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Cleaning behavior is a well-known example of trophic specialization that is widespread in marine organisms from both tropical and temperate ecosystems. Cleaner species can be more or less specialized in different aspects of cleaning interactions, and it is often assumed that the more specialized cleaners are, the more they rely on clients for food. However, cleaners can consume different items in different sites, and the factors influencing such variation are still poorly understood. Here, we investigated the diet and distribution of the barber goby Elacatinus figaro across marginal reefs of the Brazilian coast. We evaluated E. figaro's reliance on cleaning interactions for food and asked whether its diet and abundance corresponded to the availability of ectoparasites and/or clients. The diet of E. figaro varied across sites, but ectoparasite reliance was similar and did not correspond to client's infestation loads. Moreover, the density of E. figaro did not correlate with the density or richness of potential clients. These support the hypothesis that E. figaro is less reliant on cleaning interactions for food than other cleaning goby species and suggest a high feeding and behavioral plasticity in marginal reefs. This study also highlights that the current dichotomous classification scheme of dedicated versus facultative cleaners fails to capture the subtle nuances of cleaning behavior and should therefore be used with caution in future comparative studies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Social environmental complexity induces structural and biochemical changes in animals' brains, which are linked to the improvement of animals' learning abilities. The nonapeptides from the arginine vasopressin (AVP) family (arginine vasotocin, AVT, in non-mammals) play a significant role in the regulation of social behavior, particularly in the formation of social memories and individual recognition. Moreover, the role of AVT in the regulation of interspecific interactions has only recently started to be addressed in the context of cleaner fish mutualisms and learning. Variance in the distribution of AVP receptor expression, which is linked to distinct neural systems (related to the dorsolateral and the dorsomedial telencephalon), is known to be implicated in differences in individual learning processes. Here we asked if the associative learning performance of the Indo-Pacific bluestreak cleaner wrasse ( Labroides dimidiatus) is regulated by AVT. We tested the influence of AVT upon the cleaners' ability to solve two different problems (cue and place discrimination tasks) that in principle differ in ecological relevance and are associated with two different memory systems. We found that AVT affected the learning competence of cleaners differently between tasks, as individual performance showed distinct response selectivity to AVT dosage levels. However, only in the ecologically relevant task was their learning response improved by blocking AVT via treatment with the antagonist Manning compound. Our findings demonstrate that AVT pathways, which are implicated in the regulation of interspecific behavior (i.e., a cleaner's willingness to seek interactions with clients), are also linked to individual learning ability in the context of mutualistic behavior, and in tune with socio-ecological demands. [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]