Population structure of Ailanthus altissima (Simaroubaceae): The role of land-use history and management

The population structure of invasive species is determined both by species-specific breeding strategies and by region-specific conditions and events during the history of invasion. In this context, we investigate the role of human land-use policy on the gene flow within population of the widespread invasive tree, Ailanthus altissima. We predicted that genetic diversity would be elevated in urban environments and reduced in exurban, and that human mediated dispersal would allow propagules to break geographic isolation. Six populations of A. altissima, divided evenly among urban, exurban and suburban sites, were surveyed using a set of eight microsatellite loci. A total of 276 individuals were sampled. Populations were assessed for partitioning of genetic variation, gene flow between sites, and genetic cluster estimation. Effective population size based on genetic variation was also modeled using Bayesian Markov chain Monte Carlo simulations. Despite a strong propensity for clonal growth, the microsatellite data revealed no evidence of clonal reproduction at the population level. Gene flow between sites was found to be independent of geographic distance; instead, gene flow was correlated with the level of human traffic at a site. Genetic diversity was found to generally increase in correlation to human development; however, reduced admixture at managed sites suggests that land management practices were effective at inhibiting gene flow into managed sites.