Spatiotemporal asymmetry in ctenophores metachronal locomotion at intermediate Reynolds number

January 3 – Febuary 28, 2021

Meeting Abstract

S10-7  Thu Jan 7 15:00 – 15:30  Spatiotemporal asymmetry in ctenophores: metachronal locomotion at intermediate Reynolds number Herrera-Amaya, A; Byron, ML*; Pennsylvania State University; Pennsylvania State University

The cilium is a canonical low-Reynolds number propulsor, occurring primarily at the scale of microns to tens of microns (with Reynolds numbers of less than 10-2). Because of the time-reversible nature of viscous-dominated flows, the power stroke of a cilium must be spatially asymmetric in order to be effective: a completely symmetric movement would produce no net fluid displacement, even if the power stroke were much faster than the recovery stroke. However, ctenophores (comb jellies) use cilia at much larger scales—their unique millimeter-scale ciliary bundles (ctenes) produce flows at intermediate Reynolds numbers, on the order of 10-200. In this regime, inertia and viscosity both play important roles in generating fluid motion; spatial asymmetry is not as crucial, and temporal asymmetry (difference in duration between the power and recovery strokes) may begin to play a role. We measure this spatiotemporal asymmetry in two species of ctenophores (B. vitrea and B. infundibulum) across a range of body sizes and Reynolds numbers, from 7mm to 40mm in length. We use Particle Shadow Velocimetry (PSV) to observe the fluid flows generated by the ctene rows of animals across this same range, and compare flow characteristics between small, medium, and large animals. Finally, we use a simple mathematical model to explore the role of spatiotemporal asymmetry in the efficacy of metachronally coordinated appendages across scales. Our results inform our understanding of ctenophores’ interactions with their environment across ontogeny, and provide insight into drag-based swimming in the under-studied intermediate Reynolds number regime.

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