Population composition and genetic variation of water frogs (Anura : Ranidae) from Yugoslavia
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Species of the Rana kl. esculenta complex from twenty-one localities of the North-Western part of the Balkan Peninsula (Yugoslavia and Macedonia) were analyzed by electophoretic, morphometric and cytogenetic methods. The results of this research revealed that species that belong to the R. hi. esculenta complex from localities in Northern Yugoslavia form a ridibunda/esculenta/lessonae (R-E-L) population system of diploid forms of two parental species and predominantly female hybrids. Pure R ridibunda populations exist south of the Sava and Danube Rivers. The unequal sex ratio observed in water frog population systems suggests, according to Haldane's rule, that the heterogametic sex suffers the effects of hybridization. Electrophoretic analysis shows that some introgression of ridibunda alleles into R. lessonae, as well as lessonae into R. ridibunda has taken place. The occurrence of recombinations, and cytogenetic characteristics of the chromosome complements, does not support pure hybridogenesis as a general mode of reproduction in the hybrid form R. kl. esculenta from the examined localities.