SAAR, DAYLE E. and MELVIN R. DUVALL.* Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115-2861.. - Do nuclear and plastid loci in Asteraceae show substantial incongruence? A preliminary intertribal phylogenetic study of Heliantheae s. l.
Asteraceae present special technical challenges for molecular
phylogenetic studies. Less sequence divergence is generally observed
between composites at all taxonomic levels than between comparable
taxa in other families. Combining sequences from different loci into
the same analysis increases the amount of phylogenetic signal and
improves resolution in phylogenetic trees. As members of the
Compositae Alliance continue to coordinate their efforts the
motivation for combining DNA sequences from loci in different genomes
will increase. However, the relatively recent radiation of the family
suggests a greater probability of character incongruence between loci,
because of differential lineage sorting and/or interspecific
hybridization. Reported here is a preliminary molecular phylogenetic
study of Heliantheae s. l. This complex exhibits typically low levels
of intergeneric sequence divergence. Selected species in 16 genera
were analyzed to test the feasibility of combining data. Sequences
were determined or obtained for the variable 3’ portion of the plastid
locus ndhF and the nuclear ribosomal ITS region. Interlocus
congruence was assessed with two methods both of which found
significant congruence between nuclear and plastid trees. The data
sets were then combined and analyzed together. The combined tree had a
larger measure of signal content, higher resolution, and better
support values for internal nodes than trees from either of the
separate data sets.
Key words: Asteraceae, Heliantheae s. l., intergenomic incongruence, molecular phylogenetics