A comparison of two indirect methods for estimating average levels of geneflow using microsatellite data

We compare the performance of Nm estimates based on F-ST and R-ST obtained from microsatellite data using simulations of the stepwise mutation model w ith range constraints in allele size classes. The results of the simulation s suggest that the use of microsatellite loci can lead to serious overestim ations of Nm, particularly when population sizes are large (N > 5000) and r ange constraints are high (K < 20). The simulations also indicate that, whe n population sizes are small (N less than or equal to 500) and migration ra tes are moderate (Nm approximate to 2), violations to the assumption used t o derive the Nm estimators lead to biased results. Under ideal conditions, i.e. large sample sizes (n(s) greater than or equal to 50) and many loci (n (l) greater than or equal to 20), R-ST performs better than Fs, for most of the parameter space. However, F-ST-based estimates are always better than R-ST when sample sizes are moderate or small (n(s) less than or equal to 10 ) and the number of loci scored is low (n(l) < 20). These are the condition s under which many real investigations are carried out and therefore we con clude that in many cases the most conservative approach is to use F-ST.