Distribution and Origin of Two Forms of the Marsh Frog Pelophylax ridibundus Complex (Anura, Ranidae) from Kamchatka Based on Mitochondrial and Nuclear DNA Data

The formation of the first populations of the marsh frog (the Pelophylax ridibundus complex) near Petropavlovsk-Kamchatsky and in the Paratunka River valley must have been the result of human introduction in the late 1980s. At present, more than 20 localities of this species are recorded in Kamchatka. For a more precise definition of the taxonomic status of P. ridibundus sensu lato, samples from five populations (altogether, 30 individuals) from southeastern and central Kamchatka are analyzed using molecular methods. In all frogs, a mitochondrial DNA type specific for the “eastern” form (=the Anatolian P. cf. bedriagae), but not for the “western” form (=the Central European P. ridibundus), is revealed. However, the results of nuclear DNA analysis of marsh frogs from Kamchatka reveal alleles specific for both of the forms, “eastern” and “western,” with a frequency ratio of about 2 : 1. The results of sequencing the mitochondrial ND2 gene and nuclear SAI-1 gene suggest that the “ancestor” individuals might have been introduced into Kamchatka from the Volga–Don interfluve or Ciscaucasia. The absence of both haplotype and nucleotide diversity in the samples studied suggests a single successful introduction that involved a low number of frogs stemming from a single locality.