Like many organisms, individuals in the freshwater ostracod species Eucypris virens can have either obligate sexual or asexual reproductive modes. Both types of individual routinely co-occur, including in the same temporary freshwater pond (their natural habitat in which they undergo seasonal diapause). In addition to the well-known two-fold cost of sex, life-history experiments reveal additional costs of sex in this system based on hatching success, development time and survivorship. This begs the question of how sexually reproducing individuals are able to co-exist with their asexual counterparts in spite of such overwhelming costs. Environmental uncertainty in the form “false dawn” inundations (where the first hydration is ephemeral and causes loss of early hatching individuals) may provide an advantage to the sexual subpopulation, which exhibits greater variation in hatching times following inundation. I study the potential role of environmental uncertainty in this system using life-history data analysis, climate data and matrix projection models.
Results/Conclusions
The calculated growth rate (deterministic and stochastic lambda values) is significantly lower in sexual subpopulations (even ignoring the two-fold cost of sex). Climate data reveal that “false dawn” inundations are common. Using matrix projection modeling with and without environmental uncertainty I demonstrate that this phenomenon can restore competitive balance to the system, allowing coexistence of sexual and asexual individuals in spite of considerable (> two-fold) costs of sex. This provides support for the role of environmental uncertainty in helping to explain the maintenance of sex.