A comparison of single-sample effective size estimators using empirical toad (Bufo calamita) population data: genetic compensation and population size-genetic diversity correlations.

The accuracy and precision of four single-sample estimators of effective population size, N(e) (heterozygote excess, linkage disequilibrium, Bayesian partial likelihood and sibship analysis) were compared using empirical data (microsatellite genotypes) from multiple natterjack toad (Bufo calamita) populations in Britain (n = 16) and elsewhere in Europe (n = 10). Census size data were available for the British populations. Because toads have overlapping generations, all of these methods estimated the number of effective breeders N(b) rather than N(e). The heterozygote excess method only provided results, without confidence limits, for nine of the British populations. Linkage disequilibrium gave estimates for 10 British populations, but only six had finite confidence limits. The Bayesian and sibship methods both produced estimates with finite confidence limits for all the populations. Although the Bayesian method was the most precise, on most criteria (insensitivity to locus number, correlation with other effective and census size estimates and correlation with genetic diversity) the sibship method performed best. The results also provided evidence of genetic compensation in natterjack toads, and highlighted how the relationship between effective size and genetic diversity can vary as a function of geographical scale.