Data from: The melanocortin system regulates body pigmentation and social behaviour in a colour polymorphic cichlid fish

The melanocortin system is a neuroendocrine system that regulates a range of physiological and behavioural processes. We examined the extent to which the melanocortin system simultaneously regulates colour and behaviour in the cichlid fish Astatotilapia burtoni. We found that yellow males are more aggressive than blue males, in line with previous studies. We then found that exogenous α-melanocyte-stimulating hormone (α-MSH) increases yellowness of the body and dispersal of xanthophore pigments in both morphs. However, α-MSH had a morph-specific effect on aggression, with only blue males showing an increase in the rate of aggression. Exogenous agouti signalling peptide (ASIP), a melanocortin antagonist, did not affect coloration but reduced the rate of aggression in both colour morphs. Blue males had higher cortisol levels than yellow males. Neural gene expression of melanocortin receptors (mcr) and ligands was not differentially regulated between colour morphs. In the skin, however, mc1r and pro-opiomelanocortin (pomc) β were upregulated in blue males, while asip 1 was upregulated in yellow males. The effects of α-MSH on behaviour and body coloration, combined with morph-specific regulation of the stress response and the melanocortin system, suggest that the melanocortin system contributes to the polymorphism in behaviour and coloration in A. burtoni.

黑皮质素系统（melanocortin system）是一类调控多种生理与行为过程的神经内分泌系统。本研究旨在探究黑皮质素系统在慈鲷鱼（cichlid fish）伯顿柔丽鲷（Astatotilapia burtoni）中同时调控体色与行为的程度。研究结果与既往研究一致：黄色雄性个体的攻击性强于蓝色雄性个体。随后我们发现，外源性α-黑素细胞刺激素（α-melanocyte-stimulating hormone，α-MSH）可提升两种体色形态个体的身体黄色调，并促进黄色素细胞（xanthophore）色素的扩散。但α-MSH对攻击性的调控存在体色形态特异性：仅蓝色雄性个体的攻击速率出现显著提升。外源性阿古蒂信号肽（agouti signalling peptide，ASIP）作为黑皮质素拮抗剂（melanocortin antagonist），不会影响体色，但可降低两种体色形态个体的攻击速率。蓝色雄性个体的皮质醇（cortisol）水平高于黄色雄性个体。两种体色形态个体的神经组织中，黑皮质素受体（melanocortin receptors，mcr）及其配体的基因表达并无显著差异。但在皮肤组织中，蓝色雄性个体的黑素皮质素1受体（mc1r）与β-阿黑皮素原（pro-opiomelanocortin β，pomc β）的基因表达均出现上调，而黄色雄性个体的asip 1基因表达则显著上调。结合α-MSH对行为与体色的调控作用，以及应激反应和黑皮质素系统的形态特异性调控结果，本研究提示黑皮质素系统参与了伯顿柔丽鲷行为与体色的多态性形成。