Abstract

Differences in mating behavior between temperate and tropical medaka species

Tropical animals are characterized by showy ornaments and conspicuous body colors, and many biologists have long sought out a reason of them. In this study, hypothesizing that sexual selection pressures are stronger in the tropics than temperate region, we compared mating behaviors between two species of medaka fishes from two different latitudes, Oryzias woworae and Oryzias sakaizumii, as model system. It is known that O. woworae, the tropical species, exhibits a greater degree of sexual dimorphisms in fin morphologies, compared to the temperate congener, O. sakaizumii, and that O. woworae males have a characteristic bluish body. Laboratory mating experiments revealed that males of tropical species performed courtship behaviors more frequently than males of the temperate species. In addition, females of the tropical species did not accept males easily, suggesting that they are choosier than females of the temperate congener. Especially, females of the tropical species never accepted males of the temperate species. These results support our hypothesis about the latitudinal difference in sexual selection pressures. We will discuss why sexual selection pressures are stronger in tropic region from the viewpoint of breeding seasonality.