Randy Holmes-Farley
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My Tank Thread
I decided to start a series of threads that detail some problems in Reef Chemistry/Biology that are unsolved.
Not problems in how to do something as a hobbyist, but fundamental issues that remain unsolved by scientists, and that are clearly impacting your reef aquarium.
Today's Problem is the coiling of snail shells.
Snail shells of a single species typically coil in one direction only. Sometimes mutants are found that coil in the other direction, but in general, it is not a random event for each snail: each member of a single species all coil with the same chirality, or the "direction" of coiling. A different species may coil in the opposite direction while living in a similar location.
Here's a drawing to understand the issue:
https://en.wikipedia.org/wiki/Gastropod_shell
Why does this happen?
Scientists have studied it for hundreds of years. Ideas have come and gone.
The answer is still not understood on a molecular level, but it likely relates to the fact that at the most fundamental level, many biomolecules have a "handedness" or directionality inherent to them. That at least allows for a preferred directionality that can be genetic, rather than environmental.
Every amino acid, for example, can exist in at least two mirror image forms. The drawings below show what that means:
https://www.vanderbilt.edu/vicb/images/discoveries images 2010/reverse_polarity_fig_4.jpg
All living creatures on earth use a particular handedness (the same handedness) of the amino acids in their proteins, not a random mix. Hence, every protein has a particular "handedness" based on its composition.
This sort of molecular mechanism for "handedness" can then potentially propagate up to the level where you can see it in your tank, as in a coiled snail shell.
A paper from a couple of years ago makes some suggestions and summarizes the history of the issue:
Snail Chirality: The Unwinding
https://www.sciencedirect.com/science/article/pii/S0960982216300604
"Unravelling the precise mechanisms of how body and shell coiling are effected is probably a long way away, given the lack of genetic tools in snails. "
I won't give any more discussion to the paper's ideas except to say they suggest it happens at the very earliest stage of development. That somehow the stage with just a few cells gets oriented in a way that causes the coiling of the shell (and the internal body layout) in a particular direction. Beyond that, it is heavy biochemistry that you can read for yourself if interested.
Just something to think about as you watch your aquarium.
Not problems in how to do something as a hobbyist, but fundamental issues that remain unsolved by scientists, and that are clearly impacting your reef aquarium.
Today's Problem is the coiling of snail shells.
Snail shells of a single species typically coil in one direction only. Sometimes mutants are found that coil in the other direction, but in general, it is not a random event for each snail: each member of a single species all coil with the same chirality, or the "direction" of coiling. A different species may coil in the opposite direction while living in a similar location.
Here's a drawing to understand the issue:
https://en.wikipedia.org/wiki/Gastropod_shell
Why does this happen?
Scientists have studied it for hundreds of years. Ideas have come and gone.
The answer is still not understood on a molecular level, but it likely relates to the fact that at the most fundamental level, many biomolecules have a "handedness" or directionality inherent to them. That at least allows for a preferred directionality that can be genetic, rather than environmental.
Every amino acid, for example, can exist in at least two mirror image forms. The drawings below show what that means:
https://www.vanderbilt.edu/vicb/images/discoveries images 2010/reverse_polarity_fig_4.jpg
All living creatures on earth use a particular handedness (the same handedness) of the amino acids in their proteins, not a random mix. Hence, every protein has a particular "handedness" based on its composition.
This sort of molecular mechanism for "handedness" can then potentially propagate up to the level where you can see it in your tank, as in a coiled snail shell.
A paper from a couple of years ago makes some suggestions and summarizes the history of the issue:
Snail Chirality: The Unwinding
https://www.sciencedirect.com/science/article/pii/S0960982216300604
"Unravelling the precise mechanisms of how body and shell coiling are effected is probably a long way away, given the lack of genetic tools in snails. "
I won't give any more discussion to the paper's ideas except to say they suggest it happens at the very earliest stage of development. That somehow the stage with just a few cells gets oriented in a way that causes the coiling of the shell (and the internal body layout) in a particular direction. Beyond that, it is heavy biochemistry that you can read for yourself if interested.
Just something to think about as you watch your aquarium.
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, but I stand by my statement that chirality is not spontaneous and that molecular chirality is one of the current theories about how whole organisms develop chirality. 
