The Timing of Copepod Diapause as an Evolutionarily Stable Strategy

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Abstract
Diaptomus sanguineus, a small freshwater copepod, avoids periods of intense fish predation by producing diapausing eggs. A computer simulation of the copepod''s life history was developed and used to compete populations that switched to diapause at different intervals of time before the onset of fish predation (the catastrophe). With no variation about the catastrophe date, the evolutionarily stable strategy (ESS) is one in which the switch to diapause comes exactly 1 generation before the catastrophe, as Taylor (1980) has shown analytically. With increasing variation about the catastrophe date, the ESS becomes one of switching to diapause at time intervals increasingly greater than 1 generation. Using field data on copepod mortality rates from 5 yr, the mean and variance of the catastrophe date were estimated. Using field and laboratory data, the copepod generation time and the timing of the switch to diapause were estimated. In close agreement with simulation-derived ESS, D. sanguineus starts making diapausing eggs 1.3 generations before the major onset of fish-induced mortality.