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ABSTRACT Genetic variation is usually estimated empirically from statistics based on population gene frequencies, but alternative statistics based on allelic diversity (number of allelic types) can provide complementary information. There is a lack of knowledge, however, on the evolutionary implications attached to allelic-diversity measures, particularly in structured populations. In this article we simulated multiple scenarios of single and structured populations in which a quantitative trait subject to stabilizing selection is adapted to different fitness optima. By forcing a global change in the optima we evaluated which diversity variables are more strongly correlated with both short- and long-term adaptation to the new optima. We found that quantitative genetic variance components for the trait and gene-frequency-diversity measures are generally more strongly correlated with short-term response to selection, whereas allelic-diversity measures are more correlated with long-term and total response to selection. Thus, allelic-diversity variables are better predictors of long-term adaptation than gene-frequency variables. This observation is also extended to unlinked neutral markers as a result of the information they convey on the demographic population history. Diffusion approximations for the allelic-diversity measures in a finite island model under the infinite-allele neutral mutation model are also provided.
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THE analysis of the genetic structure of subdivided populations is a key issue in most evolutionary and conservation genetics studies. Genetic variation in subdivided populations is usually estimated as gene diversity (or expected heterozygosity) from gene-frequency data. In addition, genetic differentiation among subpopulations is universally estimated by Wright's (1943, 1969) fixation index (FST), by its multiallelic version (GST, Nei 1973), or by a number of statistics closely related to FST, all of them based on differences in gene frequencies among subpopulations. Moreover, FST or GST, estimated from neutral molecular markers, also provides a reference point for evaluating the strength of divergent selection on quantitative traits (Leinonen et al. 2008; Whitlock 2008).
Allelic-diversity measures, i.e.,measures based on the number of different allelic types segregating in the population, are also widely used, particularly in conservation genetics studies. For example, it is recognized that the number of alleles segregating in a population gives basic information regarding past fluctuations in population size (Nei et al. 1975; Luikart et al. 1998). Moreover, the number of rare alleles can be used as an...