Maximum-likelihood estimation of migration rates and effective population numbers in two populations using a coalescent approach

A new method for the estimation of migration rates and effective population sizes is described. It uses a maximum-likelihood framework based on coales cence theory. The parameters are estimated by Metropolis-Hastings importanc e sampling. In a two-population model this method estimates four parameters : the effective population size and the immigration rate for each populatio n relative to the mutation rate. Summarizing over loci can be done by assum ing either that the mutation rate is the same for all loci or that the muta tion rates are gamma distributed among loci but the same for all sites of a locus. The estimates are as good as or better than those from an optimized Far-based measure. The program is available on the World Wide Web at http: //evolution.genetics.washington.edu/lamarc.html/.