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.