Variation in Mating Behaviors Between a Tropical and a Temperate Species of Medaka Fishes.

In medaka fishes, the family Adrianichthyidae, tropical species are known to be sexually more dimorphic than temperate species. If this reflects that tropical species are exposed to stronger sexual-selection pressures than temperate species, mating behaviors may also differ between tropical and temperate species. Our mating experiments revealed that males of , a tropical species of the family, perform "chasing" another male more frequently than males of , a temperate congener, and that male-male "combats" of tended to be followed by chasing compared with combats of males, indicating that males are more aggressive in male-male interactions than males. Males of also performed "approaching" a female and "mating dance" more frequently than males, indicating that males are also more active in courting females. Males of often omitted "mating dance" in their mating sequences, supporting this view. Moreover, females tended to reject male "wrapping", an attempt for fertilization, more frequently than females, suggesting that females are choosier in mating than females. These findings are concordant with the view that is exposed to stronger sexual-selection pressures than .