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The composition of host-associated microbial communities may correlate with the overall status of the host, including physiology and fitness. New bi-directional hypotheses suggest that sexual behaviors can shape, and be shaped by reproductive microbiomes, which may be particularly important for species with mating systems that feature strong sexual selection. These dynamics have been particularly understudied in female animals. Using 16S rRNA sequencing, we compared the cloacal microbiome of females and males from two socially polyandrous bird species that vary in the strength of sexual selection, Jacana spinosa (Northern Jacana) and J. jacana (Wattled Jacana). We hypothesized that the strength of sexual selection would shape cloacal microbial diversity, such that the more polyandrous J. spinosa would have a more diverse microbiome, and that microbiomes would be more diverse in females than in males. If the reproductive microbiome is indicative of competitive status, we also hypothesized that cloacal microbial diversity would be associated with competitive traits, including plasma testosterone levels, body mass, or weaponry. We found no differences in microbial alpha diversity between species or sexes, but we did find that microbial beta diversity significantly differed between species. We also found a positive relationship between microbial alpha diversity and testosterone in female J. spinosa. Future experiments are needed to explore the potential drivers of correlations between the cloacal microbiome and competitive phenotypes in socially polyandrous jacanas. 

Tree swallows are North American birds that can help us understand more about biology. We already know a lot about tree swallows because they are easy to work with. These birds are popular for scientists to study. We know a lot about bird health, migration, and nesting because of tree swallows. However, tree swallows are declining because of climate change, insect loss, and habitat destruction. You can help by becoming a community scientist! Tree swallows are fascinating birds that everyone can help conserve. And along the way, we can learn more about our world. 

Abstract Stress resilience is defined as the ability to rebound to a homeostatic state after exposure to a perturbation. Organisms modulate various physiological mediators to respond to unpredictable changes in their environment. The gut microbiome is a key example of a physiological mediator that coordinates a myriad of host functions including counteracting stressors. Here, we highlight the gut microbiome as a mediator of host stress resilience in the framework of the reactive scope model. The reactive scope model integrates physiological mediators with unpredictable environmental changes to predict how animals respond to stressors. We provide examples of how the gut microbiome responds to stressors within the four ranges of the reactive scope model (i.e., predictive homeostasis, reactive homeostasis, homeostatic overload, and homeostatic failure). We identify measurable metrics of the gut microbiome that could be used to infer the degree to which the host is experiencing chronic stress, including microbial diversity, flexibility, and gene richness. The goal of this perspective piece is to highlight the underutilized potential of measuring the gut microbiome as a mediator of stress resilience in wild animal hosts.