Studies on life cycle of a protogynous crustacean, Gnorimosphaeroma naktongense

对两个淡水区(L.Koikuchino-ike，Aomori Pref.)的两性甲壳动物Gnorimosphaeroma naktongense的分布和生活史进行了研究。和微咸水(Agano River，Niigata Pref.)身体。本种分布于咸水的湖泊和河流，但它们正在进入日本海一侧的纯净淡水部分，例如它们生活在新泻县被命名为Jimoto泉水的泉水中。但在太平洋一侧，它们不像岩手河(Iwate Pref.)那样在河流的上游发现。有人建议，生活在日本海一侧微咸水的中国棉(G.chinense)将太平洋一侧的中国棉(G.naktongense)作为其一部分。在微咸水中，G.nakotngense有两代，夏季世代始于6月，秋季世代始于10月，而在淡水中，有一代明显的世代始于6月。对性别变化模式的详细分析表明，它们在第一个繁殖季节(约1岁)为雌性，在释放其子女曼卡幼虫后，它们从雌性转变为雄性，大约一年后进入下一个繁殖季节。它们表明了明显的性别二型性，雄性体重比雌性大，它们有一种倾向，在许多情况下，较大的雄性与较大的雌性交配，或者是一个大小分类的交配系统。实验室实验表明，这一现象一直存在于较大的雄性选择较大的雌性守护前，雄性将其守卫的雌性换成较大的雌性，有时唯一的较大的雄性从守卫的夫妇中取出雌性。生活在淡水中的种群产卵量比生活在微咸水中的种群小，但两个种群之间的卵大小没有变化。这表明生活在淡水中的种群还没有完全适应淡水环境。

The distribution and the life cycle of a protogynous hermaphroditic crustacean, Gnorimosphaeroma naktongense were investigated in two regions of fresh-water (L. Koikuchino-ike, Aomori Pref.) and brackish-water (Agano River, Niigata Pref.) bodies. This species was distributed in lakes along sea and rivers with brackish water, but they are entering in the part of pure fresh waters in the side of the Sea of Japan, for instance they live in a spring named as the Jimoto Spring, Niigata Prefecture. But in the side of the Pacific ocean, they were not found in the upper part of the river like as Kitakami River (Iwate Pref.). It was suggested that G. chinense which is dweller in brackish waters in the side of the Sea of Japan take a part of G. naktongense in the side of the Pacific ocean. G. nakotngense has two generations, summer generation starting from June and autumn starting from October, in brackish waters, though in fresh waters there is one clear generation starting from June. Detail analysis of sex-change pattern shows they are females in first reproductive season (about 1 year), and after they released their childrens, manca larvae, they change sex from females to males, and they have next reproductive season after about one year. They indicate clear sexual dimorphism, males are larger than female in body weight, and they have a inclination that larger males mate with larger females in many cases, or a size assorting mate system. Laboratory experiments indicated this phenomenon has been maintained in the cause that a larger male selects a larger female in precopula guarding, and a male changes his guarding female with a larger female, sometimes a sole larger male take out a female from a guarding couple. Populations inhabiting in fresh waters produced less clutch size than in brackish waters, but no change was observed in egg size between two populations. This suggests that populations inhabitiong freshwaters have not completely adapted in fresh water environments.