Isolation and Gene Flow in a Speciation Continuum in Newts

Abstract

16Because reproductive isolation often evolves gradually, differentiating lineages may retain the 17 potential for genetic exchange for prolonged periods, providing an opportunity to quantify

Differential introgression across newt hybrid zones: Evidence from replicated transects

“…Previous work on mtDNA phylogeography and nuclear gene genealogies (Babik et al, ; Pabijan et al, ; Zieliński et al, , ) has testified to a long history of genetic exchange between Lm and Lv, the hybrid zones of which studied here appear to be a recent manifestation. Note that multiple lines of evidence suggest more extensive genetic exchange between species within the Carpathian Basin, where the IN zone is located.…”

“…As a consequence, we cannot rule out the possibility that demographic and biological differences between the zones affected observed differences in the length of introgression tracts. However, longer hybridization in the IN zone remains a plausible and probable explanation, especially in the light of biogeographical evidence—long‐term persistence of Lv in the Carpathian Basin, in close proximity to the range of Lm (Babik et al, ; Pabijan et al, ).…”

“…(Depristo et al, ; McKenna et al, ) Only biallelic (i.e., meeting the infinite sites mutation model) SNPs with <20% of missing data and global minor allele frequency (MAF) ≥5% were used in analyses. The analysis of mitochondrial DNA (mtDNA) was complicated by its extensive interspecific introgression, both historical and recent (Babik et al, ; Pabijan et al, ; Zieliński et al, ). As a consequence, all five distinct mtDNA lineages that occur in Lm and Lv in Central Europe, and to some extent also haplotypes within lineages, are shared between species.…”

“…Here we investigate two hybrid zones formed by the Carpathian newt ( Lissotriton montandoni , Lm) and the smooth newt ( Lissotriton vulgaris , Lv), and assess differences between the zones and repeatability within the zones by investigating introgression in replicated transects (Figure a). The zones result from hybridization between Lm and two distinct lineages of Lv (divergence ~1 million years ago [Pabijan, Zielinski, Dudek, Stuglik, & Babik, ; Zieliński, Nadachowska‐Brzyska, Dudek, & Babik, ]): Lm hybridizes with L. v. ampelensis within the Carpathian Basin (the IN zone) and with L. v. vulgaris outside the Carpathian basin (the OUT zone). Previous studies have suggested some spatial, temporal and genomic heterogeneity of introgression (Stuglik & Babik, ; Zieliński, Dudek, Stuglik, Liana, & Babik, ; Zieliński et al, , ).…”

Massive introgression of major histocompatibility complex (MHC) genes in newt hybrid zones

“…Speciation in this system is at an advanced stage – genomes are congealed and introgression is highly restricted, although to some extent still heterogeneous throughout the genome (Zieliński et al, ). However, L. montandoni and L. vulgaris have experienced a long and apparently complex history of genetic exchange (Zieliński, Nadachowska‐Brzyska, Dudek, & Babik, ), exemplified by a complete replacement of L. montandoni mtDNA by that derived from several phylogeographic lineages of L. vulgaris (Pabijan, Zieliński, Dudek, Stuglik, & Babik, ; Zieliński et al, ). Introgression of MHC classes I and II between L. montandoni and L. vulgaris has previously been inferred using continent‐scale comparisons of differentiation and allele sharing between multiple evolutionary lineages within the L. vulgaris species complex (Fijarczyk et al, ; Nadachowska‐Brzyska et al, ).…”