Genetic architecture of the variation in male-specific ossified processes on the anal fins of Japanese medaka

Traits involved in reproduction evolve rapidly and show great diversity among closely related species. However, the genetic mechanisms that underlie the diversification of courtship traits are mostly unknown. Japanese medaka fishes (Oryzias latipes) use anal fins to attract females and to grasp females during courtship; the males have longer anal fins with male-specific ossified papillary processes on the fin rays. However, anal fin morphology varies between populations: the southern populations tend to have longer anal fins and more processes than the northern populations. In the present study, we conducted quantitative trait locus (QTL) mapping to investigate the genetic architecture underlying the variation in the number of papillary processes of Japanese medaka fish and compared the QTLs with previously identified QTLs controlling anal fin length. First, we found that only a few QTLs were shared between anal fin length and papillary process number. Second, we found that the numbers of papillary processes on different fin rays were often controlled by different QTLs. Finally, we produced another independent cross and found that some QTLs were repeatable between the two crosses, whereas others were specific to only one cross. These results suggest that variation in the number of papillary processes is polygenic and controlled by QTLs that are distinct from those controlling anal fin length. Thus, different courtship traits in Japanese medaka share a small number of QTLs and have the potential for independent evolution.

与生殖相关的性状演化速率较快，且在近缘物种间呈现出显著的多样性。然而，驱动求偶性状多样化的遗传机制目前仍知之甚少。日本青鳉（Japanese medaka，*Oryzias latipes*）在求偶过程中会利用臀鳍吸引雌性并完成抱合；雄性个体的臀鳍更长，且鳍条上分布有雄性特有的骨化乳头状突起。不过不同种群间的臀鳍形态存在显著差异：相较于北方种群，南方种群的臀鳍更长，乳头状突起的数量也更多。本研究通过数量性状位点（quantitative trait locus, QTL）定位技术，探究日本青鳉乳头状突起数量变异背后的遗传结构，并将本次定位得到的QTL与此前已报道的调控臀鳍长度的QTL进行了对比分析。其一，调控臀鳍长度与乳头状突起数量的QTL仅有少量重叠；其二，不同鳍条上的乳头状突起数量往往由不同的QTL分别调控；最后，我们通过另一组独立的杂交实验验证发现，部分QTL在两组杂交实验中均可重复检测到，而另有一些QTL仅在单一杂交组中特异性存在。上述结果表明，乳头状突起数量的变异属于多基因调控性状，其受控的QTL与调控臀鳍长度的QTL存在显著差异。因此，日本青鳉的不同求偶性状仅共享少量QTL，具备独立演化的潜力。