Gene expression of anticoagulant rodenticide target genes (vkorc1 and vkorc1l1) in a non-target wildlife species: The eagle owl (Bubo bubo).

Anticoagulant rodenticides (ARs) are globally used for rodent control, posing significant risks to non-target predators and scavengers through secondary poisoning. ARs act by inhibiting the vitamin K epoxide reductase complex (VKOR), impairing coagulation. While chemical analyses have extensively documented AR exposure in wildlife, sublethal effects remain understudied. The vkorc1 and vkorc1l1 genes encode components of VKOR. This study investigates the expression of these genes and its potential association to AR exposure in a population of free-ranging Eurasian eagle owls (Bubo bubo). Blood samples (0.3-0.5 mL) collected in 2022 from 72 nestlings were analysed for vkorc1 and vkorc1l1 mRNA levels using RT-qPCR. Additionally, Canonical Correlation Analysis allowed exploring relationships between environmental variables and gene expression. Results revealed that vkorc1 is predominantly expressed in eagle owl blood (median = 4.22 RU), while vkorc1l1 exhibits lower expression levels (median = 2.25 RU). Nevertheless, in one-third of the samples vkorc1l1 was predominant. Probably, vkorc1l1 expression acts as a compensatory mechanism, increasing in response to recent AR exposure. This pattern was evident in anthropogenic environments, such as urban areas and landfills. Conversely, vkorc1 appears to respond adaptively over time, with higher expression associated with natural watercourses and livestock farms. To our knowledge, this is the first study reporting vkorc1 and vkorc1l1 gene expression in a raptor species. The integration of molecular and environmental data provided valuable insights into AR exposure dynamics in apex predators, informing management strategies to reduce risks on wildlife and ecosystem functioning.