Low levels of genetic differentiation between Opuntia echios varieties on Santa Cruz (Galapagos)

Three processes play an important role in plant speciation: isolation, hybridization and polyploidization. Galapagos endemic Opuntia display putatively all of these processes. On this archipelago most islands are inhabited by a single Opuntia taxon. Santa Cruz, however, houses two morphologically distinct O. echios varieties (echios and gigantea). Morphological intermediates are found where these two geographically isolated varieties meet. Here we used ten microsatellite loci to reveal the population genetic structure of this system. In contrast to earlier studies, we found high genetic variability within localities. Genetic structuring was weak and no evidence for the existence of hybrids was found. The reasons for this weak genetic structure may include: the species' hexaploid nature, high levels of gene flow, recent colonization, and the lack of geographic barriers. This first detailed genetic study on these threatened species will be important for further conservation planning.