Phylogeography of a widespread species: Pre-glacial vicariance, refugia, occasional blocking straits and long-distance migration

A. unedo distribution range (grey), frequency of ancestral haplotypes (H2 and H4) and derived haplotypes. Each ancestral haplotype together with its derived haplotypes constitute one clade, the Atlantic clade (blue) and the Mediterranean clade (red). The blue and red arrows denote the deduced migrational movements for individuals of each clade.

Phylogeographic studies give us the opportunity to reconstruct the historical migrations of species and link them with climatic and geographic variation. They are, therefore, a key tool to understanding the relationships among biology, geology and history. One of the most interesting biogeographical areas of the world is the Mediterranean region. However, in this area, the description of concordant phylogeographic patterns is quite scarce, which limits the understanding of evolutionary patterns related to climate. Species with one-dimensional distribution ranges, such as the strawberry tree (Arbutus unedo) are particularly useful to unravel these patterns. In a new study published in AoB PLANTS, Santiso et al. found that the strawberry tree diverged into two groups during the Quaternary, but before the Last Glacial Maximum, surviving in refugia located in the western end of the Mediterranean region and with the Eastern Mediterranean being colonized more recently. This migration was possible because Europe and North Africa were occasionally connected through the straits of Gibraltar and Sicily. Likewise, their evidence supports arrival in Ireland from northern Iberia in post-glacial times. Altogether, their results reveal the considerable ability of the strawberry tree for dispersal, allowing it to migrate over thousands of kilometres and cross stretches of sea, which may be crucial for its future survival.

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