The symbiotic microbial communities, or “microbiomes,” that reside on animals are dynamic, and can be affected by the behavior and physiology of the host. These communities provide many critical beneficial functions for their hosts, but they can also include potential pathogens. In birds, bacteria residing in the cloaca form a complex community, including both gut and sexually-transmitted bacteria. Transmission of cloacal bacteria among individuals is likely during the breeding season, when there is direct cloacal contact between individuals. In addition, the major energetic investment in reproduction can draw resources away from immune responses that might otherwise prevent the successful establishment of microbes. We assessed dynamic variation in the cloacal microbiome of free-living rufous-collared sparrows (Zonotrichia capensis) through sequential breeding and non-breeding seasons. We found that the cloacal bacterial communities differed between the sexes when they were in breeding condition. Further, in males, but not in females, the bacterial community became more diverse with the onset of reproduction, and then decreased in diversity as males transitioned to non-breeding condition. Individuals sampled across sequential breeding seasons did not accumulate more bacterial taxa over seasons, but bacterial community composition did change. Our results suggest that the cloacal microbiome in birds is dynamic and, especially in males, responsive to breeding condition.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. abstract: Latitudinal variation in life-history traits has been the focus of numerous investigations, but underlying hormonal mechanisms have received much less attention. Steroid hormones play a central role in vertebrate reproduction and may be associated with life-history trade-offs. Consequently, circulating concentrations of these hormones vary tremendously across vertebrates, yet interspecific geographic variation in male hormone concentrations has been studied in detail only in birds. We here report on such variation in amphibians and reptiles, confirming patterns observed in birds. Using phylogenetic comparative analyses, we found that in amphibians, but not in reptiles, testosterone and baseline corticosterone were positively related to latitude. Baseline corticosterone was negatively related to elevation in amphibians but not in reptiles. For both groups, testosterone concentrations were negatively related to breeding-season length. In addition, testosterone concentrations were positively correlated with baseline corticosterone in both groups. Our findings may best be explained by the hypothesis that shorter breeding seasons increase male-male competition, which may favor increased testosterone concentrations that modulate secondary sexual traits. Elevated energetic demands resulting from greater reproductive intensity may require higher baseline corticosterone. Thus, the positive relationship between testosterone and corticosterone in both groups suggests an energetic demand for testosterone-regulated behavior that is met with increased baseline glucocorticoid concentrations.

1. Testosterone mediates several key aspects of male reproduction, but maintaining high testosterone levels can reduce long-term survival. One of the proposed pathways by which testosterone can influence survival is through increased risk of parasite infection.The hormone has the potential to affect the transmission of sexually transmitted infections by promoting behaviors that increase sexual contact rates and/or by decreasing immune function.2. We hypothesized that males with high concentrations of testosterone would increase their chances of being infected with sexually transmitted bacteria, which would manifest as increased diversity of cloacal bacteria. To test this hypothesis, we measured circulating testosterone concentrations in breeding male rufous-collared sparrows (Zonotrichia capensis) and collected cloacal swabs to quantify bacterial diversity using 16S rRNA gene amplicon sequencing.3. There was a positive correlation between testosterone concentrations and the phylogenetic diversity of cloacal bacteria. In addition, individuals with high and medium testosterone concentrations had cloacal bacterial communities that were more similar to each other than to those of low testosterone individuals. Finally, when considering bacterial taxa that are potential avian pathogens, we found that the relative abundance of Accepted ArticleThis article is protected by copyright. All rights reserved.Chlamydiae, a class of obligate intracellular parasites, was positively correlated with testosterone concentrations. 4. Two nonexclusive explanations for these results are that testosterone affects behaviors that lead to increased sexual contacts and thus the exposure and acquisition of additional phylogenetically diverse bacteria, and/or that testosterone is altering the immune system or the cloacal environment, thus making it easier for bacteria to colonize. Either way, these data suggest that increased exposure to sexually transmitted pathogens in the form of cloacal bacteria could be a cost of maintaining high testosterone levels.

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Hydration is a critical element for many physiological processes in vertebrates. While it seems intuitive that drought is stressful to animals, studies examining drought are typically observational and do not explicitly assess how the hydration state of study subjects influences their physiology and behavior. We examined how hydration affects several physiological and behavioral variables in free-ranging Northern Pacific rattlesnakes (Crotalus oreganus oreganus) by experimentally manipulating their hydration levels in the field. Our results suggest that supplemental water has a significant effect on reproduction, as all hydrated females gave birth during the experiment, while no control females did. We saw no effect of hydration on movement parameters; males moved a larger total distance and had larger home ranges than females, regardless of hydration status. Interestingly, body condition at the end of the study was significantly higher in hydrated snakes, suggesting that hydrated individuals might have been acquiring more food than control snakes. We saw no effect on baseline stress hormone concentrations or their increase in response to an acute stressor. Additional experimental studies are needed to better understand the pivotal roles of hydration in the physiology and behavior of reptiles.