Genetic comparison of introduced and native populations of Rhamnus cathartica, Common Buckthorn

Background/Question/Methods - Rhamnus cathartica (Common Buckthorn) is an Eurasian shrub that is one of the most successful invaders in parts of North America. Presumably introduced to North America for medicinal purposes and as an ornamental in the early 19th century, it has since spread in many regions throughout the United States and Canada. The shrub has recently been described as allelopathic and is also the primary host of the soybean aphid, Aphis glycines, also a non-native species. The purpose of this study was to investigate levels of genetic variation and population differentiation in R. cathartica in its introduced range compared to its native European range. This information is important to better understand the origin of R. cathartica in North America and potentially how it has spread. Additionally, this study set out to identify whether the morphologically similar species R. cathartica and Frangula alnus (previously known as Rhamnus frangula), are genetically distinct.

Results/Conclusions - By analyzing introduced and native populations using microsatellite DNA primers developed specifically for R. cathartica, we found that introduced populations generally exhibited lower levels of genetic variation (mean number of alleles = 7.5; observed heterozygosity = 0.335) than populations in the native range (mean number of alleles = 8.0; observed heterozygosity = 0.427), consistent with a bottleneck effect. However there was no substantial genetic differentiation detected between native and introduced populations of R. cathartica, which may reflect the past ornamental use of this plant species. In contrast, there were distinct genetic differences between F. alnus and R. cathartica, indicating that these genetic markers can be used to distinguish the species in the field. This information will be helpful for land managers looking to control both species in natural areas.