Evidence of local adaptation and stabilizing selection on quantitative traits in populations of the multipurpose American species Acacia aroma (Fabaceae)

Economically and ecologically important quantitative traits of Acacia aroma are related to life history and the size and shape of fruits and leaves. Substantial variation is observed for these traits in natural populations, suggesting a possible genetic basis that could be useful for selection programmes. Our objective was to detect signals of selection on 12 phenotypic traits in 170 individuals belonging to seven populations of A. aroma in the Chaco Region of Argentina. Phenotypic traits were compared with molecular markers assessed in the same populations. Here, we search for signatures of natural selection by comparing quantitative trait variation to neutral genetic variation through the P-ST-F-ST test. We further test for differences among populations for the 12 phenotypic traits, an association of phenotypic variation with environmental variables and geographical distance, and we compare the power of discrimination between the phenotypic and AFLP datasets. The P-ST-F-ST test suggested directional selection for tree height and stabilizing selection for the remaining traits. Analyses of variance showed significant differentiation for eight phenotypic traits. These results suggest selecting among provenances as a management strategy to improve tree height (which showed divergent selection), whereas significant genetic gain for the other traits might be obtained by selection within provenances.