Abstract
Armoured, rigid bodied animals, such as Testudines, must self-right should they find themselves in an inverted position. The ability to self-right is an essential biomechanical and physiological process that influences survival and ultimately fitness. Traits that enhance righting ability may consequently offer an evolutionary advantage. However, the energetic requirements of self-righting are unknown. Using respirometry and kinematic video analysis, we examined the metabolic cost of self-righting in the terrestrial Mediterranean spur-thighed tortoise and compared this to the metabolic cost of locomotion at a moderate, easily sustainable speed. We found that self-righting is, relatively, metabolically expensive and costs around two times the mass-specific power required to walk. Rapid movements of the limbs and head facilitate successful righting however, combined with the constraints of breathing whilst upside down, contribute a significant metabolic cost. Consequently, in the wild, these animals should favour environments or behaviours where the risk of becoming inverted is reduced.
Highlights
Armoured, rigid bodied animals, such as Testudines, must self-right should they find themselves in an inverted position
The actual metabolic cost of self-righting, which is an essential element for assessing fitness, has never been experimentally quantified in any Testudines
Any increases in the work of breathing would contribute to the metabolic cost of self-righting
Summary
Rigid bodied animals, such as Testudines, must self-right should they find themselves in an inverted position. Tortoises locomote with diagonally opposite feet moving together so that two feet are in contact with the ground at almost all t imes[9] These adjustment in gait are thought to limit body swaying and enable them to avoid fast and energetically expensive movements of the limbs[9]. Research into self-righting has focussed primarily on the influence of body size, body shape and how morphological variations in limb lengths or measures of flexibility habitat structure and ruggedness affect righting ability[15,19,20,21,22] These studies have demonstrated that righting ability is primarily related to carapace structure, shape and size as well as the extension length of the limbs, including the neck[19]. We placed the CoR into context by comparison to the metabolic cost of transport (CoT) at an average sustainable speed
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