Mutualistic cleaning behavior between two coral reef fish species: a molecular approach

Abstract

Aim: Social interactions are fundamental in nature, but little is known about the neural mechanisms establishing the social relationships between two species of reef fish. Marine fishes offer a great opportunity to understand these interactions as some species depend on others through symbiotic relationships. In particular, the cleaner fish Labroides dimidiatus allows us to study mutualistic cleaning interactions displaying sophisticated social behavior while interacting with other species known as ‘clients’, that can benefit from ectoparasite reduction and stress relief. Methods: To understand this essential inter-specific behavior, this study identified using transcriptomics, relevant molecular pathways related to social behavior in the fore-, mid- and hindbrain regions of the cleaner fish and one of its potential clients (Acanthurus leucosternon). Results: Comparing the brains of interacting fish vs fish alone in aquariums, we found that the social interaction of L. dimidiatus with its client fish involved several social neural systems such as the dopaminergic, glutamatergic and GABAergic pathways as well as social decision-making genes. In addition, we found immediate early gene responses related to social plasticity and transcription factor activity such as c-jun, c-fos and CREB indicating neural activation during interaction. The client fish on the other hand had less differential gene expression across the brain and genes were functionally involved in hormonal activity. For both species most of the neural activation during interaction was produced and regulated in the hindbrain and forebrain region. Main conclusions: These results suggest an important implication of hormone systems and the activation of immediate early genes during the social interaction of L. dimidiatus and A. leucosternon. Analysing the role of these molecular mechanisms in the brain provides key information on crucial inter-specific behaviours and can shed light on the key mechanisms of vertebrate mutualism among marine species.