ESTIMATING GENE FLOW IN ISLAND POPULATIONS

A new method is presented for estimating the rate of gene flow into is land populations using the distribution of alleles in samples from a n umber of islands. The pseudo maximum likelihood estimator (PMLE) that we derive may be applied to species with either discrete or continuous generation times. For Wright's discrete-generation island model, the method provides an estimate of theta = 2Nm where N is the (haploid) po pulation size on each island and nl is the fraction of individuals rep laced by immigrants in each generation. For a continuous-generation is land model, the corresponding parameter theta is the ratio of the immi gration rate phi to the individual birth rate h. Monte Carlo simulatio ns are used to compare the statistical properties of the PMLE with tho se of two alternative estimators of a derived from Wright's F-statisti cs. The PMLE is shown to have greatest efficiency (least mean square e rror) in most cases for a wide range of sample sizes and parameter val ues. The PMLE is applied to estimate theta using mtDNA haplotypes and allozymes for subdivided populations of African elephants and Channel Island foxes.