Global and local environmental changes and biological evolution : paleolimnological and molecular biological analyses using resting eggs of Daphnia in sediments

利用沉积物中的水蚤休眠卵进行遗传分析所显示的历史变化表明，自20世纪50年代以来，山形县Hataya-Onua池塘的水蚤物种在Daphnia galeata-daphna物种复合体内产生了杂交。尽管在过去的几十年里发生了彻底的环境变化，但它们仍然保持了它的人口。在20世纪80年代，其他物种的大型水蚤在池塘中建立了自己的种群，这可能是因为引入黑鳕鱼减少了浮游鱼的捕食压力。因此，从那时起，多种水蚤可能就在这个池塘里共存了。同时，对岩手县呼拉努玛湖浮游生物遗骸的分析表明，90年代以后，随着TN和TP浓度的急剧增加，浮游植物的丰度急剧增加，有一种新的水蚤种群增加。结果表明，自20世纪80年代以来，由于营养物质负荷的影响，浮游植物群落和浮游动物群落发生了变化。由于我们在流域中没有检测到直接的人为影响，最近这个湖营养物质负荷的增加很可能是由空气沉积带来的。

Historical changes shown by genetic analysis using resting eggs of Daphnia in the sediments indicated that Daphnia species in Hataya-Onuma pond, Yamagata Prefecture has produced the hybrids within Daphnia galeata-dentifera species complex since the 1950s. Despite drastic environmental changes thorough the last several decades, they have kept its population. In the 1980s, other species of Daphnia pulex established its population in the pond probably due to the reduced predation pressure from planktivore fish by introduced black bass. As a result, multiple Daphnia species could have coexisted in this pond since then. Meanwhile, the analysis of plankton remains in Lake Hourai-Numa, Iwate prefecture, showed that a new species of Daphnia population increased after the 1990s when the abundance of phytoplankton drastically increased in parallel with the abrupt increase of TN and TP concentrations. The results suggest that the phyto- and zooplankton communities have been changed due to effects of nutrient loading since the 1980s. Since we did not detect direct anthropogenic effects in the watersheds, recent increase in nutrient loadings to this lake are most likely brought by air deposition.