Invasive species can create a multitude of ecological problems. They can drastically alter resource use in ecosystems; introduce new diseases and pathogens that can negatively affect native species and human health; and generally change species interactions and ecosystem processes in ways that result in lower levels of biodiversity in the ecosystems in which they invade. When humans disturb the environment (building houses and roads, damming rivers, plowing for agriculture), invasive species often exploit these disturbances by colonizing new areas and dramatically increasing in abundance. Interactions between environmental variables in anthropogenically disturbed environments and physiological traits of invasive species have the potential to explain reasons for invasive species’ range expansions. Here we analyze how soil contamination along roadsides may influence the range expansion of Conium maculatum (poison hemlock), a plant considered invasive elsewhere and recently detected only along roadsides in Cook County, IL, USA. We combine analyses that characterize the soil where Conium is growing and measure concentrations of heavy metals and PAHs; assess the genetic structure of individuals within and among the nine known populations; and test for tolerance to heavy metals and local adaptation with greenhouse establishment experiments.
Results/Conclusions
We found elevated levels of metals and PAHs in the soil where Conium was growing. Specifically, arsenic (As), cadmium (Cd), and lead (Pb) were found at elevated levels relative to contamination thresholds in the EPA Ecological Soil Screening Levels for plants. A total of 217 individuals (approximating 30 per population) were scored with 5 ISSR primers, which yielded 114 unique loci. We found high levels of genetic diversity and heterozygosity in all nine populations. Mean mean heterozygosity for the populations was 0.433 ± 0.0137. There is some genetic structuring between populations, especially in three of the nine populations. However, theta II, a measure of differentiation similar to Fst, was low (0.013). We did not find evidence of local adaptation for seeds from a given population growing better on their own local soil. Conium is more tolerant of soil spiked with known concentrations of heavy metals (As, Cd, Pb) than both Desmodium canadense and Echinacea purpurea, two comparable native species. Although Conium shows tolerance to contamination in both the field and the greenhouse, there was not significant evidence that its tolerance is connected to either the genetic structure or the regional pattern of invasion.