Hormonal and metabolic responses to upper temperature extremes in divergent life-history ecotypes of a garter snake

Abstract

Extreme temperatures constrain organismal physiology and impose both acute and chronic effects. Additionally, temperature-induced hormone-mediated stress response pathways and energetic tradeoffs are important drivers of life-history variation. This study employs an integrative approach to quantify acute physiological responses to high temperatures in divergent life-history ecotypes of the western terrestrial garter snake (Thamnophis elegans). Using wild-caught animals, we measured oxygen consumption rate and physiological markers of hormonal stress response, energy availability and anaerobic respiration in blood plasma across five ecologically relevant temperatures (24, 28, 32, 35 and 38°C; 3 h exposure). Corticosterone, insulin and glucose concentrations all increased with temperature, but with different thermal response curves, suggesting that high temperatures differently affect energy-regulation pathways. Additionally, oxygen consumption rate increased without plateau and lactate concentration did not increase with temperature, challenging the recent hypothesis that oxygen limitation sets upper thermal tolerance limits. Finally, animals had similar physiological thermal responses to high-temperature exposure regardless of genetic background, suggesting that local adaptation has not resulted in fixed differences between ecotypes. Together, these results identify some of the mechanisms by which higher temperatures alter hormonal-mediated energy balance in reptiles and potential limits to the flexibility of this response.

Increasing temperatures increase the risk of reproductive failure in a near threatened alpine ground‐nesting bird, the Cape Rockjumper Chaetops frenatus

“…Although generally increasing at higher temperatures, snake activity does reach upper limits at which they seek out shaded microsites (Huey & Kingsolver 1989). During this study, BHNR recorded no temperatures above 36 °C, which is lower than temperatures at which snake species experience physiological stress (Gangloff et al 2016) and seek out shade (Webb & Shine 1998). Our lowest Boomslang predation temperature (14.2 °C) is below the temperature range recorded for Boomslang activity in the Kalahari (19.2 ± 1.7 to 31.4 ± 1.3 °C; G.J.…”

Convergence in reduced body size, head size, and blood glucose in three island reptiles

“…Laboratory studies suggest that pancreatic hormones act to regulate blood glucose similarly to mammals in nonmammalian vertebrates, such as reptiles (Miller & Wurster, 1958;Miller, 1960;Sidorkiewicz & Skoczylas, 1974;Putti, Varano, Cavagnuolo, & Laforgia, 1986;Gangloff, Holden, Telemeco, Baumgard, & Bronikowski, 2016).…”

Geographic variation and within-individual correlations of physiological stress markers in a widespread reptile, the common garter snake (Thamnophis sirtalis)

“…This is followed by increases in circulating glucocorticoids, which promote production of glucose via gluconeogenesis and glycogenolysis (Sapolsky et al, 2000). After the HPI axis has responded to a stressor, circulating glucose levels generally positively covary with the glucocorticoid response (e.g., Gangloff et al, 2016), providing opportunity to measure both the glucocorticoid stress response and its subsequent downstream effects. Additionally, glucocorticoids act to redistribute leukocytes to specific target tissues.…”