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 <em>Pelophylax esculentus</em> complex of 904 samples within southern East European Plain were analyzed. The proportion of “pure” populations of <em>P. ridibundus</em> is 0.667 against those 0.042 of <em>P. lessonae</em>. The RE-type populations are the most common among mixed populations (0.153). The colonies of the two parental species and <em>P.</em> kl. <em>esculentus </em>(REL-type), as well as those of <em>P. lessonae</em> with <em>P.</em> kl. <em>esculentus </em>(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 <em>P. lessonae</em> genome is eliminated during gametogenesis within hybrids while in the Lower Dnieper and Lower Danube drainages, genome of <em>P. ridibundus</em> is eliminated. In the Eastern Ukraine populations, hybrids usually produce diploid gametes or haploid gametes with the <em>P. ridibundus</em> genome, less often with the chromosome set of <em>P. lessonae</em> only, and even more rarely a mixture of different types of gametes. The predominance of <em>P. ridibundus</em> in hybrid communities and the elimination of the <em>P. lessonae</em> genome in hybrids inevitably leads to the transformation of hybrid populations into “pure” R-type populations. This circumstance makes hybridization with <em>P. ridibundus</em> a factor in the shrinking of <em>P. lessonae</em> populations. That trend is especially expressed in the Forest steppe zone, where hybridization proceeds most intensively, the <em>P. lessonae</em> genome is eliminated in hybrids, and unstable populations with a numerical superiority of <em>P. ridibundus</em> predominate.