Systematics Section / ASPT
Duvall, Melvin R. , Robinson, Jace W. , Mattson, Jeremy G. .
Incongruence between two mitochondrial gene trees suggests that cytochrome oxidase subunit 1 sequences are unreliable for angiosperm phylogenetics.
THE relatively low rates of substitution in mitochondrial genes argue for their combined use as tools that are relatively free of saturation effects when studying deep angiosperm evolution. The five most thoroughly sampled angiosperm mitochondrial sequences, atp1, matR, cox1, mtSSU and mtLSU each offers a useful starting data base from which to build matrices for separate and combined phylogenetic analyses of deep nodes. For this study we selected atp1 and cox1, both of which encode membrane-embedded components of the respiratory pathway, and might be expected to have similar functional constraints, linked selection pressures, and parallel histories. Strictly parallel sampling of 54 taxa was achieved plus four conglomerative taxa with representatives from each of the major clades. However, separate and combined analyses produced strongly incongruent results, particularly with regard to the positions of Acorus, Lilium, Joinvillea and Liriodendron, as well as selected magnoliids, Piperales, eudicots and Alismatales. BLAST searches for sequences from each of these species found closely matching unexpected targets for the cox1, but not the atp1 sequence in each case. One explanation for these results is horizontal gene transfer of cox1 loci, although in the case of Alismatales the event apparently predated the radiation of the entire order. As a further complication, pairwise comparison of duplicated cox1 sequences from the same or closely related species of Austrobaileya and Nelumbo showed unexpected divergence with a high proportion of substitutions suggesting unidirectional methylation-induced transitions. Combined analysis of these mitochondrial loci produced phylogenies that were radically incongruent with plastid and nuclear PHYC gene trees arguing against the use of cox1 for deep angiosperm phylogenetics.
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1 - Northern Illinois University, Department of Biological Sciences, Montgomery Hall, DeKalb, Illinois, 60115-2861, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 144/Performing Arts Center
Date: Tuesday, August 1st, 2006
Time: 10:30 AM