Neuro-molecular characterization of fish cleaning interactions

Abstract

Coral reef fish exhibit a large variety of behaviours crucial for fitness and survival. The cleaner wrasse Labroides dimidiatus displays cognitive abilities during interspecific interactions by providing services of ectoparasite cleaning, thus serving as a good example to understand the processes of complex social behaviour. However, little is known about the molecular underpinnings of cooperative behaviour between L. dimidiatus and a potential client fish (Acanthurus leucosternon). Therefore, we investigated the molecular mechanisms in three regions of the brain (Fore-, Mid-, and Hindbrain) during the interaction of these fishes. Here we show, using transcriptomics, that most of the transcriptional response in both species was regulated in the Hindbrain and Forebrain regions and that the interacting behaviour responses of L. dimidiatus involved immediate early gene alteration, dopaminergic and glutamatergic pathways, the expression of neurohormones (such as isotocin) and steroids (e.g. progesterone and estrogen). In contrast, in the client, fewer molecular alterations were found, mostly involving pituitary hormone responses. The particular pathways found suggested synaptic plasticity, learning and memory processes in the cleaner wrasse, while the client indicated stress relief.

Neuromolecular responses in disrupted mutualistic cleaning interactions under future environmental conditions

“…The upregulation of GABT facilitates the degradation of GABA into succinic semialdehyde, which is in charge of regulating the supply of GABA in the brain ("GABA shunt"; Deutch & Roth, 2004). As a result, succinic semialdehyde is incorporated into the Krebs cycle from which glutamine is formed and subsequently converted into glutamate (Olsen & Li, 2012), a major excitatory neurotransmitter already known to be regulating the interaction behaviour in the cleaner wrasse (Ramírez-Calero et al, 2021). Our results thus suggest an interplay between the expression of GABAergic and glutamatergic pathways in the cleaner wrasse when faced with ocean acidification.…”

“…We evaluated the fine-scale transcriptional responses across the three main regions of the brain (fore-, mid-and hindbrain) known to harbour the expression of significant neurotransmission, neurohormones and neuropeptides during cleaning interactions (Paula et al, 2019b;Soares et al, 2010). Since cleaning interactions involve the expression of the dopaminergic and glutamatergic pathways (Ramírez-Calero et al, 2021), we may expect brain molecular drivers in the response to environmental change in the cleaner wrasse and its client to include cellular stress response, changes to GABAergic neurotransmission and in gene expression levels of neuroamines. Due to the importance of this interspecific and mutualistic interaction, it is necessary to unravel the underlying mechanisms that drive such interactions.…”

Gene losses, parallel evolution and heightened expression confer adaptations to dedicated cleaning behaviour

“…For genome annotation and expression analyses, fore-, mid- and hindbrain tissue were obtained from 30 adult individuals of L. dimidiatus for RNA sequencing. The specimens were collected in the Maldives Islands and transported to the aquatic facilities of Laboratorio Maritimo da Guia in Cascais, Portugal by TMC-Iberia, further details can be found in [ 15 ] and Ramirez-Calero et al . (2023, unpublished).…”

“…At the end of the observation period, three separated regions (forebrain, midbrain, hindbrain) of the brain were immediately dissected out for each L. dimidiatus individuals for RNA sequencing. The details of sequencing and reads quality control can be found in [ 15 ].…”

“…In addition, a subterminal mouth and small body size of cleaners may enable them to effectively remove ectoparasites from larger clients [ 13 , 14 ]. Limited molecular studies on cleaner fish indicate that immediate early genes, glutamate receptors and neurohormones exhibit significant expression changes in brain regions of L. dimidiatus during cleaning interactions, and hence play critical roles in cleaning behaviours [ 15 ]. Despite parasites appearing as tiny dark dot on clients’ surface and potentially transfer to cleaners causing infections during close-contact cleaning [ 16 , 17 ], it remains unknow how cleaners can detect parasites efficiently and minimize the infection risk.…”