| Research Abstract |
At the beginning of this research, we predicted that protogynous labrid fishes could perform bi-sexual mating behavior, that is court as a male and also as a female, only for a few days in the period of sex change, and afterward they would behave only as the sex they changed to. Contrary to the first prediction, we found that Halichoeres margaritaceus performed bi-sexual mating behavior longer than a week in the course of research in 2001. But we could not observe mating behavior in the field after2001 reproductive season, because the water clearance badly diminished owing to the erosion of the soil. So we enlarged our research theme to the flexibility of the reproductive behavior in the males of labrid fishes. As a result, we found an initial phase male of H. trimaculatus changed its sex into female in the field in 2003. This shows the sex allocation of sex changing fishes are surprisingly high. Further, we found that initial phase males of H. trimaculatus used three types of reproduc
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tive strategies, sneaking, streaking, and group spawning according to their circumstances.
The population of Onchidium verruculatum, another research object, diminished on a large scale because of extraordinarily high tide occurred at Okinawan coast successively. As a result, we could not found enough number of individuals for observation in 2001. In 2003, although the overall number recovered to usual level, mature individuals were not enough for effective observation. So we decided to change study animals to nudibranchs. Although nudibranchs are simultaneous hermaphrodite as well as Onchidium, they take both male and female role simultaneously in each copulation. On the other hand, Onchidium acts as a male or a female in each mating occasion. We found a characteristic rejection to copulation in individuals of Chromodoris tinctoria that have already copulated. This is contrary to the prediction that hermaphroditic animals with internal fertilization prefer to take female role in reproduction, because they can use received sperm not only for fertilization but also as a nutrient. Less
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