Spatial structure of genetic and chemical variation in native populations of the mile-a-minute weed Mikania micrantha

We examined the spatial distribution and potential relationship of genetic and volatile terpenoid diversity in 13 Mexican populations of Mikania micrantha (Asteraceae) from the Atlantic and Pacific watersheds using six specific microsatellites. A low genetic diversity was observed in all populations (HE = 0.00–0.37), which may be attributed to clonal reproduction and/or their marginal location relative to the whole species distribution in the Americas. We found a significant genetic differentiation between regions, and more genetic structure in Atlantic populations where a Mantel test also showed a pattern of isolation by distance (r2 = 0.478, P = 0.002). In addition, we detected three genetic barriers that match geographic barriers and may be responsible for population isolation. The geographic patterns of genetic diversity were compared to those from chemical diversity but we found no correlation between the genetic and chemical distances of the populations. Our results suggest that neutral molecular markers and adaptive traits like defensive metabolites provide complementary information that may prove useful during the selection of biocontrol agents for invasive plant species.