1. ¹Department of Biology, University of Oulu, Oulu, Finland
2. ²UMR DIA-PC 1097, INRA Montpellier, Domaine de Melgueil, Mauguio, France

Correspondence: Dr M-H Muller, UMR DIA-PC 1097, INRA, Domaine de Melgueil, Mauguio F34130, France. E-mail: Marie-Helene.Muller@supagro.inra.fr

Received 28 March 2007; Revised 12 June 2007; Accepted 3 August 2007; Published online 17 October 2007.

Abstract

The perennial outcrossing Arabidopsis lyrata is becoming a plant model species for molecular ecology and evolution. However, its evolutionary history, and especially the impact of the climatic oscillations of the Pleistocene on its genetic diversity and population structure, is not well known. We analyzed the broad-scale population structure of the species based on microsatellite variation at 22 loci. A wide sample in Europe revealed that glaciations and postglacial colonization have caused high divergence and high variation in variability between populations. Colonization from Central Europe to Iceland and Scandinavia was associated with a strong decrease of genetic diversity from South to North. On the other hand, the Russian population included in our data set may originate from a different refugium probably located more to the East. These genome-wide patterns must be taken into account in studies aiming at elucidating the genetic basis of local adaptation. As shown by sequence data, most of the loci used in this study do not evolve like typical microsatellite loci and show variable levels of homoplasy: this mode of evolution makes these markers less suitable to investigate the between-continent divergence and more generally the worldwide evolution of the species. Finally, a strong negative correlation was detected between levels of within-population diversity and indices of differentiation such as F_ST. We discuss the causes of this correlation as well as the potential bias it induces on the quantification and interpretation of population structure.