Experimental Analysis of Hybridization in Leopard Frogs (Anura: Ranidae): Larval Performance in Desiccating Environments
Relative fitness of parental and hybrid Leopard Frogs was examined by measuring larval performance in artificial ponds and laboratory containers. Effect of a variable hydroperiod on growth, development, and survival was used to assess larval responses to a desiccating aquatic environment. Larvae for the artificial pond experiment were obtained from field-collected egg masses of Rana blairi and R. sphenocephala. Artificial crosses with adult animals produced larvae of one parental and three hybrid genotypes for laboratory performance assays. Experimental pond drying significantly reduced survival for both parental species. Rana blairi had higher survival than R. sphenocephala across all treatments. Both species reduced larval period lengths when exposed to a drying environment relative to constant water levels. The laboratory experiment revealed Backcross2 hybrid larvae exhibited longer larval period lengths than parental R. sphenocephala and certain F1 hybrid genotypes in the drying environment. Proportion of survivors metamorphosing was greatest for the F1 hybrid genotype SB and lowest for the Backcross2 hybrid genotype. Consequently, advanced-generation hybrid genotypes (i.e., Backcross2) did not perform well in desiccating environments. Direct measurements of important fitness components of parental and hybrid genotypes are critical for determining the evolutionary potential of natural hybridization.Abstract
(A) Proportion of total survivors, and (B) body mass at metamorphosis (mg), for Rana blairi and R. sphenocephala reared at a density of 60 larvae per artificial pond under two hydroperiods. Values plotted are least-square means (corrected for differential survival in B) from three replicate ponds ± 1 SE. Comparisons with different letters indicate significant species differences using Scheffé's multiple range tests
Larval period length (days) for Rana blairi and R. sphenocephala reared at a density of 60 larvae per artificial pond under two hydroperiods. Values plotted are least-square means (corrected for differential survival) from three replicate ponds ± 1 SE. Comparisons with different letters indicate significant species differences using Scheffé's multiple range tests
(A) Larval period length (days), and (B) proportion of survivors metamorphosing for four leopard frog genotypes (SS, BS, SB, B2) reared in laboratory containers. Values plotted are least-square means from 9–10 replicate containers ± 1 SE in (A) and genotype × hydroperiod treatment means in (B). Comparisons with different letters indicate significant genotype differences using Scheffé's multiple range tests