Systematics Section / ASPT
Stone, Robert Douglas .
Molecular phylogeny and historical biogeography of the species-rich, paleotropical genus Memecylon (Melastomataceae): testing migration and long-distance dispersal hypotheses.
Relationships in Memecylon sensu stricto and its putative sister-group, Spathandra, have been inferred from sequence variation in four nuclear DNA regions, including the rDNA internal and external transcribed spacers (ITS1, ITS2, ETS) and the third intron of the nitrate reductase gene (NIA-i3). Heterogeneity of phylogenetic signal between ITS2 and ETS was negligible, while significant incongruence was found for ITS1 and NIA-i3 (compared to both of the other two partitions and to each other). Possible explanations for the observed incongruence will be discussed. All trees resolved a sister-group relationship between the small west-African section Mouririoidea (5 species) and the main Memecylon subclade (300+ species). Internal branches at the base of the main subclade were either incompletely resolved (ITS1, ETS trees) or short and weakly supported (ITS2, NIA-i3), suggesting rapid diversification. Within the main Memecylon subclade, both the separate ITS2 and combined ITS1 + ITS2 + ETS analyses resolved reciprocally monophyletic groups from west-Africa, east-Africa, Madagascar, and Indo-Malesia. Phylogenetic evidence favors the hypothesis of an African origin for the Memecylon lineage, and given the relationships inferred by the combined ITS1 + ITS2 + ETS tree there are just two migration or dispersal events needed to explain the currently widespread, paleotropical distribution of Memecylon. Fossil-calibrated molecular dating methods are being used to test the alternative hypotheses of migration or long-distance dispersal to explain the modern presence of Memecylon in Indo-Malesia.
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1 - Uppsala University, Department of Systematic Botany, Evolutionary Biology Centre, Norbyvägen 18D, Uppsala, SE-752 36, Sweden
Presentation Type: Oral Paper
Date: Tuesday, August 16th, 2005
Time: 2:30 PM