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Informed and effective management of emerging infectious diseases can be improved by a clear understanding of host–pathogen–environment interactions. Impacts of the seasonal environment on pathogen dynamics and host responses are poorly described in most reptile host–fungal pathogen systems. Here, we describe seasonal patterns of ophidiomycosis, a disease caused by the fungus Ophidiomyces ophidiicola (Oo), in a population of pygmy rattlesnakes, Sistrurus miliarius, in central Florida. We used field observations of gross clinical signs of disease in combination with qPCR on skin swabs to examine the seasonal prevalence of Oo and patterns of clinical presentation in hosts. We monitored thermoregulatory behaviors, ecdysis, and reproductive status in free‐living snakes to examine seasonal associations between infection and host coping responses. Both the prevalence of Oo and clinical signs of disease varied strongly with the season (winter high and summer low). In both seasons, the presence of clinical signs was a strong predictor of the presence of Oo as identified by qPCR on skin swabs (78% probability across seasons). Snakes with clinical signs of disease were more likely to be observed exhibiting thermoregulatory behavior or in ecdysis compared to non‐clinical snakes across seasons. The prevalence of Oo was not significantly different in pregnant snakes compared to other reproductive categories, but pregnant females were less likely to exhibit clinical signs of disease compared to males. Our results highlight strong seasonal patterns in both host clinical signs and Oo prevalence and support the efficacy of using gross clinical signs of disease in combination with qPCR on skin swabs to assess disease dynamics in free‐living snakes. We also identify ecdysis and thermoregulatory behaviors as components of the seasonal disease‐coping response and highlight the need to examine these behaviors as potential drivers of seasonal infection outcomes in reptiles afflicted with fungal pathogens. [ABSTRACT FROM AUTHOR]

Disease may be both a cause and a consequence of stress, and physiological responses to infectious disease may involve stress coping mechanisms that have important fitness consequences. For example, glucocorticoid and glycemic responses may affect host fitness by altering resource allocation and use in hosts, and these responses may be affected by competing stressors. To better understand the factors that affect host responses to infection, we challenged the immune system of field-acclimatized pygmy rattlesnakes, Sistrurus miliarius, with a sterile antigen, lipopolysaccharide (LPS), and measured the glucocorticoid and glycemic response in healthy non-reproductive snakes, snakes afflicted with an emerging mycosis (ophidiomycosis) and pregnant snakes. We hypothesized that LPS challenge would result in a glucocorticoid and glycemic response typical of the vertebrate acute phase response (APR), and therefore predicted that LPS challenge would result in an acute increase in plasma corticosterone (CORT) and a decline in plasma glucose in all individuals. Additionally, we hypothesized that the APR would be attenuated in individuals simultaneously coping with additional challenges to homeostasis (i.e. disease or reproduction). As predicted, the immune challenge elicited an acute increase in plasma CORT and a decrease in plasma glucose. Snakes coping with ophidiomycosis and pregnant snakes were able to mount a robust glucocorticoid and hypoglycemic response to LPS challenge, which was contrary to our hypothesis. Our findings clarify directions of causality linking infection, glucocorticoids and glucose, and emphasize the importance of future research examining the fitness consequences of interactions between stress and disease in wildlife threatened by emerging pathogens., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Emerging fungal pathogens are a direct threat to vertebrate biodiversity. Elucidating the mechanisms by which mycoses impact host fitness is an important step towards effective prediction and management of disease outcomes in populations. The vertebrate acute stress response is an adaptive mechanism that allows individuals to meet challenges to homeostasis and survival in dynamic environments. Disease may cause stress, and coping with fungal infections may require shifts in resource allocation that alter the ability of hosts to mount an acute response to other external stressors. We examined the glucocorticoid and glycemic response to acute capture stress in a population of free-living pygmy rattlesnakes, Sistrurus miliarius, afflicted with an emerging mycosis (ophidiomycosis) across seasons. In all combinations of disease status and season, acute capture stress resulted in a significant glucocorticoid and glycemic response. While disease was not associated with elevated baseline or stress-induced corticosterone (CORT), disease was associated with an increased glucocorticoid stress response (post-stress minus baseline) across seasons. Both baseline and stress-induced glucose were lower in snakes with ophidiomycosis compared to uninfected snakes. The relationship between glucose and pre- and post-stress CORT depended on infection status, and positive correlations were only observed in uninfected snakes. The variables which explained CORT and glucose levels were different. The pattern of CORT was highly seasonal (winter high - summer low) and negatively related to body condition. Glucose, on the other hand, did not vary seasonally or with body condition and was strongly related to sex (male high - female low). Our results highlight the fact that circulating CORT and glucose are sensitive to different intrinsic and extrinsic predictor variables and support the hypothesis that disease alters the acute physiological stress response. Whether the effects of ophidiomycosis on the acute stress response result in sublethal effects on fitness should be investigated in future studies., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Mounting an immune response may be energetically costly and require the diversion of resources away from other physiological processes. Yet, both the metabolic cost of immune responses and the factors that impact investment priorities remain poorly described in many vertebrate groups. For example, although viviparity has evolved many times in vertebrates, the relationship between immune function and pregnancy has been disproportionately studied in placental mammals. To examine the energetic costs of immune activation and the modulation of immune function during pregnancy in a non-mammalian vertebrate, we elicited an immune response in pregnant and non-pregnant pygmy rattlesnakes, Sistrurus miliarius , using lipopolysaccharide (LPS). Resting metabolic rate (RMR) was measured using flow-through respirometry. Immune function was examined using bactericidal assays and leukocyte counts. The RMR of pygmy rattlesnakes increased significantly in response to LPS injection. There was no statistically significant difference in the metabolic response of non-reproductive and pregnant snakes to LPS. Mean metabolic increments for pregnant females, non-reproductive females, and males were 13%, 18% and 26%, respectively. The ratio of heterophils to lymphocytes was elevated in response to LPS across reproductive categories; however, LPS did not impact plasma bactericidal ability in non-reproductive snakes. Although pregnant females had significantly higher plasma bactericidal ability compared with non-reproductive snakes prior to manipulation, their bactericidal ability declined in response to LPS. LPS administration also significantly reduced several litter characteristics, particularly when administrated relatively early in pregnancy. Our results indicate that immune performance is energetically costly and is altered during pregnancy, and that immune activation during pregnancy may result in tradeoffs that affect offspring in a viviparous reptile., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2020. Published by The Company of Biologists Ltd.)

Skin permeability and lipid content were determined using shed epidermis of neonatal and adult timber rattlesnakes (Crotalus horridus) from the Coastal Plain Pine Barrens of New Jersey and from the Appalachian Mountains of northern Pennsylvania. Differences between populations due to habitat and within populations due to age were tested. Skin permeability was not found to differ according to locality (P>0.05), but rates were significantly different for age. Permeability of adult epidermis was greater than that of neonates (P<0.01). Lipid content did not differ by locality (P>0.05), but differed between ages, paralleling the results found for permeation rates. Neonate sheds had a greater amount of extractable lipids than adult sheds (P<0.01). Despite the lower skin permeability of neonates, our estimates indicate that the percentage of their total body water content lost per hour may still be 2.2 times that of adults. Resistance to cutaneous water loss may be advantageous to neonates given their relatively large surface area-to-volume ratio.