No experimental evidence of an adaptive antioxidative response induced by trace metals exposure in feral pigeons

Trace metals produced by anthropogenic activities in particular in urban environments, such as lead and zinc, can induce oxidative damage in exposed individuals. Therefore, trace metals could act as a selective pressure for higher resistance to oxidative damage by favoring individuals able to plastically produce antioxidants once exposed to metal to counterbalance the oxidative damage production. In this study, we experimentally challenge this hypothesis in 69 feral pigeons (Columba livia var. domestica) originating from an urban environment by exposing a subset of them to zinc (n = 18), lead (n = 17) or zinc and lead (n = 16) during 14 weeks to see if exposed individuals showed an increased anti-oxidant production compared to controls (n = 18). Our results reported that zinc exposure induced oxidative stress by increasing oxidative damage but failed to detect a compensatory production of antioxidants in exposed individuals. However, our results report lower oxidative damage for reproducing individuals, which is consistent with an oxidative shielding phenomenon occurring prior to reproduction in males to protect the sperm, and during egg-laying in females to protect offspring. In conclusion, our study does not support an adaptive antioxidative response in individuals exposed to trace metals, but it does partly support the oxidative shielding hypothesis.