The marine cleaning mutualism between the Indo-Pacific cleaner wrasse Labroides dimidiatus (Valenciennes, 1839) and its client reef fish: the physiological bases of cooperative and deceptive behaviour

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Neuroendocrinology of cooperation: the role of neuropeptides on the modulation of mutualistic behaviour of the Indo-Pacific Cleaner Wrasse (Labroides dimidiatus)

Publication . Cardoso, Sónia Cristina Cobra; Soares, Marta; Oliveira, Rui; Canario, Adelino V. M.

Interspecific cleaning interactions are a classical textbook example of mutualistic cooperation. One of the most notorious cleaning mutualisms involve the Indo-Pacific Bluestreak cleaner wrasse Labroides dimidiatus, which are known to interact with an average of 2300 visitor reef fish per day. In contrast to the increasing knowledge on the functional aspects of cleaning mutualisms in the last decades, their underlying physiological mechanisms are still relatively rare. One major class of neuromodulators that is involved in the control of social behaviour and that seems to be co-opted for the regulation of cleaning behaviour is a group of nonapeptides of the arginine vasopressin /oxytocin family (AVP/OT). The general aim of this study is to attempt to link functional aspects of decision-making underlying the cleaning behaviour with their proximate mechanisms, namely to determine the contribution of the neuropeptides arginine vasotocin (AVT) and isotocin (IT) for the regulation of adjustments of individual cleaner wrasses’ behavioural output. This study yielded several findings. First, I tested the influence of AVT upon the cleaners’ ability to solve two different problems that in principle differ in ecological relevance and are associated with two different memory circuits and found that AVT affected the learning competence of cleaners 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. Next I examined if neuropeptides may be implicated in the mechanisms underlying the adjustment of individuals to the existence of partner control mechanisms in cooperative interactions between unrelated individuals and discovered that solely the experimental transient higher dosage of AVT led to a decrease of cleaners’ willingness to feed against their preference, while IT and AVT antagonists had no significant effects. Then I asked if the establishment of privileged ties and the quality of association between cleaner wrasse pairs is correlated with neuroendocrine mechanisms involving forebrain neuropeptides and whether these neuropeptides level shifts relate to individual’s interspecific service quality. Here I found .that variation in pairs’ relationship influence male and female cleaner fish differently and contribute to the variation of brain neuropeptide levels, which is linked to distinct cooperative outcomes. Finally, I explore the link between these neuroendocrine pathways and the expression of mutualistic behaviour in fishes by comparing the brain quantitative distribution of AVT and IT across the overall and in selected areas of the brain; aiming at four closely related species of labrids that differ in the degree to which they depend on cleaning. The levels of both AVT and IT varied significantly across species, as measured in the whole brain or in specific macro-areas. More importantly, significantly higher AVT levels in cerebellum and in the whole brain were found in the obligate cleaner species, which seems to be related to expression of mutualistic behaviour. Overall, my study suggests that the neuropeptidergic system but mostly AVT pathways play a pivotal role in the regulation of interspecific cooperative behaviour and conspecific social behaviour among stabilized pairs of cleaner wrasses.

2015-10-05Doctoral thesis

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