolamprologus pulcher between the ages of four and twelve months. As we predicted, fish raised in larger and more complex groups showed higher social competence later in life. This was shown in several ways: they exhibited more, and earlier, submissive behaviour in response to aggression from a dominant conspecific, and-in comparison to fish raised in small groups-they exhibited more flexibility in the expression of submissive behaviour. By contrast, there was no evidence that early social complexity, as captured by the group size, affects aggression or exploration behaviour nor did it influence the propensity to disperse or show helping behaviour. Our results emphasize the importance of early-life social complexity for the development of social competence.

Colorful facial markings are associated with foraging rates and affiliative relationships in a wild group-living cichlid fish

Many animals use color to signal their quality and/or behavioral motivations. Colorful signals have been well studied in the contexts of competition and mate choice; however, the role of these signals in nonsexual, affiliative relationships is not as well understood. Here, we used wild social groups of the cichlid fish Neolamprologus pulcher to investigate whether the size of a brightly colored facial patch was related to 1) individual quality, 2) social dominance, and/or 3) affiliative relationships. Individuals with larger patches spent more time foraging and tended to perform more aggressive acts against conspecific territory intruders. We did not find any evidence that the size of these yellow patches was related to social rank or body size, but dominant males tended to have larger patches than dominant females. Additionally, patch size had a rank-specific relationship with the number of affiliative interactions that individuals engaged in. Dominant males with large patches received fewer affiliative acts from their groupmates compared to dominant males with small patches. However, subordinates with large patches tended to receive more affiliative acts from their groupmates while performing fewer affiliative acts themselves. Taken together, our results suggest that patch size reflects interindividual variation in foraging effort in this cichlid fish and offer some of the first evidence that colorful signals may shape affiliative relationships within wild social groups.

Comparing dominance relationships and movement of native marble trout (Salmo marmoratus) and introduced rainbow trout (Oncorhynchus mykiss)

Behaviour observations of the endangered native marble trout (Salmo marmoratus, Cuvier, 1829) and introduced rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) in the laboratory and in a tributary to the Idrijca River in Slovenia were combined to study the movements and dominance relationships between individuals of the two species in an open field test. Under laboratory conditions, no difference between the species was detected for neither time spent actively or distance moved. In species paired tests, rainbow trout initiated more aggressive behaviours towards marble trout than vice versa, and rainbow trout were clearly the dominant individuals. After simultaneous release in the river, marble trout immediately left the release area and spent twice as long time as rainbow trout until they settled in an area of the river; therefore, the release site was immediately occupied exclusively by rainbow trout. Thus, the dominant and aggressive behaviour of rainbow trout seen in the laboratory before release might have influenced marble trout's subsequent behaviour in the river, by marble trout leaving the areas occupied by rainbow trout and moving to locations further away from the release site. In the field, the marble trout occupied sites individually, whereas rainbow aggregated at a few locations. Rainbow trout showed higher movement activity in the morning compared to marble trout. There was a positive correlation between swimming speed in the laboratory and movement in the field for marble trout but not for rainbow trout. In conclusion, the results in this study support the need to end stocking of rainbow trout in rivers with native marble trout. To better understand the interaction between the species, and to develop efficient management plans to protect the native marble trout, reference behaviours should first be understood, and future research in sites where the two species do not co-exist is needed. This is especially important for marble trout for which behavioural research and data are lacking.

Higher ultraviolet skin reflectance signals submissiveness in the anemonefish, Amphiprion akindynos

Ultraviolet (UV) vision is widespread among teleost fishes, of which many exhibit UV skin colors for communication. However, aside from its role in mate selection, few studies have examined the information UV signaling conveys in other socio-behavioral contexts. Anemonefishes (subfamily, Amphiprioninae) live in a fascinating dominance hierarchy, in which a large female and male dominate over non-breeding subordinates, and body size is the primary cue for dominance. The iconic orange and white bars of anemonefishes are highly UV-reflective, and their color vision is well tuned to perceive the chromatic contrast of skin, which we show here decreases in the amount of UV reflectance with increasing social rank. To test the function of their UV-skin signals, we compared the outcomes of staged contests over dominance between size-matched Barrier Reef anemonefish (Amphiprion akindynos) in aquarium chambers viewed under different UV-absorbing filters. Fish under UV-blocking filters were more likely to win contests, where fish under no-filter or neutral-density filter were more likely to submit. For contests between fish in no-filter and neutral density filter treatments, light treatment had no effect on contest outcome (win/lose). We also show that sub-adults were more aggressive toward smaller juveniles placed under a UV filter than a neutral density filter. Taken together, our results show that UV reflectance or UV contrast in anemonefish can modulate aggression and encode dominant and submissive cues, when changes in overall intensity are controlled for.

