Systematics Section / ASPT
Weeks, Andrea , Simpson, Beryl .
Molecular phylogenetic analysis of Commiphora (Burseraceae) yields insight on the evolution of an "impossible" genus and the effects of multiple datasets on lineage dating.
Expansion of the arid zone of sub-Saharan tropical Africa during the Miocene is posited as a significant contributing factor in the evolution of contemporary African flora. Despite this, few studies have investigated the historical biogeography of plants within this zone as opposed to around it. The high species diversity of Commiphora (Burseraceae) within this region makes it an ideal taxon with which to test the timing of diversification events in dry-adapted species. However, aspects of Commiphora's life history, such as its predominantly dioecious breeding system, deciduous habit, its tendency to produce flowers prior to developing mature leaves, and its distribution in remote areas have effectively prevented a comprehensive revision of its species and sections. A recent author pegged Commiphora as an "impossible" genus in reaction to this combination of traits. Here we present the first molecular phylogeny of Commiphora species in order to test the monophyly of the current taxonomic sections and to identify well-supported clades that will help direct future study of this species-rich and geographically widespread taxon within an evolutionary framework. We use DNA sequence data from the nuclear external transcribed spacer region (ETS) and two chloroplast markers, the psbA-trnH intergenic spacer and the rps16 intron, to generate the phylogeny. Our taxon sampling covers approximately one-fifth of the genus (39 spp.) and includes species from most of the major geographic regions of Commiphora's distribution, including Africa, Madagascar, south Asia and South America. We use multiple fossil calibrations of Commiphora phylogeny, based on separate and combined sequence datasets, to determine the timing of well-supported diversification events. We then interpret these age estimates in light of past climate change and continental movements in order to determine the relative contributions of vicariance and dispersal in the expansion of Commiphora's geographic range.
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1 - George Mason University, Department of Environmental Science and Policy 5F2, Fairfax, Virginia, 22030, USA
2 - University of Texas at Austin, Plant Resources Center and Section of Integrative Biology, 1 University Station A6720, Austin, Texas, 78712, USA
Presentation Type: Oral Paper
Date: Tuesday, August 16th, 2005
Time: 9:30 AM