Association of Hepatic Gene Expression with Chemical Concentrations in Wild-Collected Double-Crested Cormorant Embryos using an EcoToxChip Gene Array

Contaminant monitoring programs use wild bird eggs, but determining whether measured concentrations elicit adverse effects relies on extrapolation from toxicity studies with avian model species. Here, we directly evaluated the relationships between whole embryo contaminant concentrations and mRNA expression in liver tissue of the double-crested cormorant (Nannopterum auritum). Eggs collected from three North American sites (one from Lake Erie and two from the Salish Sea) were artificially incubated until pipping. Hepatic mRNA was analyzed with an EcoToxChip quantitative polymerase chain reaction (qPCR) array containing 354 target genes. The remaining embryo was analyzed for mercury and 95 persistent organic contaminants. Lake Erie embryos had higher concentrations of most organic contaminants than those from the Salish Sea. Sparse partial least-squares regression analysis of contaminant and gene expression data indicated that chlorinated hydrocarbons, especially polychlorinated biphenyls (PCBs), were associated with variation in gene expression. Linear correlations revealed consistent pairwise associations between chlorinated contaminants and the expression of nine genes (seven genes with PCBs and two with β-hexachlorocyclohexane). Partial least-squares discriminant analysis identified embryos from the Lake Erie site accurately. Overall, gene expression in embryos from wild-collected eggs was associated with tissue contaminant concentrations, and thus, transcriptomic measurements may serve to identify individuals or populations affected biologically by contaminants.