Methodological confounds of measuring urinary oxidative stress in wild animals

Biomarkers of oxidative stress (OS) are useful in addressing a wide range of research questions, but thus far, they have had limited application to wild mammal populations due to a reliance on blood or tissue sampling. A shift towards non-invasive measurement of OS would allow field ecologists and conservationists to apply this method more readily. However, the impact of methodological confounds on urinary OS measurement under field conditions has never been explicitly investigated. We combined a cross-sectional analysis with a field experiment to assess the impact of four potential methodological confounds on OS measurements: 1) time of sampling, 2) environmental contamination from foliage; 3) delay between sample collection and flash-freezing in liquid nitrogen; 4) sample storage of up to 15 months below -80C. We measured DNA oxidative damage (8-hydroxy-2’-deoxyguanosine, 8-OHdG), lipid peroxidation (malondialdehyde, MDA), Total Antioxidant Capacity (TAC) and uric acid (UA) in 167 uri...