The origin of maize (Zea mays mays) in the US Southwest remains contentious, with conflicting archaeological data supporting either coastal1–4 or highland5,6 routes of diffusion of maize into the United States. Furthermore, the genetics of adaptation to the new environmental and cultural context of the Southwest is largely uncharacterized7. To address these issues, we compared nuclear DNA from 32 archaeological maize samples spanning 6,000 years of evolution to modern landraces. We found that the initial diffusion of maize into the Southwest about 4,000 years ago is likely to have occurred along a highland route, followed by gene flow from a lowland coastal maize beginning at least 2,000 years ago. Our population genetic analysis also enabled us to differentiate selection during domestication for adaptation to the climatic and cultural environment of the Southwest, identifying adaptation loci relevant to drought tolerance and sugar content.
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The authors acknowledge the following grants: Marie Curie Actions IEF 272927 and COFUND DFF-1325-00136, Danish National Research Foundation DNRF94, Danish Council for Independent Research 10-081390 and 1325-00136, Lundbeck Foundation grant R52-A5062, Vand Fondecyt Grant 1130261, a grant from the UC Davis Genome Center for the highland maize sequence and NSF IOS-1238014. R.F. is supported by a Young Investigator grant (VKR023446) from Villum Fonden. P.S. was funded by the Wenner-Gren foundation. The authors thank Ângela Ribeiro, Shohei Takuno and Philip Johnson for comments and discussion and staff at the Danish National High-Throughput DNA Sequencing for technical support.
The authors declare no competing financial interests.
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da Fonseca, R., Smith, B., Wales, N. et al. The origin and evolution of maize in the Southwestern United States. Nature Plants 1, 14003 (2015). https://doi.org/10.1038/nplants.2014.3
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