Air pollution, but not physiological stress, is associated with genomic damage of invasive grey squirrels from urban and agricultural areas

Anthropogenic disturbances, such as habitat fragmentation and pollutants, can act as stressors limiting wildlife persistence and adaptation, and mammals are particularly vulnerable to airborne pollutants and pesticides that disrupt glucocorticoid (GC) signalling. The synergic impact of pollution and chronic GCs exposure may cause genomic damage reducing genetic diversity and adaptative potential. Using the invasive Eastern grey squirrel (Sciurus carolinensis), we assessed genomic damage, micronuclei (MNi) and nuclear buds (NBUDs), along a gradient from urban centres to agricultural areas, with increasing air pollution, and related this to faecal glucocorticoid metabolites (FGMs). Genomic damage varied significantly among study areas, with lower MNi and NBUDs in a hilly urban area. In the central urban area, MNi frequency was lower than in the agricultural areas. Conversely, in the peripheral urban area, near major roadways, MNi and NBUDs were comparable to those in agricultural areas, suggesting a similar exposure to genotoxic stressors, likely originating from different sources. A curvilinear relationship was observed between air pollutants and genomic damage: MNi and NBUDs levels remained stable at low pollution levels and decreased as pollution increased. Sex, body condition and age had no significant effects. FGMs did not significantly influence MNi or NBUDs across urban and agricultural areas. Our results show that squirrels in a hilly urban area had less genomic damage than those in high-traffic peripheral or agricultural areas. These findings highlight the importance of urban planning that incorporates refuges capable of mitigating environmental stressors and strategies that limit genotoxic effects in urban and agricultural areas.