Variation in male courtship activeness between latitudinal populations of Northern medaka

Abstract

It has been demonstrated from free mating experiments using multiple males and females of the medaka, Oryzias latipes species complex, that lower-latitude males exhibit more active courtship behavior than higher-latitude males. In this study, courtship activeness in males from two latitudinal populations of Northern medaka, Oryzias sakaizumii, was measured in the presence of only one male and one female, where male–male interactions were completely eliminated. We found that males from the low-latitude population performed quick circles (i.e., courtship dance) and approached females more frequently than males from the high-latitude population. Moreover, the low-latitude males tended to start courtships sooner after encountering a female than the high-latitude males. Thus, the latitudinal variation in male courtship activeness persisted even in the absence of rival males. These probably reflect that sexual selection pressures are stronger at low latitudes.