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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.
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Red squirrel gestation length is unchanged by maternal traits, litter composition, or future food availability
Despite considerable research on reproductive timing, factors influencing intraspecific variation in gestation length in wild mammals have received limited attention, largely due to a lack of high-resolution data. We examined potential drivers of gestation length variation in a wild population of North American red squirrels ( Tamiasciurus hudsonicus Erxleben, 1777) in Yukon, Canada. Drawing on 27 years of conception and parturition data, we found that gestation length was highly conserved, with minimal variation (35.4 ± 1.49 days; mean ± standard deviation). Gestation length was unaffected by maternal age, litter size, or litter sex ratio. Likewise, the anticipation of an upcoming food pulse, caused by synchronous conifer seed masting, had no statistically significant influence on gestation length. This finding stands in contrast to other reproductive traits in red squirrels, which are known to shift in response to food pulses. Overall, our results suggest that gestation length in red squirrels is buffered against environmental variability, likely due to stabilizing selection or strong heritability.
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- PAR ID:
- 10655893
- Publisher / Repository:
- Canadian Science Publishing
- Date Published:
- Journal Name:
- Canadian Journal of Zoology
- Volume:
- 103
- ISSN:
- 0008-4301
- Page Range / eLocation ID:
- 1 to 7
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1139/cjz-2025-0075
