Gómez Africa, Serra Manuel, Carvalho Gary R, Lunt David H
Department of Biological Sciences, University of Hull, United Kingdom.
Evolution. 2002 Jul;56(7):1431-44. doi: 10.1111/j.0014-3820.2002.tb01455.x.
Continental lake-dwelling zooplanktonic organisms have long been considered cosmopolitan species with little geographic variation in spite of the isolation of their habitats. Evidence of morphological cohesiveness and high dispersal capabilities support this interpretation. However, this view has been challenged recently as many such species have been shown either to comprise cryptic species complexes or to exhibit marked population genetic differentiation and strong phylogeographic structuring at a regional scale. Here we investigate the molecular phylogeny of the cosmopolitan passively dispersing rotifer Brachionus plicatilis (Rotifera: Monogononta) species complex using nucleotide sequence variation from both nuclear (ribosomal internal transcribed spacer 1, ITS1) and mitochondrial (cytochrome c oxidase subunit I, COI) genes. Analysis of rotifer resting eggs from 27 salt lakes in the Iberian Peninsula plus lakes from four continents revealed nine genetically divergent lineages. The high level of sequence divergence, absence of hybridization, and extensive sympatry observed support the specific status of these lineages. Sequence divergence estimates indicate that the B. plicatilis complex began diversifying many millions of years ago, yet has showed relatively high levels of morphological stasis. We discuss these results in relation to the ecology and genetics of aquatic invertebrates possessing dispersive resting propagules and address the apparent contradiction between zooplanktonic population structure and their morphological stasis.
长期以来，尽管大陆湖泊中的浮游动物栖息地相互隔离，但它们一直被视为世界性物种，地理变异很小。形态上的一致性和高扩散能力的证据支持了这一解释。然而，最近这一观点受到了挑战，因为许多这样的物种已被证明要么包含隐存种复合体，要么在区域尺度上表现出明显的种群遗传分化和强烈的系统地理学结构。在这里，我们利用来自核基因（核糖体内部转录间隔区1，ITS1）和线粒体基因（细胞色素c氧化酶亚基I，COI）的核苷酸序列变异，研究世界性被动扩散轮虫褶皱臂尾轮虫（轮虫纲：单巢目）物种复合体的分子系统发育。对来自伊比利亚半岛27个盐湖以及四大洲湖泊的轮虫休眠卵进行分析，发现了9个遗传上不同的谱系。观察到的高水平序列差异、无杂交现象和广泛的同域分布支持了这些谱系的物种地位。序列差异估计表明，褶皱臂尾轮虫复合体在数百万年前就开始分化，但形态上却表现出相对较高的稳定性。我们结合具有扩散性休眠繁殖体的水生无脊椎动物的生态学和遗传学来讨论这些结果，并探讨浮游动物种群结构与其形态稳定性之间明显的矛盾。
