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First published online May 29, 2009
Journal of Experimental Biology 212, 1801-1810 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.027094

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Seasonal changes in thermoregulatory responses to hypoxia in the Eastern chipmunk (Tamias striatus)

Danielle L. Levesque and Glenn J. Tattersall^*

Department of Biological Sciences, Brock University, St Catharines, ON, Canada, L2S 3A1

^* Author for correspondence (e-mail: gtatters{at}brocku.ca)

Accepted 22 March 2009

Mammalian heterotherms are known to be more tolerant of low oxygen levels than homeotherms. However, heterotherms demonstrate extreme seasonality in daily heterothermy and torpor expression. Because hypoxia depresses body temperature (T_b) and metabolism in mammals, it was of interest to see if seasonal comparisons of normothermic animals of a species capable of hibernation produce changes in their responses to hypoxia that would reflect a seasonal change in hypoxia tolerance. The species studied, the Eastern chipmunk (Tamias striatus, Linnaeus 1758), is known to enter into torpor exclusively in the winter. To test for seasonal differences in the metabolic and thermoregulatory responses to hypoxia (9.9 kPa), flow-through respirometry was used to compare oxygen consumption, minimum thermal conductance and T_b under fixed ambient temperature (T_a) conditions whereas a thermal gradient was used to assess selected T_a and T_b in response to hypoxia, in both summer- and winter-acclimated animals. No differences were observed between seasons in resting metabolism or thermal conductance in normoxic, normothermic animals. Providing the animals with a choice of T_a in hypoxia attenuated the hypoxic drop in T_b in both seasons, suggesting that the reported fall in T_b in hypoxia is not fully manifested in the behavioural pathways responsible for thermoregulation in chipmunks. Instead, T_b in hypoxia tends to be more variable and dependent on both T_a and season. Although T_b dropped in hypoxia in both seasons, the decrease was less in the winter with no corresponding decrease in metabolism, indicating that winter chipmunks are more tolerant to hypoxia than summer animals.

Key words: hypoxia tolerance, heterothermy, hibernator, thermal conductance, resting oxygen consumption, body temperature, behavioural thermoregulation

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