Geographic structure of molecular variation of Gentiana ligustica (Gentianaceae) in the Maritime and Ligurian regional hotspot, inferred from ITS sequences.

The Maritime and Ligurian Alps represent a regional hotspot of plant biodiversity found in the Mediterranean. Historical factors, complex geomorphology and habitat diversity may have played key roles to mould the bio-geographical singularity of this area. This study represents the first regional phylogeographic attempt to better assess the complex evolutionary history of an endemic plant (Gentiana ligustica), which is found throughout this hotspot, across a large altitudinal and ecological gradient. Here, we examine how historical and topographical factors have affected the geographic structure of sequence variation at internal transcribed spacers (ITS) of ribosomal DNA. Sequence data revealed a fine-scale geographical structure of molecular variation, and the presence of contact areas between groups of populations differentiated by ITS ribotypes. A comparison between the sequence distribution and topography suggests that the genetic structure of G. ligustica is the result of isolation and drift. Combined phylogeographic, Pleistocene glaciation, topographic and geologic data suggest the presence of several genetically differentiated refugia, at the margins of the ice sheets in the southern part of the Maritime and Ligurian Alps during the last two glaciations (Riss and Würm), as well as in some valleys and cliffs during the Würm. [ABSTRACT FROM AUTHOR]