Systematics Section / ASPT
Albert, Victor A. , Farris, James S. .
Support weighting resolves basal eudicot relationships using the 500-sequence rbcL matrix alone.
Källersjö et al. (Cladistics 15, 91-93), among others, have demonstrated that nucleotide sites in third positions of codons can enhance tree-resolving power, even while exhibiting more parallelisms and reversals (homoplasy) than the other two positions. These authors also demonstrated empirically that the performance of nucleotides in third positions increased as the number of taxa sampled increased, at least in terms of initial similarities retained as hierarchically informative in most-parsimonious trees. Support Weighting (Cladistics 17, 389-394) was developed to highlight the degree to which changes in a character are concentrated in the supported branches of a tree. In doing so, it circumvents the problem of down-weighting homoplastic sites. We used Support Weighting to re-evaluate the 500-sequence rbcL matrix of Chase et al. (Ann. Missouri Bot. Gard. 80, 526-580). Support Weighting provides added structure to a number of tree regions that are poorly resolved in the strict consensus of most parsimonious trees ( http://www.cladistics.com/zillaframe.htm), including the basal branches of the eudicots. Ranunculales are resolved as the sister clade to all other eudicots; the next branch is (Nelumbonaceae, Platanaceae, (Proteaceae, Sabiaceae)), followed by (Buxaceae, Trochodendraceae), and finally Gunneraceae sister to all remaining eudicots. Similar, most-parsimonious resolutions with jackknife support have been obtained only from a 4-gene data set including rbcL (Am. J. Bot. 90, 461-470). Use of Support Weighting on the 500-sequence rbcL matrix therefore reveals more corroborated tree structure than does equally weighted parsimony analysis.
1 - Naturhistoriska Riksmuseet, Molekylärsytematiska Laboratoriet, Box 50007, Stockholm, SE-104 05, Sweden
2 - University of Oslo, Botanical Garden, Natural History Museums and Botanical Garden, P.O. Box 1172 Blindern, Oslo, NO-0318, Norway
large data matrices.
Presentation Type: Paper
Location: Cottonwood B (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 9:30 AM