A key gap in our understanding of the process of biological invasion is the winnowing steps that select the successful invaders from the failed introductions. Temporally referenced data may help us understand this selection as species spreads across novel environments. While evolutionary studies often describe adaptation to novel environments over millions of years, evolution in invasive species can occur over decades. Typically, our knowledge of evolution in invasive species is based only on current and static patterns of genetic variation in invasive populations. Since static patterns may be the result of multiple and opposing processes, such patterns reveal little about the initial stages or key transitions of invasion. Genomic analyses are powerful tools to understand the evolutionary processes affecting introduced populations through time. We use genomic data from herbarium specimens to directly observe the initial stages of invasion and the genetic changes that occur as a species spreads through novel environments. We use specimens of blue mustard (Chorispora tenella, Brassicaceae), a widespread noxious invasive weed, collected throughout the North American invasion to investigate the evolutionary ecology of invasive species.
Results/Conclusions
We present preliminary analyses of whole genome libraries produced from four individuals from a contemporary native population cultivated by the USDA GRIN and 20 herbarium specimens collected from the North American invaded range between 1941 and 1993. Most of these collections are from the region of the earliest introduction. First, we assemble a de novo reference from a contemporary individual. Characteristic ancient DNA damage patterns are minimal and most sequencing reads map back to the reference assembly, indicating that non-target species contamination is low. We estimate genetic change over time, population structure, relatedness, and effective population size. We further investigate variation related to genes of functional interest, based on similarity to the model organism, Arabidopsis thaliana.