Plant Introductions

Contemporary biological invasions represent a major threat to biodiversity and understanding the biological mechanisms that allow certain species to dominate in their non-native ranges is an important conservation goal. Because the environmental and economic impact of weeds and invasive plants is profound there is considerable incentive to prevent and control invasions. Several strategies have been employed to manage the global epidemic of invasive weeds. Yet, there is still a need to develop efficient methods for effective and environmentally benign control strategies. Despite the importance of invasive species, there has been little effort to identify the genomic basis of weediness and invasiveness. Presently, our research attempts to address this knowledge gap.

There is no set of traits common to all invaders, but many weedy species occur in less stressful conditions than in their natural habitats. In favourable habitats plants can trade-off investment in self-defence or abiotic tolerance for increased investment in growth and reproduction. Common ragweed is a highly invasive plant in Europe and we found evidence for enhanced growth and reproduction of European populations of ragweed in benign and competitive environments, but reduced survival under drought stress, providing evidence supporting such a trade-off. We have also examined differences in gene expression between native and invasive populations in three environments to identify the molecular basis of the phenotypic differences we have observed between the ranges. We found many genes that were differentially expressed between the ranges including several genes potentially involved in stress response, herbicide tolerance and growth.

Is there evidence for local adaptation of common ragweed in the native and introduced ranges? What is the genetic architecture of local adaptation?

Recent range expansions brought about by invasive species represent natural ecological and evolutionary experiments as invading species must rapidly adapt to geographical variation in climatic and local ecological conditions. Using common gardens, we have already identified evidence for clinal variation in female reproduction and flowering time in the introduced range, suggesting rapid local adaptation occurring within the past 200 years. We are using genomic scans to identify outlier loci, as well as association of SNPs with climate and latitude to identify variants that may be important in determining local adaptation in this species.

What are the genomic changes that accompany range expansion of common ragweed into Europe and Australia?

We are using genotype by sequencing (GBS) to identify loci in this species that may have been under selection during invasion and to determine the demographic history of common ragweed. We will also look for associations between SNPs and important traits related to invasiveness in common ragweed such as growth rate, drought tolerance and herbicide resistance. We would also like to conduct reciprocal transplant experiments between the native and invasive ranges to examine patterns of selection on phenotypic traits (e.g. growth rate, drought tolerance). Our long-term goal is to detect the genes responsible for invasiveness in common ragweed and demonstrate their ecological relevance through fitness assays in the field. Our research aims to detect the subset of the phenotypes and genes that have contributed recently to the adaptation during invasion.

Which genes have accelerated rates of evolution in weedy and invasive groups in the Compositae?

We are also interested in broader phylogenomic patterns associated with invasiveness. By identifying orthologs in the transcriptomes we have assembled for weeds and their relatives we will identify genes that have experienced positive selection in weedy and invasive groups (e.g. ragweeds, knapweeds). This will allow us to potentially characterize the genes that contribute to the invasive nature of these lineages. This work is in collaboration with Itay Mayrose (Tel Aviv University) and Loren Rieseberg (UBC).