Genetic diversity, differentiation and phylogeography of the Stenocereus griseus (Haw.) Buxb. species complex (Cactaceae)

Genus Stenocereus (Cactaceae) is formed by about 23 species, most of them under different type and intensity of management, including forms of silvicultural management and cultivation. Some management types involve domestication processes; previous studies have demonstrated that management determines significant effect increasing frequency of phenotypes favorable to humans in silvicultural managed and cultivated populations. Effects of management on genetic variation have been documented to increase variation in some populations and to decrease in others, but its effect on genetic differentiation between wild and domesticated populations remains unclear. In this study, we evaluate the genetic variation of four species forming the Stenocereus griseus complex (SGSC), the differentiation among populations of species under different management and phylogeographic patterns of the complex. We analyzed population genetics through nine microsatellites and phylogeography by two nuclear regions. Genetic differentiation was higher within than among populations, management therefore accounting for low attributable variance. We identified a genetic spatial pattern of maximum genetic diversity in southern Mexico (Stenocereus pruinosus) dropping down to minimum values in Northern Mexico (S. huastecorum). Phylogeography showed a bottleneck in S. huastecorum and a close relationship between S. laevigatus and S. griseus. We found that genetic diversity and differentiation of the SGSC is associated to spatial factors rather than to management. The discordance between patterns of phenotypic differentiation previously reported and the low or null genetic differentiation can be explained because the neutral markers are not correlated with human selected traits. Use of NGS and genomic approaches could provide a different panorama of genetic variation and differentiation associated to management.