Meeting Abstract

69.2  Wednesday, Jan. 6  Feeling the Squeeze: the Energetic Cost of Tunnel Locomotion HORNER, Angela M*; HANNA, Jandy B; BIKNEVICIUS, Audrone R; Ohio University; West Virginia School of Osteopathic Medicine; Ohio University College of Osteopathic Medicine ah312505@ohio.edu

Many mammals enter tunnels and burrows to escape predators, forage for food or for access to a thermoneutral environment. Although the energetics of digging burrows has been studied in a few fossorial mammals, the locomotion of animals passing through tunnels is less well understood. The physical constraints of entering tunnels present a considerable challenge to semi-fossorial animals that must navigate through them and yet maintain the ability to travel overground efficiently. In this study we investigated the kinematics and energetic cost of locomotion in two semi-fossorial taxa with disparate morphologies and phylogeny—a carnivoran (the domestic ferret, Mustela putorius furo) and a rodent (the degu, Octodon degus). The animals were trained to run in metabolic chambers on treadmills over a range of speeds for several weeks prior to data collection to ensure behavioral and metabolic stability. The tunnel condition was simulated with a lowered ceiling in the metabolic chambers such that each animal experienced approximately 25% reduction in hip height from the unconstrained condition. Due to the ferrets’ tall, arched trunk, the lowered ceiling also resulted in a 35% reduction of profile height, as well as an extension in the functional trunk length of nearly 30%. Oxygen consumption and carbon dioxide production were measured with an open-flow respirometry system. Metabolic rates in each condition were compared within species using a mixed model ANCOVA. Both ferrets and degus demonstrated a higher metabolic rate in tunnels when compared to overground locomotion, and a nearly 20% increase in the net cost of transport. Although ferrets experience a more pronounced change in posture when entering tunnels, some physiological adaptations may counteract the expected increase in metabolic cost relative to the more general bauplan of the degu.