Evol Ecol Res 3: 107-116 (2001) Full PDF if your library subscribes.
Hybridization in leopard frogs (Rana pipiens complex): Variation in interspecific hybrid larval fitness components along a natural contact zone
Matthew J. Parris*
Division of Biological Sciences, University of Missouri, Columbia, MO 65211-7400, USA
Address all correspondence to Matthew J. Parris, Department of Biology, University of Memphis, Memphis, TN 38152, USA.
Although hybrid zones between North American leopard frog species pairs (Rana pipiens complex) are usually narrow, the contact zone between R. blairi and R. sphenocephala varies from sharp parapatry to relatively broad sympatry. I compared fitness components using larval life-history traits for R. blairi, R. sphenocephala and F1 hybrid genotypes from Texas populations where the hybrid zone is sharply parapatric, and genotypes from Missouri populations where hybridization occurs in broadly sympatric areas. Texas F1 hybrids had significantly reduced survival and metamorphosis relative to Missouri F1 hybrids. Texas hybrids also demonstrated reduced performance in terms of survival, body mass and metamorphosis when reared in experimental populations with R. sphenocephala or both parental species, but not R. blairi alone. Larval fitness estimates as measured by survival, body mass at metamorphosis, proportion of survivors metamorphosing and length of larval period for Missouri F1 hybrids were equal or higher than those of their parental genotypes in all mixtures. These patterns suggest selection may be dependent on the larval rearing environment and strongest against hybrid genotypes in the southern region of the hybrid zone (Texas), but not directional against F1 hybrids in the northern region (Missouri). Thus, fitness data from a single location within hybrid zones may lead to inaccurate conclusions concerning the evolutionary potential of hybridization.
Keywords: amphibian larvae, endogenous selection, exogenous selection, fitness, geographic variation, hybridization, Rana.
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