Inverse Dynamics of Lesser Egyptian Jerboa

(Jaculus jaculus) vertical leaping

TY Moore, AM Rivera, AA Biewener

Abstract

Background: Numerous historical descriptions of the Lesser Egyptian jerboa, Jaculus jaculus, a small bipedal mammal with elongate hindlimbs, make special note of their extraordinary leaping ability. We observed jerboa locomotion in a laboratory setting and performed inverse dynamics analysis to understand how this small rodent generates such impressive leaps. We combined kinematic data from video, dynamic data from a force platform, and morphometric data from dissections to calculate the relative contributions of each hindlimb muscle and tendon to the total movement.

 

Results: Jerboas leapt in excess of 10 times their hip height. At the maximum recorded leap height (not the maximum observed leap height), peak moments for metatarso-phalangeal, ankle, knee, and hip joints were 5.1, 23.5, 31.2, and 17.4 mNm, respectively. Muscles acting at the ankle joint contributed the most work (218.6 mJ / Body Mass) to produce the energy of vertical leaping, while muscles acting at the metatarso-phalangeal joint produced the most stress (231.7 kPa). The plantaris, digital flexors, and gastrocnemius tendons encountered peak stresses of 23.6, 17.2, and 7.0 MPa, respectively, transmitting the forces of their corresponding muscles (peak force 3.0, 1.8, and 4.4 N, respectively). Notably, we found that the mean elastic energy stored in the primary hindlimb tendons comprised only 6.0% of the energy of the associated leap.

 

Conclusions: The limited use of tendon elastic energy storage in the jerboa parallels the morphologically similar heteromyid kangaroo rat, Dipodomys spectabilis. When compared to larger saltatory kangaroos and wallabies that sustain hopping over longer periods of time, these small saltatory rodents store and recover less elastic strain energy in their tendons. The large contribution of muscle work, rather than elastic strain energy, to the vertical leap suggests that the fitness benefit of rapid acceleration for predator avoidance dominated over the need to decrease locomotor economy in the evolutionary history of jerboas.

 

Keywords: jerboa; inverse dynamics; muscle-tendon stresses; ricochetal bipedal locomotion

Media
Paper
BibTeX

@article{Moore2017a,
author = {Moore, Talia Y. and Rivera, Alberto M. and Biewener, Andrew A.},
doi = {10.1186/s12983-017-0215-z},

journal = {Frontiers in Zoology},

volume = {14},

number = {32},

pages = {1--12},

title = {{Vertical leaping mechanics of the Lesser Egyptian Jerboa (\emph{Jaculus jaculus}) reveal specialization for maneuverability rather than elastic energy storage}},
year={2017}

}

Code
Funding

This research was funded in part by a Harvard College Research Program grant (to A. Rivera).

© 2017 by Talia Yuki Moore

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