SUBSTITUTION BIAS, WEIGHTING OF DNA-SEQUENCE EVOLUTION, AND THE PHYLOGENETIC POSITION OF FEA VIPER

The evolution of mitochondrial ribosomal DNA sequences was investigated to infer the phylogenetic position of the Asian viper Azemiops feae and to refine weighting methodology for phylogenetic analysis of DNA sequences. To compare characteristics of sequence evolution and weighting methodology in a different group of vertebrates, the published mitochondrial ribosomal DNA data included in the study of chiropteran monophyly by Mindell et al. (1991, Proc. Natl. Acad. Sci. USA 88:10322-10326) were also analyzed. Sequence evolution in all taxa was marked by extreme substitution bias. For the L-strand, both mono- and ditypic substitutions involving G were rare in comparison with expected occurrences based on sequence composition. Character state weights were assigned prior to phylogenetic analysis in proportion to the ratio of expected to observed nucleotide differences in pairwise comparisons of sequences. Application of expected to observed ratio (EOR) weights strengthened support for an Azemiops/pitviper clade and for the monophyly of Chiroptera. This method may help in resolving rapid radiations and other relationships obscured by homoplasy.