Dehydration enhances multiple physiological defense mechanisms in a desert lizard, Heloderma suspectum

Abstract

The physiological challenges associated with dehydration can induce an increase in plasma glucocorticoid concentrations, a response thought to provide the mechanism for dehydration suppressing immune function. However, a comprehensive examination of the inter-relationship of dehydration, stress and immune function has not been conducted within a single species. We previously demonstrated that Gila monsters (Heloderma suspectum), which inhabit a xeric environment with a predictable seasonal drought, have enhanced measures of innate immunity when dehydrated. These results suggest that, in this species, dehydration may not induce a glucocorticoid response, but, instead, enhances physiological defense mechanisms. To explore this possibility, we examined multiple measures of innate immunity as well as initial and reactive plasma concentrations of glucocorticoids in captive and free-ranging Gila monsters at various hydration states. Our results show that, in this species, dehydration alone does not cause a substantial increase in plasma glucocorticoids, and we provide broader evidence that dehydration enhances defensive mechanisms including stress reactivity and various measures of innate immune function. These findings suggest that physiological responses to dehydration may depend heavily on an organism's ecology. More research on the effects of dehydration on the glucocorticoid response and immunity will help clarify the interactive roles they play in response to hydration challenges and whether adaptations to water-limited environments influence these interactions.

Dehydration as a stressor in toads (Rhinella ornata)

“…An elevation of GC plasma levels has been previously documented in response to dehydration for other tetrapods with a large interspecific variation. Rats, birds, and lizards, for example, showed an increase in GCs when exposed to dehydration stress (Arnhold, Wotus, & Engeland, ; Cain & Lien, ; Moeller et al, ). Previous studies have shown that dehydration affects amphibian locomotor performance and thermal tolerance (Anderson & Andrade, ; Titon & Gomes, ; Titon et al, ), increases body fluid concentration (hematocrit, hemoglobin content, plasma osmolarity, and urea concentration; Anderson, Bovo, Eismann, Menegario, & Andrade, ; Degani, Silanikove, & Shkolnik, , Jørgensen, ; Lillywhite, ; Ruibal 1962; Ruibal, Tevis, & Roig, ; Shoemaker, ; Shoemaker & Nagy, ; Shoemaker, McClanahan, & Ruibal, ), and decreases the mass of visceral organs the rates of evaporative water loss (Anderson et al, ).…”

“…In response to several stressors, including dehydration (Moeller, Demare, Davies, & DeNardo, ), the hypothalamic–pituitary–adrenal/interrenal (HPA/I) axis is activated resulting in glucocorticoids (GCs) secretion in vertebrates with corticosterone (CORT) being the main GC present in amphibians (Rollins‐Smith, ). The activation of the HPA/I axis modulates several physiological functions, contributing to an integrative and adaptive response to short‐term stressors.…”

Altitudinal Effects on Innate Immune Response of a Subterranean Rodent

“…Therefore, our main result appears robust despite the possibility of an effect of sex on immune response. While we acknowledge that our sample size is small, the use of approximately eight replicates per category is common for immunological studies using nonmodel organisms (Gardner et al, 2018, cane toad, n = 9 per group, total 27; Gao and Deviche, 2018, house sparrow, n = 10 per group, total 20; Georgiev et al, 2015, rhesus macaques, n = 10-15 per immunological test; Matson et al, 2012, homing pigeons, n = 8 per group, total 16;Moeller et al, 2017, Gila monster, n = 3 females, 5 males, 8 total; Neuman- Lee et al, 2019, common gartersnake, n = 22).…”

Dehydration enhances innate immunity in a semiaquatic snake from the wet‐dry tropics

“…Recent work has begun to examine the relationship between dehydration and immune function. Notably, aspects of immunity are often enhanced in response to dehydration, at least for the xeric‐adapted squamate reptiles studied to date (Brusch, Billy, Blattman, & DeNardo, ; Moeller, Demare, Davies, & DeNardo, ). As effective functioning of the immune system is vital for fending off pathogens and thus survival (Zuk & Stoehr, ), a better understanding of the relationship between hydration state and immune function will be valuable for predicting organismal impacts of altered rainfall patterns associated with global climate change (Dai, ; Mukherjee, Mishra, & Trenberth, ).…”