Principles of crucifer evolution
O'Kane, Jr., Steve L. .
Evolution and classification of Physaria (Brassicaceae).
The genus Physaria (Brassicaceae) was recently vastly expanded by the inclusion of most of the species of Lesquerella. A few species were placed in the newly decribed genus Paysonia. In addition to Physaria and Paysonia, Lyrocarpa, Dimorphocarpa, Dithyrea, Nerisyrenia, and Synthlipsis together constitute a clade, Tribe Physarieae, that share the synapomorphy of pollen grains with more than three colpi. Phylogenetic studies within Physaria using the internal transcribed spacer (ITS) of nuclear ribosomal DNA, using the other genera as outgroups, and both maximum likelihood and Bayesian reconstructions, present a problem often encountered in studies of the entire Brassicaceae and of particular genera; namely, often good resolution in parts of the tree but little stastical support for its backbone. Using ITS alone several intrageneric problems can, however, be resolved. Physaria is strongly supported as distinct from Paysonia (100% bootstrap support). Physaria in its classic (small) sense is polyphyletic and its recognition as distinct from Lesquerella causes the latter to be paraphyletic. Several small clades are shown to be geographically bounded; for example, two small clades are Mexican and the Argentinian/Bolivian species form a clade. Another small clade includes most of the annual species of the genus. Inflated, notched, or didymous fruits have evolved several times independently. Recent work is beginning to incorporate sequences of introns and intergenic spacers from the chloroplast genome. Among several candidate loci examined, the rps16 intron, the trnV-ndhC intergenic spacer, and the ndhF-rpl32 intergenic spacer have been especially useful. Support values for each region typically exceeds that for ITS alone, combined these loci can provided fairly high statistical support for nodes otherwise poorly supported. Analyses which further incorporate coded gaps provide the best statistical support.
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1 - University of Northern Iowa, Biology, McCollum Hall, Cedar Falls, IA, 50614-0421, USA
trnV-ndhC intergenic spacer
ndhF-rpl32 intergenic spacer.
Presentation Type: Symposium or Colloquium Presentation
Location: Delaware C/Hyatt
Date: Tuesday, July 10th, 2012
Time: 4:00 PM