Local variation in embryo development rate in annual fish.

Extreme asynchrony in embryo development, a typical feature of annual killifish living in temporary pools, represents a bet-hedging strategy to cope with unpredictable rainfall. African annual killifish are distributed across a large precipitation gradient, raising the potential for local adaptation in the degree of developmental asynchrony (e.g. higher in arid areas, lower in humid areas). Eight populations of two sister species, Nothobranchius furzeri and Nothobranchius kadleci, from sites along the rainfall gradient were tested and compared for asynchrony and duration of embryo development. Degree of asynchrony and mean duration of embryo development did not differ across the examined range. Despite generally high developmental variability, fish from more arid regions (where rain is more erratic) produced a significantly higher proportion of short-developing embryos. Comparable developmental asynchrony, regardless of precipitation level, suggests that all populations tested need to cope with some level of rainfall stochasticity. By producing more short-developing embryos, however, fish in more arid areas with relatively more erratic rains are better adapted to very short pool durations and are more likely to produce multiple offspring generations within a single rainy season.