Semlitsch, R. D. 1993. Effects of different predators on the survival and development of tadpoles from the hybridogenetic Rana esculenta complex. - Oikos 67: 4-46.

I studied the effects of predation on two genotypes of tadpoles from the hybridogenetic Rana lessonae-Rana esculenta complex. Tadpoles were reared at two larval densities in artificial ponds with fish, newts, dragonfly larvae, and in a control with no predators. Survival was significantly reduced by the presence of predators. but was not differentially affected by larval density. Only 0.33% of the tadpoles survived with fish, 48.9% with newts, and 7.8% with odonates. Survival was highest (93.4%) in control ponds. Survival in ponds with fish newts, and control ponds was not affected by genotype, however, in ponds with odonates the survival of R. esculenta was higher than that of R. lessonae. The higher survival of R. esculenta appeared to be correlated with lower activity of tadpoles. The percentage of survivors that metamorphosed was significantly affected by larval density, but not by predators or genotype of tadpole. Of the surviving tadpoles, 90.6% reared at high larval density and 96.4% reared at the low density metamorphosed. Metamorphs emerged larger in ponds with more intense predation and at low larval density. Rana esculenta tadpoles emerged sooner than those of R. lessonae. Rana esculenta hybrid tadpoles outperformed the parental species R. lessonae in days to metamorphosis. Results from my experiment suggest that the hybrid R. esculenta is equally or more successful than the parental species R. lessonae when reared with some aquatic predators. Differential activity of tadpoles is suggested as a possible mechanism accounting for the success of the hybrid

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Peter Beerli, Dept. of Genetics, University of Washington, Seattle 98195,