Factorial analysis of bootstrap variances of population genetic parameter estimates

RESUMO

We presented an alternative way to verify the relative contribution to the total variance, of the sources of variation due to populations (P), individuals within populations (I), the (P*I) interaction, and the standard error of the following parameter estimates total (F) and intrapopulation (f) fixation indices, and divergence among populations (q). The knowledge of this relative contribution is important to establish sampling strategies of natural populations. To attain these objectives, the bootstrap method was used to resample simultaneously populations and individuals, considering different combinations of P and I. This procedure was repeated five times for a given combination of each analyzed data set. For each data set, five estimates of these variances were obtained for each combination of P and I, and a given parameter estimate. These variance estimates were submitted to an analysis of variance, considering a factorial structure. The sources of variation considered in this analysis were P, I and P*I. The coefficient of determination (R²) was calculated for each source of variation. Sources of variation with greater R² are responsible for bigger errors of the estimates. The method applied was efficient for answering the questions initially proposed, and the results indicated that there are no ideal sample sizes for a species, but rather for a specific data set, because each data set has its own particularities. However, for investigations on the genetic structure of natural populations using population parameters, the number of populations to be sampled is a critical factor. Thus, more efforts should be made to increase the number of sampled populations, rather than the number of individuals within populations. A sampling strategy is given as a guide for investigations of this kind, when there is no previous knowledge about the genetic structure and the mating system of the populations.