Behaviour 2019
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Understanding the link between glucocorticoids and microbiome diversity in North American red squirrels
Lauren Petrullo1, Tian Tian Ren2, Martin Wu2, Stan Boutin3, Andrew McAdam4, Jeffrey Lane5, Ben Dantzer1,6. 1Department of Psychology, University of Michigan, Ann Arbor, MI, United States; 2Department of Biology, University of Virginia, Charlottesville, VA, United States; 3Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada; 4Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, United States; 5Department of Biology, University of Saskatchewan, Saskatoon, SK, Canada; 6Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, United States

An increase in host glucocorticoids (GCs) is associated with reduced microbiome alpha diversity in animal models, but our understanding of how ecological pressures contribute to this relationship in wild populations remains poor. In this study, we investigated the relationship between GCs and gut microbiome diversity in a wild population of red squirrels (Tamiasciurus hudsonicus) and tested the hypothesis that host and ecological factors modify this relationship. In line with prior studies, we found that higher GCs predicted lower gut microbiome diversity and identified changes in the relative abundance of microbial taxa with changes in host GCs. Using a path analysis, we found that dietary heterogeneity and food pulses exhibited direct positive effects on gut microbiome diversity. Age, reproductive activity, and increased population density reduced microbial diversity indirectly via increases to host GCs. Taken together, our findings suggest that GCs integrate host and ecological factors to impact gut microbiome diversity, highlighting the importance of considering these variables when investigating the GC-microbiome relationship.