Phylogeography and regional endemism of a passively dispersing zooplankter: mitochondrial DNA variation in rotifer resting egg banks

We investigated the phylogeography of the salt water rotifer Brachionus pli catilis, a cyclical parthenogen with passive dispersal mechanisms, using re sting eggs recovered from saline lake sediments. Individual resting eggs we re obtained from a large selection of lakes which were representative of fi ve endorheic basins and the chain of coastal ponds in the Iberian Peninsula . The novel use of resting eggs allows the integration of seasonal and annu al variations as well as the impact of stochastic effects such a drift and local extinction. A 653 bp fragment of the mitochonrial cytochrome oxidase subunit I (COI) gene was sequenced from 98 eggs. Our results revealed a dee p phylogeographical structure in this species, with a division into two mai n lineages with distinct geographical distributions, which probably diverge d at the beginning of the Pleistocene period. Most of the mitochondrial DNA haplotypes were restricted to single lakes. Nested clade analysis supporte d Early Pleistocene fragmentation of populations, low gene flow and some lo ng-distance colonization. These conclusions contrast strongly with previous ideas on rotifer biogeography and this pattern is consistent with a recolo nization of the Iberian Peninsula from two glacial refugia. The results pro vide new insights into the processes responsible for the genetic diversific ation of passive dispersers, a life-history trait typical of zooplanktonic biotas.