ANALYSIS OF GENETIC-STRUCTURE AND DISPERSAL PATTERNS IN A POPULATION OF SEA BEET

A model of the migration patter in a metapopulation of sea beet (Beta vulgaris L. ssp. maritima), based on the continuous distributions of s eed and pollen movements, is fitted to gene frequency data at 12 isozy me and RFLP loci by maximum likelihood by using an approximation of th e simultaneous equilibrium distribution of the gene frequencies genera ted by the underlying multivariate stochastic process of genetic drift in the population. Several alternative restrictions of the general mo del are fitted to the data, including the island model, a model of com plete isolation, and a model in which the seed and pollen dispersal va riances are equal. Several likelihood ratio tests between these altern atives are performed, and median bias in the estimated parameters is c orrected by using parametric bootstrapping. To assess the fit of the s elected model, the predicted covariances are compared with covariances computed from the data directly. The dependency of estimated paramete rs on the ratio between effective and absolute subpopulation sizes, wh ich is treated as a known parameter in the analysis, is also examined. Finally, we note that the data also appear to contain some informatio n about this ratio.