Potential Paths of Migration and Genetic Basis of Herbicide Resistance in a Noxious Agricultural Weed

Herbicide resistance is an unfortunate consequence of relying on a single method of weedy plant control. The evolution of resistance in natural plant populations will depend on various factors, such as the presence of genetic variation and the potential for gene flow between populations. Here we examine migration potential between populations of the common morning glory, Ipomoea purpurea, that show variable levels of resistance to the herbicide glyphosate, using a combined genetic analysis of 15 SSR loci and 8210 SNPs. Our analyses show strikingly different patterns of population connectivity in I. purpurea. While the SSR loci supported an effectively panmictic population, the SNP loci provided evidence of highly structured populations, with localities isolated primarily by geographic distance and landscape cover between sampled localities. Such different pictures of the population dynamic of this species could be attributed to the different temporal scope and coalescent history of both sets of markers, yet further analyses are needed to address this hypothesis. Furthermore, we scanned the genome for signals of adaptation to glyphosate using BAYESCAN to identify loci that were more differentiated between resistant and susceptible populations than expected. Our results yield novel insight into the genetic basis of resistance in this species as well as the potential avenues of migration between populations.