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(American Journal of Botany. 2003;90:561-570.)
© 2003 Botanical Society of America, Inc.

Population Biology

Contrasting selection modes at the Adh1 locus in outcrossing Miscanthus sinensis vs. inbreeding Miscanthus condensatus (Poaceae)1

Yu-Chung Chiang2, Barbara A. Schaal2, Chang-Hung Chou3, Shong Huang4 and Tzen-Yuh Chiang5,6

2Department of Biology, Washington University, St. Louis, Missouri 63119 USA; 3National Pingtung University of Science and Technology, Pingtung, Taiwan; 4Department of Biology, Taiwan Normal University, Taipei, Taiwan 116; 5Department of Biology, Cheng-Kung University, Tainan, Taiwan 701

We estimated DNA sequence variation of the Adh1 locus in the outcrossing Miscanthus sinensis (Poaceae) and its close selfing relative, M. condensatus. Tajima's test of selection is significantly negative for both overall exons and replacement sites in M. sinensis. Among its entire sample, nucleotide diversity of nonsynonymous sites is higher than that of synonymous sites. A McDonald and Kreitman test of neutrality indicates an excess of intraspecific replacement polymorphisms, suggesting possible directional selection toward advantageous mutants. However, frequent intragenic recombination suggests both purifying and positive selection is unlikely. Recent demographic expansions coupled with relaxation of purifying selection may have resulted in elevated genetic diversity at the Adh1 locus as well as the trnL-trnF intergenic spacer of cpDNA in this outcrossing species. In contrast, low levels of genetic diversity were detected at both the Adh1 locus and the cpDNA spacer in M. condensatus, consistent with bottlenecks associated with selfing in all populations. While Tajima's D and Fu and Li's F statistics did not reveal deviation from neutrality at the Adh1 locus in M. condensatus, 12 replacements vs. 10 synonymous changes were detected. Based on pairwise comparisons of the dN/dS ratio, lineages of closely related populations of the species distributed along saline habitats appeared to be under directional selection.

Key Words: alcohol dehydrogenase 1 • mating systems • Miscanthus condensatus • Miscanthus sinensis • modes of selection • Poaceae • population demography




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W.-L. Wu, B. A. Schaal, C.-Y. Hwang, M.-D. Hwang, Y.-C. Chiang, and T.-Y. Chiang
Characterization and adaptive evolution of {alpha}-tubulin genes in the Miscanthus sinensis complex (Poaceae)
Am. J. Botany, October 1, 2003; 90(10): 1513 - 1521.
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