skip to main content

This content will become publicly available on April 1, 2023

Title: Chronic stress and captivity alter the cloacal microbiome of a wild songbird
ABSTRACT There are complex interactions between an organism's microbiome and its response to stressors, often referred to as the ‘gut–brain axis’; however, the ecological relevance of this axis in wild animals remains poorly understood. Here, we used a chronic mild stress protocol to induce stress in wild-caught house sparrows (Passer domesticus), and compared microbial communities among stressed animals, those recovering from stress, captive controls (unstressed) and a group not brought into captivity. We assessed changes in microbial communities and abundance of shed microbes by culturing cloacal samples on multiple media to select for aerobic and anaerobic bacteria and fungi. We complemented this with cultivation-independent 16S and ITS rRNA gene amplification and sequencing, pairing these results with host physiological and immune metrics, including body mass change, relative spleen mass and plasma corticosterone concentrations. We found significant effects of stress and captivity on the house sparrow microbiomes, with stress leading to an increased relative abundance of endotoxin-producing bacteria – a possible mechanism for the hyperinflammatory response observed in captive avians. While we found evidence that the microbiome community partially recovers after stress cessation, animals may lose key taxa, and the abundance of endotoxin-producing bacteria persists. Our results suggest an overall link between more » chronic stress, host immune system and the microbiome, with the loss of potentially beneficial taxa (e.g. lactic acid bacteria), and an increase in endotoxin-producing bacteria due to stress and captivity. Ultimately, consideration of the host's microbiome may be useful when evaluating the impact of stressors on individual and population health. « less
Authors:
; ; ; ; ; ; ; ;
Award ID(s):
1655269 1048529
Publication Date:
NSF-PAR ID:
10351064
Journal Name:
Journal of Experimental Biology
Volume:
225
Issue:
7
ISSN:
0022-0949
Sponsoring Org:
National Science Foundation
More Like this
  1. Cooke, Steven (Ed.)
    Abstract Wild animals brought into captivity frequently experience chronic stress and typically need a period of time to adjust to the conditions of captivity (restraint, artificial lighting, altered diet, human presence, etc.), to which they may never fully acclimate. Changes in mass, the hypothalamic–pituitary–adrenal axis and heart rate parameters have been observed over the first week in newly captive house sparrows (Passer domesticus). In this study, we tested the effects of two drugs, diazepam and mitotane, in preventing the chronic stress symptoms caused by captivity, compared with oil-injected control animals. Diazepam is an anxiolytic that is widely prescribed in humans and other animals and has been shown in some cases to reduce physiological stress. Mitotane is an agent that causes chemical adrenalectomy, reducing the body’s capacity to produce glucocorticoid hormones. Our mitotane treatment did not cause the expected change in corticosterone concentrations. Baseline corticosterone was higher after a week in captivity regardless of the treatment group, while stress-induced corticosterone did not significantly increase above baseline after a week in captivity in any treatment group. However, mitotane treatment did have some physiological effects, as it reduced the resting heart rate and the duration of the heart rate response to a suddenmore »noise. It also prevented the increase in nighttime activity that we observed in control animals. There was no effect of diazepam on corticosterone, resting heart rate, activity or heart rate response to a sudden noise, and no effect of either treatment on the sympathetic vs parasympathetic control of the resting heart rate. Together, these data suggest that mitotane, but not diazepam, can have a modest impact on helping house sparrows adapt to captive conditions. Easing the transition to captivity will likely make conservation efforts, such as initiating captive breeding programs, more successful.« less
  2. Bacterial communities in and on wild hosts are increasingly appreciated for their importance in host health. Through both direct and indirect interactions, bacteria lining vertebrate gut mucosa provide hosts protection against infectious pathogens, sometimes even in distal body regions through immune regulation. In house finches ( Haemorhous mexicanus ), the bacterial pathogen Mycoplasma gallisepticum (MG) causes conjunctivitis, with ocular inflammation mediated by pro- and anti-inflammatory cytokines and infection triggering MG-specific antibodies. Here, we tested the role of gut bacteria in host responses to MG by using oral antibiotics to perturb bacteria in the gut of captive house finches prior to experimental inoculation with MG. We found no clear support for an impact of gut bacterial disruption on conjunctival pathology, MG load, or plasma antibody levels. However, there was a non-significant trend for birds with intact gut communities to have greater conjunctival pathology, suggesting a possible impact of gut bacteria on pro-inflammatory cytokine stimulation. Using 16S bacterial rRNA amplicon sequencing, we found dramatic differences in cloacal bacterial community composition between captive, wild-caught house finches in our experiment and free-living finches from the same population, with lower bacterial richness and core communities composed of fewer genera in captive finches. We hypothesize thatmore »captivity may have affected the strength of results in this experiment, necessitating further study with this consideration. The abundance of anthropogenic impacts on wildlife and their bacterial communities, alongside the emergence and spread of infectious diseases, highlights the importance of studies addressing the role of commensal bacteria in health and disease, and the consequences of gut bacterial shifts on wild hosts.« less
  3. The microbiome is critical for host survival and fitness, but gaps remain in our understanding of how this symbiotic community is structured. Despite evidence that related hosts often harbor similar bacterial communities, it is unclear whether this pattern is due to genetic similarities between hosts or to common ecological selection pressures. Here, using herbivorous rodents in the genusNeotoma, we quantify how geography, diet, and host genetics, alongside neutral processes, influence microbiome structure and stability under natural and captive conditions. Using bacterial and plant metabarcoding, we first characterized dietary and microbiome compositions for animals from 25 populations, representing seven species from 19 sites across the southwestern United States. We then brought wild animals into captivity, reducing the influence of environmental variation. In nature, geography, diet, and phylogeny collectively explained ∼50% of observed microbiome variation. Diet and microbiome diversity were correlated, with different toxin-enriched diets selecting for distinct microbial symbionts. Although diet and geography influenced natural microbiome structure, the effects of host phylogeny were stronger for both wild and captive animals. In captivity, gut microbiomes were altered; however, responses were species specific, indicating again that host genetic background is the most significant predictor of microbiome composition and stability. In captivity, diet effectsmore »declined and the effects of host genetic similarity increased. By bridging a critical divide between studies in wild and captive animals, this work underscores the extent to which genetics shape microbiome structure and stability in closely related hosts.