Subordinate submissive responses are predicted by dominant behaviour in a cooperatively breeding fish

In complex social groups, animals rely on communication to facilitate priority access to resources and minimise the costs of conflict. Animals typically have more aggression signals than submission signals. However, some social species do show multiple submission signals, and the context in which these different signals are used is often not well understood. In the current study, we assessed agonistic interactions within groups of the cooperatively breeding daffodil cichlid fish (Neolamprologus pulcher) to investigate the relationship between the aggressive behaviours of the dominant breeding pair, and the submissive responses of the highest ranked subordinate within the group. Daffodil cichlids may respond to aggression by fleeing or by the production of either a tail quiver display or a head up display. Among the two submission signals, the tail quiver display was used more frequently in response to a threat display, while head up displays were produced approximately equally in response to both threat displays and overt aggression. An exaggerated version of the head up display was given more often in response to overt aggression, suggesting a graded submissive response both within and between the two submission signals. Within fish, the frequency of head up displays, but not tail quiver displays, correlated positively with the frequency of threat displays received. The current study helps us to better understand the use of submission signals in a highly social vertebrate and sheds light on submission as an understudied aspect of communication.

Territorial behaviour and conflict management in a semi-social cichlid fish, Neolamprologus caudopunctatus

Conflict solving strategies can prevent fights from escalating and reduce the costs of aggressive encounters. Having the capacity to efficiently assess an opponent’s fighting abilities before fully committing to a fight is a useful social skill. Here, we conducted two experiments to investigate how a colony living, cichlid species, Neolamprologus caudopunctatus, changes its aggressive behaviour when faced with familiar vs unfamiliar opponents. First, we staged size matched, same-sex, dyadic resource contests and found that fights were always of low-intensity with neither familiarity nor sex influencing how quickly the conflict ended. Second, we explored the dual defence of mated territorial pairs together defending their territory boundaries against other pairs, either familiar or unfamiliar ones, and discovered that fights between two pairs were more vigorous, and that unfamiliar neighbouring pairs were attacked significantly more often than familiar pairs. We also observed that dark bars sometimes appeared on the sides of contestant’s bodies, and that these bars were far more common in winners than in losers, suggesting that these might be visual signals of dominance. However, conflicts where contestants displayed bars were of longer duration than those without. Taken together, our results further advance our understanding of territoriality and conflict resolution strategies and set the stage for future studies focusing on how animals manage to co-exist in closely aggregated breeding territories and to form colonies.

Rapid spatial learning in cooperative and non-cooperative cichlids

The number, duration and depth of social relationships that an individual maintains can impact social cognition, but the connection between sociality and other aspects of cognition has hardly been explored. To date, the link between social living and intelligence has been mainly supported by studies on primates, and far fewer tests connecting sociality to cognitive abilities have used other taxa. Here, we present the first comparative study in fishes that examines whether complex social living is associated with better performance on a cognitively demanding spatial task. Using three cooperative, group-living cichlid fish species and three of their non-cooperative, more solitary close relatives, we studied maze learning and employed a new statistical extension for the 'lme4' and 'glmmTMB' packages in R that allows phylogeny to be included as a random effect term. Across trials, the three cooperative and the three non-cooperative species completed the maze faster, made fewer mistakes, and improved their inhibitory control. Although fish improved their performance, we did not detect any differences in the extent of improvement between cooperative and non-cooperative species. Both the cooperative species and the non-cooperative species took similar amounts of time to complete the maze, had comparable numbers of mistakes, and exhibited similar inhibitory control while in the maze. Our results suggest that living and breeding in complex social groups does not necessarily imply enhancement of other forms of cognition nor, more specifically, an enhanced spatial learning capacity.

