The role of rare morph advantage and conspicuousness in the stable gold-dark colour polymorphism of a crater lake Midas cichlid fish

1. Genetically based stable colour polymorphisms provide a unique opportunity to study the evolutionary processes that preserve genetic variability in the wild. Different mechanisms are proposed to promote the stability of polymorphisms, but only few empirical examples have been documented, resulting in an incomplete understanding of these mechanisms.
2. A remarkable genetically-determined stable colour polymorphism is found in the Nicaraguan Midas cichlid species complex (Amphilophus cf. citrinellus). All Midas cichlids start their life with a dark-grey colouration (dark morph), but individuals carrying the dominant “gold” allele (~10%) lose their melanophores later in life, revealing the underlying orange colouration (gold morph). How this polymorphism is maintained remains unclear. Two main hypotheses have been proposed, both suggesting differential predation upon colour morphs as the proximate mechanism. One predicts that the conspicuous gold morph is more likely to be preyed upon,...

1. 基于遗传的稳定体色多态性（genetically based stable colour polymorphisms）为探究野生种群遗传变异维持的进化过程提供了独特契机。目前学界已提出多种可促进多态性稳定的机制，但已得到实证记录的案例寥寥无几，致使对这类机制的认知仍不全面。
2. 尼加拉瓜的米达斯科丽鱼物种复合群（Amphilophus cf. citrinellus）中存在一类极具代表性的遗传决定型稳定体色多态性。所有米达斯科丽鱼幼体均呈深灰色体色，属于深色型（dark morph）；携带显性"金色"等位基因（约占种群的10%）的个体在生长后期会丧失黑素细胞（melanophores），从而显现出潜藏的橙色体色，即金色型（gold morph）。目前该多态性的维持机制仍未明确。学界已提出两类核心假说，均认为不同体色型遭遇的捕食压力差异是其直接作用机制。其中一项假说预测，醒目显眼的金色型个体被捕食的概率更高，...