Systematics/Phytogeography / Taxonomie/ Section
Marazzi, Brigitte , Sanderson, Michael .
Large-scale diversification of Senna (Leguminosae) in the American continent: implications for the evolution of morphological diversity.
Although older, species-rich clades may display an intriguing diversity, their diversification is generally little investigated, mainly because it is more difficult to study radiations deeper in the past, and extinction must also be considered. The widespread legume genus Senna is such a challenging clade: fossil fruits have been described from the Eocene, and the highly diverse, buzz-pollinated flowers and the extrafloral nectaries (EFNs) visited by ants are interesting evolutionary aspects in the genus. The ca. 300 species have successfully colonized a wide range of habitats in different climates and latitudes, 80% of which occur in the Americas, the remaining are found in tropical Africa, Madagascar, and Australia, with only a few species in southeast Asia and some on the Pacific Islands. We investigated the ‘timing’ and ‘mode’ of the large-scale diversification of Senna, especially in the Americas, to detect biogeographic patterns and gain insights on the suggested evolutionary key role which EFNs seem to have played in this genus. We present results of our molecular dating analyses (Penalized Likelihood and/or Bayesian dating approaches), which followed a two-step strategy using two different sources of phylogenetic (chloroplast DNA) information: (1) age estimation of Senna as a whole, using a subset of a legume-wide phylogeny (partial sequence of the matK gene) and multiple calibration points, and subsequently, (2) estimation of ages of the major clades of Senna, using a comprehensive Senna phylogeny (rpL16 and rpS16 introns, and partial matK gene) and age estimates of step 1 as calibration points. We finally estimate diversification rates within Senna, in order to detect significant shifts in rates between major clades. We also discuss implications of our results for the evolution of morphological diversity in Senna and for the origin of EFNs in relation to ant diversification.
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1 - University of Arizona, Ecology and Evolutionary Biology, Tucson, AZ, 85721, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 8:30 AM