Figure 1.

Likelihood that a set AL_total of ancestral AFLP loci, among which a number AL_fixed are fixed, leads to the observed pattern of fixation in the two albatross species after their divergence. The current pattern is 184 loci fixed in both species and one locus fixed differentially (i.e. present in the wandering Albatross and absent in the Amsterdam Albatross). Results are from 10 000 simulations for each starting values of AL_total and AL_fixed. Note that the maximum number of fixed ancestral loci cannot exceed its current number (184) since pure drift will maintain monomorphic loci as monomorphic. In addition, the number of ancestral loci has to be at least as large as the number of loci found in the dataset (185) since loci subjected to pure drift can only disappear through drift, i.e. after fixating for absence in both species (see the worked out example in Appendix A).