Strong human-mediated selection via herbicide application in agroecosystems has repeatedly led to the evolution of resistance in weedy plants. Although resistance can occur among separate populations of a species across the landscape, the spatial scale of resistance in many weeds is often left unexamined. We assessed the potential that resistance to the herbicide glyphosate in the agricultural weed Ipomoea purpurea has evolved independently multiple times across its North American range. We examined both adaptive and neutral genetic variations in 44 populations of I. purpurea by pairing a replicated dose–response greenhouse experiment with SSR genotyping of experimental individuals. We uncovered a mosaic pattern of resistance across the landscape, with some populations exhibiting high-survival postherbicide and other populations showing high death. SSR genotyping revealed little evidence of isolation by distance and very little neutral genetic structure associated with geography. An approximate Bayesian computation (ABC) analysis uncovered evidence for migration and admixture among populations before the widespread use of glyphosate rather than the very recent contemporary gene flow. The pattern of adaptive and neutral genetic variations indicates that resistance in this mixed-mating weed species appears to have evolved in independent hotspots rather than through transmission of resistance alleles across the landscape.

Glyphosate dose response data for the common morning gloryDose response data from field-collected seed material. RoundUp PowerMax was used in herbicide resistance screen. All data was collected in University of Georgia Plant Sciences greenhouses (Athens, GA). Shown are individual ID (ID), Experimental replicate (Experiment), Treatment Dose (TreatmentLevel), Population ID number (POPID),State in which population was samped, region in which population was sampled, Survival to glyphosate (Survivorship, 1= survived, 0= died).DoseResponseData.csvSSR data for population genetic screen of the common morning glorySSR loci data for I. purpurea field collections. Leaf material used for DNA isolation and SSR genotyping was obtained from field collections in 2012 growing season. in GenalEx format from 2012 sampling period. Shown are population ID (POPID), and each SSR locus size for 2 alleles per 15 loci used in the data set. Data are shown in 30 subsequent columns (2 columns per locus): 31, 2, 27, 8, 34, 18, 1, 36, 47, 12, 21, 6, 45, 26, 42. A zero indicates missing data at a locus.SSRData.csv