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The crouching of the shrew: Mechanical consequences of limb posture in small mammals

An important trend in the early evolution of mammals was the shift from a sprawling stance, whereby the legs are held in a more abducted position, to a parasagittal one, in which the legs extend more downward. After that transition, many mammals shifted from a crouching stance to a more upright one....

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Autores principales: Riskin, Daniel K., Kendall, Corinne J., Hermanson, John W.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: PeerJ Inc. 2016
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4933088/
https://www.ncbi.nlm.nih.gov/pubmed/27413633
http://dx.doi.org/10.7717/peerj.2131
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author Riskin, Daniel K.
Kendall, Corinne J.
Hermanson, John W.
author_facet Riskin, Daniel K.
Kendall, Corinne J.
Hermanson, John W.
author_sort Riskin, Daniel K.
collection PubMed
description An important trend in the early evolution of mammals was the shift from a sprawling stance, whereby the legs are held in a more abducted position, to a parasagittal one, in which the legs extend more downward. After that transition, many mammals shifted from a crouching stance to a more upright one. It is hypothesized that one consequence of these transitions was a decrease in the total mechanical power required for locomotion, because side-to-side accelerations of the body have become smaller, and thus less costly with changes in limb orientation. To test this hypothesis we compared the kinetics of locomotion in two mammals of body size close to those of early mammals (< 40 g), both with parasagittally oriented limbs: a crouching shrew (Blarina brevicauda; 5 animals, 17 trials) and a more upright vole (Microtus pennsylvanicus; 4 animals, 22 trials). As predicted, voles used less mechanical power per unit body mass to perform steady locomotion than shrews did (P = 0.03). However, while lateral forces were indeed smaller in voles (15.6 ± 2.0% body weight) than in shrews (26.4 ± 10.9%; P = 0.046), the power used to move the body from side-to-side was negligible, making up less than 5% of total power in both shrews and voles. The most power consumed for both species was that used to accelerate the body in the direction of travel, and this was much larger for shrews than for voles (P = 0.01). We conclude that side-to-side accelerations are negligible for small mammals–whether crouching or more upright–compared to their sprawling ancestors, and that a more upright posture further decreases the cost of locomotion compared to crouching by helping to maintain the body’s momentum in the direction of travel.
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spelling pubmed-49330882016-07-13 The crouching of the shrew: Mechanical consequences of limb posture in small mammals Riskin, Daniel K. Kendall, Corinne J. Hermanson, John W. PeerJ Evolutionary Studies An important trend in the early evolution of mammals was the shift from a sprawling stance, whereby the legs are held in a more abducted position, to a parasagittal one, in which the legs extend more downward. After that transition, many mammals shifted from a crouching stance to a more upright one. It is hypothesized that one consequence of these transitions was a decrease in the total mechanical power required for locomotion, because side-to-side accelerations of the body have become smaller, and thus less costly with changes in limb orientation. To test this hypothesis we compared the kinetics of locomotion in two mammals of body size close to those of early mammals (< 40 g), both with parasagittally oriented limbs: a crouching shrew (Blarina brevicauda; 5 animals, 17 trials) and a more upright vole (Microtus pennsylvanicus; 4 animals, 22 trials). As predicted, voles used less mechanical power per unit body mass to perform steady locomotion than shrews did (P = 0.03). However, while lateral forces were indeed smaller in voles (15.6 ± 2.0% body weight) than in shrews (26.4 ± 10.9%; P = 0.046), the power used to move the body from side-to-side was negligible, making up less than 5% of total power in both shrews and voles. The most power consumed for both species was that used to accelerate the body in the direction of travel, and this was much larger for shrews than for voles (P = 0.01). We conclude that side-to-side accelerations are negligible for small mammals–whether crouching or more upright–compared to their sprawling ancestors, and that a more upright posture further decreases the cost of locomotion compared to crouching by helping to maintain the body’s momentum in the direction of travel. PeerJ Inc. 2016-06-29 /pmc/articles/PMC4933088/ /pubmed/27413633 http://dx.doi.org/10.7717/peerj.2131 Text en ©2016 Riskin et al. http://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/) , which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ) and either DOI or URL of the article must be cited.
spellingShingle Evolutionary Studies
Riskin, Daniel K.
Kendall, Corinne J.
Hermanson, John W.
The crouching of the shrew: Mechanical consequences of limb posture in small mammals
title The crouching of the shrew: Mechanical consequences of limb posture in small mammals
title_full The crouching of the shrew: Mechanical consequences of limb posture in small mammals
title_fullStr The crouching of the shrew: Mechanical consequences of limb posture in small mammals
title_full_unstemmed The crouching of the shrew: Mechanical consequences of limb posture in small mammals
title_short The crouching of the shrew: Mechanical consequences of limb posture in small mammals
title_sort crouching of the shrew: mechanical consequences of limb posture in small mammals
topic Evolutionary Studies
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4933088/
https://www.ncbi.nlm.nih.gov/pubmed/27413633
http://dx.doi.org/10.7717/peerj.2131
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