Contrasting genetic diversity and the level of clonality of parental genomes in a water frog population system with the prevalence of Pelophylax esculentus hybrids

Abstract Pelophylax esculentus (genotype LR), an interspecific hybrid of P. ridibundus (genotype RR) and P. lessonae (genotype LL), is one of the most studied examples of hemiclonal hybridogenic vertebrates. In most populations, hybrids produce clonal gametes of one parental species and backcross with the other parental species, forming a new generation of hybrids. In this study, we focused on the population system of water frogs in the Siverskyi Donets river basin (eastern Ukraine) with the aim to determine the genetic diversity of parental genomes and clarify how such a system is maintained in nature. Of the 55 frogs analyzed, only one individual was P. ridibundus , 48 belonged to diploid LR and five to triploid LRR hybrids. Using 16 microsatellite loci, we found significantly lower genetic diversity and significantly higher clonality in the L-genome of hybrids compared to the R-genome. This contrasting diversity might be attributed to the absence of P. lessonae in the studied region and the clonal inheritance of the L-genome. Our population-genetic results are partially inconsistent with previous studies focusing on hybrid gametogenesis in the Siverskyi Donets river basin, according to which hybrids form both clonal R and L gametes. We hypothesize that discrepancies between the type of clonally formed gametes and the genotypic composition of the studied population may be due to the selective mortality of some genotypes during larval development and metamorphosis. Selective mortality thus may play an important role in the dynamics of the hybridogenetic systems in eastern Ukraine.