Induction of Male Courtship Behavior by Olfactory Cues Released From Ovulating Female in the Medaka, Oryzias latipes.

Chemical communication between males and females is important for successful reproduction of animals. The activation of male courtship behavior by female olfactory cues has only been demonstrated in a limited number of teleost species. In the present study, we showed that in the model animal medaka, courtship behavior in males are activated by olfactory cues released by females and that at least one of them is released through urine. Male medaka perform a series of courtship behaviors, such as "following" (chasing the female), "positioning" (positioning slightly behind the female), and "quick-circle" (performing a somersault around the female's nose), before spawning. Males rarely showed courtship behavior toward post-spawning females; however, in the waters that had been reared ovulating female or other mating pairs, males significantly increased their following toward post-spawning females. Furthermore, males tended to make more frequent quick-circle toward post-spawning females in the water of other mating pairs had been spawned in it. When males were paired with post-spawning females in water supplemented with ovulating-female urine, only the frequency of quick-circle increased significantly. This suggested that the urine of ovulating females contains a component that induces the quick-circle and that the component inducing the following is a different component released via a route separate from urine. Ovulating females store more than ten times the amount of urine in their bladders than non-ovulating females and males, and releasing this urine during male courtship behavior may increase male motivation.