Biogeographical patterns in morphological traits of insect host-parasitoid communities provide open niche opportunities for a range-expanding host

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Kelly McGourty, Dylan G. Jones, Julia Kobelt, Rachel Chen, Aly Milks, Haley Hurst, Sarah Martin and Catherine Ruis, Department of Biological Sciences, Binghamton University (SUNY), Kirsten M. Prior, Department of Biological Sciences, Binghamton University (SUNY), Binghamton, NY

Background/Question/Methods
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. A loss of or less effective interactions with competitors and enemies may provide open niche opportunities and result in “ecological release.” Niche opportunities are determined by traits of interacting species and are facilitated by non-overlapping traits in recipient communities. Here, we study a poleward range-expanding oak gall wasp, Neuroterus saltatorius (NS) (Hymenoptera: Cynipidae), which occurs on Quercus garryana, and experiences ecological release in oak ecosystems. We measure morphological traits of co-occurring cynipid hosts and interacting parasitoids to examine if community traits of interacting species vary along a latitudinal gradient and in the native and expanded range of NS. We identified 23 cynipid morphospecies at 18 sites in 6 regions along the range of Q. garryana and reared out and identified parasitoid wasps. We measured cynipid and parasitoid traits. We ask if trait mismatching between NS and recipient communities of interacting host and parasitoids provides open niche opportunities at higher latitudes where NS is outbreaking.
Results/Conclusions
We performed a Principal Coordinates Analysis of trait measurements for cynipid morphospecies and plotted cynipid trait space using the first two axes. For each site, we measured the distance in trait space of NS to each co-occurring cynipid species. We calculated the mean distance between NS and co-occurring species at sites and compared trait distance among regions. We found that trait distance increased with latitude and was highest in the expanded range (regions 5 and 6). NS is a foliar detachable leaf gall, and the diversity of other morphologically similar detachable leaf gall morphospecies decreased with latitude. Cynipid morphospecies with fewer overlapping traits may have reduced apparent competition via shared enemies. Future work includes plotting parasitoid trait space and calculating interaction centroids for each cynipid morphospecies, which represents composite traits of parasitoids interacting with cynipid hosts. We will calculate the distances of co-occurring cynipid morphospecies to NS in interaction trait space at sites. Greater trait distances at high latitudes will suggest that NS is released from apparent competition due to parasitoids in recipient communities lacking traits enabling them to attack the novel host. This study demonstrates how altered interactions with competitors and enemies contribute to ecological release of range-expanding species.