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

对沉积物中水蚤休眠卵的遗传分析表明，自20世纪50年代以来，山形县高谷-小沼池水蚤种群在小齿水蚤种群复合体内产生了杂交种。尽管在过去的几十年里环境发生了剧烈的变化，它们仍然保持着它们的数量。在20世纪80年代，其他种类的水蚤在池塘中建立了种群，可能是由于引入黑鲈鱼减少了浮游生物鱼类的捕食压力。因此，从那时起，多个水蚤物种可能在这个池塘中共存。同时，对岩手县Hourai-Numa湖浮游生物残留分析表明，20世纪90年代后，随着TN和TP浓度的急剧增加，浮游植物丰度急剧增加，水蚤新种群数量增加。结果表明，自20世纪80年代以来，由于营养负荷的影响，浮游植物和动物群落发生了变化。由于我们没有在流域中发现直接的人为影响，因此最近该湖泊营养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.