Genome size variation from a phylogenetic perspective in the genus Cheirolophus Cass. (Asteraceae): biogeographic implications

Abstract

Nuclear DNA amount has been assessed in 21 populations of 19 species of the genus Cheirolophus, and phylogenetic analyses have been performed in order to find the relationships between the species of the Mediterranean Basin and those of Macaronesia. A combined analysis of nuclear ribosomal DNA ITS and ETS has been performed based on Bayesian inference, and nuclear DNA amount has been assessed by flow cytometry. The monophyly of the Macaronesian group and its relationship with Ch. sempervirens indicate a unique colonization event of Macaronesia from the continent. This single event has not been proved in the case of the Canarian archipelago. DNA amount is significantly lower in the insular species than in the continental ones, and a connection appears between the evolution of the genus Cheirolophus (colonization of islands) and the loss of DNA, probably due to the selection pressure existing on the oceanic islands.