RELATIVE APPARENT SYNAPOMORPHY ANALYSIS (RASA)-I - THE STATISTICAL MEASUREMENT OF PHYLOGENETIC SIGNAL

We have developed a new approach to the measurement of phylogenetic si gnal in character state matrices called relative apparent synapomorphy analysis (RASA). RASA provides a deterministic, statistical measure o f natural cladistic hierarchy (phylogenetic signal) in character state matrices. The method works by determining whether a measure of the ra te of increase of cladistic similarity among pairs of taxa as a functi on of phenetic similarity is greater than a null equiprobable rate of increase. Our investigation of the utility and limitations of RASA usi ng simulated and bacteriophage T7 data sets indicates that the method has numerous advantages over existing measures of signal. A first adva ntage is computational efficiency, A second advantage is that RASA emp loys known methods of statistical inference, providing measurable sens itivity and power. The performance of RASA is examined under various c onditions of branching evolution as the number of characters, characte r states per character, and mutations per branch length are varied. RA SA appears to provide an unbiased and reliable measure of phylogenetic signal, and the general approach promises to be useful in the develop ment of new techniques that should increase the rigor and reliability of phylogenetic estimates.