APS-DBIO Profile picture
25 Mar, 11 tweets, 8 min read
It's a beautiful thursday! time for a #DBIOtweetorial commissioned by the awesome folks at #engageDBIO!
First up: “this feather star has too many arms and is too heavy to swim – instead it creeps along the seafloor”

How goes this amazing creature coordinate so many appendages? what kind of physics does it encounter?
When discussing limb coordination, it's probably easier to define what we mean by coordination than 'limb'...

You might recognise this famous image of '#synchronization', referred to by Huygens as 'an odd kind of sympathy' (1665)

Typically, coordination requires some form of nervous control, a central pattern generator that tells the limbs what to do and when!

Here is a video of the graceful gait of a #giraffe
And from the land to the ocean, organisms coordinate limbs, appendages, moving parts to get themselves to where they need to go.

Just watch this "sea butterfly" literally fly through water (limacina)...its peculiar 'wing' stroke generates extra lift!
From fluid back up to the surface... where we have all kinds of ethereal winged beings, such as the humble bumble bee... watch as it deftly negotiates turbulence
Does coordination become more difficult with decreasing size? How about the famous #tardigrade? How does it walk?

Check out this great preprint from @jasnir_ @DJCohenEtAl and colleagues!
What about even smaller organisms? Single cells even?
Here's a unicellular walker exhibiting a rather unusual stochastic gait using tiny appendages called 'cirri' (made up of bundles of cilia) biorxiv.org/content/10.110… from @BEuplotes, @WallaceUcsf et al
One can go down to even smaller scales, and can find deterministic limb coordination in a 10 micron cell! Here is an alga with just four cilia, arranged at the apex of the organism like a windmill.
(video shows side view)

Even smaller? But there you hit a fundamental physical limit - at the size of a bacterium (1 micron), rotational diffusion starts to overwhelm the system, and precise coordination becomes much more difficult...

See this classic Berg video of E. coli
Let's end with a bug playing the piano.

Note the #metachronal waves (fixed phase difference between oscillators) propagating along the length of this millipede...

Sometimes, you just need to switch off your brain (and your computer) and get moving...🎶

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