Genome size in Filago L. (Asteraceae, Gnaphalieae) and related genera: phylogenetic, evolutionary and ecological implications

Recent studies have proposed a monophyletic circumscription of Filago and a new subgeneric treatment for this genus. The aim of this study was to analyse the nuclear genome size in a phylogenetic framework in order to evaluate the systematic significance of this trait to provide insights into the dynamics of genome size evolution and to assess relationships among DNA content, specific life and ecological features within the study group. A holoploid genome size of 76 samples corresponding to 27 taxa was determined using flow cytometry, which represents the first estimates of genome size in Bombycilaena, Filago, Ifloga and Logfia. Chromosome counts were performed for six species. Parsimony and Bayesian analysis of ITS, ETS and rpl32-trnL intergenic spacer sequence data were used to construct molecular phylogenetic trees. The evolution of genome size was investigated troughout the Brownian motion model with the three scaling parameters lambda, kappa and delta. The mean 2C-value in the Filago group is relatively low (1.3644 +/- A 0.0079 pg) and homogeneous among species. A high degree of congruence was found between genome size distribution and the major phylogenetic lineages obtained. The generally accepted assumption that annual, ephemeral and autogamous species show low genome sizes was confirmed. Also the relatively high DNA contents found for a couple of species could be correlated with their highly specific ecological requirements. Phylogeny seems to represent the most important factor explaining the pattern of DNA amount variation in the Filago group. The DNA amount does not seem to be strongly influenced by selection.