Solanum ptycanthum (eastern black nightshade) is a serious weed of tomato and soybean crops at the northern margin of its distribution in southwestern Ontario. Evidence for direct immigration, albeit at low, sporadic frequencies, of nightshade into these agrestal habitats occurs via tomato transplants imported from Georgia and North Carolina. Northern ruderal populations are also common in a variety of natural habitats. Outcrossing rates in northern and southern genotypes were compared in simulated populations grown in northern agricultural habitats. Greenhouse experiments were used to examine levels of genetic variation and phenotypic plasticity in life history traits among ruderal, agrestal and southern populations in response to abiotic factors which would be experienced when invading northern agroecosystems.;Genotypes from recently colonized northern populations (both agrestal and ruderal) had lower outcrossing rates ({dollar}\u3c{dollar}3%) than those originating from the south (3-17%).;Northern agrestal populations were not less genetically variable, and did not express greater phenotypic plasticity than northern ruderal or southern agrestal populations under a wide range of greenhouse conditions. Germination speed was greater, and the number of degree days to reach 50% germination was less in ruderal families, suggesting that ruderal populations would emerge earlier than agrestal populations. The germination response to temperature was similar between northern and southern agrestal populations, suggesting that these populations would emerge synchronously.;Ruderal and northern agrestal populations were equally tolerant to low doses of metribuzin, while populations originating from Georgia were extremely susceptible to both levels of metribuzin tested. North Carolina seedlings were as tolerant as northern agrestal populations. Northern agrestal populations were more tolerant than ruderal populations at the highest dose of metribuzin.;There was no divergence in the phenotype expressed by ruderal and northern agrestal individuals in response to variation in nutrients. There was no evidence for selection for increased yield response in agrestals grown under high nutrient conditions. However, delayed reproduction of southern compared to northern plants may limit the production of viable seed in northern short-season crops. Developmental pattern and age to first reproduction were canalized within southern populations, suggesting lack of sufficient genetic variability to respond to selection encountered during colonization of northern agroecosystems
