Adaptive strategies in reproduction to be a simultaneous hermaphrodite

在这项研究开始时，我们预测，雌雄同体的多倍体鱼可能会有双性交配行为，即以雌雄同体的身份交配，在变性期只有几天的时间，之后它们的行为就只会变成自己的性别。与第一次预测相反，我们在2001年的研究过程中发现，玛格丽特海蛞蝓的双性交配行为持续时间超过一周。但在2001年繁殖季之后，由于土壤侵蚀导致净水区严重减少，我们无法在野外观察到交配行为。因此，我们将研究主题扩大到雌雄杂交鱼生殖行为的灵活性。结果发现，2003年在野外发现了一只初生雄斑蝽变性为雌斑蝽。这表明变性鱼类的性别分配惊人地高。此外，我们还发现，在初始阶段，三角斑马鱼的雄性会根据自己的环境采取三种更有效的繁殖策略：潜行、裸奔和群体产卵。另一研究对象疣状石斛（Onchidium verruculatum）种群因冲绳海岸连续发生异常涨潮而大规模减少。因此，我们在2001年无法找到足够数量的个体进行观察。2003年，虽然总体数量恢复到正常水平，但成熟个体不足以进行有效观察。所以我们决定把研究动物换成裸鳃动物。虽然裸枝属植物同时是雌雄同体，但它们在每次交配中同时扮演雄性和雌性角色。另一方面，在每一次交配中，盘尾草都扮演雄性或雌性的角色。我们在已经交配的染色蛾个体中发现了典型的拒绝交配的现象。这与内部受精的雌雄同体动物在繁殖中更倾向于扮演雌性角色的预测相反，因为它们不仅可以使用接收到的精子进行受精，还可以作为营养物质。少

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 … More 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