Deep Time: Integrating Paleobotany and Phylogenetics
Sanderson, Michael .
Is divergence time estimation too relaxed?
Hundreds of phylogenetic analyses of plant diversification published in the last decade have included estimates of divergence times derived from sequence data. Most of these have relied on so-called “relaxed clock” methodologies that do not require the strong assumption of constant rates of sequence divergence. Few theoretical results are known about the statistical performance of these approaches, but it is clear that much depends on the tempo and mode of molecular evolution across loci—particularly whether patterns of accelerated or decelerated evolution between lineages are highly correlated among loci or genomes. In this talk I review the relevant theory and address the empirical question of whether typical sequence data sets sampled from plant genomes exhibit the required properties for divergence time estimation to be a statistically reasonable procedure. Analysis of data sets ranging from EST libraries to whole plastid genomes suggests the existence of pervasive problematic patterns of rate variation at least at the level of relatively deep splits in plant phylogeny. The situation for more recent divergences may be considerably better. In either case, however, quantitative analysis employing multiple fossil calibration points can expose especially sensitive divergence estimates.
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1 - University of Arizona, Ecology and Evolutionary Biology, Tucson, AZ, 85721, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Stevens 4/Hilton
Date: Monday, July 9th, 2007
Time: 4:00 PM