The origin and evolution of maize in the American Southwest

Maize offers an ideal system through which to demonstrate the potential of ancient population genomic techniques for reconstructing the evolution and spread of domesticates. The diffusion of maize from Mexico into the North American Southwest (SW) remains contentious with the available evidence being restricted to morphological studies of ancient maize plant material. We captured 1 Mb of nuclear DNA from 32 archaeological maize samples spanning 6000 years and compared them with modern landraces including those from the Mexican West coast and highlands. We found that the initial diffusion of domesticated maize into the SW is likely to have occurred through a highland route. However, by 2000 years ago a Pacific coastal corridor was also being used. Furthermore, we could distinguish between genes that were selected for early during domestication (such as zagl1 involved in shattering) from genes that changed in the SW context (e.g. related to sugar content and adaptation to drought) likely as a response to the local arid environment and new cultural uses of maize.