We studied the genetic structure of populations of the invasive shrub Amur honeysuckle (Lonicera maackii) in 41 woodlots in an agricultural landscape in a recently invaded area in southwest Ohio. Using six polymorphic microsatellite loci, we found high allelic diversity and high heterozygosity in all populations and low to moderate levels of genetic differentiation among populations. We also found significant positive correlations between geographic distance and (1) Nei’s genetic distance and (2) the coefficient of genetic differentiation (FST/(1 − FST) among all possible pairs of populations. These relationships were stronger when we tested the correlations of each of five putative source populations against the remaining non-source populations; and were especially strong when only the populations located within 30 km of each putative source were included in the analyses. Genetic analysis also revealed the existence of four distinct clusters that were not equally distributed across the study area, with high levels of admixture within populations. In particular, our findings indicate that the individuals present in six newly established populations in Darke county are made up of individuals belonging to multiple clusters, suggesting that these new populations were colonized from multiple nearby source populations. From these findings, we infer that the genetic structure of these L. maackii populations is determined by a combination of long-distance dispersal events and shorter distance diffusion from neighboring uninvaded woodlots, as well a history of multiple introductions into Ohio, and a predominantly outcrossing mating system.
