Wallace, Lisa , Weller, Stephen G. , Sakai, Ann K. , Wagner, Warren , Nepokroeff, Molly .
Merging distinct histories from different genes to tell a story: phylogeography of Schiedea globosa (Caryophyllaceae) on the Hawaiian Islands.
THE effects of Pleistocene climate change on genetic structure are well documented in a variety of continental taxa. For insular taxa, the presence of deep ocean channels between islands during interglacial periods of the Pleistocene and/or the inability of organisms to cross land bridges that existed during periods of low sea stands is considered to have been a formidable barrier to gene flow. In this study, we test the hypothesis that genetic variation among populations of Schiedea globosa on the Hawaiian Islands of Oahu, Maui, Molokai, and Hawaii is strongly shaped by limited dispersal between islands. Specifically, we predict that populations are monophyletic by island, intra-island dispersal is more important than inter-island colonization, and genetic variation is structured according to the age of the islands (i.e., Oahu is ancestral). We tested these hypotheses by examining DNA sequence variation in two nuclear (ncpGS and pepC) and one chloroplast (psbM-trnD) marker for 59 individuals from 10 populations located throughout the range of S. globosa. AMOVA indicated that most of the variation in psbM-trnD occurs among the islands (FCT = 0.71); much weaker, albeit significant, inter-island structure was detected for ncpGS sequences (FCT = 0.18), and most of the variation in pepC sequences occurs within populations (FST = 0.16). We tested the hypothesis that shared nuclear haplotypes between islands are actually retained ancestral polymorphisms rather than recent gene flow by comparing actual gene trees with simulated gene trees constrained within a population tree consistent with a single founding event for each island. Additionally, we estimated effective population sizes and migration rates between populations using Bayesian analyses. These analyses suggest historically small population sizes and low levels of gene flow between islands. The phylogeographic history of S. globosa and implications of using nuclear markers for phylogeographic studies will be discussed.
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1 - University of South Dakota, Department of Biology, 414 East Clark Street, Vermillion, South Dakota, 57069, USA
2 - University of California Irvine, Department of Ecology & Evolutionary Biology, 321 Steinhaus Hall, Irvine, California, 92697-2525, USA
3 - Smithsonian Institution, Department of Botany MRC 166, National Museum Of Natural History, Po Box 37012, Washington, DC, 20560-0166, USA
Presentation Type: Oral Paper:Papers for Topics
Date: Monday, July 31st, 2006
Time: 9:15 AM