title: Unsteady motion: escape jumps in planktonic copepods, their kinematics and energetics.
abstract: We describe the kinematics of escape jumps in three species of 0.3-3.0 mm-sized planktonic copepods. We find similar kinematics between species with periodically alternating power strokes and passive coasting and a resulting highly fluctuating escape velocity. By direct numerical simulations, we estimate the force and power output needed to accelerate and overcome drag. Both are very high compared with those of other organisms, as are the escape velocities in comparison to startle velocities of other aquatic animals. Thus, the maximum weight-specific force, which for muscle motors of other animals has been found to be near constant at 57 N (kg muscle)(-1), is more than an order of magnitude higher for the escaping copepods. We argue that this is feasible because most copepods have different systems for steady propulsion (feeding appendages) and intensive escapes (swimming legs), with the muscular arrangement of the latter probably adapted for high force production during short-lasting bursts. The resulting escape velocities scale with body length to power 0.65, different from the size-scaling of both similar sized and larger animals moving at constant velocity, but similar to that found for startle velocities in other aquatic organisms. The relative duration of the pauses between power strokes was observed to increase with organism size. We demonstrate that this is an inherent property of swimming by alternating power strokes and pauses. We finally show that the Strouhal number is in the range of peak propulsion efficiency, again suggesting that copepods are optimally designed for rapid escape jumps.
authors.affiliation: National Institute for Aquatic Resources, Technical University of Denmark, Charlottenlund, Denmark. tk@aqua.dtu.dk
authors.forename: Thomas
authors.initials: T
authors.lastname: Kiørboe
authors.forename: Anders
authors.initials: A
authors.lastname: Andersen
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Langlois
authors.forename: Hans H
authors.initials: HH
authors.lastname: Jakobsen
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D033342:Copepoda / Q000502:physiology*; D004924:Escape Reaction; D057446:Hydrodynamics; D008124:Locomotion / Q000502:physiology
references.citation: J Exp Biol. 2005 May;208(Pt 9):1653-64
references.pmid: 15855397
references.citation: Proc Natl Acad Sci U S A. 2002 Apr 2;99(7):4161-6
references.pmid: 11917097
references.citation: J Exp Biol. 2002 Aug;205(Pt 15):2153-60
references.pmid: 12110648
references.citation: J Exp Biol. 2003 Jan;206(Pt 2):269-79
references.pmid: 12477897
references.citation: J Exp Biol. 2006 Jan;209(Pt 2):238-48
references.pmid: 16391346
references.citation: Nature. 2003 Oct 16;425(6959):707-11
references.pmid: 14562101
references.citation: Microb Ecol. 1992 Jul;24(1):1-10
references.pmid: 24193035
references.citation: Proc Biol Sci. 2007 Feb 22;274(1609):471-7
references.pmid: 17476766
references.citation: J Exp Biol. 2003 Jan;206(Pt 2):255-67
references.pmid: 12477896
references.citation: Proc Natl Acad Sci U S A. 2009 Jul 28;106(30):12394-9
references.pmid: 19622725