Landscape genetic structure of natural populations of Acacia caven in Argentina

Abstract

Acacia caven is a South American species whichshows remarkable climate tolerance and ecological adaptability;as such, this species is suitable for colonizinganthropogenically degraded sites. This species is widelydistributed, and six varieties have been described based onboth morphological traits and molecular markers. Moreover,Aronson (1992) suggests that, for this species, geographicalseparation could be associated with ecological differentiation.In this study, amplified fragment length polymorphismswere used to study genetic variation within andamong 15 populations of A. caven from five eco-regionsof Argentina and to investigate (1) whether the varieties aregenetically coherent, (2) whether the varieties correspondconsistently to a single eco-region, (3) the proportion of thespecies diversity explained within and among varieties andeco-regions. Eight of the 225 bands appear to be underpositive selection. The remaining 217 neutral loci showeda high percentage of polymorphism (99.1%). The estimatesof genetic diversity Hj were generally high. The FST (0.315)was highly significant, providing evidence for genetic structureamong populations. Hierarchical analysis of molecularvariance indicated that variation among eco-regions was8.2% and highly significant. The higher component ofvariance was found within populations (67.5%). STRUCTUREanalysis suggested that the optimal number of K011.The results showed that, in most cases, geographic separationis associated with ecological differentiation. Since differentiationof A. caven populations studied here in ecoregionswas highly significant, sampling should include alarge number of trees within populations as well as coveringthe wide ecological diversity of the species.