Surviving glaciations in the Mediterranean region: an alternative to the long-term refugia hypothesis

The simultaneous application of species distribution modelling (SDM) and study of genetic imprints left by range dynamics is appropriate when examining the biogeographical processes that have favoured the survival of plants through past climate changes. Nevertheless, such an approach is rarely performed on the scale of the entire Mediterranean and almost never concerns widespread thermophilous plants. Here, we examine the biogeographical responses of an important Mediterranean shrub, Myrtus communis (Myrtaceae), to severe Quaternary climate conditions. Our analysis combines SDM and phylogeography based on plastid/nuclear DNA sequences and AFLP data. Palaeoclimatic models using MaxEnt and levels of genetic diversity in M. communis are used to infer drastic changes in areas of climatic suitability during the last 130000 years, with a southward range contraction during the Last Glacial Maximum. Modelling of past areas of suitability for M. communis identifies a few relatively small long-term refugia, suggesting that it survived in temporary refugia during glacial periods. Myrtus communis is characterized by a higher genetic diversity and distinctiveness in the southern part of its range, where it was less impacted by glaciations. The structure of genetic diversity reveals stronger range expansions in the western part of the range, whereas migration processes remained much more restricted in the eastern Mediterranean.