Recent and rapid radiation of the lichen genus Sticta in the Western Indian Ocean islands

In the framework of a global project on the phylogeny of the lichen genus Sticta (Lobariaceae), extensive sampling was performed on the islands of Reunion and Mauritius as well as in several parts of Madagascar (mainly in two National Parks : Marojejy and Amber Mountain). The aim of this study is to provide the first comprehensive molecular phylogeny of the genus in the Western Indian Ocean islands (and more specifically of a presumably local endemic lineage), and to date its local radiation. DNA sequences were obtained from 69 specimens for four loci and phylogenetic relationships were inferred using maximum likelihood and Bayesian inferences methods. We estimated divergence times using BEAST. Thirty putative species can be recognized, only 5 have a validly published epithet. All these species form a well-supported monophyletic group within the genus Sticta, and display interesting patterns of endemism: a single species is present in all islands, while the others are restricted either to Madagascar, to Reunion and Mauritius, or to Reunion only. The estimated divergence time of the radiation of this clade occurred in the upper Miocene, apparently concurrent with the emergence of Mauritius. The tree topology obtained supports an original diversification of the clade in the Mascarenes archipelago rather than in Madagascar.