Patterns of chloroplast DNA variation in <Emphasis Type="Italic">Cycas debaoensis</Emphasis> (Cycadaceae): conservation implications |
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Authors: | Qing-Qing Zhan Jin-Feng Wang Xun Gong Hua Peng |
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Institution: | (1) Key Laboratory of Biodiversity and Biogeography, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, 650204, People’s Republic of China;(2) Graduate School of the Chinese Academy of Sciences, Beijing, 100049, China; |
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Abstract: | Climate changes during glacial periods have had significant effects on the current distribution of plant species. Palaeontologial
data suggest that modern cycads originated in southwest China. Cycas debaoensis (Cycadaceae) is an endangered species restricted to a small area of southwest China. This species has been classified into
two types: sand and karst, according to the soil matrix they grow on. To determine the locations of its glacial refugia and
its genetic structure, we examined chloroplast sequence variation of the atpB-rbcL and psbA-trnH intergenic spacers. Four chloroplast DNA haplotypes were obtained from 120 individuals collected from 11 populations covering
the entire extant distribution range of the species. Significant population subdivision was detected (G
ST = 0.684 and F
ST = 0.74160), suggesting low levels of gene flow between regions and populations. There was marked haplotype differentiation
between populations in the sand and karst regions, with only one haplotype being present in both. The molecular phylogenetic
data, together with the geographic distribution of the haplotypes, suggest that C. debaoensis experienced range contraction during glacial periods, and that the current populations are still confined to the areas of
the original refugia. These results implied that isolated refugia might have maintained in both sand and karst regions during
the last glacial maximum and even earlier glaciations. The low within-population diversity of C. debaoensis suggested that there were strong bottleneck events or founder effects within each separate region during the Quaternary climatic
oscillations. These findings are important for the conservation of this endangered species. |
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