Predator-induced life history changes in amphibians: egg predation induces hatching

Authors

  • Douglas P. Chivers,

  • Joseph M. Kiesecker,

  • Adolfo Marco,

  • Jill Devito,

  • Michael T. Anderson,

  • Andrew R. Blaustein


D. P. Chivers, Dept of Biology, Univ. of Saskatchewan, 112 Science Place, Saskatoon, SK, Canada S7N 5E2 (doug.chivers@usask.ca). – J. M. Kiesecker, Dept of Biology, Pennsylvania State Univ., 208 Mueller Laboratory, University Park, PA, 16802, USA. – A. Marco, Estación Biológica de Donana, CSIS, Apartado 1056, E-41080 Sevilla, Spain. – J. Devito, Dept of Biology, Box 19498, Univ. of Texas, Arlington, TX 76019, USA. – M. T. Anderson, Biological Research Laboratories, 130 College Place, Syracuse Univ., Syracuse, NY 13244, USA. – A. R. Blaustein, Dept of Zoology, Oregon State Univ., 3029 Cordley Hall, Corvallis, OR 97331, USA.

Abstract

The timing of transitions between life history stages should be affected by factors that influence survival and growth of organisms in adjacent life history stages. In a series of laboratory experiments, we examined the influence of predation risk as a cue to trigger a life history switch in amphibians. In the Oregon Cascade Mountains, some populations of Pacific treefrogs (Hyla regilla) and Cascades frogs (Ranacascadae) are under intense egg predation by predatory leeches (families Glossiphonidae and Erpobdellidae). We document that both treefrogs and Cascades frogs show plasticity in hatching characteristics in response to the threat of egg predation. Pacific treefrogs hatch sooner and at an earlier developmental stage when either predatory leeches or non-predatory earthworms are allowed direct contact with the developing egg mass. The same response is elicited even without direct contact. Chemical cues of predatory leeches and chemicals released from injured 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 early hatching response. Hatching early in response to egg predators may reduce predation. Plasticity of hatching characteristics has rarely been examined. However, we suspect that it may be common, particularly in populations or species that experience high variability in predation pressure between years.

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