“Sex allocation theory for facultatively sexual organisms inhabiting seasonal environments: the importance of bet-hedging”

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Nina Gerber, Isobel Booksmythe, and Hanna Kokko (Aug 2018)

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Adaptive explanations for dormancy often invoke bet-hedging, where reduced mean fitness can be adaptive if it associates with reduced fitness variance. Sex allocation theory typically ignores variance effects and focuses on mean fitness. For many cyclical parthenogens, these themes become linked, as only sexually produced eggs undergo dormancy needed to survive harsh conditions. We ask how sex allocation and the timing of sex evolve when this constraint exists in the form of a trade-off between asexual reproduction and sexual production of dormant eggs—the former being crucial for within-season success, the latter for survival across seasons. We show that male production can be temporally separated from or co-occur with sex, depending on whether direct (time) or indirect (population density) cues of the season’s end are available, and whether population growth is density-dependent. Sex generally occurs late in the season, but is induced earlier in unpredictable environments. When only indirect cues are available, the temporal spread of sex, and with it the production of dormant stages, is even larger, and given sufficient mortality leads to endogenous population cycles in which frequent sex coincides with high densities. In all scenarios, algorithms maximizing geometric mean fitness have reduced fitness variance compared to a hypothetical non-bet-hedger, confirming that the timing of male production and sex in facultative seasonal settings can be bet-hedging traits.