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First published online October 5, 2006
Journal of Experimental Biology 209, 4061-4066 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02473
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What explains the trot–gallop transition in small mammals?

José Iriarte-Díaz1,2,*, Francisco Bozinovic3 and Rodrigo A. Vásquez1

1 Institute of Ecology and Biodiversity, Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile
2 Department of Ecology and Evolutionary Biology, Box G-W, Brown University, Providence, RI 02912, USA
3 Center for Advanced Studies in Ecology and Biodiversity, and Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago 6513677, Chile

* Author for correspondence (e-mail: jose_iriarte{at}brown.edu)

Accepted 8 August 2006

The transition from trot to gallop in quadruped mammals has been widely hypothesized to be a strategy to minimize the energetic costs of running. This view, however, has been challenged by some experimental evidence suggesting instead that this transition might be triggered by mechanical cues, and would occur when musculoskeletal stresses reach a certain critical value. All previous experiments to test those hypotheses have used relatively large species and their results, therefore, may not be applicable to small mammals. In this study we evaluated the effect of carrying loads on the locomotor energetics and gait transitions of the rodent Octodon degus running on a treadmill. Metabolic rate and cost of transport increased about 30% with a 20% increment in body mass. This increment was higher than expectations based on other mammals, where energy consumption increases in proportion to the added mass, but similar to the response of humans to loads. No abrupt change of energy consumption between gaits was observed and therefore no evidence was found to support the energetic hypothesis. The trot–gallop transition speed did not vary when subjects were experimentally loaded, suggesting that the forces applied to the musculoskeletal system do not trigger gait transition.

Key words: gait transition, body mass, energetics, Froude number, loading


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© The Company of Biologists Ltd 2006