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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 Historically, the fields of ecoimmunology, psychoneuroimmunology and disease ecology have taken complementary yet disparate theoretical and experimental approaches, despite sharing critical common themes. Researchers in these areas have largely worked independently of one another to understand mechanistic immunological responses, organismal level immune performance, behavioral changes, and host and parasite/disease population dynamics, with few bridges across disciplines. Although efforts to strengthen and expand these bridges have been called for (and occasionally heeded) over the last decade, more integrative studies are only now beginning to emerge, with critical gaps remaining. Here, we briefly discuss the origins of these key fields, and their current state of integration, while highlighting several critical directions that we suggest will strengthen their connections into the future. Specifically, we highlight three key research areas that provide collaborative opportunities for integrative investigation across multiple levels of biological organization, from mechanisms to ecosystems: (1) parental effects of immunity, (2) microbiome and immune function and (3) sickness behaviors. By building new bridges among these fields, and strengthening existing ones, a truly integrative approach to understanding the role of host immunity on individual and community fitness is within our grasp. 

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 There is nothing like a pandemic to get the world thinking about how infectious diseases affect individual behavior. In this respect, sick animals can behave in ways that are dramatically different from healthy animals: altered social interactions and changes to patterns of eating and drinking are all hallmarks of sickness. As a result, behavioral changes associated with inflammatory responses (i.e. sickness behaviors) have important implications for disease spread by affecting contacts with others and with common resources, including water and/or sleeping sites. In this Review, we summarize the behavioral modifications, including changes to thermoregulatory behaviors, known to occur in vertebrates during infection, with an emphasis on non-mammalian taxa, which have historically received less attention. We then outline and discuss our current understanding of the changes in physiology associated with the production of these behaviors and highlight areas where more research is needed, including an exploration of individual and sex differences in the acute phase response and a greater understanding of the ecophysiological implications of sickness behaviors for disease at the population level.