PHYLOGENIES FROM RESTRICTION SITES: A MAXIMUM-LIKELIHOOD APPROACH

Restriction sites data can be analyzed by maximum likelihood to obtain estimates of phylogenies. The likelihood methods of Smouse and Li, who were able to compute likelihoods for up to four species under a simplified model of base change, can be extended numerically to deal with any number of species. The computational methods for doing so are outlined. The resulting algorithms are slow but take multiple gains and losses of restriction sites fully into account, unlike parsimony methods. They allow for the failure to observe potential sites that are absent from all species. Analysis of the five-species hominoid data of Ferris and coworkers confirms the pattern found by Smouse and Li with four species-that a chimpanzee-gorilla clade is favored, but not statistically significantly over other tree topologies. A large data set produced by computer simulation has also been analyzed to confirm that the method works properly. The methods used here do not allow for different rates of transitions and transversions. They can be extended to do so, but only at a cost of considerably slower computations. The present method is available in a computer program.