Meeting Abstract

45.2  Sunday, Jan. 5 10:30  Bigger is not Better: The Effects of Body Size on 3D Burrowing Kinematics in the Earthworm Lumbricus terrestris KURTH, J. A. *; KIER, W. M. ; Univ. of North Carolina, Chapel Hill; Univ. of North Carolina, Chapel Hill jkurth@live.unc.edu

Relatively little is known about the effects of body size on both soft-bodied invertebrates and terrestrial burrowing. We studied the ontogenetic scaling of burrowing kinematics using Lumbricus terrestris earthworms. Previous analyses had suggested that small worms might use existing cracks and soil spaces as ‘tunnels’ to assist in underground movement, but larger worms are too large and must forcefully displace soil to excavate a burrow. We thus hypothesized that the kinematics of burrowing change as a function of size and large animals would show reduced burrowing speed. To test the hypothesis, we glued several lead markers on specific sites on the anterior portion of L. terrestris worms ranging in body mass from 0.075g-7.812g. We then used bi-planar x-ray cinematography to film the marked worms burrowing through topsoil in three dimensions. We tracked the lead markers and analyzed the kinematic data in MATLAB. We controlled for moisture content and bulk density between experiments, and used soil properties that have been previously recorded in natural topsoils. Our results indicate that the scaling of burrowing kinematics is fundamentally different from the scaling of surface crawling kinematics in this species. In contrast to crawling, the absolute speed and duty factor (time stationary/ total stride period) for L. terrestris decreased significantly with size during burrowing, while the absolute stride length did not change significantly with size. As in crawling, stride frequency decreased with body size during burrowing, but the scaling exponent during burrowing was significantly lower than the scaling exponent during crawling. Overall, our results support our hypothesis.