Arginine Vasotocin Neuronal Phenotype and Interspecific Cooperative Behaviour

Abstract

The nonapeptide arginine vasotocin (AVT) and its mammalian homologue arginine vasopressin are well known for their role in the modulation of several intraspecific social behaviours, such as social approach/withdrawal and aggression. Recently, we suggested that AVT might also be important in the regulation of interspecific social behaviours as it modulates interspecific cooperative behaviours in the Indo-Pacific bluestreak cleaner wrasse Labroides dimidiatus. AVT injections decreased cleaners' propensity to engage in cleaning interactions with their clients, suggesting that high levels of this peptide compromise the cleaners' cooperative motivation. Therefore, we hypothesise that low endogenous levels of AVT are a prerequisite for the expression of interspecific cleaning behaviour in cleaner wrasses, since it allows them to approach and interact with interspecific individuals, and that this should be reflected in their AVT neuronal phenotype. Here we test this hypothesis by comparing the AVT neuronal phenotypes of two phylogenetically closely related species that live in similar environments but diverge in the expression of interspecific cooperative behaviour: an obligate cleaner wrasse (L. dimidiatus) and a non-cleaner corallivore wrasse (Labrichthys unilineatus). The two species are predicted to differ in their AVT neuronal phenotypes as a reflection of their ability/inability to approach and interact with interspecific individuals, with cleaners presenting smaller and/or less numerous AVT-immunoreactive (ir) neurons. A sex difference in AVT neuronal phenotypes was also predicted because males of both species appear to be more aggressive than females. As described for most of the other teleost species, AVT-ir neurons were restricted to the preoptic area, and in agreement with our first prediction cleaners presented smaller and less numerous AVT-ir neurons in the gigantocellular preoptic area (gPOA) compared to non-cleaners. Contrary to our second prediction, AVT neuronal phenotypes did not differ between sexes in either species, but differences in other features of the AVT system cannot be ruled out. In summary, the results presented here suggest a putative role for AVT gPOA neurons in the ability of a cleaner wrasse to approach and interact with a client, through their projections to extrahypothalamic brain areas.

Social Status and Arginine Vasotocin Neuronal Phenotypes in a Cichlid Fish

“…The vasotocin system of the Mozambique tilapia is restricted to the POA where parvocellular, magnocellular and gigantocellular AVT-ir cells can be recognized forming three distinct populations (pPOA, mPOA and gPOA) that follow a distribution previously described for other teleost [Goodson and Bass, 2000;Miranda et al, 2003;Lema and Nevitt, 2004;Maruska et al, 2007;Dewan et al, 2008;Maruska, 2009;Mendonça et al, 2013].…”

“…No stained neurons were observed, thus confirming the specificity of the antibody used. Other studies had already shown this antibody specificity for different species, including another cichlid species [Maruska et al, 2007;Dewan et al, 2008;Maruska, 2009;Mendonça et al, 2013].…”

“…butterfly fishes, Chaetodon spp. [Dewan et al, 2008]; halfspotted goby, Asterropteryx semipunctata [Maruska et al, 2007], and cleaner wrasse, Labroides dimidiatus [Mendonça et al, 2013]). On day 2, after two 0.1 M PBS washes (7 min each), mounted sections were incubated with the biotinylated goat anti-rabbit secondary antibody (KPL) for 30 min, followed by two additional washes (7 min each) and incubation with peroxidase-labelled streptavidin (KPL) for another 30 min.…”

“…Each AVT-ir cell was assigned to either the pPOA, mPOA or gPOA cell group based on neuroanatomical location, cell size and cell morphology (following Bradford and Northcutt [1983]). This nomenclature has been widely used in similar studies [Semsar and Godwin, 2003;Lema, 2006;Maruska, 2009;Mendonça et al, 2013]. Digital images were captured at a magnification of ×400 with a digital camera (Olympus C-2020 Z) attached to a microscope (Olympus BX50).…”

Gene expression correlates of social evolution in coral reef butterflyfishes

“…AVT regulation of social behavior has been studied extensively, albeit almost exclusively in males, where it has functionally been shown to promote spawning [107][108][109] , mate guarding or other forms of conspecific aggression/avoidance 43,108,[110][111][112][113][114][115] , social communication 116 , social preference 117 , and approach behavior 118 . Few studies have functionally examined IT involvement in teleost social behavior and again, those which have are exclusive to males.…”