Asexual reproduction in nonmarine ostracods

Asexual reproduction has evolved repeatedly in nonmarine ostracods and take s a variety of forms from ancient asexuals to species in which sexual and a sexual lineages coexist. Clonal diversity is highly variable. There is evid ence that some of this diversity is maintained by ecological differentiatio n. Hybridization between asexual females and males, of the same or related species, contributes to clonal diversity. Molecular data suggest that some clonal lineages are surprisingly old (more than 5 Myr). In the ancient asex ual Darwinula stevensoni, from a lineage that has apparently been without s ex for more than 100 Myr, a remarkable lack of sequence variation in ITS1 m ay be explained by occasional automixis, gene conversion or somatic recombi nation, or by efficient DNA repair. Overall, the ostracods provide an excel lent system in which to study the evolution of reproductive modes.