Why?

[Caitlin]

As I first said. this one is deep. It could take a book of chapters to really answer. I certainly have no answers, only questions...... Who knows what specific questions will unlock this secret? We have to either find the answers, maybe even on the Google, or keep on asking questions in a variety of frameworks until we find the key.

Now I am infected with wondering about this question........

 

[Lagoon Island Pearls]

As I first said. this one is deep. It could take a book of chapters to really answer. I certainly have no answers, only questions...... Who knows what specific questions will unlock this secret? We have to either find the answers, maybe even on the Google, or keep on asking questions in a variety of frameworks until we find the key.

Now I am infected with wondering about this question........

I thought it was an excellent question, which was answered to the best of our knowledge.

Douglas said it best.

Color means nothing to a color blind animal.

And Wendy, although you might not be convinced, never, ever stop wondering. That's a gift.

 

[Nerida]

This thread has provided some treasures. I totally get where Wendy is coming from - science usually does work that way! But I am sticking with Mikey's first response, and thank Eli for his poem, Mike for the sunsets, and Dave for the fascination with colors and feathers...

I will keep wondering, too.

 

[SteveM]

I wonder?

If we were not here to see it, would nacre have color?

Perhaps we will never know.


Either the question has been answered clearly and unequivocally here, or the question definitely requires rephrasing!

 

[pearlescence]

No, not answered.
I did receive one reasonable answer by another route - to the effect that the colours help the mollusc to blend in with colourful corals and thereby not get eaten.
But I'm not convinced by that one because the outsides of the shells are simply drab. if the camoflage worked to stop being eaten then the outside would surely show some patterning. In fact in a mass bed of drab for some molluscs to open and show bright colour would attract attention....?
I'm throwing the question out into the wider world as well. Will keep you posted. This may take some time.

 

[Mikeyy]

I think I might have an answer as to why the animals lay down nacre in different colors. I am thinking it's because some of our customers like GSS and Chinese FW, and some cutomers like SS and Tahitians. The wider the color range the wider the customer base. Hey, I know it's lame, but it's a theory.

Sadly, this palatte wasn't wide ranging enough for some people so they created "Cranberry" colored pearls.

 

[pearlescence]

Hahahashahha Mikeyy.
best answer yet

 

[Ramona]

Color in nature is usually used as a from of communication. This would make it necessary to have the inside colorful if you are a sessile clam sitting on a reef. Your open shell would be visible to anything swimming above, particularly in shallower water. The question then would be who do you need to communicate with? Do young oysters distribute randomly or are they seeking out the company of others? Or maybe they try to attract cleaning fish?

 

[pearlescence]

Now we are getting somewhere.
could it be a way for freeswimming spat to find eachother to make a colony? But what sort of light sensitivity do molluscs have? If they don't have any..then with what are they trying to communicate, as ramona says? And why do only some molluscs want to talk while others don't say anything (no colour or nacre)

 

[SteveM]

?the colours help the mollusc to blend in with colourful corals and thereby not get eaten.

But I'm not convinced by that one because the outsides of the shells are simply drab. if the camoflage worked to stop being eaten then the outside would surely show some patterning.

As I observed earlier, gastropods certainly do pigment their exterior shells in bright colors and patterns. Bivalves are ugly. Both would supposedly be camouflage mechanisms, related to their respective habitats.

Our marine biologists here will hopefully comment about the respective habitats. Meanwhile, I'm not at all tempted by the open shell theory. The mantle is attached to the growth front of the shell and very little if any nacre is visible. Again, marine biologists!

 

[Caitlin]

I think if the answers lies within the evolutionary biological POV we have not yet discussed the best fitting answer. It is OK to be content with what we have discussed, or it is OK to keep the question open. I, personally, enjoy the answers so far, but do not yet feel satisfied.

 

[CortezPearls]

Dedicated to Mikeyy and Douglas.
This is from Nora's Eli:

The discussion sort of reminds me of the song we used to sing at summer camp around the camp fire. The one that went:
Tell me why the stars do shine,
Tell me why the ivy climbs,
Tell me why the sky is blue,
And I will tell you just why I love you.
The official answer, if you remember, was:
Because God made the stars to shine,
Because God made the ivy climb,
Because God made the sky so blue,
Because God made you, that's why I love you.
Of course, I sort of prefer the subversive response:
Nuclear fusion is why the stars do shine,
Geotropisms are why the ivy climbs,
Scattering of light rays is why the sky is blue,
And endocrine imbalance is why I love you.

