Evidence from a specialist parasitic insect supports range expansion of cultivated sunchoke (Helianthus tuberosus) in the Eastern Agricultural Complex

Abstract

A suite of plants, the Eastern Agricultural Complex (EAC), was domesticated in North America beginning around 4000 YBP by Indigenous peoples. At the time of European colonization, another plant, the sunchoke (Helianthus tuberosus), was in wide cultivation. It is unknown whether this sunflower species was intentionally moved around the continent along with the EAC plants or if instead sunchoke was already widespread and experienced separate and independent cases of local husbandry and cultivation. Evidence of a sunchoke range expansion coincident with the timing of the EAC would support a hypothesis of intentional anthropogenic movement. For plants like H. tuberosus, genome complexity makes direct inferences of historical demography from plant genetic data difficult. Therefore, we use a specialist insect parasite of sunchoke, the fly Strauzia longitudinalis (Loew), to test a hypothesis of sunchoke range expansion. Using reduced-representation sequencing data, demographic models suggest S. longitudinalis from western sites split from flies in the Ohio Valley and further east approximately 6850-2700 YBP, overlapping the timing of the EAC. Further, several metrics of genetic diversity and differentiation implicate the Ohio Valley as a pre-cultivation range for sunchoke. These findings are consistent with a hypothesis of anthropogenic range expansion for sunchoke in North America.