Species and hybrid composition and genetic diversity of water frogs (Pelophylax esculentus complex) in western Ukrainian hemiclonal population systems

Abstract

Background. Two species of water frogs, Pelophylax ridibundus and Pelophylax lessonae, and their hybrid, Pelophylax kl. esculentus, are widespread in Ukraine. The purpose of this study was to investigate the population structure of various types of hemiclonal population systems (HPS) of water frogs formed due to the coexistence of frogs in the same territory. In Ukraine, a hybridization centre with the spread of triploid individuals of hybrid nature has been identified. Triploid hybrids are an intriguing research subject due to the diverse hypotheses about their origin and role in HPS. Outside the hybridization centre in Kharkiv Region, triploids are not commonly found. In our study, we describe the initial findings of triploid specimens in Lviv Region and analyze the genetic structure of the HPS where such individuals were detected. Methods. In total, 193 specimens of green frogs were collected between 2011 and 2015. Here we present population structure analysis which was conducted using two microsatellite loci, Rrid059A and RlCA1b5. A wide range of software programs were utilized for processing the genetic analysis data, including GenePop 4.7.5, Micro-Checker and NewHybrids 1.1. Results. Three types of hemiclonal population systems were identified: R-E type in Perekalky and Lake Pisochne, L-E type in Lake Luky, and R-E-L type in Nyzhankovychi, Velykyi Lyubin, Zhovtantsi and Cholgyni. Additionally, population systems with hybrids of mixed ploidy (diploids and triploids) were found in Perekalky, Velykyi Lyubin and Zhovtantsi. Conclusions. Genetic diversity analysis revealed variations in the number of alleles per population. P. ridibundus individuals exhibited higher genetic diversity compared to P. lessonae individuals, whereas hybrids showed intermediate genetic diversity. Further investigations of the localities where potential triploids were detected are necessary to assess the survival and reproductive potential of hybrid individuals and determine all types of hybrids and individuals of both marsh and pool frogs.