Taylor Derek J, Finston Terrie L, Hebert Paul D N
Department of Biological Sciences, State University of New York, Buffalo, New York, 14260.
Department of Zoology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
Evolution. 1998 Dec;52(6):1648-1670. doi: 10.1111/j.1558-5646.1998.tb02245.x.
The lack of morphological variation in many freshwater invertebrates over vast distances has been cited as evidence for their frequent, long-distance dispersal. This scenario implies that vicariance will be an insignificant determinant of species distributions or diversity. We carried out a phylogeographic and population genetics study of one widespread crustacean group, the North American Daphnia laevis complex. Allozyme and sequence variation of two mtDNA genes (12S and 16S rRNA) clearly indicates the existence of five morphologically cryptic, largely allopatric groups (Daphnia dubia, D. laevis laevis, D. laevis gessneri, D. magniceps magniceps, and D. magniceps pacifica ssp. n.). Within each of these groups, there is weak or no genetic differentiation over large geographic areas suggesting their recent long-distance dispersal. The present-day distributions and phylogeography of the regional groups suggests the occurrence of both deep and shallow vicariance events. Although divergence times from mtDNA sequences do indicate both deep and shallow divergences, these estimates are incongruent with their proposed vicariance times. The results show that even within closely related freshwater invertebrates, a complex biogeography exists, whose analysis is made difficult by long-distance dispersal, cryptic endemism, and pseudocongruence.
许多淡水无脊椎动物在广阔区域内缺乏形态变异，这被视为它们频繁进行长距离扩散的证据。这种情况意味着地理隔离对物种分布或多样性的影响微不足道。我们对一个广泛分布的甲壳类动物群体——北美平滑水蚤复合体进行了系统地理学和种群遗传学研究。两种线粒体DNA基因（12S和16S rRNA）的等位酶和序列变异清楚地表明存在五个形态上难以区分、基本异域分布的类群（杜比水蚤、平滑水蚤指名亚种、平滑水蚤格斯纳里亚种、巨头水蚤指名亚种和新种巨头水蚤太平洋亚种）。在这些类群中的每一个内部，在大的地理区域内遗传分化较弱或没有分化，这表明它们近期进行了长距离扩散。区域类群目前的分布和系统地理学表明既发生了深度地理隔离事件，也发生了浅度地理隔离事件。尽管线粒体DNA序列的分歧时间确实表明了深度和浅度分歧，但这些估计与所提出的地理隔离时间不一致。结果表明，即使在亲缘关系密切的淡水无脊椎动物中，也存在复杂的生物地理学，长距离扩散、隐性特有现象和假一致性使得对其分析变得困难。
