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 measu ring larval performance in artificial ponds and laboratory containers. Effe ct 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 mass es of Rana blairi and R .sphenocephala. Artificial crosses with adult anima ls produced larvae of one parental and three hp brid genotypes for laborato ry performance assays. Experimental pond drying sig significantly reduced s urvival for both parental species. Rana blairi had higher survival than R. sphenocephala across all treatments. Both species reduced larval period len gths when exposed to a drying environment relative to constant water levels . The laboratory experiment revealed Backcross, hybrid larvae exhibited lon ger larval period lengths than parental R sphenocephala and certain F-1 hyb rid genotypes in the drying environment. Proportion of survivors metamorpho sing was greatest for the F-1 hybrid genotype SE and lowest for the Backcro ss, hybrid genotype, Consequently, advanced-generation hybrid genotypes (i, e., Backcross(2)) did not perform web in desiccating environments. Direct m easurements of important fitness components of parental and hybrid genotype s are critical for determining the evolutionary potential of natural hybrid ization.