title: 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 trade-offs 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.
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA gangloff@iastate.edu.
authors.forename: Eric J
authors.identifier: http://orcid.org/0000-0002-9074-8009
authors.initials: EJ
authors.lastname: Gangloff
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Kaitlyn G
authors.initials: KG
authors.lastname: Holden
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Rory S
authors.initials: RS
authors.lastname: Telemeco
authors.affiliation: Department of Animal Science, Iowa State University, Ames, IA 50011, USA.
authors.forename: Lance H
authors.initials: LH
authors.lastname: Baumgard
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Bronikowski
keywords: Corticosterone; Glucose; Insulin; Metabolic rate; Oxygen and capacity-limited thermal tolerance (OCLTT); Thamnophis elegans