The evolution of invasiveness in common ragweed

Introduced species represent opportunities to observe evolution over contemporary timescales, and as exotics encounter new environments adaptive responses can occur, potentially contributing to invasion. We compared native North American populations and introduced European populations of common ragweed (Ambrosia artemisiifolia) in common gardens. We found evidence for improved growth and reproduction of the introduced populations in most environments. However, under drought conditions, introduced populations experienced more rapid wilting and mortality than their native counterparts. These data provide evidence supporting an apparent life-history trade-off between rapid growth and drought tolerance. Moreover, we found parallel latitudinal clines in flowering time, and correlations between fitness components and the local climate of the source populations in both ranges. Together these data provide evidence for adaptation to local environmental conditions in the native and introduced range of common ragweed. To identify the molecular basis of invasiveness in ragweed, we sequenced transcriptomes of native and introduced populations and examined the assemblies for evidence of hybridization. Using a transcriptome assembly from an introduced individual, we then designed a custom NimbleGen microarray for common ragweed with probes for 45062 unigenes. We were able to identify differentially expressed genes between the native and introduced ranges across a number of common gardens, providing a list of candidate genes for future investigation.