Microswimmers · Low Reynolds number
The fine hairs on algal flagella do not change swimming or flow
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Short answer
Removing mastigonemes did not measurably change Chlamydomonas swimming speed, beating or generated flow.
What happened
Researchers compared a hairless mutant with wild-type and cell-wall-deficient strains using swimming tracks (about 50 per strain), waveform analysis (6 cells per strain), optical-tweezers flow measurements (9–14 cells per strain) and Stokes-flow simulations of smooth flagella. Swimming speed and waveform did not differ significantly, and the smooth-flagellum simulation fitted all strains equally, with errors around 0.15 of the flow amplitude. Rigid hairs would have raised drag by an estimated 30–50%.
Why it matters
Flagellar hairs are often assumed to be hydrodynamic appendages, as they are in some other organisms. This result shows structure does not imply a propulsive function at low Reynolds number, and reopens what the hairs are for.
Evidence
- Study type
- Lab comparison of mutant and control strains with boundary-element simulations
- Sample
- About 50 swimming tracks per strain; 6 cells per strain for waveforms; 9–14 for flow
- Journal
- Biophysical Journal · peer reviewed
- Replication
- Single study; not yet replicated in this library
- Limitations
- Hair bending stiffness not measured; confound of cell-wall loss handled via a control strain; small samples for waveform analysis.
What this connects to
Sources
The one study this explanation is built from, by the role each plays. Every source links to PaperFren’s explanation of it and to the original paper.
Primary study
- Do the tiny hairs on algal flagella help the cell swim?
Removing the fine hairs from Chlamydomonas flagella does not change how fast the cells swim, how their flagella beat, or how much fluid they push.
What it does not showLimitations
The study does not reveal what the hairs are for; the authors suggest sensing, adhesion or feeding but test none of these. The mutant also lacks a cell wall, so comparisons depend on the cell-wall-deficient cw15 strain as the proper control, and wall loss itself changed beat frequency. The proposed explanation, that the hairs are too flexible to add drag, was not measured, since hair bending stiffness was not determined. Waveform analysis used only six cells per strain, so small differences could have been missed.
PaperFren explanationStudy with cards and a quizOriginal paper (DOI)cc by
Before
Hairs on a flagellum were expected to increase its effective surface and so its thrust or drag.
Now
No swimming or flow difference was found; the extra turning of the mutant traced to beating asymmetry, not hydrodynamics. Hair stiffness was not measured, the mutant also lacks a cell wall, and small waveform differences could hide in six-cell samples. The hairs' actual role is untested.