Geographic peculiarities of structure and hemicloning reproduction of Pelophylax esculentus water frog complex (Anura, Ranidae) populations in the East European Plain within Ukraine

Geographic peculiarities of population structure and hemicloning reproduction of the water frog Pelophylax esculentus complex of 904 samples within southern East European Plain were analyzed. The proportion of populations of P. ridibundus is 0.667 against those 0.042 of P. lessonae. The RE-type populations are the most common among mixed ones (0.153). The colonies of the two parental species and P. kl. esculentus (REL-type), as well as those of P. lessonae with P. kl. esculentus (LE-type), have the frequencies 0.072 and 0.046, respectively. All-hybrid populations (E-type) are not numerous across the region (0.017). In the populations of Central, Northern and Western Ukraine, the P. lessonae genome is eliminated during gametogenesis within hybrids while in the Lower Dnieper and Lower Danube drainages, genome of P. ridibundus is eliminated. In the Eastern Ukraine populations, hybrids usually produce diploid gametes or haploid gametes with the P. ridibundus genome, less often with the chromosome set of P. lessonae only, and even more rarely a mixture of different types of gametes. The predominance of P. ridibundus in hybrid communities and the elimination of the P. lessonae genome in hybrids inevitably leads to the transformation of hybrid populations into “pure” R-type populations. This circumstance makes hybridization with P. ridibundus a factor in the shrinking of P. lessonae populations. That trend is especially expressed in the Forest steppe zone, where hybridization proceeds most intensively, the P. lessonae genome is eliminated in hybrids, and unstable populations with a numerical superiority of P. ridibundus predominate.