Relating ciliary propulsion morphology and flow to particle acquisition in marine planktonic ciliates II: the oligotrich ciliate Strombidium capitatum

Abstract

Abstract The marine oligotrich ciliate Strombidium capitatum is a cruise-feeder, relying on ciliary motion and propulsion flow to individually detect and capture particles. High-speed, high-magnification digital imaging revealed that the cell swims forward by sweeping its anterior adoral membranelles (AAMs) backward, achieving a mean path-averaged speed of U = 1.7 mm s−1 (31 cell-lengths per second). Particle detection occurs through either hydrodynamic signal perception or ciliary contact perception, with a mean reaction distance of R = 20.4 μm. While executing a ciliary reversal of AAMs to handle and capture a perceived particle, the cell coordinates the ciliary motion of ventral adoral membranelles (VAMs, the “lapel”) with the ciliary reversal of AAMs (the “collar”), causing a sudden halt of cell motion, thereby functioning as a motion “brake” that is crucial for effective particle capture. The encounter rate with small prey particles is calculated using πR2U (~8.0 μL h−1, equivalent to ~ 3.5 × 106 cell volumes per day). Based on hydrodynamic modeling results, it is hypothesized that spatial structures of the flow velocity vector and acceleration fields in front of the swimming cell are essential for pushing an embedded particle forward, creating a strong enough slip velocity and hydrodynamic signal for prey perception, even for a neutrally buoyant small particle.