Evolutionary history, biogeography and eco-climatological differentiation of the genus Anthemis L. (Compositae, Anthemideae) in the circum-Mediterranean area

Abstract

Aim: To reconstruct the temporal, geographical and eco-climatological differentiation of the genus Anthemis (Compositae, Anthemideae) in the circum-Mediterranean region, in order to evaluate the relative importance of geographical vs. climatological differentiation processes in influencing the actual distribution patterns in this plant group.
Location  The circum-Mediterranean region, including the Iberian Peninsula, northern Africa, the Italian and Balkan peninsulas, the Aegean region and Anatolia, the Caucasus, the Arabian Peninsula and western Asia.
Methods: The phylogeny of the genus Anthemis was obtained from a maximum likelihood analysis based on nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) sequence data, and the chronology of diversification was derived using a penalized likelihood approach. The reconstruction of the spatial diversification of the genus was based on a dispersal/vicariance (DIVA) analysis. Eco-climatological niche differentiation was inferred by optimizing 19 bioclimatic variables onto the phylogeny. A multi-dimensional hypervolume, proposed as a representation of the eco-climatological niche and defined by the combination of ranges for all bioclimatic variables, was calculated for each taxon and each internal node. To identify ‘eco-climatological vicariance’ events in the phylogeny, the pairwise overlap among hypervolumes of sister groups was calculated. Finally, the temporal and clade-wise relative importance of geographical vs. eco-climatological vicariance events was estimated.
Results: The temporal reconstruction shows a constant increase of lineages through the last 12 Myr. The geographical reconstruction suggests that Anthemis diverged from the rest of the Compositae–Anthemideae in the eastern Mediterranean region, and from there radiated into the whole circum-Mediterranean region through successive dispersal and vicariance events. The reconstruction of the eco-climatological niches suggests a progressive adaptation from a montane-humid climate towards arid environments and the typical mediterranean climate.
Main conclusions: The results presented here involved phylogenetic, geographical and eco-climatological reconstructions; joint analyses of all of these aspects have assessed the relative importance of geological vs. climatic forces that have affected the distributional history of the genus Anthemis. Large-scale differentiation patterns triggered by geological forces appear to have influenced the evolutionary history of the genus in a rather constant manner over the last 12 Myr, whereas climatic forces seem to have played an important role in two phases of the radiation process: at around 9 Ma, when the area experienced the onset of a trend towards aridification, and during the last 3.5 Myr, with the establishment of the typical mediterranean climate and the influence of Pleistocene climate oscillations.