The central Mediterranean as a phytodiversity hotchpotch: phylogeographical patterns of the Anthemis secundiramea group (Compositae, Anthemideae) across the Sicilian Channel

摘要

Aim We investigated the phylogeography of the Anthemis secundiramea group (Compositae, Anthemideae) to assess the role of palaeogeographical events in its genetic and taxonomic differentiation. We also evaluated the contribution of hybridization to the complexity of these diversification processes in an area of phytogeographical overlap.Location Central Mediterranean: North Africa, Tyrrhenian Islands, Sicily, and its surrounding islands and islets.Methods The geographical distribution of the genetic variability and differentiation of 207 individuals belonging to 42 populations was analysed through chloroplast DNA variation (sequences of the two spacer regions psbA-trnH and trnC-petN), and 290 individuals belonging to 35 populations were analysed using amplified fragment length polymorphism (AFLP) fingerprinting.Results We found three well-defined groups of taxa. The first includes all populations located in North Africa belonging to the species Anthemis confusa, A. glareosa and A. ubensis, which show a significant pattern of isolation by distance from one another. They share the same chloroplast DNA haplotypes, possibly reflecting range expansion/contraction during the Quaternary. Within the second group, which comprises all populations belonging to A. secundiramea, an absence of genetic structure suggests contemporary or at least recent gene flow among its populations. The third group includes the populations belonging to Anthemis urvilleana, which is endemic to the Maltese archipelago. While hybridization with Anthemis arvensis or A. peregrina is hypothesized for four populations of A. urvilleana, the sharing of a haplotype between one population and A. muricata, endemic to Sicily, is interpreted as a relict of the ancient connection between the Maltese archipelago and south-eastern Sicily.Main conclusions The strong genetic differentiation observed between circum-Sicilian and North African populations of the A. secundiramea group suggests the paramount importance of the Sicilian Strait as a barrier to dispersal and gene flow. The present distribution of A. secundiramea, however, demonstrates that this barrier may be crossed by long-distance dispersal overseas, or by anthropogenic dispersal. Sea-level oscillations during the Pleistocene were responsible for the divergence between the Sicilian endemic A. muricata and the Maltese endemic A. urvilleana. Incongruent AFLP patterns and chloroplast haplotype distributions indicate that hybridization of members of the A. secundiramea group with eastern (A. arvensis or A. peregrina) as well as with western (the clade of A. maritima and A. pedunculata) Mediterranean elements has strongly influenced the genetic and taxonomic diversity in this species group.