Conclusions
Here we present, to our knowledge, the first example of the real-time establishment of a clinal hybrid zone between a non-native invasive insect pest and a native species. This hybrid zone appears to be a tension hybrid zone, with hybrid individuals having reduced fitness compared to their parents, with the geographic center of the hybrid zone constrained by the population sizes of the two parent-species, rather than directly in relationship to an environmental or landscape variable. By examining two transects (separated by less than 125 km), we find evidence that the temporal and spatial dynamics of hybrid zones are complex, and we encourage further examination of the spatial and temporal dynamics of hybrid zones between native and non-native species so that comparative analyses can be conducted. Lastly, our results highlight the importance of long-term datasets for the study of evolutionary biology and invasion ecology, and we encourage future work to reexamine the movement and stability of this hybrid zone.
Acknowledgments: The authors are extremely grateful to Ron Weeks at USDA APHIS for encouraging our research into the population genetics of winter moth. We would also like to thank Stephanie Sayson, DeAdra Newman, David Mikus, and Brian Griffin for their laboratory assistance, and Rodger Gwiazdowski and Michelle Labbé for comments on earlier versions of this manuscript. Funding was provided by grants from USDA APHIS AP17PPQS&T00C068, AP18PPQS&T00C070, and AP19PPQFO000C125, awarded to JSE, and USDA Forest Service, Northern Research Station award 17-CR-11242303-066 to AC.