As far as I'm concerned, pearls are a glorious natural accident and let's just relish them.

Love the song! I'm going to sing it with my children on our next campfire...and I'll even include the second part of the song

 

[CortezPearls]

Sadly enough it won't work this way...the mantle will cover all signs of the colorful nacre. Instead, all you will see some "black grins" (if they are black-lips). And if you do see the nacre it means the oyster is sick or dead.

This is what you see if you swim above some black-lips...

Ask any farmer that cares for his oysters...I've never felt they can communicate, but they do respond to external stimuli. When I see oysters with beautiful, intense colors in their nacreous shell the first thing that pops in my mind is "This is a Very Happy & Healthy Pearl Oyster". When I see dull or colorless shells I usually think the opposite: unhappy or sick oyster. And this shows in many other things: their weight (heavier if healthy), a strong shell with nice shape, good byssus secretion, plenty of growth spines...

My meager contribution...I still believe it was made for us to enjoy!

 

[SteveM]

I think if the answers lies within the evolutionary biological POV we have not yet discussed the best fitting answer. It is OK to be content with what we have discussed, or it is OK to keep the question open. I, personally, enjoy the answers so far, but do not yet feel satisfied.

Since the PERCEPTION of color by humans is a guaranteed and bona fide physical property of nacre, the only possible justification I can conceive for keeping the biological question open would be the yet-to-be-addressed matter of the degree (if any) to which the organic component (conchiolin) contributes to the overall pearl/shell color.

 

[CortezPearls]

Now we are getting somewhere.
could it be a way for freeswimming spat to find each other to make a colony? But what sort of light sensitivity do molluscs have? If they don't have any..then with what are they trying to communicate, as ramona says? And why do only some molluscs want to talk while others don't say anything (no color or nacre)

Pearl Oysters Larvae display "Inverse Phototropism" and when they settle and become "spat" they reverse that trend to "look upwards", towards the surface. They are photosensitive through their lives and this helps them to close their shells if somethings swims on top of them -thus creating a light differential- and this basically triggers an "alarm" that makes the abductor muscle close the shells. This makes them harder to detect to predators...

 

[CortezPearls]

An Excellent Theory Mike!

 

[pearlescence]

I passed the question to a friend of mine who is a fellow of the Royal Institution and an emeritus professor. This is his response:
'Good question...

I have no idea, but I'm inclined to ask whether it is any more
difficult for them to make coloured surfaces than it is to make
plain ones. Possibly the colours are a side effect of the smoothness
(where I agree with you). They look a bit like diffraction patterns
to me, and may be caused by the process that lays down the inner
shell material. Being on the inside their effect on fitness will be
minimal, so they won't be selected against.

It may also be a a side effect of the growth of the entire shell,
and its external surface markings, I suppose.'

Caitlin - you and he are ad idem that this is a good question!

Ian is going to pass the question on to a biologist friend (who taught the bods who discovered DNA testing) for his thoughts.

Steve - you persist in mentioning human eyes, yet human eyes have nothing to do with oyster nacre evolution (at least until recently, when they do as we are now influencing selection)

 

[Lagoon Island Pearls]

... yet human eyes have nothing to do with oyster nacre evolution

You may have answered your own question there, or at least excluded half of the hypothosis when it comes to their relationship with other beings.

It's also important to note, there are more than 2000 species of clams, more than 100 of mussels. Lord knows how many scallops or gastropods in the mix. Most of which are not highly nacreous.

 

[Lagoon Island Pearls]

you will see some "black grins"

It's funny you should mention this. Everytime I look at a bucket of clams, I see the same thing, but never see them as frowns even though there is a 50% chance of them appearing that way.

I wonder if this where the saying "happy as a clam" came from?

 

[pearlescence]

Lagoon Island, you make my point for me in a way..out of all of those species of shellfish happily not being particularly nacreous, why do those few go to all that bother? There must be a reason otherwise the colours would not be there, or at least the colour would be more homogonised after xmillion years of happy evolution. What is it that triggers those few species to make colourful shell?