Bet hedging in stochastic habitats: an approach through large branchiopods in a temporary wetland.

Organisms evolve to maintain fitness across generations, while short-term fitness in stochastic habitats such as temporary wetlands may be highly varied. As typical temporary wetland inhabitants, large branchiopods rely on bet hedging hatching that helps them survive throughout generations. An optimal hatching rate is predicted to be approximate to the successful reproduction probability (SRP). We tested the difference between hatching rate and SRP of large branchiopods Branchinella kugenumaensis and Eulimnadia braueriana in a temporary wetland in Taiwan, through field surveys and climatic records to evaluate their SRP. Comparisons were performed under two proposed scenarios, where a population's hatching was bet hedged for a hydroperiod or for a wet season (with several hydroperiods), respectively. Population size fluctuations were simulated for these two scenarios under assumed egg mortalities and reproductive replenishments. Results showed that the hatching rates only fitted to SRP for E. braueriana under the scenario of bet hedging on a wet season, not for B. kugenumaensis, nor for both species under the scenario of bet hedging on a hydroperiod. Bet hedging on a wet season would have a smaller range of population size fluctuation and a lower rate of population size decrease. This implies that large branchiopods adopt a conservative hatching strategy, lowering the hatching fraction in each hydroperiod to reduce long-term egg bank size fluctuation. Bet hedging strategies could occur during other life cycle stages, coexist with other life history strategies, and lead to the diversified hatching fraction distribution rather than a single, optimal fraction throughout hydroperiods.