Mate recognition as a reproductive barrier in sexual and parthenogenetic Eucypris virens (Crustacea, Ostracoda)

Mate selection is one of the motors of evolution and of particular importance in the case of organisms in which sexual and parthenogenetic populations coexist. Sexual populations of the ostracod species complex Eucypris virens are often mixed with parthenogenetic ones. A powerful mate selection mechanism must exist to avoid time, energy and sperm loss, for the maintenance and success of sexual reproduction in these mixed populations. There are four types of E. virens individuals: males (diploid), sexual females (diploid) and asexual females (parthenogenetic and either di- or triploid). From one parthenogenetic population and two populations with males of E. virens, we sampled early stage juveniles, and reared them to adulthood in isolation. We combined three virgin ostracods, one male and two females, these latter of contrasting reproductive mode (sexual versus asexual) and origin (allopatric versus sympatric to the males). A posteriori molecular analyses further allowed identification of the mitochondrial clade and ploidy level of the individuals. Strong mate preferences were detected: sexual encounters occurred almost exclusively between males and sexual females and those involving asexual females (either di- or triploid) occurred rarely. The clear recognition of sexual individuals among each other implies that the presence of parthenogens does not greatly disturb the reproductive process in the sexual population. Moreover, this behaviour might play a role in the emergence and cohesiveness of cryptic species within E. virens. Although rare in small populations and at short timescales, copulations between males and asexual females support the hypothesis of hybrid origin for polyploidy.