ASYMMETRIC COMPETITION IN MIXED POPULATIONS OF TADPOLES OF THE HYBRIDOGENETIC RANA-ESCULENTA COMPLEX

Hybridogenetic Rana esculenta tadpoles display tolerance to extreme en vironmental conditions and fit criteria of the ''general-purpose'' gen otype. A trade-off between generality and competitive ability is assum ed to occur in asexual species, but the evidence remains unclear. The purpose of my experiment was to test the competitive ability of hemicl onal hybrid Rana esculenta tadpoles relative to the parental species R ana lessonae. Mixed and single genotype populations of R. esculenta an d R. lessonae tadpoles were reared at three densities in artificial po nds. Survival of R. esculenta was higher than for R. lessonae tadpoles , but did not differ among densities. Body size at metamorphosis was t he same between genotypes, but decreased with increasing density. Larv al period was not affected by density, but R. esculenta tended to meta morphose earlier than R. lessonae. Percentage of individuals metamorph osing was higher for R. esculenta at both medium and high densities, b ut the same as R. lessonae at the low density. The difference in survi val, body size, and larval period between tadpoles reared in single an d mixed genotype populations was unaffected by genotype or density. Th e difference in the percentage of metamorphs, however, was strongly af fected. The percentage of hybrids metamorphosing was 9% above the resp onses of single genotype populations at the highest density. Conversel y, the percentage of R. lessonae metamorphosing was 12% below the resp onses of single genotype populations at the same density. Hybrid succe ss in this experiment further supports the criterion of a ''general-pu rpose'' genotype without assumptions of reduced competitive ability.