A comparison of patterns of genetic structure in two co-occurring Agave species (Asparagaceae)that differ in the patchiness of their geographical distributions and cultivation histories

Spatial genetic structure in plants can be affected by continuity of geographical distribution, cultivation history, pollination and seed dispersal mechanisms. Here, we examined the relative effects of these factors on the genetic structure of Agave palmeri and A. parryi, which share similar pollination syndromes and seed dispersal mechanisms but differ in the continuity of their distributions and cultivation history. Agave parryi has a patchy distribution and was cultivated by Native Americans, whereas A. palmeri has a more continuous distribution and no documented history of cultivation. We sampled populations of each species in their North American ranges, genotyped individuals with microsatellite loci and analysed patterns of genetic structure. No genetic structuring was detected in A. palmeri, but A. parryi formed three distinct genetic clusters, corresponding to geographical locations. One genetic cluster of A. parryi contained populations from lower elevations and had lower levels of genetic diversity, probably indicating anthropogenic origins. We conclude that continuity of distribution, pollinators and cultivation history all may affect patterns of genetic connectivity.