On the role of copepod antennae in the production of hydrodynamic force during hopping

Abstract

SUMMARYWe integrate high-resolution experimental observations of a freely hopping copepod with three-dimensional numerical simulations to investigate the role of the copepod antennae in production of hydrodynamic force during hopping. The experimental observations revealed a distinctive asymmetrical deformation of the antennae during the power and return strokes, which lead us to the hypothesis that the antennae are active contributors to the production of propulsive force with kinematics selected in nature in order to maximize net thrust. To examine the validity of this hypothesis we carried out numerical experiments using an anatomically realistic, tethered, virtual copepod, by prescribing two sets of antenna kinematics. In the first set, each antenna moves as a rigid, oar-like structure in a reversible manner, whereas in the second set, the antenna is made to move asymmetrically as a deformable structure as revealed by the experiments. The computed results show that for both cases the antennae are major contributors to the net thrust force during hopping, and the results also clearly demonstrate the significant hydrodynamic benefit in terms of thrust enhancement and drag reduction derived from the biologically realistic, asymmetric antenna motion. This finding is not surprising given the low local Reynolds number environment within which the antenna operates, and points to striking similarities between the copepod antenna motion and ciliary propulsion. Finally, the simulations provide the first glimpse into the complex, highly 3-D structure of copepod wakes. Supplementary material available online at

Hydrodynamic Trails Produced by Daphnia: Size and Energetics

“…The turbulent drag law applied by Huntley and Zhou [9], in contrary, is only valid for high Reynolds number flow (). Swimming of most zooplankton organisms, however, is associated with Reynolds numbers in the transitional range [53]–[55], where both approaches are not valid. Our measurements show that in the hydrodynamic trails of Daphnia , kinetic energy is dissipated at rates even exceeding current estimates.…”

The hydrodynamics of swimming at intermediate Reynolds numbers in the water boatman (Corixidae).

“…It is therefore interesting to consider how other strategies for generating propulsion may also vary with size for other animals within this regime. For example, copepods (100<Re<1000) propagate a wake from their antennae to abdominal paddles during impulsive 'hopping' (Borazjani et al, 2010). This mechanism could fail as a result of viscous attenuation at lower Reynolds numbers, or could lack the necessary cohesion at larger scales.…”

How the bending mechanics of setae modulate hydrodynamic sensing in copepods

“…For example, Visser () utilized a far‐field multipole representation of prey‐induced Stokes flows to study the spatial variation of hydrodynamic flow signals at the first antenna. Others have addressed the effect of the copepod itself on flow fields near the body that could be sensed by setae, variously modeling the copepod as an infinite cylinder (Bundy et al ), a sphere (Jiang et al ; Jiang and Paffenhöfer ; Jiang and Strickler ), a plane wall or spheres depending on which part of the copepod is closest to the prey (Jiang and Paffenhöfer ), or even considering the detailed geometry of a copepod (Jiang et al , ; Gilmanov and Sotiropoulos ; Borazjani et al ). Generally, it is found that flows near the body, including at setae, are significantly affected by hydrodynamic interactions with the copepod itself.…”