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The Journal of Experimental Biology 206, 1153-1161 (2003)
doi: 10.1242/jeb.00221

Diving experience and the aerobic dive capacity of muskrats: does training produce a better diver?

Robert A. MacArthur^*, Gillian L. Weseen and Kevin L. Campbell

Department of Zoology, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2

^* Author for correspondence (e-mail: rmacarth{at}ms.umanitoba.ca)

Accepted 10 January 2003

We tested the hypothesis that the body oxygen stores, aerobic dive limit (ADL) and dive performance of muskrats can be enhanced by dive-conditioning in a laboratory setting. We compared several key variables in 12 muskrats trained to swim a 16 m underwater course to a feeding station (`divers') with those of 12 animals precluded from diving but required to travel identical distances in water to feed (`surface swimmers'). Acclimated muskrats assigned to each group were trained concurrently over a 9–11 week period. We observed significant gains in the haematocrit (P=0.0005) and blood haemoglobin concentration (P=0.015) of `divers', but not `surface swimmers'. The post-training blood O₂ store calculated for `divers' (22.9 ml O<sub>2</sub> kg<sup>–1</sup>) was nearly 26% higher than that (18.2 ml O<sub>2</sub> kg<sup>–1</sup>) derived for `surface swimmers' (P=0.03). Dive-conditioning had no apparent effect on lung volume, whole blood and plasma volumes, nor on the glycogen level and buffering capacity of skeletal muscles. Cardiac and skeletal muscle myoglobin levels were also similar in both test groups following training. The mean total body oxygen store of `divers' (37.8ml O<sub>2</sub> STPD kg<sup>–1</sup>) was 13.5% higher (P=0.037) than for `surface swimmers' (33.3 ml O₂ STPD kg^–1), an increase attributed entirely to the gain in blood O₂ storage capacity of the former group. However, owing to a slightly higher estimate of diving metabolic rate in dive-conditioned animals, the calculated ADL for this group (61.3 s) was indistinguishable from that of `surface swimmers' (61.8 s). Few differences were observed in the post-training dive behaviour of `surface swimmers' and `divers', a finding consistent with the strong similarity in their calculated aerobic dive capacities.

Key words: dive conditioning, body oxygen store, dive behaviour, myoglobin, haemoglobin, muscle buffering capacity, metabolism, aerobic dive limit, muskrat, Ondatra zibethicus

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