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Aim: Several drivers explain the global distribution of all reef fish. However, whether these drivers also explain the distribution and traits of a functional subgroup involving cleaner fishes remain unclear. Here we examine the variation in traits of cleaner fishes and test whether historical, environmental, ecological and geographical drivers are correlated with cleaner species richness and abundance at global reefs. Location: Tropical and subtropical reefs. Taxon: Actinopterygii. Methods: We tested whether species traits and trait space vary between facultative (i.e. species that clean only during the juvenile stages or sporadically) and dedicated (i.e. species that clean during their whole lives) cleaner types. We compiled data from local checklists (relative richness) and belt transects (standardized richness and abundance). We built four models to test whether past and current isolation (i.e. distance from Quaternary refugia and biodiversity centres), sea temperature, primary productivity, local species pool and abundance of potential clients influenced the relative richness and abundance of cleaners. Results: Facultative cleaners had high trait variability that contributed disproportionally to the trait space, whereas dedicated cleaners exhibited low trait variability. Cleaner species richness was higher in the Indo‐Pacific and Caribbean provinces, but the relative richness and standardized abundance of cleaners were higher in the Atlantic (i.e. North Eastern and Southwestern) and Eastern Pacific. Isolation influenced the relative richness of facultative cleaners, whereas the distance to Quaternary refugia, sea temperature and isolation influenced the relative richness of dedicated cleaners. Local species richness and standardized abundance of cleaner fish exhibited a strong relationship with regional diversity. The standardized abundance of both facultative and dedicated cleaners was influenced by the abundance of potential clients and the local species pool. Main conclusions: The small trait space occupied by cleaner fishes may reflect their restricted origin among lineages of reef fishes. Differences in the relative richness and standardized abundance of cleaner fishes across marine realms suggest a strong influence on biogeographical history. Our results also indicate that cleaner fishes originated mostly in peripheral areas in high latitudes due to the absence of dedicated cleaners. Our results imply that cleaner fishes do not follow the pattern of main centres of origin described for reef fishes due to opportunistic cleaning behaviour that originated with higher frequency at locations with low species richness. [ABSTRACT FROM AUTHOR]

Social species often show intraspecific variation in the size and composition of their social units, i.e. the social organization. This variation represents a challenge for comparative studies trying to understand evolutionary transitions in social organization complexity. Most studies on intraspecific variation in social organization (IVSO) have focused on the environmental factors selecting for variation in social organization but the mechanisms underlying such variation remain relatively unexplored. Here we investigated the potential mechanisms giving rise to IVSO in the Caribbean cleaning goby Elacatinus prochilos. This small reef fish typically exhibits two types of social organization, pair living or group living, which not only differ in group size but also in feeding strategy and social behaviour. Pair-living gobies cooperatively feed on ectoparasites removed from larger visiting fish, while group-living gobies feed on microinvertebrates living inside sponges and aggressively defend the best feeding spots against each other. We tested how flexible the social organization, social structure and competition over a food source of E. prochilos are by experimentally manipulating group composition, habitat structure and feeding condition of pair-living and group-living wild adult gobies in laboratory. Despite having different original social organizations in the wild, both pair-living and group-living gobies formed dominance hierarchies and exhibited affiliative behaviours in our group manipulations. This indicates that IVSO in this species is not driven by pre-determined or early-developed mechanisms, but rather a consequence of flexibility in social organization, also known as social flexibility. • We investigated the mechanisms of social organization variation in E. prochilos. • We used a controlled group manipulation to test the behavioural flexibility of individuals. • Individuals exhibiting different social organizations in the wild converged in social behaviour. • This indicates that variable social organization is driven by social flexibility. [ABSTRACT FROM AUTHOR]

It is proposed herein that the juvenile parrotfish Scarus zelindae is a mimic of the barber goby Elacatinus figaro. Juvenile S. zelindae not only resemble E. figaro but also present changes in behaviour that helps establish the existence of a mimic–model system. When approached by divers juvenile S. zelindae remained stationary at the bottom adopting a site-attached behaviour similar to E. figaro. Because of S. zelindae's colour similarity and behaviour changes, we propose that juvenile S. zelindae may be acting as a mimic to the model E. figaro gaining advantage due to the low rate of predation upon cleaner fish. [ABSTRACT FROM AUTHOR]

Mathematical modelling regarding evolutionary theory typically assumes that optimal strategies are not constrained through mechanistic processes. In contrast, recent studies on brain anatomy and neurobiology suggest that flexibility in social behaviour is rather constrained by the physiological state of the social decision-making network. Changing its state may yield selective advantages in some social contexts but neutral or even detrimental effects in others. Here we provide field evidence for such physiological trade-offs. We subjected wild female cleaner wrasse to injections of testosterone or of saline solution (control) and then observed both intraspecific interactions and interspecific cleaning behaviour with other reef fish, referred to as clients. Testosterone-treated females intensified intraspecific social interactions, showing more aggression towards smaller females and tendencies of increased aggressive and affiliative contacts with dominant males. Such testosterone-mediated changes fit the hypothesis that an increase in testosterone mediates female's focus on status in this protogynous hermaphrodite species, where females eventually change sex to become males. Moreover, we also identified other effects on interspecific social interactions: testosterone-treated females interacted less with client reef fishes and hence obtained less food. Most importantly, they selectively reduced service quality for species that were less likely to punish after being cheated. Overall, our findings suggest that testosterone causes pleiotropic effects on intra and interspecific social behaviour by broadly influencing female cleaners' decision-making. [ABSTRACT FROM AUTHOR]