We examined whether embryos of the green frog (Rana clamitans) would adaptively alter hatching times in the presence of both egg predators (the crayfish Procambarus nigrocinctus) and tadpole predators (the dragon nymph Anax junius). Under laboratory conditions, we exposed eggs with developing embryos to four experimental treatments that varied in the type of caged predator: egg predator only, tadpole predator only, both predators together, or no predator. As predicted, the presence of an egg predator caused a significant reduction in time to hatching. However, contrary to our prediction, eggs also hatched sooner in the presence of a tadpole predator. Moreover, there was no significant interaction between the effects of the two predators and thus no evidence that R. clamitans embryos can distinguish between predator types. We also found significantly lower hatching success in the presence of an egg predator, despite the fact that the predator did not have direct contact with the eggs. These results suggest adaptive early and delayed hatching do not co-occur in this species with this particular predator regime.
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Vol. 65 • No. 2