Tracking the altitudinal adaptation of Andean maize using archaeogenomics

Understanding how crops can adapt to conditions of lower water availability, lower temperatures and shorter growing seasons is of importance as we consider new environments for agriculture to meet our food security needs. Such adaptations have occurred in the past, in particular adaptations to high altitude. The adaptation of maize from the sea level lowlands to the heights of the Andes at over 4000 metres above sea level represents one of the most extreme altitudinal adaptations of any crop and is recorded in a series of archaeological samples of maize over time spanning the last 2600 years as a complex series of Andean cultures expanded into the mountain chain. Much is still not understood about how these cultures may have interacted, and how maize achieved such an extreme adaptation in a relatively short period of time.

In recent years we have discovered that maize expanded out of its area of origin from its teosinte progenitor not once but on multiple occasions, each wave carrying different compositions of genetic diversity that may have had different adaptive potential. In particular, later waves of maize expansion carried genetic diversity from a second wild progenitor species of teosinte that was adapted to the highlands of Mesoamerica. We do not know to what extent this later wave was responsible for maize's progression to high altitude or whether high altitude adaptations had already been achieved through novel adaptations locally. Nor do we know how such maize might have been exchanged throughout the different cultural spheres. To tease apart these factors it would be ideal to examine the genomes of the maize of that time to identify the nature of their adaptations and their ancestry and when they changed.

The state of archaeogenomics technology is such now that recovery of genomes from archaeological materials has become mainstream and can be carried out at scale. We have a unique collection of 277 archaeological maize samples that cover the expansion of maize from just above sea level to over 4000 metres - higher than any maize is known to grow today. In this project we will recover at least 150 archaeogenomes from across 10 cultures in the Andean area to track the adaptation of maize to high altitude. In this way we will be able to answer the questions above about how maize adapted, if and how it was exchanged between cultures, and whether the maize of the past had properties that meant that it could grow higher than maize today. Together these findings will be important for understanding Andean archaeology, maize biology and evolutionary studies in general with potential outputs for maize breeding in the future.