Systematics Section / ASPT
Raubeson, Linda A. , McCoy, Skip K R , Müller, Kai , Wall, P. Kerr , Leebens-Mack, Jim , Boore, Jeffrey L. , Jansen, Robert K. , dePamphilis, Claude W. .
Seed plant phylogeny based on sequences from 61 (mostly) shared plastid genes.
RELATIONSHIPS among the five (or six) extant lineages of seed plants are poorly understood. Current controversies focus mainly on the placement of Gnetales. Four hypotheses receive varying amounts of support – Gnetales sister to angiosperms (the anthophyte hypothesis), Gnetales sister to remaining seed plants, Gnetales sister to conifers, and Gnetales sister to Pinaceae within conifers. To address this and other questions of seed plant phylogeny, we extracted data from our draft gymnosperm chloroplast genome sequences and assembled a data matrix including 61 plastid genes and over 46,000 nucleotide characters. Our matrix includes angiosperms, one representative of each other extant seed plant lineage – Ginkgo, Cycas (Cycadales), Welwitschia (Gnetales), Pinus (conifer I) and Podocarpus (conifer II) – and multiple outgroups. In preliminary analyses, these data behave similarly to those reported by others relative to this issue -- Rooted parsimony analyses yield the Gnetales basal tree when including all nucleotide positions (although Gnetales are placed within conifers in unrooted trees). Alternatively, Gnetales are embedded within conifers whether rooted or unrooted MP trees are generated when 3rd positions are excluded and in all ML analyses (with or without 3rd positions). The surprise here is that, when Welwitschia is placed within conifers, it is sister to Podocarpus not Pinus (probably due to rate heterogeneity). SH test results indicate that the likelihoods of a Pinus-Welwitschia grouping and a Podocarpus-Welwitschia grouping do not differ significantly (although Gnetales basal trees do have significantly lower likelihood). A second question in seed plant phylogeny involves the placement of cycads and Ginkgo on the seed plant tree. On our rooted MP trees Cycas and Ginkgo are well-supported sister taxa whereas on unrooted trees (MP or ML) Cycas is the basal gymnosperm. However SH tests indicate no significant differences in likelihood between these two hypotheses in unrooted analyses (p=0.789). Additional analyses are underway.
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1 - Central Washington State University, Department of Biological Sciences, Ellensburg, Washington, 98926-7537, USA
2 - Rheinische Friedrich-Wilhelms-Universität Bonn, Nees-Institut für Biodiversität der Pflanzen, Meckenheimer Allee 170, Bonn, D-53115, Germany
3 - Pennsylvania State University, Department of Biology, 403 Life Sciences Building, University Park, Pennsylvania, 16802, USA
4 - University of Georgia, Department of Plant Biology, Athens, Georgia, 30602, USA
5 - DOE Joint Genome Institute, Department of Evolutionary Genomics, 2800 Mitchell Drive, Walnut Creek, California, 94598, USA
6 - University of Texas Austin, Section of Integrative Biology, 1 University Station, A6700, Austin, Texas, 78712-7640, USA
7 - Pennsylvania State University, Department of Biology and Institute of Molecular Evolutionary Genetics, University Park, Pennsylvania, 16801, USA
seed plant phylogeny
Presentation Type: Oral Paper:Papers for Sections
Location: 144/Performing Arts Center
Date: Tuesday, August 1st, 2006
Time: 8:45 AM