Diversity of Brachionus plicatilis species complex (Rotifera) in inland saline waters from China: Presence of a new mitochondrial clade on the Tibetan Plateau.

The biogeography and molecular phylogeny of invertebrate zooplankton populations from inland saline waters remains under-explored in the Eastern Palearctic, especially the Qinghai-Tibetan Plateau. Here, we surveyed the diversity of the Brachionus plicatilis Müller, 1786 species complex from inland saline waters across China. We compared morphometrics with DNA taxonomy (using two genetic markers: the mitochondrial cytochrome c oxidase subunit I (COI) gene and the nuclear internal transcribed spacer (ITS-1)). Our phylogenies based on the sequences of ITS-1 recognized two distinct clades (i.e. two species: B. plicatilis sensu stricto (s.s.) and B. asplanchnoidis) in China. We detected two mitochondrial clades within B. plicatilis s.s and one within B. asplanchnoidis across China, consistent with the three morphogroups present. One of these three clades was novel and restricted to the Qinghai-Tibetan Plateau, where it exhibited evidence of recent expansion across the region. The new mitochondrial clade fell within B. plicatilis s.s. but was sister to all other mitochondrial sequences of that species, suggesting a period of isolation from other populations. Moreover, significant morphological differences were identified: B. plicatilis s.s. from the Qinghai-Tibetan Plateau had a larger lorica length and width than did members of this species from lowland China. Our data demonstrate the successful adaptation of this species complex to the harsh environment of the Qinghai-Tibetan Plateau.