Risk Analysis of Gene Flow from Cultivated, Addictive, Social-Drug Plants to Wild Relatives

Addictive “social drugs” that are derived from plants range from reputable stimulants (e.g., coffee and tea) to stigmatized and dangerous preparations (e.g., ephedrine and cocaine). Both legal and illicit global trade has increased the geographic distribution of plants from which the principal social drugs are obtained. In turn, this range expansion increased opportunities to transfer genes controlling production of high levels of secondary chemicals because of increases in overlapping geographic distributions with sexually compatible domesticated, wild, and weedy relatives. We review the literature for evidence that the introduction of these chemicals into ecosystems could occur through gene flow in ten common, addictive, social drug crops: coca, coffee, cola, ephedra, khat, marijuana, opium poppy, tea, tobacco and yerbe maté. From the published literature of the potential evolutionary and environmental consequences of gene flow from popular social drug crops, we also analyse the subsequent unintended ecological or evolutionary consequences, such as increased weediness, loss of genetic diversity in sexually compatible wild relatives, or health and fitness consequences for herbivores of these crops. Given the rapid industrialization of many of these crops, we identify knowledge gaps and call for renewed attention to the study of their ecology and evolution.