Catbirds are the New Chickens: High Sensitivity to a Dioxin-like Compound in a Wildlife Species.

Dioxins and dioxin-like compounds (DLCs) are highly toxic and persistent global pollutants with extremely large differences in sensitivity across taxonomic groups. The chicken has long been considered uniquely sensitive to DLCs among avian species; but DLC toxicity in nondomesticated birds is largely untested, and the relevance of the chicken as an ecological model is uncertain. New approaches that use genotyping of the AHR1 ligand binding domain to screen for DLC sensitivity among avian species predicted that the gray catbird, a relevant wildlife species, is also highly sensitive. We tested this prediction using egg injections of a dioxin-like PCB (PCB-126) and found that the catbird is at least as sensitive as the chicken to DLCs, based on both embryotoxicity and mRNA induction of phase I metabolizing enzymes (CYP1A4/5). This study is the first to confirm that there are wildlife species as sensitive as the chicken and demonstrates how using predictive genotyping methods and targeted bioassays can focus toxicity assessments on ecologically relevant species.