Mendonça Rute, Soares Marta C, Bshary Redouan, Oliveira Rui F
Unidade de Investigação em Eco-Etologia, ISPA - Instituto Universitário, Lisbon, Portugal.
Brain Behav Evol. 2013;82(3):166-76. doi: 10.1159/000354784. Epub 2013 Oct 2.
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.
九肽精氨酸加压催产素（AVT）及其哺乳动物同源物精氨酸加压素因其在调节多种种内社会行为中的作用而广为人知，比如社会接近/回避和攻击行为。最近，我们提出AVT在调节种间社会行为中可能也很重要，因为它能调节印度-太平洋蓝带清洁鱼裂唇鱼（Labroides dimidiatus）的种间合作行为。注射AVT会降低清洁鱼与客户进行清洁互动的倾向，这表明这种肽的高浓度会损害清洁鱼的合作动机。因此，我们推测AVT的内源性低水平是清洁鱼表达种间清洁行为的一个先决条件，因为这使它们能够接近种间个体并与之互动，而且这应该会在它们的AVT神经元表型中得到体现。在这里，我们通过比较两种系统发育关系密切、生活在相似环境但种间合作行为表达不同的物种的AVT神经元表型来检验这一假设：一种是专性清洁鱼（裂唇鱼），另一种是不进行清洁行为的食珊瑚鱼（单带海猪鱼，Labrichthys unilineatus）。预计这两个物种的AVT神经元表型会有所不同，以反映它们接近种间个体并与之互动的能力或无此能力，清洁鱼的AVT免疫反应（ir）神经元数量更少且/或体积更小。还预计AVT神经元表型存在性别差异，因为这两个物种的雄性似乎都比雌性更具攻击性。正如大多数其他硬骨鱼物种所描述的那样，AVT-ir神经元局限于视前区，与我们的第一个预测一致：与非清洁鱼相比，清洁鱼在巨细胞视前区（gPOA）的AVT-ir神经元数量更少且体积更小。与我们的第二个预测相反，两个物种的AVT神经元表型在性别上没有差异，但不能排除AVT系统其他特征存在差异。总之，这里呈现的结果表明，通过AVT gPOA神经元投射到下丘脑外脑区，AVT gPOA神经元在清洁鱼接近客户并与之互动的能力方面可能发挥作用。
