Ref ID : 4441
Africa Gomez, Manuel Serra, Gary R. Carvalho, and David H. Lunt; Speciation in ancient cryptic species complexes: Evidence from the molecular phylogeny of Brachionus plicatilis (Rotifera). Evolution 56(7):1431-1444, 2002
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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 investigated 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 egg from 27 salt lakes in the Iberian Peninsula plus lakes from four continents revealed nine genetically divergent lineages. The high level of sequences 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 age, 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.