Hitting and Unhitting the Pause Button: Variable Hatching Patterns of Annual Killifish Embryos Over a Wetland Wet–Dry Cycle

Abstract

Hatching dynamics is key to population structure of annual fishes in temporary wetlands. Given the risk of false starts due to unpredictable hydroperiods, annual fish may employ risk-spreading strategies in their hatching patterns consistent with bet hedging (such as the partial hatching of their egg bank and variable number of hatching cues) after being exposed to floods. However, the extent to which annual fish resort to bet hedging (as well as their potential drivers) over a wet–dry cycle is poorly understood. We assessed the hatching patterns of a South American killifish (Matilebias cyaneus; Cyprinodontiformes: Rivulidae) collected at different hydrological phases of a temporary wetland to test for variation in bet hedging over a wet–dry cycle. We incubated wild eggs of M. cyaneus obtained from male–female pairings separately reared in tanks originating in the ‘early-wet’, ‘drying’ and ‘late-wet’ phases of a temporary wetland and examined hatching patterns across a sequence of hydration trials under common-garden conditions. We found variation in (i) the number of hatched and unhatched eggs and (ii) the number of hatched eggs across hydration trials among clutches from each phase (while controlling for parentage). Our results show that M. cyaneus variably commit to bet-hedging hatching strategies over a wet–dry cycle, and suggest that the environmental conditions at specific periods of the year and the parental age at which eggs are produced drive annual fish hatching patterns.