Temporal and spatial diversification of Circum-Mediterranean Compositae-Anthemideae

A combination of dispersal-vicariance analysis (DIVA) and molecular clock dating of a calibrated, rate-smoothed maximum-likelihood tree based on sequence information from the internal transcribed spacer region of the ribosomal repeat (nrDNA ITS) was used to reconstruct the biogeographical history of the Circum-Mediterranean clade of Compositae-Anthemideae. The reconstructions suggest that the ancestor of this clade diverged from the basal African lineages in the late Early Miocene (18 Myr), presumably in conjunction with the collision of the African and Eurasian platform through the Arabian plate. Recurrent dispersal/vicariance events during the Middle and Late Miocene (16-11 Myr) both between the eastern and western Mediterranean regions and (in the latter region) between the northern and southern Peri-Tethys platforms caused the further diversification of the clade and may have been triggered by episodes of marine regression/transgression events on the Eurasian platform and in the area of the Strait of Gibraltar, respectively. The analyses further show that both the western part of the North African platform and the Anatolian region played a paramount role in the radiation of different subclades of the Circum-Mediterranean Anthemideae, leading to the present day genus-richness of the western subclade and to the species-richness in the large genera (Achillea, Anthemis, Cota, Tanacetum, Tripleurospermum) of the eastern subclade. Whereas in the present analyses these radiations are reconstructed as sympatric speciation events, they may actually correspond to allopatric speciation events on a finer geographical scale within the two main centres of diversification (NW Africa, Anatolia). The Messinian salinity crisis (5.96-5.33 Myr) and the following re-inundation of the Mediterranean basin (Early Pliocene) triggered dispersal/vicariance events observable today on the level of species or species groups, as did the climatic changes during the Pleistocene.