Abstract

We examined the functional prediction of covariation between relative hind limb morphology and jumping performance for newly metamorphosed frogs from the hybridogenetic Rana esculenta complex. For the two parental species, R. lessonae and R. ridibunda, and three coexisting hybrid hemiclones (GUT1, GUT2, GUT3), we varied larval densities to test the relationship of morphology to performance at both the intraspecific and interspecific levels. Across all genotypes, frogs raised at low density were larger and jumped farther than those raised at high densities. Size-independent maximum jumping performance was repeatable for all hemiclones and species. Comparisons across densities indicated that covariation between morphology and performance matched the biomechanical prediction except for R. ridibunda. Rana ridibunda frogs raised at low larval density jumped relatively farther than those raised at high larval density but, in spite of differing growth environments, did not show differences in relative length of the hind limb. At the intraspecific level, significant performance gradients for hind limb length were found in the hemiclones GUT1 and GUT3 and in R. ridibunda at low larval density. Relative jumping performance of GUT2 and R. lessonae at low larval density and all genotypes at high larval density were not explained by the partial effect of any morphological trait. At the interspecific-interclonal level the biomechanical prediction was confirmed only at the high larval density. These results reveal a lack of congruence of the morphofunctional relationships both at different larval growth conditions within populations and also at intra- and interpecific levels.