New insights on patterns of genetic admixture and phylogeographic history in Iberian high mountain populations of midwife toads

Abstract

Multiple Quaternary glacial refugia in the Iberian Peninsula, commonly known as “refugia within refugia”, allowed diverging populations to come into contact and admix, potentially boosting substantial mito-nuclear discordances. In this study, we employ a comprehensive set of mitochondrial and nuclear markers to shed light onto the drivers of geographical differentiation in Iberian high mountain populations of the midwife toads Alytes obstetricans and A. almogavarii from the Pyrenees, Picos de Europa and Guadarrama Mountains. In the three analysed mountain regions, we detected evidence of extensive mito-nuclear discordances and/or admixture between taxa. Clustering analyses identified three major divergent lineages in the Pyrenees (corresponding to the eastern, central and central-western Pyrenees), which possibly recurrently expanded and admixed during the succession of glacial-interglacial periods that characterised the Late Pleistocene, and that currently follow a ring-shaped diversification pattern. On the other hand, populations from the Picos de Europa mountains (NW Iberian Peninsula) showed a mitochondrial affinity to central-western Pyrenean populations and a nuclear affinity to populations from the central Iberian Peninsula, suggesting a likely admixed origin for Picos de Europa populations. Finally, populations from the Guadarrama Mountain Range (central Iberian Peninsula) were depleted of genetic diversity, possibly as a consequence of a recent epidemic of chytridiomycosis. This work highlights the complex evolutionary history that shaped the current genetic composition of high mountain populations, and underscores the importance of using a multilocus approach to better infer the dynamics of population divergence.

Increasing the evolutionary potential of threatened species - genetic and genomic insights from the common midwife toad (Alytes obstetricans) at its range limits

“…Accordingly, genetic differentiation and genetic diversity is relatively low in this part of the species range when compared with the remainder of its range (e.g. in southern and western Europe through France, Spain and Portugal, Goncalves et al 2015, Lucati et al 2022, Ambu et al 2023. The low genetic diversity in these peripheral range populations of A. obstetricans seemingly represent signals of gradual and accumulated genetic erosion due to a combination of range expansions from glacial refugia, incorporating founder effects, population bottlenecks and lack of intermixing with populations with high genetic diversity, a common pattern evident in other European amphibian species Perrin, 2015, Bernabò et al 2022).…”

Alien amphibian introductions via the plant trade: a breeding population of the Catalonian midwife toad (Alytes almogavarii) in Central Spain

“…We used primers AlytesND4_196F -AlytesND4_814R (Vliegenthart et al, 2023) to amplify a fragment of about 600 base pairs (bp) of the target gene (methods as in Vliegenthart et al, 2023), which was then sequenced in the forward and reverse directions at Macrogen (Madrid, Spain). Sequences were edited using MEGA X (Kumar et al, 2018), manually aligned in Seaview 5 (Gouy et al, 2021), and compared to the Alytes ND4 sequences available in GenBank (originating from Gonçalves et al, 2015;Dufresnes and Martínez-Solano, 2020;Lucati et al, 2022). We recovered two haplotypes identical to the haplotypes previously documented in the subspecies A. a. almogavarii: H66 (2 samples) and H68 (4 samples) -haplotype labels as in Vliegenthart et al (2023).…”