Originally published as Genetics Published Articles Ahead of Print on January 21, 2007.

Genetics, Vol. 175, 1823-1834, April 2007, Copyright © 2007
doi:10.1534/genetics.106.067728

Selective Sweeps Reveal Candidate Genes for Adaptation to Drought and Salt Tolerance in Common Sunflower, Helianthus annuus

Nolan C. Kane*,{dagger},1 and Loren H. Rieseberg*,{dagger}

* Department of Biology, Indiana University, Bloomington, Indiana 47405 and {dagger} Department of Botany, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada

1 Corresponding author: Department of Biology, Indiana University, Jordan Hall, Box B055, 1001 E. Third St., Bloomington, IN 47405.
E-mail: nkane{at}indiana.edu

Here we report the results of an analysis of variation at 128 EST-based microsatellites in wild Helianthus annuus, using populations from the species' typical plains habitat in Kansas and Colorado, as well as two arid desert and two distinct brackish marsh areas in Utah. The test statistics lnRV and lnRH were used to find regions of the genome that were significantly less variable in one population relative to the others and thus are likely to contain genes under selection. A small but detectable percentage (1.5–6%) of genes showed evidence for selection from both statistics in any particular environment, and a total of 17 loci showed evidence of selection in at least one environment. Distance-based measures provided additional evidence of selection for 15 of the 17 loci. Global FST-values were significantly higher for candidate loci, as expected under divergent selection. However, pairwise FST-values were lower for populations that shared a selective sweep. Moreover, while spatially separated populations undergoing similar selective pressures showed evidence of divergence at some loci, they evolved in concert at other loci. Thus, this study illustrates how selective sweeps might contribute both to the integration of conspecific populations and to the differentiation of races or species.




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