Pollutant Exposure Shapes Mitochondrial Bioenergetics in a Wild Seabird

Laboratory studies show that mercury (Hg) and per- and polyfluoroalkyl substances (PFAS) can impair mitochondrial bioenergetics, which is a vital process for cellular energy production. However, their effects on wild, free-living organisms remain unexplored. Using red blood cells, we investigated how foraging habits, inferred from stable isotopes, and contaminant exposure were associated with mitochondrial bioenergetics in breeding Scopoli's shearwaters (Calonectris diomedea), a top marine predator in the Mediterranean Sea. We found higher concentrations of Hg, but not of total PFAS, in older individuals and in males compared to females. Our results also indicate dietary pollutant exposure: Hg, but not total PFAS, was higher in birds with a higher trophic position and in those foraging closer to shores. Additionally, higher Hg concentration was linked to higher mitochondrial proton leakage (LEAK), reflecting reduced efficiency to couple oxygen consumption to energy production. In contrast, specific PFAS were negatively associated with LEAK, suggesting a potential impairment in the regulation of mitochondrial membrane potential through proton conductance, a key mechanism protecting cells from oxidative stress. Our study highlights how foraging ecology shapes pollutant exposure and its consequences for mitochondria bioenergetics in an apex predator of conservation interest.