https://phaidra.vetmeduni.ac.at/o:1790 Glucocorticoids coordinate changes in gut microbiome composition in wild North American red squirrels Petrullo, Lauren Lauren Petrullo University of Michigan Dantzer, Ben Ben Dantzer University of Michigan McAdam, Andrew G. Andrew G. McAdam University of Colorado Boutin, Stan Stan Boutin University of Alberta Palme, Rupert Rupert Palme 0000-0001-9466-3662 University of Veterinary Medicine Vienna Boonstra, Rudy Rudy Boonstra University of Toronto Ren, Tiantian Tiantian Ren University of Virginia Wu, Martin Martin Wu University of Virginia Nature Portfolio text eng Abstract: The gut microbiome impacts host health and fitness, in part through the diversification of gut metabolic function and pathogen protection. Elevations in glucocorticoids (GCs) appear to reduce gut microbiome diversity in experimental studies, suggesting that a loss of microbial diversity may be a negative consequence of increased GCs. However, given that ecological factors like food availability and population density may independently influence both GCs and microbial diversity, understanding how these factors structure the GC-microbiome relationship is crucial to interpreting its significance in wild populations. Here, we used an ecological framework to investigate the relationship between GCs and gut microbiome diversity in wild North American red squirrels (Tamiasciurus hudsonicus). As expected, higher GCs predicted lower gut microbiome diversity and an increase in metabolic taxa. Surprisingly, but in line with prior empirical studies on wild animals, gastrointestinal pathogens decreased as GCs increased. Both dietary heterogeneity and an upcoming food pulse exhibited direct effects on gut microbiome diversity, whereas conspecific density and reproductive activity impacted diversity indirectly via changes in host GCs. Our results provide evidence of a gut-brain axis in wild red squirrels and highlight the importance of situating the GC-gut microbiome relationship within an ecological framework. Population-Growth; Brain Axis; Metabolism; Responses; Behavior; Stress; Sex; Corticosterone; Reproduction; Evolution http://creativecommons.org/licenses/by/4.0/ https://phaidra.vetmeduni.ac.at/api/object/o:1790/download 10.1038/s41598-022-06359-5 https://phaidra.vetmeduni.ac.at/o:605 application/pdf Scientific Reports 12(1) (2022) Scientific Reports 12 1 1.57 MB 2022