Submission signals in animal groups

Aggression is costly, and animals have evolved tactics to mitigate these costs. Submission signals are an underappreciated example of such adaptations. Here we review submissive behaviour, with an emphasis on non-primates. We highlight the design of submission signals and how such signals can reduce costs. Animal societies necessitate frequent social interactions, which can increase the probability of conflict. Where maintaining group proximity is essential, animals cannot avoid aggression by fleeing. Mutual interest between group members may also select for efficient conflict avoidance and resolution mechanisms. As a result, submission signals may be especially well developed among group living species, helping social animals to overcome potential costs of recurring conflict that could otherwise counter the benefits of group living. Therefore, submission signalling can be a crucial aspect of social living and is deserving of specific attention within the broader context of social evolution and communication.

Glucocorticoids do not promote prosociality in a wild group-living fish

Individuals often respond to social disturbances by increasing prosociality, which can strengthen social bonds, buffer against stress, and promote overall group cohesion. Given their importance in mediating stress responses, glucocorticoids have received considerable attention as potential proximate regulators of prosocial behaviour during disturbances. However, previous investigations have largely focused on mammals and our understanding of the potential prosocial effects of glucocorticoids across vertebrates more broadly is still lacking. Here, we assessed whether experimentally elevated glucocorticoid levels (simulating endogenous cortisol responses mounted following disturbances) promote prosocial behaviours in wild groups of the cichlid fish, Neolamprologus pulcher. Using SCUBA in Lake Tanganyika, we observed how subordinate group members adjusted affiliation, helping, and submission (all forms of prosocial behaviour) following underwater injections of either cortisol or saline. Cortisol treatment reduced affiliative behaviours-but only in females-suggesting that glucocorticoids may reduce overall prosociality. Fish with elevated glucocorticoid levels did not increase performance of submission or helping behaviours. Taken together, our results do not support a role for glucocorticoids in promoting prosocial behaviour in this species and emphasize the complexity of the proximate mechanisms that underlie prosociality.

Emotion in animal contests

Emotions encompass cognitive and behavioural responses to reward and punishment. Using contests as a case-study, we propose that short-term emotions underpin animals' assessments, decision-making and behaviour. Equating contest assessments to emotional 'appraisals', we describe how contestants appraise more than resource value and outcome probability. These appraisals elicit the cognition, drive and neurophysiology that governs aggressive behaviour. We discuss how recent contest outcomes induce long-term moods, which impact subsequent contest behaviour. Finally, we distinguish between integral (objectively relevant) and incidental (objectively irrelevant) emotions and moods (affective states). Unlike existing ecological models, our approach predicts that incidental events influence contest dynamics, and that contests become incidental influences themselves, potentially causing maladaptive decision-making. As affective states cross contexts, a more holistic ethology (incorporating emotions and moods) would illuminate animal cognition and behaviour.

Sensory cues underlying competitive growth in the clown anemonefish (Amphiprion percula)

In some animal societies, access to breeding depends on the individual's position in a hierarchy, which often depends on an individual's size. In such societies, individuals may try to outgrow one another to attain a higher rank by engaging in a form of strategic growth (competitive growth). This suggests that members of the hierarchy can track changes in the growth and size of potential competitors and respond accordingly. The clown anemonefish, Amphiprion percula, is one species known to exhibit competitive growth at the initiation of size hierarchies. Here, we use 5 combinations of sensory cues to determine which cues must be available for individuals to engage in competitive growth. Our results show that mechanosensory (pressure and/or touch) cues or unobstructed interactions are necessary for competitive growth to occur. This study provides an understanding of the relationship between sensory cues and phenotypic responses to different social contexts.

Head up displays are a submission signal in the group-living daffodil cichlid

Dominance hierarchies can reduce conflict within social groups and agonistic signals can help to establish and maintain these hierarchies. Behaviours produced by subordinates in response to aggression are often assumed to function as signals of submission, however, these behaviours may serve other purposes, for example, defence or escape. For a behaviour to act as a submission signal, the receiver must respond by reducing their likelihood of further aggression towards the signaller. In the current study, we examine the receiver response to a putative signal of submission, the head up display, within established social groups of the cooperatively breeding fish, the daffodil cichlid (Neolamprologus pulcher). We found that when subordinate signallers produce the head up display in response to aggression from the breeder male, he exhibited a longer latency to behave aggressively towards that individual again. We also report that head up displays are rarely produced without being elicited by aggression, and the number of head up displays correlates with the amount of aggression received. Our results demonstrate that the head up display is used as a signal of submission in the daffodil cichlid and provide insight into intragroup communication in an emerging model system for the study of social behaviour.