Jumping and overcoming diffusion limitation of nutrient uptake in the photosynthetic ciliate Mesodinium rubrum

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Abstract
Fast, frequent, and spontaneous jumping by the photosynthetic ciliate Mesodinium rubrum is highly adaptive for overcoming diffusion limitation of nutrient uptake. Using high‐speed, high‐magnification, digital imaging, jumping behaviors of an Antarctic and temperate North American strain of M. rubrum were investigated. Both strains displayed multiple‐beat long jumps, wherein maximum jump speeds and total jump durations varied significantly with strain, temperature, and illumination. However, jump distances were surprisingly similar with means approximating six body lengths, which were just above the thickness of nutrient diffusive boundary layer surrounding the cell. Total jump durations scaled by diffusion time scale were < 1 for almost all observed jumps. Moreover, jump distances and square roots of pre‐jump residence times were linearly correlated. Thereby, jumping by M. rubrum is physically constrained by the small‐scale advection‐diffusion physics of the cell's immediately surrounding water. Additionally, to achieve similar jump distances as the temperate strain at warm temperature, the Antarctic strain lengthened each beat cycle of cilia to kinematically compensate low jump speed at cold temperature, but the ratio of power to recovery stroke duration (∼ 6 : 1) remained unchanged with temperature. As further shown by computational fluid dynamics simulations driven by empirical data, multiple‐beat long jumping allows both strains to completely detach the boundary layer and achieve similar Sherwood numbers significantly > 1, despite substantially different jumping kinematics. All these results support the notion that jumping is an essential behavior for M. rubrum to enhance nutrient uptake, and help to explain their high photosynthetic rates and ecological success.
Funding Information
  • National Science Foundation (NSF OCE‐1433979, NSF OCE‐1031718, IOS‐1354773)

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