Systematics Section / ASPT
Davis, Jerrold I. , Petersen, Gitte , Seberg, Ole , Stevenson, Dennis Wm. .
Mitochondrial genes, chloroplast genes, and monocot relationships.
MITOCHONDRIAL genes frequently exhibit variation patterns suggestive of marked changes in evolutionary rates. This phenomenon is observed in the nuclear and plastid genomes as well, but against the backdrop of extremely low evolutionary rates, as is typical for many mitochondrial genes, even minor increases in rate, particularly when localized in two or more clades, can have profound effects on the phylogenetic relationships that are inferred. Correlations in rate changes among genes contribute to the potential for error in phylogenetic inference. Within the monocots, evolutionary rate changes have been characterized by previous investigators (B. Gaut and others) in several groups (e.g., acceleration in Poaceae, deceleration in Arecaceae), so the monocots are a fertile system in which the effects of rate heterogeneity among genes and lineages can be examined. A phylogenetic matrix representing four genes, two each from the plastid genome (rbcL and matK) and mitochondrial genome (atpA and cob), as sampled across all major lineages of monocots, has been assembled and analyzed. Sensitivity analyses identify genes and particular regions within the genes that influence the relationships that are resolved. Dramatic shifts in evolutionary rate are observed in all four genes, and these have profound results on the relationships that are resolved. Some of the more controversial outstanding problems in monocot phylogenetics involve particularly long branches, while others involve short branches, and relationships in both of these categories often are affected by the inclusion vs. exclusion of taxa that are distant from the problematic nodes. The results indicate that several key aspects of large-scale monocot relationships remain unsettled, and that the downweighting or elimination of particular genes or gene sets from analyses is not likely to add to our understanding of relationships among the monocots.
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1 - Cornell University, L.H. Bailey Hortorium, Department of Plant Biology, Ithaca, New York, 14853, USA
2 - Natural History Museum of Denmark, Sølvgade 83, Opg. S, Copenhagen, DK-1307, Denmark
3 - New York Botanical Garden, Institute of Systematic Botany, 200Th Street & Southern Boulevard, Bronx, New York, 10458-5126, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 144/Performing Arts Center
Date: Tuesday, August 1st, 2006
Time: 11:30 AM