Mccarthy, Diane , Mason-Gamer, Roberta .
Phylogeography of Tilia americana s.l. (Malvaceae) based on chloroplast DNA variation.
Tilia (Malvaceae) is a genus of 20-25 species of trees in the temperate northern hemisphere. Most botanists treat all North American members of Tilia as a single species, Tilia americana s.l., although in the past the group was divided into as many as 20 taxa based on morphology. Many of the morphological types within Tilia americana are associated with certain physiographic provinces or represent intermediates between nearby types. One explanation for the heterogeneous distribution of variation is divergence in isolated refugia during the last glacial maximum followed by recolonization and hybridization between refugial types. Proposed refugia include the Cumberland Plateau and the Driftless Area of southwestern Wisconsin, but recent studies have also proposed that mesic tree species persisted at low densities throughout the unglaciated landscape. In order to clarify Tilia americana’s biogeographic history, I am analyzing genetic diversity in multiple individuals from 50 populations across its eastern North American range, including representatives from most physiographic provinces. I have sequenced up to six individuals per population using 1100 bp of the cpDNA spacer rpL32-trnL and sixteen chloroplast haplotypes have been identified. A second cpDNA spacer, ndhF-rpL32, is being added in order to increase resolution. The haplotypes show a strong geographic structure dominated by three widely distributed haplotypes with non-contiguous ranges, a pattern that suggests that these three haplotypes persisted in different locations during glaciation and followed independent recolonization routes. To test hypotheses about the contribution of glacial and post-glacial population histories to the modern distribution of variation in Tilia americana, I will apply two widely-used phylogeographic analysis methods, nested clade analysis and statistical phylogeography, to the chloroplast data set. While the two methods differ in their assumptions and statistical power, they both offer valuable insights into the historical processes underlying intraspecific variation.
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1 - University of Illinois Chicago, Department of Biological Sciences, M/C 066, 845 W Taylor St., Chicago, IL, 60607, USA
2 - University of Illinois Chicago, Department of Biological Sciences, M/C 066, 845 W Taylor Street, Chicago, Illinois, 60607, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Cottonwood B/Snowbird Center
Date: Monday, July 27th, 2009
Time: 2:30 PM