Evidence of Selective Response in the Free-Breeding Dog Population in Chornobyl

Background/Objectives: Understanding genomic responses to environmental contamination is essential for assessing long-term ecological and genetic risk. The free-breeding dogs inhabiting the Chornobyl Exclusion Zone (CEZ) offer a unique, multigenerational model for investigating these responses within a chronically contaminated landscape. Following the 1986 radioecological disaster at the Chornobyl Nuclear Power Plant, and subsequent remediation activities, the surrounding environment was contaminated by ionizing radiation, heavy metals, organic compounds, and other environmental toxicants. Our previous work identified significant genetic differentiation between two distinct but geographically proximate dog populations within the CEZ, a pattern not explained by breed composition, spatial isolation, or increased mutation rates. Methods: In this study, we tested the hypothesis that the dogs residing at the nuclear power plant show genomic signatures consistent with adaptive evolution in response to chronic environmental stressors. This work extends prior population-genetic analyses by integrating whole-genome selection scans with estimates of effective population size and comparative measures of population divergence, providing a framework to evaluate whether the observed genomic differentiation is more consistent with selection than demography. Using these whole genomic data, we evaluated chromosome-level F_ST metrics, estimated effective population size (N_e), and analyzed a geographically isolated island dog population as a comparative reference for genetic divergence. Results: We continued to find that the levels of genetic differentiation are not comparable to other free-breeding dog populations. Genome-wide outlier analyses identified candidate loci showing evidence of positive selection across multiple metrics. Conclusions: Genes associated with these loci were enriched for biological functions related to DNA replication and repair, cell death and survival, cellular compromise, immune response, and cancer-associated pathways, suggesting biologically plausible mechanisms through which chronic environmental stress could influence fitness. These findings are consistent with directional selection in the nuclear power plant population, which could potentially be associated with the environmental variables present, and advance our understanding of local adaptation and genomic resilience under chronic environmental contamination.