Multilocus phylogeography of the common lizard Zootoca vivipara at the Ibero-Pyrenean suture zone reveals lowland barriers and high-elevation introgression.

Borja Milá,Benoît Heulin,Alberto Gosá,Patrick S Fitze,Yann Surget-Groba

doi:10.1186/1471-2148-13-192

Abstract

BackgroundThe geographic distribution of evolutionary lineages and the patterns of gene flow upon secondary contact provide insight into the process of divergence and speciation. We explore the evolutionary history of the common lizard Zootoca vivipara (= Lacerta vivipara) in the Iberian Peninsula and test the role of the Pyrenees and the Cantabrian Mountains in restricting gene flow and driving lineage isolation and divergence. We also assess patterns of introgression among lineages upon secondary contact, and test for the role of high-elevation trans-mountain colonisations in explaining spatial patterns of genetic diversity. We use mtDNA sequence data and genome-wide AFLP loci to reconstruct phylogenetic relationships among lineages, and measure genetic structure.ResultsThe main genetic split in mtDNA corresponds generally to the French and Spanish sides of the Pyrenees as previously reported, in contrast to genome-wide AFLP data, which show a major division between NW Spain and the rest. Both types of markers support the existence of four distinct and geographically congruent genetic groups, which are consistent with major topographic barriers. Both datasets reveal the presence of three independent contact zones between lineages in the Pyrenean region, one in the Basque lowlands, one in the low-elevation mountains of the western Pyrenees, and one in the French side of the central Pyrenees. The latter shows genetic evidence of a recent, high-altitude trans-Pyrenean incursion from Spain into France.ConclusionsThe distribution and age of major lineages is consistent with a Pleistocene origin and a role for both the Pyrenees and the Cantabrian Mountains in driving isolation and differentiation of Z. vivipara lineages at large geographic scales. However, mountain ranges are not always effective barriers to dispersal, and have not prevented a recent high-elevation trans-Pyrenean incursion that has led to asymmetrical introgression among divergent lineages. Cytonuclear discordance in patterns of genetic structure and introgression at contact zones suggests selection may be involved at various scales. Suture zones are important areas for the study of lineage formation and speciation, and our results show that biogeographic barriers can yield markedly different phylogeographic patterns in different vertebrate and invertebrate taxa.

Highlights

The geographic distribution of evolutionary lineages and the patterns of gene flow upon secondary contact provide insight into the process of divergence and speciation
In line with previous phylogeographic studies on the species, our study shows that populations of Z. vivipara at the Ibero-Pyrenean zone do not show an actual “suture zone” between Iberian and northern European lineages [8,24], in sharp contrast to patterns found in other species, like the grasshopper Chorthippus parallelus [25] or the warbler Phylloscopus collybita [26]
Our results show that lineages of Z. vivipara in northern Iberia and the Ibero-Pyrenean suture zone show marked levels of differentiation that is congruent with major topographical features in the region

Summary

Introduction

The geographic distribution of evolutionary lineages and the patterns of gene flow upon secondary contact provide insight into the process of divergence and speciation. In Europe, glacial dynamics over the last several million years had a major impact on the phylogeography of animal and plant lineages, which underwent repeated cycles of rapid expansions from southern refugia as species recolonized northern latitudes following glacial maxima [3,4,5] These range expansions gave rise to a series of suture zones across the continent as lineages that diverged during glacial periods came into secondary contact during interglacials, providing us with unique natural experimental areas in which to study the process of lineage divergence and the evolution of reproductive isolation [5]. Because of limited regional sampling in previous phylogeographic studies, and the lack of biparentally inherited markers examined in this system to date, our understanding of region-wide genetic structure, patterns of introgression among lineages and the relative importance of the Pyrenees and other mountain ranges as barriers to gene flow remain general and tentative

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