Persistence of asexuality through mixed reproduction in Eucypris virens (Crustacea, Ostracoda).

The ostracod species Eucypris virens exhibits geographical parthenogenesis, with rare sexual populations in southern Europe and widespread asexual populations elsewhere. DNA sequence data from the nuclear ITS1 and mitochondrial COI regions have been used to estimate genetic variabilities and reconstruct phylogenies. The observed divergence was exceptionally high, with intraspecific maxima of 10.3% (ITS1) and 20.9% (COI) among European lineages, levels reported for interspecific comparisons of other taxa. Phylogenetic reconstructions reveal multiple origins of asexual clones from sexual populations. However, we argue that such data can only provide a lower limit on the number of origins of asexual reproduction, and an upper limit on the age of asexual lineages. Congruence between gene trees for different loci can provide support for the inference of long-term apomictic reproduction. Nuclear and mitochondrial data differ in their placement of some asexual clones, possibly indicating that genetic exchange has taken place between sexual and asexual lineages. Such intraspecific hybridization is one route to combine the benefits of both reproductive modes, and it might explain how asexuality managed to persist in E. virens even in long, evolutionary terms.