Quercus glabrescens Benth. (white oak) is a widespread temperate forest species endemic to Mexico, known to form hybrids with related species in regions of sympatry. Q. glabrescens presents weak reproductive barriers with other white oak species; hence, in this study, we tested whether increasing the richness of sympatric white oak species contributes to greater genetic diversity in Q. glabrescens. In total, eight microsatellite primers (eight nSSRs and four cpSSRs) were analyzed in five Q. glabrescens populations: one allopatric (without the presence of other white oak) and four sympatric populations, across which the number of white oak species occurring in sympatry with Q. glabrescens ranged from one to four (Q. obtusata, Q. rugosa, Q. laeta, and Q. potosina). In total, 100 individuals were analyzed. In general, sympatric populations had the highest levels of genetic diversity (Gd), Shannon diversity index (H), and expected heterozygosity (He) compared with the allopatric population of Q. glabrescens, regardless of microsatellite origin. Furthermore, estimates of genetic differentiation (FST and RST) were consistently higher for cpSSRs than for nSSRs. Genetic diversity in Q. glabrescens (H, cpSSRs; He and F nSSRs) increased significantly with the number of white oak species occurring in sympatry. Our results support the hypothesis that as the number of white oak species growing in sympatry with Q. glabrescens increases, its genetic diversity also increases, possibly due to introgressive hybridization. This pattern provides a robust framework for predicting how associated oak species may influence the genetic diversity of Q. glabrescens, which permits the assignment of a new conservation status based on species richness growing in sympatry.
Sánchez-Ortiz et al. (Wed,) studied this question.