Tests of the outlier status of locus EFbis. A: Heterozygosity in Mytilus edulis populations of the North Sea plotted against heterozygosity in populations of the Bay of Biscay. The 5 allozyme loci are represented by squares and the 6 DNA loci by dots. Locus EFbis is indicated by an arrow. B: FST values between M. edulis of the North Sea and M. edulis of the Bay Biscay plotted against heterozygosity. Single locus FST values are estimated from 5 allozyme loci (squares) and 6 nuclear DNA loci (dots). The outlier EFbis locus is indicated by an arrow. Average (bold line) and 95% confidence envelope (thin lines) are the results from simulations performed with the fdist2 program with the following parameters: infinite-allele model of mutation, 50 islands, two samples and the average gene flow deduced from the all eleven loci.