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Studies on life cycle of a protogynous crustacean, Gnorimosphaeroma naktongense

原生甲壳动物 Naktongense Gnorimosphaeroma naktongense 生命周期的研究

基本信息

批准号：
10640611
负责人：
FUKUHARA Haruo
金额：
$ 1.28万
依托单位：
NIIGATA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

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.

本文报道了一种雌雄同体的原生甲壳动物Naktongense的分布和生活史。（青森县小池池池）和半咸水（新泻Pref.）尸体本种分布于沿着湖泊和河流的咸水中，但它们正在进入日本海一侧的纯净淡水沃茨，例如它们生活在新泻县名为次本泉的泉水中。但是在太平洋一侧，它们并没有像北上川（岩手县）那样在河流的上游发现。认为G. chinense是生活在日本海一侧半咸水沃茨中的一部分G.位于太平洋一侧的naktongense。G. nakotngense有两个世代，从6月开始的夏季世代和从10月开始的秋季世代，在半咸水沃茨，虽然在淡水沃茨有一个从6月开始的清澈世代。对变性模式的详细分析表明，它们在第一个生殖季节（约1年）是雌性，在释放子女曼卡幼虫后，它们的性别从雌性变为雄性，大约一年后进入下一个生殖季节。它们具有明显的两性异形，雄性体重大于雌性，在许多情况下，它们倾向于较大的雄性与较大的雌性交配，或者是一种大小不等的交配系统。实验结果表明，这种现象之所以得以维持，是因为在前尾叶保卫中，体型较大的雄虫选择体型较大的雌虫，雄虫用体型较大的雌虫替换保卫雌虫，有时一个体型较大的雄虫从保卫雌虫的配偶中淘汰一个雌虫。栖息在淡水沃茨中的种群的窝卵数低于半咸水沃茨中的种群，但两个种群之间的卵大小没有变化。这表明栖息在淡水中的种群还没有完全适应淡水环境。