Recent Topics Posters
Marazzi, Brigitte , Sanderson, Michael .
Large-scale patterns of diversification in the legume genus Senna and the role of extrafloral nectaries.
Inferring the history of diversification in old, species-rich and morphologically diverse clades is challenging, not least because extinction cannot be neglected. Fossil evidence indicates that the widespread legume genus Senna dates from the Eocene, predating many legume genera. The ca. 350 extant species have successfully colonized a wide range of habitats in different climates and latitudes, 80% of which occur in the Americas. Extrafloral nectaries (EFNs) characterize one large clade within Senna that includes the majority of its species (“EFN clade”). EFNs secrete nectar and attract ants, forming ant-plant protective mutualisms. We investigated the timing and mode of diversification of Senna, to gain insights into the evolutionary role of its EFNs. Molecular dating analyses using cpDNA sequence data suggest that Senna diverged from its sister group Cassia in the early Eocene, and its major lineages appeared between early/mid-Eocene and mid-Oligocene. EFNs seem to have evolved during the late Eocene, after the main radiation of ants. Estimates of net diversification rates suggest that the EFN clade diversified significantly faster than clades lacking EFNs, and the shift in rates is associated with the origin of EFNs. This shift, together with the ecological significance of the EFNs-ant mutualism supports the hypothesis that EFNs represent a key innovation in Senna. Indeed, EFNs may have promoted the colonization of the new habitats appearing with the uplift of the Andes. This might explain the distinctive geographic distribution of the EFN clade versus non-EFN Senna clades in the Americas.
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1 - University of Arizona, Ecology and Evolutionary Biology, Tucson, AZ, 85721, USA
Presentation Type: Recent Topics Poster
Location: Event Tent/Cliff Lodge
Date: Monday, July 27th, 2009
Time: 5:30 PM