Meeting Abstract
Using 3D X-ray (XMA) and our custom built Tunnel-tube, we measured burrowing kinematics and dynamics. Here we present an analysis of burrowing data collected from three closely-related, yet morphologically disparate rodent species. Botta’s pocket gophers (Thomomys bottae) spend most of their lives foraging underground, making them an ideal test subject for studies of burrowing. Further, pocket gophers are closely related to kangaroo rats (Dipodomys merriami) and pocket mice (Chaetodipus penicillatus), all of which fall within the superfamily Geomyoidea. These rodent species each dig their own burrows, yet have very different body types and body sizes (from 20g to 200g). Pocket gophers have short limbs, long claws, and a compact body, whereas kangaroo rats have long hindlimbs and short forelimbs for bipedal hopping. Pocket mice have a generalist rodent body plan with crouched posture and hindlimbs slightly longer than forelimbs. All three species burrowed through the Tunnel-tube in two substrate conditions: a soft radiolucent substrate and soft natural soil. In both substrates, all species exhibited scratch-digging, using the forelimbs to loosen and remove the substrate. In the radiolucent substrate, digging force was lowest for pocket mice, yet kangaroo rats and pocket gophers produced nearly identical forces. However, in natural soil, digging force scaled as expected with body weight. These findings suggest that the low compressive strength of the radiolucent substrate may limit digging force in this substrate. Furthermore, we found that for digging force, body weight scaled to 0.63. We would expect a similar finding for muscle cross-sectional area (XSA), where body weight0.66. This contrasts with force during terrestrial locomotion, where force is directly proportional to body weight because limb posture compensates for muscle XSA. Thus, we suspect that digging force is limited by muscle XSA.
