Cross-species testing of nuclear markers in Pelophylax water frogs in Greece and examination of their power to detect genetic admixture

Abstract

The genus Pelophylax has been considered a model organism for understanding hybridization. Despite being the most diverse within the Western Palearctic group of Pelophylax, the ridibundus/bedriagae lineage that includes six species, remains largely understudied, revealing many knowledge gaps in regards to their evolution and conservation. Using genetic data from populations among species inhabiting contact zones could prove vital in filling these gaps. We tested 17 microsatellite markers for cross-species amplification in mainland Pelophylax species distributed in southern Balkans and evaluated their power to successfully detect population/species structure. Importantly, we examined their potential for identifying hybrids and backcrosses between known hybridized species. We detected 12 highly polymorphic loci that cross-amplified all species that showed no significant Linkage Disequilibrium and were able to discriminate among species and between parental and hybrids. We suggest their future use in genetic studies for the genus Pelophylax in Greece, including the identification of contact zones.

Piecing the barcoding puzzle of Palearctic water frogs (Pelophylax) sheds light on amphibian biogeography and global invasions

“…The nuclear analyses conducted in parallel primarily aimed at distinguishing hybrid forms from their parental species, and most datasets are not combinable per design, for example, microsatellites (e.g., Dufresnes, Di Santo, et al., 2017; Papežík et al., 2021; Sagonas et al., 2020), allozymes (e.g., Hotz et al., 2013), and RAD‐sequencing (e.g., Doniol‐Valcroze et al., 2021; Dubey, Maddalena, et al., 2019; Dufresnes & Dubey, 2020). The only re‐usable nuclear markers are targeted gene sequences (e.g., Cuevas et al., 2022), but these also differ between geographic areas and species complexes, and each gene provides little phylogenetic resolution if not combined in multilocus analyses (e.g., Komaki et al., 2015).…”

“…Their widespread distribution warrants many paleographic candidate events of vicariance for the BPT, both in the western (Ehl et al., 2019) and the eastern (Dufresnes & Litvinchuk, 2022) regions of the Palearctic. In addition, the outcome of hybridization between taxa has been relatively well‐documented, both regarding hybridogenetic mechanisms (reviewed by Dufresnes & Mazepa, 2020) and the contact zones between several phylogeographic lineages (e.g., Dufresnes & Dubey, 2020; Hotz et al., 2013; Nagai et al., 2018; Papežík et al., 2021; Sagonas et al., 2020; Santucci et al., 1996), thus allowing to experiment the use of the LCPT for the first time.…”

“…Under calibration A, two of them (cf. ridibundus D/F vs. mented(Sofianidou, 1996), allozyme and microsatellite allele sharing characteristics of F2s and backcrosses (suggestive of genetic admixture) were suspected in a few individuals(Hotz et al, 2013;Papežík et al, 2021;Sagonas et al, 2020). Hybridization with or without restricted admixture is compatible with either calibration A (13.8 My), B (8.3 My) and C (8.5 My).…”

Proximate Composition, Predictive Analysis and Allometric Relationships, of the Edible Water Frog (Pelophylax epeiroticus) in Lake Pamvotida (Northwest Greece)

“…Alternations of morphological traits can be explained by the biological cycle of the frog and variation of abiotic and biotic parameters. Significant morphological variation reported across Pelophylax species, and particularly between mainland P. epeiroticus, P. ridibundus and P. kurtmuelleri species, does not always allow a reliable morphological discrimination of the different species in their overlapping regions [8]. According to [59], there is a strong sexual size dimorphism in P. epeiroticus, with females growing larger than males, related to differences in the age at which maturity is reached.…”

“…The species is also present in Albania; however, the main part of its range is within Greece [3]. The western Palaearctic water frog of the genus Pelophylax includes several distinct species and has been investigated in several phylogenetic, morphological, and ecological studies [4][5][6][7][8][9][10]. The populations of P. epeiroticus (Epirus Water Frog) are suspected to be decreasing due to ongoing decline in the extent and quality of its habitat, thus improved management measures are required for the protected areas and Natura 2000 sites where the species appears [3].…”