I use marine species invasions as natural experiments in rapid adaptation, examining how – and how quickly – populations respond to novel conditions. By coupling high-throughput sequencing with physiology and ecology, I examine adaptation at multiple levels. My main areas of research are thermal adaptation in green crabs (Carcinus maenas), and coevolution in the crab-barnacle Rhithropanopeus harrisii-Loxothylacus panopaei host-parasite system.