Can secondary contact following range expansion be distinguished from barriers to gene flow?

PeerJ. 2018 Oct 1;6:e5325. doi: 10.7717/peerj.5325. eCollection 2018.

Abstract

Secondary contact is the reestablishment of gene flow between sister populations that have diverged. For instance, at the end of the Quaternary glaciations in Europe, secondary contact occurred during the northward expansion of the populations which had found refugia in the southern peninsulas. With the advent of multi-locus markers, secondary contact can be investigated using various molecular signatures including gradients of allele frequency, admixture clines, and local increase of genetic differentiation. We use coalescent simulations to investigate if molecular data provide enough information to distinguish between secondary contact following range expansion and an alternative evolutionary scenario consisting of a barrier to gene flow in an isolation-by-distance model. We find that an excess of linkage disequilibrium and of genetic diversity at the suture zone is a unique signature of secondary contact. We also find that the directionality index ψ, which was proposed to study range expansion, is informative to distinguish between the two hypotheses. However, although evidence for secondary contact is usually conveyed by statistics related to admixture coefficients, we find that they can be confounded by isolation-by-distance. We recommend to account for the spatial repartition of individuals when investigating secondary contact in order to better reflect the complex spatio-temporal evolution of populations and species.

Keywords: Barrier of gene-flow; Hybrid zone; Isolation with migration models; Isolation-by-distance; Landscape genetics; Quaternary glaciation; Secondary contact.

Associated data

  • figshare/10.6084/m9.figshare.4986545.v2

Grant support

Johanna Bertl was supported by the Vienna Graduate School of Population Genetics (Austrian Science Fund (FWF): W1225-B20) and worked on this project while employed at the Department of Statistics and Operations Research, University of Vienna, Austria. This article was developed in the framework of the Grenoble Alpes Data Institute, which is supported by the French National Research Agency under the “Investissments d’avenir” program (ANR-15-IDEX-02). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.