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 “pure” populations of P. ridibundus is 0.667 against those 0.042 of P. lessonae. The RE-type populations are the most common among mixed populations (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.

本研究针对东欧平原南部的904份样本，分析了欧洲池蛙复合群（Pelophylax esculentus complex）的种群结构地理特征及其半克隆繁殖模式。其中，欧洲池蛙（P. ridibundus）的纯种群占比为0.667，莱桑池蛙（P. lessonae）的纯种群占比仅为0.042。混合种群中以RE型种群最为常见，占比达0.153；双亲物种与克隆型食用池蛙（P. kl. esculentus，REL型）的种群、以及莱桑池蛙与克隆型食用池蛙（LE型）的种群占比分别为0.072和0.046。全杂交种群（E型）在研究区域内占比稀少，仅为0.017。

在乌克兰中部、北部与西部的种群中，杂交个体在配子发生过程中会排除莱桑池蛙的基因组；而在第聂伯河下游及多瑙河下游流域的种群中，杂交个体则会排除欧洲池蛙的基因组。乌克兰东部种群的杂交个体通常产生二倍体配子，或携带欧洲池蛙基因组的单倍体配子，较少产生仅携带莱桑池蛙染色体组的配子，更罕见多种配子类型的混合组合。

杂交群落中欧洲池蛙占据主导地位，且杂交个体内莱桑池蛙基因组被排除，这一过程必然会导致杂交种群向"纯"R型种群转化。该现象使得与欧洲池蛙的杂交成为莱桑池蛙种群萎缩的驱动因素。这一趋势在森林草原带尤为显著：此处杂交活动最为剧烈，杂交个体内莱桑池蛙基因组被排除，且以欧洲池蛙数量占优的不稳定种群占据主导地位。