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First published online December 10, 2003
Journal of Experimental Biology 207, 295-305 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00760
Cold-acclimation in Peromyscus: temporal effects and individual variation in maximum metabolism and ventilatory traits
Department of Biology, University of California, Riverside, California 92521, USA
* Author for correspondence (e-mail: erezende{at}citrus.ucr.edu)
Accepted 20 October 2003
Thermal acclimation in small endotherms provides an excellent model for the
study of physiological plasticity, as energy requirements can be easily
manipulated and the results are relevant for natural conditions. Nevertheless,
how physiology changes throughout acclimation, and how individuals vary in
their response to acclimation, remain poorly understood. Here we describe a
high temporal-resolution study of cold acclimation in the deer mouse
Peromyscus maniculatus. The experimental design was based on repeated
measures at short intervals throughout cold acclimation, with controls
(maintained at constant temperature) for measurement artifacts. We monitored
body mass, maximum metabolic rate in cold exposure and ventilatory traits
(respiratory frequency, tidal and minute volume and oxygen extraction) for 3
weeks at 23°C. Then, half of the individuals were held for 7 weeks at
5°C. Body mass was differently affected by cold acclimation depending on
sex. Maximal metabolism
(
O2max)
increased significantly during the first week of cold acclimation, `overshot'
after 5 weeks and dropped to a plateau about 34% above control values at week
7. Similarly, ventilatory traits increased during cold acclimation, though
responses were different in their kinetics and magnitude. Body mass, maximum
metabolism, and most ventilatory traits were repeatable after 7 weeks in
control and cold-acclimated animals. However, repeatability tended to be lower
in the cold-acclimated group, especially while animals were still acclimating.
Our results show that acclimation effects may be under- and/or overestimated,
depending on when trials are performed, and that different traits respond
differently, and at different rates, to acclimation. Hence, future studies
should be designed to ensure that animals have attained steady-state values in
acclimation experiments.
Key words: acclimation, ambient temperature, maximal oxygen consumption, physiological plasticity, Peromyscus maniculatus, repeatability, thermogenesis, ventilation
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