Molecular Ecology and Evolution
Torke, Benjamin M. , Schaal, Barbara A. .
Phylogeography of the Central American apetalous clade of Swartzia (Leguminosae): geographic isolation and population subdivision trump dispersal and gene flow in a tropical tree diversification.
A molecular phylogeographic study of the Central American apetalous clade of Swartzia (Leguminosae), based on sequences of the chloroplast accD-psaI spacer, was performed to examine patterns of diversification and genetic variation within and among closely related species. This clade includes about eight species ranging from small understory to large canopy trees distributed mostly in lowland rainforests of Central America, from Oaxaca, Mexico to northern Panama. Population-level sampling focused on S. cubensis in the Yucatan Peninsula, S. nicaraguensis in northern Costa Rica and southern Nicaragua, and a complex of one to three undescribed species in the Pacific lowlands of central and southern Costa Rica. A statistical parsimony haplotype network approach was adopted to examine relationships among the 22 chloroplast halplotypes recovered from the sample. Most haplotypes were species-specific; there was only one case of haplotype sharing between species. This pattern of marked interspecific genetic divergences and the present-day mostly non-overlapping geographic distributions of species suggest a history of allopatric speciation. The locations of geographic barriers to gene flow, including mountain ranges, dry-adapted vegetation zones, and historical oceanic barriers, often correlate with species boundaries and spatial patterns of genetic divergences within species. In contrast to the generally accepted notion that most tropical trees experience high levels of gene flow among populations, the vast majority of genetic variation within S. cubensis and S. nicaraguensis is due to differences between populations, which are highly subdivided. In some species, the presence of highly divergent chloroplast haplotypes, which in some cases are more closely related to haplotypes from different species than to other conspecific haplotypes, may be due to lineage sorting or to chloroplast capture from ancient hybridization events.
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1 - Academy of Natural Sciences, Laboratory for Molecular Systematics and Ecology, 1900 Benjamin Franklin Parkway, Philadelphia, Pennsylvania, 19103-1195, USA
2 - Washington University, Department of Biology, St Louis, Missouri, 63130, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Boulevard B/Hilton
Date: Wednesday, July 11th, 2007
Time: 8:30 AM