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.

本研究针对东欧平原南部的904份样本，分析了食用侧褶蛙（*Pelophylax esculentus*）复合群的种群结构与半克隆生殖的地理特征。沼侧褶蛙（*P. ridibundus*）的纯种种群占比为0.667，莱桑侧褶蛙（*P. lessonae*）的纯种种群占比仅为0.042。混合种群中以RE型种群最为常见，占比达0.153。兼具两种亲本物种与半克隆食用侧褶蛙的REL型种群，以及仅含莱桑侧褶蛙与半克隆食用侧褶蛙的LE型种群，其占比分别为0.072与0.046。全杂交种群（E型）在该区域内分布稀少，占比仅为0.017。
在乌克兰中部、北部及西部的种群中，杂交个体在配子发生过程中会淘汰莱桑侧褶蛙的基因组；而在第聂伯河下游与多瑙河下游流域的种群中，被淘汰的则为沼侧褶蛙的基因组。乌克兰东部种群内的杂交个体通常产生二倍体配子，或携带沼侧褶蛙基因组的单倍体配子；仅少数个体产生仅携带莱桑侧褶蛙染色体组的配子，极少数个体还会产生多种类型配子的混合体。
杂交群落中沼侧褶蛙占据优势，且杂交个体普遍淘汰莱桑侧褶蛙的基因组，这一过程不可避免地会推动杂交种群向纯R型种群转变。该现象使得与沼侧褶蛙的杂交成为莱桑侧褶蛙种群萎缩的关键诱因，这一趋势在森林草原带尤为显著：此处杂交活动最为剧烈，杂交个体可淘汰莱桑侧褶蛙的基因组，且以沼侧褶蛙数量占优的不稳定种群占据主导地位。