    « less
  4. Reguera, Gemma (Ed.)
    ABSTRACT Mucosal defenses are crucial in animals for protection against pathogens and predators. Host defense peptides (antimicrobial peptides, AMPs) as well as skin-associated microbes are key components of mucosal immunity, particularly in amphibians. We integrate microbiology, molecular biology, network-thinking, and proteomics to understand how host and microbially derived products on amphibian skin (referred to as the mucosome) serve as pathogen defenses. We studied defense mechanisms against chytrid pathogens, Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal), in four salamander species with different Batrachochytrium susceptibilities. Bd infection was quantified using qPCR, mucosome function (i.e., ability to kill Bd or Bsal zoospores in vitro ), skin bacterial communities using 16S rRNA gene amplicon sequencing, and the role of Bd-inhibitory bacteria in microbial networks across all species. We explored the presence of candidate-AMPs in eastern newts and red-backed salamanders. Eastern newts had the highest Bd prevalence and mucosome function, while red-back salamanders had the lowest Bd prevalence and mucosome function, and two-lined salamanders and seal salamanders were intermediates. Salamanders with highest Bd infection intensity showed greater mucosome function. Bd infection prevalence significantly decreased as putative Bd-inhibitory bacterial richness and relative abundance increased on hosts. In co-occurrence networks, some putative Bd-inhibitory bacteria were found asmore »hub-taxa, with red-backs having the highest proportion of protective hubs and positive associations related to putative Bd-inhibitory hub bacteria. We found more AMP candidates on salamanders with lower Bd susceptibility. These findings suggest that salamanders possess distinct innate mechanisms that affect chytrid fungi. IMPORTANCE How host mucosal defenses interact, and influence disease outcome is critical in understanding host defenses against pathogens. A more detailed understanding is needed of the interactions between the host and the functioning of its mucosal defenses in pathogen defense. This study investigates the variability of chytrid susceptibility in salamanders and the innate defenses each species possesses to mediate pathogens, thus advancing the knowledge toward a deeper understanding of the microbial ecology of skin-associated bacteria and contributing to the development of bioaugmentation strategies to mediate pathogen infection and disease. This study improves the understanding of complex immune defense mechanisms in salamanders and highlights the potential role of the mucosome to reduce the probability of Bd disease development and that putative protective bacteria may reduce likelihood of Bd infecting skin.« less
  5. Background Insects are the most diverse group of animals which have established intricate evolutionary interactions with bacteria. However, the importance of these interactions is still poorly understood. Few studies have focused on a closely related group of insect species, to test the similarities and differences between their microbiota. Heliconius butterflies are a charismatic recent insect radiation that evolved the unique ability to use pollen as a protein source, which affected life history traits and resulted in an elevated speciation rates. We hypothesize that different Heliconius butterflies sharing a similar trophic pollen niche, harbor a similar gut flora within species, population and sexes. Methods To test our hypothesis, we characterized the microbiota of 38 adult male and female butterflies representing six species of Heliconius butterflies and 2 populations of the same species. We sequenced the V4 region of the 16S rRNA gene with the Roche 454 system and analyzed the data with standard tools for microbiome analysis. Results Overall, we found a low microbial diversity with only 10 OTUs dominating across all individuals, mostly Proteobacteria and Firmicutes, which accounted for  99.5% of the bacterial reads. When rare reads were considered, we identified a total of 406 OTUs across our samples. Wemore »identified reads within Phyla Chlamydiae , found in 5 butterflies of four species. Interestingly, only three OTUs were shared among all 38 individuals ( Bacillus, Enterococcus and Enterobacteriaceae ). Altogether, the high individual variation overshadowed species and sex differences. Thus, bacterial communities were not structured randomly with 13% of beta-diversity explained by species, and 40 rare OTUs being significantly different across species. Finally, 13 OTUs, including the intercellular symbiont Spiroplasma, varied significantly in relative abundance between males and females. Discussion The Heliconius microbial communities in these 38 individuals show a low diversity with few differences in the rare microbes between females, males, species or populations. Indeed, Heliconius butterflies, similarly to other insects, are dominated by few OTUs, mainly from Proteobacteria and Firmicutes. The overall low microbial diversity observed contrasts with the high intra-species variation in microbiome composition. This could indicate that much of the microbiome maybe acquired from their surroundings. The significant differences between species and sexes were restricted to rare taxa, which could be important for microbial community stability under changing conditions as seen in other host-microbiome systems. The presence of symbionts like Spiroplasma or Chlamydiae , identified in this study for the first time in Heliconius , could play a vital role in their behavior and evolution by vertical transmission. Altogether, our study represents a step forward into the description of the microbial diversity in a charismatic group of closely related butterflies.« less