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ABSTRACT The present work aimed to study whether a high sugar diet can alter immune responses and the gut microbiome in green iguanas. Thirty-six iguanas were split into four treatment groups using a 2×2 design. Iguanas received either a sugar-supplemented diet or a control diet, and either a lipopolysaccharide (LPS) injection or a phosphate-buffered saline (PBS) injection. Iguanas were given their respective diet treatment through the entire study (∼3 months) and received a primary immune challenge 1 and 2 months into the experiment. Blood samples and cloacal swabs were taken at various points in the experiment and used to measure changes in the immune system (bacterial killing ability, lysis and agglutination scores, LPS-specific IgY concentrations), and alterations in the gut microbiome. We found that a sugar diet reduces bacterial killing ability following an LPS challenge, and sugar and the immune challenge temporarily alters gut microbiome composition while reducing alpha diversity. Although sugar did not directly reduce lysis and agglutination following the immune challenge, the change in these scores over a 24-h period following an immune challenge was more drastic (it decreased) relative to the control diet group. Moreover, sugar increased constitutive agglutination outside of the immune challenges (i.e. pre-challenge levels). In this study, we provide evidence that a high sugar diet affects the immune system of green iguanas (in a disruptive manner) and alters the gut microbiome. 

Abstract To promote survival and fitness, organisms use a suite of physiological systems to respond to both predictable and unpredictable changes in the environment. These physiological responses are also influenced by changes in life history state. The continued activation of physiological systems stemming from persistent environmental perturbations enable animals to cope with these challenges but may over time lead to significant effects on the health of wildlife. In the present study, we tested how varying environmental perturbations driven by tourism and associated supplemental feeding affects the energetics, corticosterone and immunity of six discrete populations of the northern Bahamian rock iguana (Cyclura cychlura inornata and Cyclura cychlura figginsi). We studied populations within and outside the reproductive season and quantified tourist numbers during sample collection. Specifically, we measured clutch size, body condition, plasma energy metabolites, reactive oxygen species, baseline corticosterone concentrations and immune function of male and female iguanas from each population to address whether (i) disparate physiologies are emerging across a gradient of tourism and feeding, (ii) both subspecies respond similarly and (iii) responses vary with season/reproductive condition. We found significant effects of tourism level, season and their interaction on the physiology of both C. c. inornata and C. c. figginsi, supporting the idea that tourism is leading to the divergence of phenotypes. Specifically, we found elevated plasma energy metabolites, oxidative stress and a measure of innate immunity (bactericidal ability), but reduced corticosterone concentrations with increasing tourism in both subspecies of rock iguanas. These physiological metrics differ according to the level of tourism in both subspecies and persist across seasons despite variation with natural seasonal and reproductive changes. These findings suggest that anthropogenic disturbance results in disparate physiologies in northern Bahamian rock iguanas. 

ABSTRACT There is great interspecific variation in the nutritional composition of natural diets, and the varied nutritional content is physiologically tolerated because of evolutionarily based balances between diet composition and processing ability. However, as a result of landscape change and human exposure, unnatural diets are becoming widespread among wildlife without the necessary time for evolutionary matching between the diet and its processing. We tested how a controlled, unnatural high glucose diet affects glucose tolerance using captive green iguanas, and we performed similar glucose tolerance tests on wild Northern Bahamian rock iguanas that are either frequently fed grapes by tourists or experience no such supplementation. We evaluated both short and longer-term blood glucose responses and corticosterone (CORT) concentrations as changes have been associated with altered diets. Experimental glucose supplementation in the laboratory and tourist feeding in the wild both significantly affected glucose metabolism. When iguanas received a glucose-rich diet, we found greater acute increases in blood glucose following a glucose challenge. Relative to unfed iguanas, tourist-fed iguanas had significantly lower baseline CORT, higher baseline blood glucose, and slower returns to baseline glucose levels following a glucose challenge. Therefore, unnatural consumption of high amounts of glucose alters glucose metabolism in laboratory iguanas with short-term glucose treatment and free-living iguanas exposed to long-term feeding by tourists. Based on these results and the increasing prevalence of anthropogenically altered wildlife diets, the consequences of dietary changes on glucose metabolism should be further investigated across species, as such changes in glucose metabolism have health consequences in humans (e.g. diabetes). 

Abstract Dehydration is considered a physiological challenge, and many organisms live in environments that undergo periods of reduced water availability that can lead to dehydration. Recent studies have found a positive relationship between dehydration and innate immune function in animals adapted to xeric or semixeric environments. To explore the generality of this relationship, we examined the impact of dehydration on innate immune performance in water pythons (Liasis fuscus), a semiaquatic snake from the wet‐dry tropics of Australia. We collected blood samples from male and female water pythons held in the laboratory without food and water for 4 weeks. We also collected blood from free‐ranging snakes throughout the Austral dry‐season. We evaluated plasma osmolality and innate immune function (agglutination, lysis, and bacterial‐killing ability) and found that increased osmolality, whether manipulated in the laboratory or as a result of natural water limitation, resulted in enhanced aspects of innate immune performance. Counter‐intuitively, snakes in the wild became more hydrated as the dry season progressed, suggesting the dehydrated snakes move to water sources periodically to rehydrate. Comparing our data with those from previous studies, we suspect species divergence in the level of dehydration (i.e., hyperosmolality) that triggers enhanced immune capabilities.