Differential morphology and jumping performance of newly metamorphosed frogs of the hybridogenetic Rana esculenta complex.

Abstract

Closely related clonal and sexual populations may coexist in spite of the theorized lower potential for the evolution of clonal genotypes. Water frogs of the Rana esculenta complex have hemiclonal inheritance but most populations coexist with one of the recombinant parental species. We examine whether hemiclonal lineages may counterbalance their limitations of genetic variability by the adoption of one or more non-exclusive mechanisms: the general-purpose genotype or the frozen niche-variation model. Three coexisting hemiclones of the hybrid R. esculenta (GUT1, GUT2, GUT3) and both parental species (syntopic R. lessonae and allopatric R. ridibunda) were raised at two larval densities to examine morphological traits affecting jumping performance at the time of metamorphosis and size-independent jumping ability tested at three temperatures. Hind leg length and body mass at metamorphosis, traits that explain most of the variance in jumping performance, differed across hemiclones of R. esculenta. Metamorphs of hemiclone GUT1 had the longest hindlimbs and were bigger than metamorphs of the other hemiclones at low larval density but not at high density. Size adjusted jumping performance exhibited a significant genotype by larval density interaction. Metamorphs of GUT1 showed maximal jumping performance when raised at low larval density but at high density metamorphs of GUT2 were the best jumpers. In addition, within particular traits, differences were found between hemiclones across densities. These results appear to be consistent with both frozen niche-variation model and the general-purpose genotype model. Comparison with parental species revealed syntopic R. lessonae was smaller than hemiclones at metamorphosis but conversely exhibited better size-adjusted jumping performance when raised at low larval density. Temperature affected size-adjusted jumping performance only for frogs raised at low larval density but not for those raised at high larval densities. There was no significant temperature by hemiclone interaction.