Predator-induced life history changes in amphibians: egg predation induceshatching

The timing of transitions between life history stages should be affected by factors that influence survival and growth of organisms in adjacent life h istory stages. In a series of laboratory experiments, we examined the influ ence of predation risk as a cue to trigger a life history switch in amphibi ans. In the Oregon Cascade Mountains, some populations of Pacific treefrogs (Hyla regilla) and Cascades frogs (Rana cascadae) are under intense egg pr edation by predatory leeches (families Glossiphonidae and Erpobdellidae). W e document that both treefrogs and Cascades frogs show plasticity in hatchi ng characteristics in response to the threat of egg predation. Pacific tree frogs hatch sooner and at an earlier developmental stage when either predat ory leeches or non-predatory earthworms are allowed direct contact with the developing egg mass. The same response is elicited even without direct con tact. Chemical cues of predatory leeches and chemicals released from injure d eggs appear to elicit the same early hatching response in treefrogs. For Cascades Frogs, cues of leeches, but not those of injured eggs, elicit an e arly hatching response. Hatching early in response to egg predators may red uce predation. Plasticity of hatching characteristics has rarely been exami ned. However, we suspect that it may be common, particularly in populations or species that experience high variability in predation pressure between years.