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.
The authors declare no competing or financial interests.
A.M.B., E.J.G., K.G.H. and R.S.T. conducted the experiment; E.J.G. and K.G.H. performed lab work; E.J.G. performed data analysis and drafted the manuscript; and all authors contributed to experimental design, interpretation of results and manuscript revisions.
Funding was provided by the Chicago Herpetological Society, the Iowa Science Foundation (13-07) and the National Science Foundation (IOS-0922528). We also recognize the support of fellowships from the Iowa State University Office of Biotechnology to E.J.G., the Environmental Protection Agency (FP-91723101) to R.S.T., and additional support to R.S.T. during manuscript preparation from the National Science Foundation (EF-1065638 to L. B. Buckley).
All data are available in the Dryad Digital Repository http://dx.doi.org/10.5061/dryad.cs5th
- Received May 11, 2016.
- Accepted July 15, 2016.
- © 2016. Published by The Company of Biologists Ltd