title: Visceral-locomotory pistoning in crawling caterpillars.
abstract: Animals with an open coelom do not fully constrain internal tissues, and changes in tissue or organ position during body movements cannot be readily discerned from outside of the body. This complicates modeling of soft-bodied locomotion, because it obscures potentially important changes in the center of mass as a result of internal tissue movements. We used phase-contrast synchrotron X-ray imaging and transmission light microscopy to directly visualize internal soft-tissue movements in freely crawling caterpillars. Here we report a novel visceral-locomotory piston in crawling Manduca sexta larvae, in which the gut slides forward in advance of surrounding tissues. The initiation of gut sliding is synchronous with the start of the terminal prolegs' swing phase, suggesting that the animal's center of mass advances forward during the midabdominal prolegs' stance phase and is therefore decoupled from visible translations of the body. Based on synchrotron X-ray data and transmission light microscopy results, we present evidence for a two-body mechanical system with a nonlinear elastic gut that changes size and translates between the anterior and posterior of the animal. The proposed two-body system--the container and the contained--is unlike any form of legged locomotion previously reported and represents a new feature in our emerging understanding of crawling.
authors.affiliation: Department of Biology, Tufts University, 163 Packard Ave, Medford, MA 02155, USA. michael.simon@tufts.edu
authors.forename: Michael A
authors.initials: MA
authors.lastname: Simon
authors.forename: William A
authors.initials: WA
authors.lastname: Woods
authors.forename: Yevgeniy V
authors.initials: YV
authors.lastname: Serebrenik
authors.forename: Sharotka M
authors.initials: SM
authors.lastname: Simon
authors.forename: Linnea I
authors.initials: LI
authors.lastname: van Griethuijsen
authors.forename: John J
authors.initials: JJ
authors.lastname: Socha
authors.forename: Wah-Keat
authors.initials: WK
authors.lastname: Lee
authors.forename: Barry A
authors.initials: BA
authors.lastname: Trimmer
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D007814:Larva / Q000033:anatomy & histology / Q000502:physiology; D008124:Locomotion / Q000502:physiology*; D018402:Manduca / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology*; D017356:Synchrotrons; D014781:Viscera / Q000502:physiology*; D014965:X-Rays