Systematics Section / ASPT
Duvall, Melvin R. , Leseberg, C. H. , Robinson, J. W. , Mathews, Sarah .
Lineage-specific differences in numbers of nucleotide substitutions in mitochondrial loci of basal monocots; impact on angiosperm phylogenetics.
Disparate levels of molecular evolution, which can indicate either accelerated rates or substitutions accumulated through longer times, may bias phylogenetic results.A nine-fold excess of substitution mutations was observed in sequences of the mitochondrial atp1 locus of Sagittaria latifolia and Acorus calamus relative to atp1 in other angiosperms and there is evidence of bias or error in trees inferred from atp1.A survey indicated similarly elevated substitutions in A. gramineus and A. americanus and representative Alismataceae, Juncaginaceae and Potamogetonaceae contrasting with typical substitution levels in other Alismatales (Tofieldiaceae, Araceae, and Hydrocharitaceae).Hypotheses relating to increased substitution rates are readily tested.Elevated substitution rates in cytoplasmic loci can be a signature of intergenomic transfer to the nucleus where rates are higher.Alternatively, there might be a genome-wide elevation of substitution rates in the mitochondria of selected basal monocots, possibly because of reduced error correcting mechanisms and/or relaxed selection.The ratio of nonsynonymous to synonymous substitutions suggested relaxed selection of function.However, other indications of relaxed selection were not apparent.Attempts to amplify from polyadenylated atp1 RNA templates extracted from A. americanus and S. latifolia with poly-T and atp1-specific primers (and a cox1 primer; see below) by RT-PCR failed, even though positive controls produced the expected product.This result argued against a hypothesis of intergenomic transfer and was consistent with previously published hybridization screens.cox1 shows similarly elevated substitutions in some of the same lineages together with Hydrocharitaceae although not in Juncaginaceae and Potamogetonaceae.Thus, the effect is not consistently genome-wide in the mitochondria of affected taxa.Hypotheses relating to lineage persistence require verification from other data that are independent of the sequences.
1 - Harvard University, Arnold Arboretum, 22 Divinity Avenue, Cambridge, Massachusetts, 02138, USA
2 - Northern Illinois University, Department of Biological Sciences, Montgomery Hall, DeKalb, Illinois, 60115, USA
Presentation Type: Paper
Location: Cottonwood B (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 5:15 PM