Differential Predation on Experimental Populations of Parental and Hybrid Leopard Frog (Rana blairi and Rana sphenocephala) Larvae

Abstract

We estimated fitness components for parental and F1 hybrid genotypes between Rana blairi and Rana sphenocephala by measuring larval performance in wading pools. The effect of three predators (papershell crayfish, Orconectes immunis; eastern newt, Notophthalmus viridescens; green sunfish, Lepomis cyanellus) on larval growth and survival was used to assess differential performance of genotypes in a predatory aquatic environment Larval genotypes were obtained from artificial crosses between adults col- lected from a natural population sympatric with these predators in central Missouri. After hatching, larvae were reared in single-genotype groups in outdoor experimental wading pools for 14 days. A higher propor- tion of R. sphenocephala survived than did R. blairi, and F1 hybrids did not differ significantly in survival from either parental genotype. Fish predation was severe for all genotypes and reduced survival to a greater degree than other predators. Body mass did not differ significantly among genotypes or predator treatments. Relatively high survival and growth for F1 hybrid larvae suggests natural hybridization between R. blairi and R. sphenocephala can produce novel and relatively fit hybrid genotypes that can cope with predators just as successfully as parental genotypes. Furthermore, low survival of all genotypes in experimental pools containing fish is consistent with the observation that leopard frog larvae do not normally coexist with fish. Natural hybridization between closely related taxa may be an important evolutionary process, leading to novel diversification and adaptive evolution (Arnold, 1997; Arnold and Emms, 1998; Parris, 1999), or a process with evolution-