RIPLEY, B. J.*; BOHONAK, A. J.; SIMOVICH, M. A. ; Univ. San Diego; San Diego State Univ.; Univ. San Diego: Magnitude of environmental variation and mechanisms of hatching in ephemeral pool crustaceans

Crustacean species persist in ephemeral wetlands because they “weather” the dry phases as resistant cysts. Cyst hatching is risky in these environments because the pool may dry before reproduction is completed. One proposed mechanism for spreading this risk over multiple pool filling events is a bet-hedging strategy where 1) the proportion of cysts that hatch increases with the proportion of successful pool fillings; 2) all females lay cysts that hatch at different times; and 3) some cysts are somehow “programmed” not to hatch at the first filling even if environmental conditions are appropriate. We examined the available data for fairy shrimp (Anostraca:Crustacea), and found a significant positive correlation between hatching fraction and pool hydroperiod, which supports the first strategy. Evidence for strategies 2 and 3 has also been found in many fairy shrimp species. The available data suggest that a combination of factors (such as light, temperature, or change in osmolarity) are required for diapause emergence, although 100% hatching success is not seen under any circumstances. Underlying mechanisms that lead to incomplete hatch may be intrinsic to the embryo (genetic) or associated with maternal influences (e.g., cyst biochemical composition or wall structure). We review alternative hypotheses relevant to the evolution of hatching mechanisms and weigh the evidence for each. We suggest that a quantitative, predictive framework for studying bet-hedging in fairy shrimp is possible only if the type and magnitude of environmental variation is quantified.