Systematics Section / ASPT
Wojciechowski, Martin F. , Steele, Kelly P. , Sanderson, MJ , Lavin, Matt .
Absolute age estimates in legumes indicate larger genera have higher rates of diversification.
HYPOTHESES to explain the existence of species-rich genera have often invoked differences in rates of morphological character evolution, differences in rates of lineage diversification, a complex association of the two, or their interaction with taxonomic history. Most attempts to estimate diversification rates in plants have relied on i) absolute ages of specific clades estimated using macrofossil/geologic evidence, ii) correlating rates of molecular evolution with species numbers, and iii) absolute ages of clades estimated from fossil-calibrated studies of divergence times. Using two plastid gene phylogenies of Fabaceae, fossil-calibrated, penalized likelihood rate smoothed analyses of divergence times indicate a rapid, family-wide (i.e., caesalpinioid, mimosoid, and papilionoid crown clades) Early Tertiary diversification immediately following its origin. A preliminary analysis of diversification rates (assuming a Yule process) of 19 representative genera using their extant diversity (number of species) and ages estimated from our analysis of a well-supported phylogeny of the family based on matK sequences (335 taxa) demonstrated a statistically significant relationship (p< 0.01) between the rate of diversification and genus size within legumes. Our results show that large genera (60 to 2,500 spp.) do have higher rates of diversification, but are not significantly older, than small genera (2 to 6 spp.). We have extended this analysis to a larger matK phylogeny (435 taxa) of the family and will present the results of more comprehensive tests using a larger number of genera of legumes of various sizes.
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1 - Arizona State University, School of Life Sciences, P.O. Box 874501, Tempe, Arizona, 85287-4501, USA
2 - Arizona State University, Polytechnic Campus, Department of Applied Biological Sciences, Mesa, Arizona, 85212, USA
3 - University of California, Davis, Section of Evolution and Ecology, One Shields Ave., Davis, California, 95616, USA
4 - Montana State University, Department of Plant Sciences, Bozeman, Montana, 59717, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 31st, 2006
Time: 2:45 PM