Physiological responses to both natural and anthropogenic perturbations involve changes in glucose use and metabolism to enable animals to respond to challenges. The responses are at least partially mediated via the glucocorticoids, and the proper functioning of these systems are critical to animal health. Prolonged high-sugar diets in humans can compromise physiological functions and lead to a range of diseases including diabetes. Such outcomes are less common in natural, non-human systems, likely because of evolutionarily based balances between sugar intake and the ability to process it. Due to both landscape changes and human feeding of wildlife, the introduction of unnatural diets to wildlife is becoming increasingly common. However, the implications of unnatural dietary changes, and in particular changes in dietary glucose, are not well understood in non-human systems. We tested the effects of a high glucose diet on glucose tolerance in a controlled setting using captive juvenile Green Iguanas (Iguana iguana). In the field, we similarly performed glucose challenges (i.e., glucose tolerance tests) on Northern Bahamian Rock Iguanas (Cyclura cychlura) that are either fed or unfed by tourists, and we evaluated both short (within 8 hrs) and longer-term (within 19 hrs) blood glucose responses as well as plasma corticosterone (CORT) concentrations. Overall, we found significant effects of both experimental glucose supplementation in the laboratory and tourist feeding in the wild on glucose metabolism. In all instances where iguanas received a glucose-rich diet, we found greater acute increases in blood glucose following a glucose challenge. In the wild, tourist-fed iguanas, relative to unfed iguanas, had significantly lower baseline CORT levels, higher baseline blood glucose levels, and slower returns to baseline glucose levels following a glucose challenge. Therefore, glucose intolerance in response to unnatural glucose consumption is manifesting in both laboratory animals with relatively short-term glucose treatment and free-living iguanas exposed to long-term supplemental feeding by tourists. We also found more rapid increases in CORT response to capture and processing in tourist-fed iguanas and that CORT was positively related to blood glucose one-hour post glucose challenge, but only in tourist exposed and fed iguanas. Based on these results and the increasing prevalence of wildlife feeding on unnatural diets, further research is needed to understand how dietary changes affect glucose metabolism broadly across species and whether such changes cause any health ramifications.
Author ORCID Identifier
Susannah French https://orcid.org/0000-0001-8923-9728
NSF, Division of Integrative Organismal Systems (IOS)
Utah State University
NSF, Division of Integrative Organismal Systems (IOS) 1752908
Collaborative Research: The interplay between host diet, immunity, reproduction, and the microbiome across an anthropogenic-disturbed landscape
Physiological and morphological metrics of green and rock iguanas
Iguana iguana, Cyclura cychlura
Susannah S. French, Spencer B. Hudson, Alison C. Webb, Charles R. Knapp, Emily E. Virgin, Geoffrey D. Smith, Erin L. Lewis, John B. Iverson, Dale F. DeNardo; Glucose tolerance of iguanas is affected by high-sugar diets in the lab and supplemental feeding by ecotourists in the wild. J Exp Biol 15 April 2022; 225 (8): jeb243932. doi: https://doi.org/10.1242/jeb.243932
See ReadMe.txt file.
This work is licensed under a Creative Commons Attribution 4.0 License.
French, S. (2022). Data from: Glucose Tolerance of Iguanas is Affected by High Sugar Diets in the Lab and Supplemental Feeding by Ecotourists in the Wild [Data set]. Utah State University. https://doi.org/10.26078/94W0-3V59
Additional FilesFrenchetal_iguanaglucosestudy1.csv (1 kB)
Frenchetal_iguanaglucosestudy2.csv (5 kB)
Frenchetal_iguanaglucosestudy3.csv (7 kB)
ReadMe.txt (7 kB)