Wire Black Coral helix ?

[Genady]

8 minutes ago, joigus said:

In other words, you said the polyps are cilindrically-symmetric. In that case, whatever you call the left, turn around 180 degrees and, voila, it's the right.

For some reason I can't see the attached image. I think what you said is not correct. When you look outside from the cylinder's central axis, you have right and left well defined regardless of your orientation. (And the baby polyp is attached to the outside of the cylinder.)

Edited December 27, 2021 by Genady

[joigus]

28 minutes ago, Genady said:

For some reason I can't see the attached image. I think what you said is not correct. When you look outside from the cylinder's central axis, you have right and left well defined regardless of your orientation. (And the baby polyp is attached to the outside of the cylinder.)

It's the mirror image of the picture you attached...

Picture a human as a perfect cilinder. Now picture an arm growing from somewhere. The human says: 'This is my right arm'

Well she may say so, but something's not right.  

And yes, I'm right.

Edited December 27, 2021 by joigus

[Genady]

4 minutes ago, joigus said:

It's the mirror image of the picture you attached...

Picture a human as a perfect cilinder. Now picture an arm growing from somewhere. The human says: 'This is my right arm'

Well she may say so, but there's nothing right about it.  

And yes, I'm right.

Ah, I see what you mean. But the baby coral doesn't grow radially but tangentially to the cylinder surface. Here is a scheme (borrowed from the circular polarization of light.) As you move along X, each arrow, representing next baby polyp, is tilted to the right. The result is right-handed helix. (My previous image was only to illustrate a budding process in general, nothing to do with my suggestion.)

[mistermack]

I don't think it's likely to be local currents. 

If you grow climbing beans, they grow clockwise or anticlockwise depending on the species. I know that most grow anti-clockwise, seen from below, but runner beans grow clockwise. 

[joigus]

1 hour ago, Genady said:

Ah, I see what you mean. But the baby coral doesn't grow radially but tangentially to the cylinder surface. Here is a scheme (borrowed from the circular polarization of light.) As you move along X, each arrow, representing next baby polyp, is tilted to the right. The result is right-handed helix. (My previous image was only to illustrate a budding process in general, nothing to do with my suggestion.)

 

 

Replacing 'left' by 'tangential' doesn't exactly clinch the case, IMO. There is a clockwise tangential, and an anti-clockwise tangential. But I think you touched a very important point that for some reason you don't recognise as having a molecular basis (homeobox genes, which are what determines developmental hormones, which in turn determine relative placement of organs, cells, etc.): It's the pattern with which the next polyp buds out of the progenitor polyp. As far as I can see, you need another plane of assymmetry to complement the axis defined by the growth, and always keep it 'doing the same thing', so to speak. The simplest hypothesis that would explain the appearance of this plane of 'slight asymmetry' is how growth hormones flow away from one side of that plane and onto the other.

Environmental factors cannot be excluded, of course (See image below.) Plants always grow their stems towards the Sun and their roots towards the ground due to combination of growth hormones + light, gravity, etc.

Consider a spherically symmetric phase of the embryo previous to the blastocyst (the first 'axial' phase.) There's no up, no down, no front, no back, no left, no right. After that stage, a migration of subsequent-generation stem cells has to decide what's up and what's down (blastocyst). 'Up' and 'down' don't mean anything in themselves. It's cellular development that decides that. And who decides these placements? Hormones do. You've got an equivalent to your polyps here, because the organism is cilindrically symmetric.

Next, stem cells of another generation have to decide what's front and rear. A second axis, perpendicular to the first, defines this, forming a plane with the previous one. Migration is induced with respect to this plane. 

Now the fact that you've defined two perpendicular directions, in 3-dimensional space, automatically determines the third. This is a peculiarity of 3 dimensions. What is right and what is left is only possible because we've agreed first what's up and down, front and rear.

The curious aspect of these corals seems to be that chirality is minimally and elegantly defined, not having to do with migration of specialised tissue, and resembling very much the (minimal) mathematical definition.

Why it's fixed once an ancestor organism evolved it that way I think boils down to macromolecules, the very same reason why our liver is on the right, and our children's liver is also on the right. These orientation factors rarely ever change once they've been decided.

 

[Genady]

Yes, I completely agree. There is one thing left unanswered still, on the next level up rather then down the scale. This scheme explains a helix that polyps make around the tube that they grow on, but it does not explain yet the helix that the tube itself presents to us.

[Genady]

Regarding this last unanswered issue, I don't know the specific answer, but it is not a puzzle anymore, because we already got asymmetry where it is needed. E.g. since new polyps are added not linearly, but helically, they secrete a new piece of the tube in an asymmetrical way, which can easily lead to a helical tube.

And sorry @joigus, I should've clarified it already: regarding a front-back direction for the polyp I kept it in a spirit of the earlier "assumption 2", i.e. back is where the closest neighbor is while front is open. As we know by the "assumption 1", they sense each other.

Edited December 28, 2021 by Genady

[joigus]

But I did answer that part, I think, although implicitly. The key words are 'inward pointing' in my drawing. The new polyp would grow 'radially apart' from the parent one and continue describing an ever opening helix, because with every new 'generation', the plane shifts, as well as the radial distance with respect to the first 'ancestor'. The radius of that definite-chirality helix would increase more and more or less depending at a rate that depends on the ratio between the radius at which the offshoot buds and the angles (both with respect to that radius, and to the drawing's plane).

I don't know if coral polyps can be grown in laboratory conditions. I suspect not. But if that could be done, it would be very interesting to set up a laboratory assay to test what environmental factors affect the growth pattern (by the way, I forgot prevalent direction of light, as corals are heavily dependent on it). 

I think it's a very interesting observation you made. I've scanned for different similar corals of the same family, and it seems to me that they all are right-handed helices.

Edit: Sorry for the abundance of quotation marks, but I think you understand what I mean.

Edited December 28, 2021 by joigus
minor correction

[Genady]

@joigus Yes, of course.

Regarding the experimental tests or microscopic studies, I wish, but (a) they don't grow in aquarium, as you suspected, and (b) I can't and wouldn't cut a piece off a living coral, as all terrain here from the water surface down to the depth of 200 m is a protected Marine Park.

Regarding prevalent direction of light - no such thing at that depth (30+ m). The water is very clear but the light is scattered and comes "from everywhere."

Thank you.