Environmental radionuclide contamination is associated with the diet and gut microbiota of wild passerines Parus major and Ficedula hypoleuca.

Organisms that occupy environments contaminated by radionuclides such as the area surrounding the former nuclear power plant at Chornobyl, Ukraine, face putative detrimental effects. How radioactive pollution affects organisms, especially in their early life, is not well studied in the wild. Our study focused on two interconnected factors that might be impacted by environmental radionuclide contamination: 1) diet, as biodiversity may be altered in response to contamination, and its concomitant effect on 2) the early-life gut microbiota. We quantified fitness components, diet, and gut microbiota (using amplicon sequencing) from nestlings of two passerine bird species (Great tit Parus major and Pied flycatcher Ficedula hypoleuca) by sampling animals in nest-boxes located in contaminated and uncontaminated areas within the Chornobyl Exclusion Zone. Out of studied components of breeding and fitness (nest occupancy, hatching time, brood size, body-condition) only hatching time was significantly negatively associated with environmental radiation. Diversity of dietary insects and diversity of the gut microbiota showed no connection to environmental contamination but, in both bird species, the composition of diet and gut microbiota was associated with exposure to radionuclides. Networks formed by gut microbial taxa were also reorganized in contaminated areas in P. major nestlings. These novel results, while covering only one breeding season, give valuable insight into how contaminated environment affects avian physiology and ecology.