Inferring Geographic Origin of White-Tailed Deer (Odocoileus virginianus) Using Single Nucleotide Polymorphisms in a Region Experiencing Long-Term Effects of Chronic Wasting Disease.

Chronic wasting disease (CWD) is a contagious, 100% fatal disease affecting North American cervids. White-tailed deer (Odocoileus virginianus) is the most abundant host, and movements of this species, either natural or human-mediated, have been considered primary drivers of CWD spread. Inferring the geographic origin of CWD-positive individuals can help identify source-sink dynamics of disease spread and anthropogenic translocation of carcasses. We explored two approaches to infer origin of wild white-tailed deer: (1) a combination of genetic structure inference and categorical assignment tests, and (2) continuous assignment methods (SPA and LOCATOR) to infer coordinates of origin, based on comparisons between test and reference genotypes. We analyzed 1749 samples genotyped using a recently developed single nucleotide polymorphism panel, retaining > 63,000 markers. Genetic structure analyses identified four, five, or ten clusters, with barriers to gene flow that were consistent between the different analyses and explainable by landscape features. We used the ten-cluster configuration to perform categorical assignment tests, but these tests showed low-moderate performance (assignment accuracy ranged between 41% and 100% among clusters, average was 71%). SPA produced a high level of inaccuracy in inferred origins. In contrast, LOCATOR assigned most individuals (82%) to an origin < 50 km from their sampling coordinates. Given the species' life history traits (e.g., vagility, overlapping generations, polygamy), this level of accuracy suggests that continuous assignment tests may be a valuable tool for wildlife managers. Additionally, the inferred genetic structure can inform the delineation of management units, with implications for population control and mitigation of contagious diseases.