Relating ciliary propulsion morphology and flow to particle acquisition in marine planktonic ciliates I: the tintinnid ciliate Amphorides quadrilineata

Abstract

Abstract The marine tintinnid ciliate Amphorides quadrilineata is a feeding-current feeder, creating flows for particle encounter, capture and rejection. Individual-level behaviors were observed using high-speed, high-magnification digital imaging. Cells beat their cilia backward to swim forward, simultaneously generating a feeding current that brings in particles. These particles are then individually captured through localized ciliary reversals. When swimming backward, cells beat their cilia forward (=ciliary reversals involving the entire ring of cilia), actively rejecting unwanted particles. Cells achieve path-averaged speeds averaging 3–4 total lengths per second. Both micro-particle image velocimetry and computational fluid dynamics were employed to characterize the cell-scale flows. Forward swimming generates a feeding current, a saddle flow vector field in front of the cell, whereas backward swimming creates an inverse saddle flow vector field behind the cell; these ciliary flows facilitate particle encounter, capture and rejection. The model-tintinnid with a full-length lorica achieves an encounter rate Q ~29% higher than that without a lorica, albeit at a ~142% increase in mechanical power and a decrease in quasi-propulsive efficiency (~0.24 vs. ~ 0.38). It is also suggested that Q can be approximated by π(W/2 + l)2U, where W, l and U represent the lorica oral diameter, ciliary length and swimming speed, respectively.