ON WEIGHTING AND CONGRUENCE

A priori differential weighting of molecular characters is a common me thodological practice in molecular phylogenetics and evolution. This h as been a largely subjective exercise with few criteria for deciding w hich characters to down-weight and how much to do so. A priori differe ntial weighting is conducted to remove heterogeneity from the data set s and to improve the congruence among the informative, and usually mor e conservative characters. Herein, we test whether congruence is impro ved with a priori differential weighting by using the incongruence len gth difference test on a linked genetic data set consisting of 14 mamm alian taxa and the 13 protein coding genes of the mitochondrial genome . Weighting by omitting the third codon position did not improve congr uence dth respect to the equally weighted data, while weighting transv ersions did improve the congruence between the 13 protein coding genes . Nonetheless, the most parsimonious tree found from transversion weig hting did not differ from one using all of the data equally weighted. (C) 1996 The Willi Hennig Society.