The effects of crayfish predation on phenotypic and life-history variation in fathead minnows

Ecological theory predicts that the timing of the transition between life-history stages should vary with the costs and benefits associated with each stage. For example, the timing of hatching or metamorphosis may vary with the predation risk in each stage. Predator-induced changes in hatching time are well documented in some taxa but have not been reported in fishes. We provide the first empirical evidence that a species of fish can alter its hatching time in response to predator cues. We showed that fathead minnows, Pimephales promelas Rafinesque, 1820, exposed to chemical cues from virile crayfish, Orconectes virilis (Hagen, 1870), foraging on minnow embryos hatch sooner than those exposed to a blank control. Moreover, in the presence of cues from virile crayfish feeding on minnow embryos, the hatchlings exhibited a change in morphology because they had significantly shorter total lengths. There was a significant positive correlation between hatchling size and length of the developmental period, except in the high predation threat treatment. By hatching earlier, the fathead minnows escaped predation from virile crayfish that were actively foraging on fathead minnow eggs. Hatching at a smaller size, however, may make the fry more vulnerable to other predators.