Inbreeding and outbreeding depression in geographical parthenogens Heterocypris incongruens and Eucypris virens (Crustacea: Ostracoda)

Heterocypris incongruens and Eucypris virens are geographic parthenogens inhabiting temporary ponds. Several authors proposed that, after the last glaciation, asexual lineages would spread throughout Europe more efficiently than sexual ones. The range expansion, that followed a metapopulation dynamics characterized by genetic bottlenecks and subsequent inbreeding / outbreeding depression, had strong negative fitness consequences in sexuals. Using controlled crosses we estimated inbreeding and outbreeding depression in sexual populations of H. incongruens and E. virens and compared the experimental reproduction rate in sexual and asexual females of both species. Inbreeding depression varied according to species and fitness components but, in general, were not significantly different between inbred and outbred crosses. In H. incongruens, inbred crosses produced a higher percentage of resting eggs and had higher fecundity than intrapopulation outbred crosses. Reproduction rate in asexuals of both species was about twice than in sexuals. Our data do not support the hypothesis that sexual populations exhibit inbreeding depression in geographic parthenogens. However, outbreeding depression and the lower efficiency of sexuals in establishing new populations may account for the role of metapopulation dynamics in geographic parthenogenesis of both species.