Re-association of an invasive plant with its specialist herbivore provides a test of the Shifting Defence Hypothesis

1. The shifting defence hypothesis (SDH) predicts that after invasive plants are introduced to new ranges, they will evolve reduced resistance to specialist herbivores and increased resistance to generalist herbivores because they can escape from specialists but are still attacked by generalists in their non-native ranges. For this to be true, the subsequent introduction of native specialist herbivores should reverse the above evolutionary processes, but evidence collected so far is scarce.
2. Here, we address this research gap by comparing resistance to specialist and generalist herbivores and resistance-related traits in the invasive plant Ambrosia artemisiifolia from five populations with about a decade history of infestation by the accidentally introduced native specialist leaf beetle Ophraella communa (infested populations), and three populations without such infestation history (uninfested populations).
3. In common garden experiments, the specialist O. communa performed better ...