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1. Effect of captivity on the vertebral bone microstructure of xenarthran mammals

   https://doi.org/10.1002/ar.24817  

   Zack, Ellianna H.; Smith, Stephanie M.; Angielczyk, Kenneth D. (November 2021, The Anatomical Record)

   null (Ed.)

   Captive specimens in museum collections facilitate study of rare taxa, but the lifestyles, diets, and lifespans of captive animals differ from their wild counterparts. Trabecular bone architecture adapts to in vivo forces, and may reflect interspecific variation in ecology and behavior as well as intraspecific variation between captive and wild specimens. We compared trunk vertebrae bone microstructure in captive and wild xenarthran mammals to test the effects of ecology and captivity. We collected μCT scans of the last six presacral vertebrae in 13 fossorial, terrestrial, and suspensorial xenarthran species (body mass: 120 g to 35 kg). For each vertebra, we measured centrum length; bone volume fraction (BV.TV); trabecular number and mean thickness (Tb.Th); global compactness (GC); cross-sectional area; mean intercept length; star length distribution; and connectivity and connectivity density. Wild specimens have more robust trabeculae, but this varies with species, ecology, and pathology. Wild specimens of fossorial taxa (Dasypus) have more robust trabeculae than captives, but there is no clear difference in bone microstructure between wild and captive specimens of suspensorial taxa (Bradypus, Choloepus), suggesting that locomotor ecology influences the degree to which captivity affects bone microstructure. Captive Tamandua and Myrmecophaga have higher BV.TV, Tb.Th, and GC than their wild counterparts due to captivity-caused bone pathologies. Our results add to the understanding of variation in mammalian bone microstructure, suggest caution when including captive specimens in bone microstructure research, and indicate the need to better replicate the habitats, diets, and behavior of animals in captivity. 

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2. Microbiome stability and structure is governed by host phylogeny over diet and geography in woodrats ( Neotoma spp.)

   https://doi.org/10.1073/pnas.2108787118  

   Weinstein, Sara B.; Martínez-Mota, Rodolfo; Stapleton, Tess E.; Klure, Dylan M.; Greenhalgh, Robert; Orr, Teri J.; Dale, Colin; Kohl, Kevin D.; Dearing, M. Denise (November 2021, Proceedings of the National Academy of Sciences)

   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 effects 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. 

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3. Effects of captivity on the bone microstructure of xenarthrous vertebrae

   Zack, Ellianna H; Smith, Stephanie M; Angielczyk, Kenneth D (March 2021, Integrative and comparative biology)

   Captive specimens in natural history collections allow researchers to inspect the morphologies of rare taxa, but the lifestyles,diets, and lifespans of captive animals differ from those of their wild counterparts. To quantify these differences, we compared bone microstructure of trunk vertebrae in captive and wild xenarthran mammals (sloths, armadillos, anteaters). Because trabecular bone architecture (TBA) adapts to in vivo forces, bone microstructure reflects ecology and behavior, but this means that it may differ between captive and wild specimens of the same species. We collected μCT scans of the last six presacral vertebrae in 13 species of fossorial, terrestrial, and suspensorial xenarthrans ranging in body mass from 120g (Chlamyphorus) to 35kg (Myrmecophaga). For each vertebra, we measured bone volume fraction (BVF); trabecular number, mean thickness (TbTh), and orientation; global compactness; and cross sectional area. Wild specimens generally have more robust trabeculae, but this differs based on species, vertebral position, ecology, and pathology. The wild specimens of fossorial taxa (Dasypus) have more robust trabeculae than their captive counterparts, but there is no clear difference in TBA of wild and captive specimens in suspensorial and terrestrial taxa (Bradypus, Choloepus, Cyclopes). These data suggest that locomotor ecology affects the level to which captivity affects bone microstructure. The captive specimens of both Tamandua and Myrmecophaga have higher BVF and TbTh than their wild counterparts, indicating more brittle trabeculae due to bone pathologies caused by captivity. Our results add to the overall understanding of variation in mammalian bone microstructure and suggest caution when including captive specimens in research on TBA. 

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4. The effects of daily mitotane or diazepam treatment on the formation of chronic stress symptoms in newly captured wild house sparrows

   https://doi.org/10.1093/conphys/coaa118  

   Fischer, Clare P; Romero, L Michael (January 2020, Conservation Physiology)

   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 sudden 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. 

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5. Chronic stress and captivity alter the cloacal microbiome of a wild songbird

   https://doi.org/10.1242/jeb.243176  

   Madden, Anne A.; Oliverio, Angela M.; Kearns, Patrick J.; Henley, Jessica B.; Fierer, Noah; Starks, Philip T.; Wolfe, Benjamin E.; Romero, L. Michael; Lattin, Christine R. (April 2022, Journal of Experimental Biology)

   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 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. 

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