Due to the combined effects of global warming and eutrophication, the frequency of deleterious cyanobacterial blooms in freshwater ecosystems has increased. In line with this, local adaptation of the aquatic keystone herbivore Daphnia to cyanobacteria has received major attention. Besides microcystins, the most frequent cyanobacterial secondary metabolites in such blooms are protease inhibitors (PIs). Recently, it has been shown that a protease gene showed copy number variation between four D. magna populations that differed in tolerance to PIs. From that study, we chose two distinct populations of D. magna which had or had not coexisted with cyanobacteria in the past. By calculating FST values, we found that the two populations were genetically more distant in the protease loci than in neutral loci. Population genetic tests applied to the tolerant population revealed that positive selection was most probably acting on the gene loci of the digestive protease CT448 and CT802. We conclude that the selection of digestive proteases and subsequent reduction in copy number is the molecular basis of evolutionary changes leading to local adaptation to PIs.

中文翻译：

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在水蚤中积极选择消化蛋白酶：局部适应蓝藻蛋白酶抑制剂的机制。

由于全球变暖和富营养化的共同作用，淡水生态系统中有害的蓝藻水华的发生频率增加了。与此相适应，水生梯形食草动物水蚤对蓝藻的局部适应已引起广泛关注。除微囊藻毒素外，此类水华中最常见的蓝细菌次级代谢产物是蛋白酶抑制剂（PIs）。近来，已经显示蛋白酶基因显示出在四个D.magna种群之间的拷贝数变异，其对PI的耐受性不同。从该研究中，我们选择了过去与蓝细菌共存或不共存的两个不同的D. magna种群。通过计算FST值，我们发现在蛋白酶基因座上这两个种群比中性基因座在遗传上更远。对耐性种群进行的种群遗传学测试显示，阳性选择最有可能作用于消化蛋白酶CT448和CT802的基因位点。我们得出结论，消化蛋白酶的选择和随后拷贝数的减少是导致局部适应PI的进化变化的分子基础。