Imagine that you are a microscopic cell with two thin “arms” and that you would like to survive in the ocean. How should you arrange and move your arms to swim fast and efficiently, to avoid predators, and to get enough food?
Microswimmers form an essential part of the marine ecosystem. Many of them are unicellular flagellates that use long, slender appendages (flagella) to create flows that propel them, support their feeding, but also make them vulnerable by exposing them to flow-sensing predators.
We have, in collaboration with marine ecologists at DTU Aqua, used observations of freely swimming individual flagellates and theoretical modeling to study the flagellar arrangement and beat pattern as a key trait. Our hydrodynamics model adequately represents the near-cell flow by modelling the cell as a solid sphere and the flagellar beat as a number of point forces on the water.
With focus on biflagellates with two symmetrically arranged flagella, we have found that equatorial breast-stroke arrangements are advantageous for fast and stealthy swimming, but not for creating favorable currents for prey capture. The observed organisms are able to perform photosynthesis and dissolved nutrient uptake additionally to prey capture. We have found this so-called mixotrophic strategy to be necessary for survival, since prey capture alone seems not to fulfill the energy needs of the organisms in the typical marine environment.
Individual of the flagellate species Heterosigma akashiwo (left), helical trajectory of a model flagellate (middle), and velocity field for the theoretical model of H. akashiwo (right).
Read the papers and find more information on Centre for Ocean Life
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Read the paper "Swimming and feeding of mixotrophic biflagellates" - by Dölger, Nielsen, Kiørboe, and Andersen, Scientific Reports 7, 39892 (2017)
Read the paper "An analytical model of flagellate hydrodynamics" - by Dölger, Bohr, and Andersen, Physica Scripta 92, 044003 (2017).