BCB Faculty member in the Ecology, Evolution and Organismal Biology Department
The evolution of maize during post-domestication expansion across the Americas
Maize, like many crop species, colonized a much larger area following its domestication in a narrow center of origin. Many population genomic questions regarding the demography of maize during this expansion remain unanswered. Here, we report high-depth (20-40X) re-sequencing of 31 maize landrace genomes spanning the Americas. Genome-wide demographic analyses reveal a continuous 9000-year genetic bottleneck in maize landraces during expansion with a substantially stronger bottleneck in the Andes of South America. These results suggest a history of serial founder effects in maize during expansion. Andean landraces, located at the expansion wave front of maize, demonstrate the lowest genetic diversity, the highest level of derived homozygous genotypes and runs of homozygosity, and the highest genetic load. Previously detected introgression from teosinte (Zea mays ssp. mexicana) into Mexican highland landraces was confirmed using our genomic data and unreported introgression from this taxon was found extending into the Guatemalan highlands and the southwestern United States. In addition to clarifying the demography of maize during its history of spread, our work has practical implications for maize breeding. For example, efforts to improve Andean material may be particularly challenged by its high level of genetic load, a symptom of its evolutionary history.