Genetic population divergence: markers and traits

Abstract

In a recent review in TREE [1xAdaptive population divergence: markers, QTL and traits. McKay, J.K. and Latta, R.G. Trends Ecol. Evol. 2002; 17: 285–291Abstract | Full Text | Full Text PDF | Scopus (510)See all References[1], McKay and Latta survey the literature for studies examining adaptive population divergence using molecular markers (Fst) and quantitative genetic trait variation (Qst). Although their paper dealt primarily with theoretical considerations, the authors also presented a large data set in an attempt to elucidate patterns that exist in nature. They show that Qst is on average larger than Fst and that, across studies, the relationship between Qst and Fst is weak. This last result is in contrast to our review of the literature [2xComparison of genetic differentiation at marker loci and quantitative traits. Merila, J. and Crnokrak, P. J. Evol. Biol. 2001; 14: 892–903Crossref | Scopus (520)See all References[2] where we show a strong positive relationship between Qst and Fst. We believe that this discrepancy stems from several errors made by the authors.In Table 1, McKay and Latta give Qst and Fst estimates derived from 29 species: 16 were obtained from published reviews, including ours, whilst 12 were new (the Pinus sylvestris estimate could not be verified). Of these 12 estimates, five (references [49–52,54–59] in [1xAdaptive population divergence: markers, QTL and traits. McKay, J.K. and Latta, R.G. Trends Ecol. Evol. 2002; 17: 285–291Abstract | Full Text | Full Text PDF | Scopus (510)See all References[1]) were for species in which Qst and Fst estimates were derived from separate studies involving different, nonoverlapping populations frequently measured years apart. We see no rational reason why these studies should be included, because Fst/Qst-based divergence studies are population and generation specific and cannot be generalized to all populations of a species. Furthermore, the Sequoiadendron ([60] in [1]) estimate of quantitative divergence was based on ANOVA results, in which percent variation explained by population was used rather than a formal calculation of Qst. Similarly the Phlox (Table 5 in [53] in [1xAdaptive population divergence: markers, QTL and traits. McKay, J.K. and Latta, R.G. Trends Ecol. Evol. 2002; 17: 285–291Abstract | Full Text | Full Text PDF | Scopus (510)See all References[1]) estimate of quantitative trait divergence was based on phenotypic rather than genetic variation, even though a formal breeding design was conducted; therefore it is not an estimate of Qst. Additionally, the Picea glauca (46) Fst/Qst estimates were incorrectly given (reported = 0.36/0.035, correct = 0.098/0.014). Finally, we were unable to obtain the same results for the correlation between Fst/Qst presented in the legend to Fig. 1 [1xAdaptive population divergence: markers, QTL and traits. McKay, J.K. and Latta, R.G. Trends Ecol. Evol. 2002; 17: 285–291Abstract | Full Text | Full Text PDF | Scopus (510)See all References[1] (reported: r = 0.363, P = 0.053; our calculation: r = 0.451, P = 0.014). These errors bring into question the validity of the results and conclusions presented by the authors.In a re-analysis of the data excluding the seven inappropriate species and correcting the Picea glauca Fst/Qst estimates, we found a positive and significant relationship between Fst/Qst: r = 0.52, df = 21, P = 0.013. When we updated our original data set [2xComparison of genetic differentiation at marker loci and quantitative traits. Merila, J. and Crnokrak, P. J. Evol. Biol. 2001; 14: 892–903Crossref | Scopus (520)See all References[2] with five new estimates from [1xAdaptive population divergence: markers, QTL and traits. McKay, J.K. and Latta, R.G. Trends Ecol. Evol. 2002; 17: 285–291Abstract | Full Text | Full Text PDF | Scopus (510)See all References[1] and a further two unpublished estimates, we found a similar positive relationship: r = 0.59, df = 24, P = 0.002.In closing, we found that the inclusion of studies inappropriate to the hypothesis outlined in the McKay and Latta paper, masked a highly significant, positive relationship between molecular marker and quantitative genetic trait variation for population divergence.