Data from: Natural allelic variations of xenobiotic metabolizing enzymes affect sexual dimorphism in Oryzias latipes

Sexual dimorphisms, which are phenotypic differences between males and females, are driven by sexual selection. Interestingly, sexually selected traits show geographical variations within species despite strong directional selective pressures. This paradox has eluded many evolutionary biologists for some time, and several models have been proposed (e.g. ‘indicator model’ and ‘trade-off model’). However, disentangling which of these theories explains empirical patterns remains difficult, because genetic polymorphisms that cause variation in sexual differences are still unknown. In this study, we show that polymorphisms in cytochrome P450 (CYP) 1B1, which encodes a xenobiotic-metabolizing enzyme, are associated with geographical differences in sexual dimorphism in the anal fin morphology of medaka fish (Oryzias latipes). Biochemical assays and genetic cross experiments show that high- and low-activity CYP1B1 alleles enhanced and declined sex differences in anal fin shapes, respectively. Behavioural and phylogenetic analyses suggest maintenance of the high-activity allele by sexual selection, whereas the low-activity allele possibly has experienced positive selection due to by-product effects of CYP1B1 in inferred ancestral populations. The present data can elucidate evolutionary mechanisms behind genetic variations in sexual dimorphism and indicate trade-off interactions between two distinct mechanisms acting on the two alleles with pleiotropic effects of xenobiotic-metabolizing enzymes.性二态性（sexual dimorphisms）即雄性与雌性个体间的表型差异，由性选择所驱动。值得注意的是，尽管存在强烈的定向选择压力，经性选择演化的性状仍在物种类群内呈现地理变异。这一悖论长期以来困扰着众多进化生物学家，目前已提出多种解释模型，例如‘指示物模型’与‘权衡模型’。然而，由于导致性差异变异的遗传多态性（genetic polymorphisms）仍未被探明，厘清上述哪种理论能够解释实证观测到的模式仍颇具挑战。本研究发现，编码异生物质代谢酶（xenobiotic-metabolizing enzyme）的细胞色素P450 1B1（cytochrome P450 (CYP) 1B1）的遗传多态性，与青鳉（Oryzias latipes）臀鳍形态的性二态性地理差异显著相关。生化实验与遗传杂交实验表明，高活性与低活性的CYP1B1等位基因（alleles）分别增强与减弱了臀鳍形态的性差异。行为学与系统发育分析显示，高活性等位基因通过性选择得以维持；而在推断的祖先种群中，低活性等位基因可能因CYP1B1的副产物效应经历了正向选择（positive selection）。本研究数据阐明了性二态性遗传变异背后的演化机制，并揭示了异生物质代谢酶多效性（pleiotropic effects）作用下，作用于两个等位基因的两种不同机制之间存在权衡互作。