Phylogeny reconstruction and molecular dating in four Neotropical genera of Annonaceae : the effect of taxon sampling in age estimations

Preliminary results are presented comparing the timing of diversification in four predominantly Neotropical genera of Annonaceae: Cremastosperma, Duguetia, Guatteria and Mosannona. With the exception of a few basal lineages, the majority of the ca. 2500 species of the Annonaceae diverge into two major sister clades. One comprises relatively few, larger, genera (including Duguetia and Guatteria) representing roughly twice as many species in total and with an apparent rate of molecular divergence (revealed by branch lengths in most parsimonious trees) around three times as high as the other (including Cremastosperma and Mosannona), in which more genera each comprise fewer species. Explanations for the disparity in numbers of species in these four genera are explored from the perspective of phylogeny reconstruction and molecular dating techniques (using nonparametric rate smoothing), aiming to assess monophyly and to arrive at preliminary estimates of the relative ages of their most recent common ancestors (MRCAs). The effects, in particular, of taxon and character sampling on date estimates in these genera is assessed and compared. Results in the species rich genus Guatteria show higher sampling of crown group taxa resulting in significantly older age estimation for the MRCA