Dybdahl Mark F, Lively Curtis M
Department of Biology, Indiana University, Bloomington, Indiana, 47405.
Evolution. 1996 Dec;50(6):2264-2275. doi: 10.1111/j.1558-5646.1996.tb03615.x.
Gene flow and the genetic structure of host and parasite populations are critical to the coevolutionary process, including the conditions under which antagonistic coevolution favors sexual reproduction. Here we compare the genetic structures of different populations of a freshwater New Zealand snail (Potamopyrgus antipodarum) with its trematode parasite (Microphallus sp.) using allozyme frequency data. Allozyme variation among snail populations was found to be highly structured among lakes; but for the parasite there was little allozyme structure among lake populations, suggesting much higher levels of parasite gene flow. The overall pattern of variation was confirmed with principal component analysis, which also showed that the organization of genetic differentiation for the snail (but not the parasite) was strongly related to the geographic arrangement of lakes. Some snail populations from different sides of the Alps near mountain passes were more similar to each other than to other snail populations on the same side of the Alps. Furthermore, genetic distances among parasite populations were correlated with the genetic distances among host populations, and genetic distances among both host and parasite populations were correlated with "stepping-stone" distances among lakes. Hence, the host snail and its trematode parasite seem to be dispersing to adjacent lakes in a stepping-stone fashion, although parasite dispersal among lakes is clearly greater. High parasite gene flow should help to continuously reintroduce genetic diversity within local populations where strong selection might otherwise isolate "host races." Parasite gene flow can thereby facilitate the coevolutionary (Red Queen) dynamics that confer an advantage to sexual reproduction by restoring lost genetic variation.
基因流动以及宿主和寄生物种群的遗传结构对于协同进化过程至关重要，包括对抗性协同进化有利于有性生殖的条件。在这里，我们使用等位酶频率数据比较了新西兰淡水蜗牛（Potamopyrgus antipodarum）及其吸虫寄生物（Microphallus sp.）不同种群的遗传结构。发现蜗牛种群之间的等位酶变异在不同湖泊间具有高度的结构化；但对于寄生物来说，湖泊种群间几乎没有等位酶结构，这表明寄生物的基因流动水平要高得多。主成分分析证实了变异的总体模式，该分析还表明蜗牛（而非寄生物）的遗传分化组织与湖泊的地理布局密切相关。阿尔卑斯山附近山口两侧的一些蜗牛种群彼此之间的相似性高于与阿尔卑斯山同一侧的其他蜗牛种群。此外，寄生物种群之间的遗传距离与宿主种群之间的遗传距离相关，宿主和寄生物种群之间的遗传距离都与湖泊之间的“踏脚石”距离相关。因此，宿主蜗牛及其吸虫寄生物似乎以踏脚石的方式扩散到相邻湖泊，尽管寄生物在湖泊间的扩散显然更大。高寄生物基因流动应有助于在局部种群中持续重新引入遗传多样性，否则强大的选择可能会隔离“宿主种族”。寄生物基因流动从而可以促进协同进化（红皇后）动态，通过恢复失去的遗传变异为有性生殖带来优势。
