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Climate change is causing species to expand their ranges poleward into new locations. As species move, they will lose interactions with species that fail to follow and gain new interactions with species with which they are not coevolved or coadapted. As a result, one common outcome for range expansions is that species outbreak in their expanded ranges in response to altered antagonistic interactions (“ecological release”). Insect hosts have a suite of morphological adaptations to evade parasitoid enemies, and enemies have adaptations to effectively attack hosts. Here, we study a recent range expansion of an insect host. Neuroterus saltatorius (Hymenoptera: Cynipidae) is a gall-forming wasp specializing on oaks that has undergone a recent range expansion from Washington state to Vancouver Island, British Columbia. In its expanded range, it experiences ecological release, causing foliar damage and impacting oak ecosystems. It interacts with an array of insect host competitors on its host plant Quercus garryana (other cynipids wasps) that are attacked by a suite of enemies (parasitoid wasps). The aim of this study is to measure morphological traits of cynipid hosts and parasitoids to examine if community traits of interacting hosts and enemies vary along a latitudinal gradient, and in the native and expanded range of N. saltatorius. Specifically, we ask if trait diversity of insect host-parasitoid communities provides biological resistance or facilitates ecological release of N. saltatorius in the native and expanded ranges. We predict that if trait mismatching contributes to ecological release, the degree of trait matching between the range-expanding host and other cynipid hosts and parasitoids will be lower in the expanded range, where it interacts with non-coadapted community members. Understanding factors that lead to ecological release is crucial to predicting outcomes of range expansions and to mitigate negative impacts of range-expanding species



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Do Biogeographical Patterns in Morphological Traits of Insect Host and Parasitoid Wasp Communities Contribute to Ecological Release of a Range-Expanding Host via Trait Mismatching?