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Systematics Section / ASPT

Kelch, Dean [1], Baldwin, Bruce G. [1].

Phylogenetically useful nuclear markers in Cirsium (Compositae), a recently radiated clade.

Previously, we used sequence data from transcribed spacers of nuclear ribosomal DNA to resolve historical biogeography and ecology of true thistles, genus Cirsium. Although sequences from ribosomal DNA spacers proved useful as a beginning in understanding the phylogeny of Cirsium, many branches within putative phylogenetic trees were poorly supported. Therefore, we have developed other, variable markers that are contributing to an increased understanding of relationships within Cirsium. To date, we have successfully sequenced 35 Cirsium taxa for a region of glyceraldehyde 3-phosphate dehydrogenase (G3pdh; 930 bp long within Cirsium) and two currently unidentified nuclear regions, B1 (880 bp long within Cirsium) and HK (942 bp long within Cirsium). These markers are easily alignable within Cirsium, with 146, 122, and 135 potentially phylogenetically informative characters, respectively. Primer pairs specifically designed to amplify these three gene regions in tribe Cynareae or subclass Asteridae each gave amplification of one band that was cloned and easily sequenced. Parsimony analysis of data from each marker produced strict consensus trees with significant structure and some well-supported branches including New World Cirsium and a Western American clade of Cirsium with n=32. Most importantly, strong grouping of cloned sequence variants from the same individual or taxon indicates rapid lineage sorting; in other words, based on allelic sampling to date, the rate of fixation of new mutations has evidently exceeded the rate of diversification for the three gene regions. Given the high potential for misleading phylogenetic results in the face of delayed allelic/lineage sorting, our findings for the cloned sequences illustrate molecular evolutionary properties that enhance phylogenetic utility of these markers.


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1 - University of California, Berkeley, Integrative Biology, University and Jepson Herbaria, 1001 Valley Life Sciences Building, Berkeley, California, 94720, USA

Keywords:
Cirsium
Phylogeny.

Presentation Type: Oral Paper
Session: 45-6
Location: 400/Hilton
Date: Wednesday, August 17th, 2005
Time: 9:15 AM
Abstract ID:335


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