Introduced Brassica nigra populations exhibit greater growth and herbivore resistance but less tolerance than native populations in the native range.

Rapid post-introduction evolution has been found in many invasive plant species, and includes changes in defence (resistance and tolerance) and competitive ability traits. Here, we explored the post-introduction evolution of a trade-off between resistance to and tolerance of herbivory, which has received little attention. In a common garden experiment in a native range, nine invasive and 16 native populations of Brassica nigra were compared for growth and defence traits. Invasive populations had higher resistance to, but lower tolerance of, herbivore damage than native populations. Invasive populations survived better and produced more seeds than native ones when released from herbivores; but fitness was equivalent between the regions under ambient herbivory. The invasive populations grew taller, and produced more biomass and lighter seeds than natives, irrespective of insecticide treatment. In addition to supporting the idea of post-introduction rapid evolution of plant traits, our results also contribute to an emerging pattern of both increasing resistance and growth in invasive populations, contrary to the predictions of earlier theories of resistance-growth trade-offs.