What explains the trot–gallop transition in small mammals?

Abstract

SUMMARY 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.

Comparison of the morphology of the limbs of juvenile and adult horses (Equus caballus) and their implications on the locomotor biomechanics

“…Thus, instead of a universal criterion, different criteria have been developed (Day and Jane, 2007). It has also been suggested that certain variables should have a size-dependent interpretation (Iriarte-Diaz, 2002;Iriarte-Diaz et al, 2006). Several hypotheses different to the principle of dynamic similarity may help explain our results.…”

Effects of early-stage aging on locomotor dynamics and hindlimb muscle force production in the rat

“…Initially, these larger limb loads in the aged rats would seem to support the critical force hypothesis for symmetrical-asymmetrical gait transitions, which posits that animals change gait to reduce loading of the musculoskeletal system (Biewener and Taylor, 1986;Farley et al, 1991). However, a previous study found little support for force-motivated gait transitions in another small, crouched mammal -the degu, a caviomorph rodent (Iriarte-Diaz et al, 2006). When adult degus were injected with saline solution to experimentally increase their mass by 20%, they demonstrated no difference in gait transitions when compared with controls.…”

Evidence for energy savings from aerial running in the Svalbard rock ptarmigan (Lagopus muta hyperborea)

“…The primary alternative hypothesis for a mechanism driving gait changes is the reduction of forces applied to the musculoskeletal system [11,42,43], and, again, some support this [11] while others using the same species (horse) conclude the opposite [3]. Interestingly, a study of the small rodent Octodon degus [10] found no evidence for either hypothesis. Unlike horses [2], ptarmigans cannot be made to overlap their gaits.…”

“…horse Equus ferus caballus [2,3]; red kangaroo Megaleia rufa [4]; camel Camelus dromedaries and donkey Equus asinus [5]; ostrich Struthio camelus and emu Dromaius novaehollandiae [6,7]; and human Homo sapiens [8,9]), supporting the view that energy savings play a role in the evolution of gait changes. However, an abrupt reduction in COT with gait change is not always seen [10]. In addition, if allowed to select their gaits naturally, the trot-gallop transition in the horse [11,12] and walk -run in humans [13] occur at significantly lower speeds than would be expected if energy saving alone was being optimized.…”