Postglacial Colonisation Patterns and the Role of Isolation and Expansion in Driving Diversification in a Passerine Bird

Bengt Hansson,Maja Tarka,Pavel Zehtindjiev,Dennis Hasselquist,Staffan Bensch,Peter M Bennett

doi:10.1371/journal.pone.0002794

Bengt Hansson, Maja Tarka + Show 4 more

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https://doi.org/10.1371/journal.pone.0002794

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Journal: PLoS ONE	Publication Date: Jul 30, 2008
Citations: 97	License type: CC BY 4.0

Affiliation: Lund University, Bulgarian Academy of Sciences

Abstract

Pleistocene glacial cycles play a major role in diversification and speciation, although the relative importance of isolation and expansion in driving diversification remains debated. We analysed mitochondrial DNA sequence data from 15 great reed warbler (Acrocephalus arundinaceus) populations distributed over the vast Eurasian breeding range of the species, and revealed unexpected postglacial expansion patterns from two glacial refugia. There were 58 different haplotypes forming two major clades, A and B. Clade A dominated in Western Europe with declining frequencies towards Eastern Europe and the Middle East, but showed a surprising increase in frequency in Western and Central Asia. Clade B dominated in the Middle East, with declining frequencies towards north in Central and Eastern Europe and was absent from Western Europe and Central Asia. A parsimonious explanation for these patterns is independent postglacial expansions from two isolated refugia, and mismatch distribution analyses confirmed this suggestion. Gene flow analyses showed that clade A colonised both Europe and Asia from a refugium in Europe, and that clade B expanded much later and colonised parts of Europe from a refugium in the Middle East. Great reed warblers in the eastern parts of the range have slightly paler plumage than western birds (sometimes treated as separate subspecies; A. a. zarudnyi and A. a. arundinaceus, respectively) and our results suggest that the plumage diversification took place during the easterly expansion of clade A. This supports the postglacial expansion hypothesis proposing that postglacial expansions drive diversification in comparatively short time periods. However, there is no indication of any (strong) reproductive isolation between clades and our data show that the refugia populations became separated during the last glaciation. This is in line with the Pleistocene speciation hypothesis invoking that much longer periods of time in isolation are needed for speciation to occur.

Highlights

Pleistocene glacial cycles cause repeated range expansions and contractions with important present-day demographic consequences for temporal and boreal populations and species in the Northern Hemisphere [1,2,3]
As formulated in the ‘‘Pleistocene speciation hypothesis’’, a common view is that these speciation events took place in isolated refugia over one to several full glacial cycles [4,5,6]
Since this scenario does not invoke long-term isolation in refugia, the postglacial expansion hypothesis poses an alternative to traditional models of Pleistocene speciation

Summary

Introduction

Pleistocene glacial cycles cause repeated range expansions and contractions with important present-day demographic consequences for temporal and boreal populations and species in the Northern Hemisphere [1,2,3]. In the present study we reveal a more complex colonization history of the great reed warbler (i) by using mtDNA sequence data from a total of 15 populations distributed over most of the species’ Eurasian breeding range including Eastern Europe, the Middle East and Western and Central Asia, and (ii) by using recently developed statistical tools that make it possible to test more sophisticated hypotheses regarding the divergence and expansion, e.g. inferring asymmetric gene flow between populations and time since divergence [19,20].

Results

Conclusion