Adhikari, Binaya , Wallace, Lisa Ellen .
Evaluating evolutionary diversification in scentbottle orchids, Platanthera dilatata, based on phylogeography.
Platanthera dilatata, with morphologically and genetically variable populations in North America, shows signs of active and primitive level of divergence, thus forming a useful model for understanding the early stages of evolution in plants. Three varieties of P. dilatata: vars. dilatata, albiflora, and leucostachys are classified by spur length and geographical distribution. However, morphological and genetic characters are not always consistent with varietal designations. Owing to apparently more specialized floral morphology and more restricted distributions of var. albiflora and var. leucostachys, we hypothesize that var. dilatata is ancestral to the former two varieties. The current distributions of the former varieties could have been achieved by a single ancestral population of each variety spreading out across the landscape after morphological divergence from var. dilatata. Alternatively, convarietal populations could have multiple origins if they survived in different refugia during the last glaciation and later converged morphologically due to selection by similar pollinators. These alternative scenarios are expected to provide different genetic signatures. We used microsatellite markers and cpDNA sequences to test our hypotheses in populations throughout western North America. High levels of genetic variation in both data sets were observed across all the varieties and populations. Populations of var. dilatata cluster with both of the other varieties in using both data sets, suggesting var. dilatata as progenitor of the other two varieties. Additionally, some geographically isolated populations in the western U. S. are genetically distinct, suggesting isolation by distance. The cpDNA data do not show structure by variety or geography, although haplotypic diversity was great. To further quantify the extent of ancestral polymorphism vs. current gene flow, we quantified migration rates and estimated divergence times. The results of these analyses will be discussed in relation to the taxonomy of this group. These patterns suggest an actively diverging complex.
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1 - Mississippi State University, Department of Biological Sciences, 208 Harned Hall Lee Blvd., Starkville, MS, 39762, USA
Presentation Type: Poster:Posters for Sections
Location: Hall A/Convention Center
Date: Monday, August 2nd, 2010
Time: 5:30 PM