Genetic traces of hybrid zone movement across a fragmented habitat

Abstract

Theoretical and empirical studies suggest that the structure and position of hybrid zones can change over time. Evidence for moving hybrid zones has been directly inferred by repeated sampling over time, or indirectly through the detection of genetic footprints left by the receding species and the resulting asymmetric patterns of introgression across markers. We here investigate a hybrid zone formed by two subspecies of the Iberian golden-striped salamander, Chioglossa lusitanica, using a panel of 35 nuclear loci (31 SNPs and 4 allozymes) and one mitochondrial locus in a transect in central Portugal. We found concordant and coincident clines for most of the nuclear loci (n = 22, 63%), defining a narrow hybrid zone of ca. 6 km wide, with the centre positioned ca. 15 km south of the Mondego River. Asymmetric introgression was observed at another 14 loci. Their clines are displaced towards the north, with positions located either close to the Mondego River (n = 6) or further northwards (n = 8). We interpret these profiles as genetic traces of the southward displacement of C. lusitanica lusitanica by C. l. longipes over the wider Mondego River valley. We noted the absence of significant linkage disequilibrium, and we inferred low levels of effective selection per locus against hybrids, suggesting that introgression in the area of species replacement occurred under a neutral diffusion process. A species distribution model suggests that the C. lusitanica hybrid zone coincides with a narrow corridor of fragmented habitat. From the position of the displaced clines, we infer that patches of locally suitable habitat trapped some genetic variants that became disassociated from the southward moving hybrid zone. This study highlights the influence of habitat availability on hybrid zone movement.

Spatial Genetic Structure in European Marbled Newts Revealed with Target Enrichment by Sequence Capture

“…Divergence of populations from central and northern Iberia may be the consequence of major rivers flowing in a West-East orientation acting as a barrier to dispersal, initiating incipient speciation. Similar patterns of differentiation are observed in other amphibians, such as Chioglossa lusitanica (Sequeira et al, 2022), Lissotriton boscai (Martinez-Solano et al, 2006), Alytes obstetricans (Dufresnes and Hernandez, 2021;Gonçalves et al, 2015;Maia-Carvalho et al, 2018), and Discoglossus galganoi (Martinez-Solano, 2004). Remarkably, the phylogeographic transition between the two T. marmoratus lineages coincides with the contact area of two phylogeographic lineages attributed to the midwife toad A.…”

Integrative systematic revision of the Montseny brook newt (Calotriton arnoldi), with the description of a new subspecies

“…As the absence of taxonomic designation hampers conservation and unnamed lineages face higher extinction risk than described taxa ( Liu et al, 2022 ; Dufresnes, Poyarkov & Jablonski, 2023 ), we recognize the uniqueness of the Western Montseny brook newt by providing it with a formal name. Finally, as advocates of the use of trinomial names, we must point out that the use of the subspecific rank is currently increasing among European amphibians, with many examples of their application based on genetic or genomic evidence ( e.g ., in the genera Salamandra ( Šunje et al, 2019 ; Burgon et al, 2021 ), Triturus ( Arntzen, 2023 ), Ichthyosaura ( Vörös et al, 2021 ), Chioglossa ( Sequeira et al, 2022 ), Alytes ( Dufresnes & Hernandez, 2021 ) and Rana ( Dufresnes et al, 2023 )). This re-popularization of the subspecies is in line with a deeper understanding of complex evolutionary histories, such as those shaped by the Pleistocene glacial cycles in Europe, only fully unveiled with the advent of genomics.…”