If shell colors are generally visible to predators, then variation in
color can be a way to disrupt the predator's search image.  This works
in some land snails preyed on by birds, e.g. Cepaea.  If one pattern
is particularly common, the birds learn to look for it, which tends to
make that pattern rarer (they're all getting eaten) and others more
common, until the birds learn a new pattern.  However, many scallops
aren't that conspicuous due to epibionts, etc., and probably more of
the marine predation is by chemical rather than visual detection.

On Wed, Sep 8, 2010 at 9:55 AM, Stanley Francis <[log in to unmask]> wrote:
> As a devoted Pectinidae collector for many years,I have read the recent
> exchanges on shell colour with great interest.  This has probably been the
>  most imponderable question, which has ever been raised with me at so many
> shell talks.
> One can understand the reasoning that that the colour of our garden snail
> shells is attributable to the colour of its waste products. Food source is
> also also offered as the reason for colour sub-forms. The influenze of light
> is also a reasonable explanation with certain varieties , but at the same
> time we find that many other varieties have equally colourful left and right
> hand valves.
> You always return however to 'albino' forms and say to yourself " whatever
> the explanation, if it is waste, food products or influence of light that
> produces such beautiful colours, how can we have so many pure white albino
> forms ?".
>
> Stanley Francis.
>
> ----- Original Message -----
> From: Paul Callomon
> To: [log in to unmask]
> Sent: Tuesday, September 07, 2010 5:54 PM
> Subject: Re: [CONCH-L] scallop shell colors
> There are any number of theories about shell coloration, but in very few
> cases has it been shown to be a deliberate camouflage or tactical ploy. It
> has been found that colored parts of the shell are stronger than the
> non-colored parts (in some species at least; the black parts of Cittarium
> pica resist erosion more than the white parts, for example) and if that is
> so for all shells, then the presence of netted and zigzag patterns might
> represent optimum reinforcement of the shell using a limited supply of
> pigment. For the most part, however, patterning  in things like scallops
> remains unexplained, though simple colors like those found in Chlamys
> nobilis are just genetic. Variation for its own sake, the best insurance a
> species has against mass obliteration.
>
> PC.
>
> Paul Callomon
> Collections Manager
> Malacology, Invertebrate Paleontology and General Invertebrates
> Department of Malacology
> Academy of Natural Sciences
> 1900 Parkway, Philadelphia PA 19103-1195, USA
> Tel 215-405-5096
> Fax 215-299-1170
>
>>>> John Varner <[log in to unmask]> 9/7/2010 12:32 PM >>>
> The color variation as camoflage would seem more plausible if scallop
> "swimming" wasn't such a haphazard affair.  They aren't consistantly
> oriented with one valve up, one down.  Also, with bay scallops in New
> England, at least, one valve is sometimes rayed, the other not, or both are
> colored, and differently.
> What preys on scallops, and how well do they see?
> As with so many shells, in which colors are obscured by encrustations,
> periostracum, or just low ambient light in the animals' natural environment,
> scallop shell coloration seems related to something other than camoflage or
> vision.  Maybe a sense we are not endowed with, or maybe it's just random,
> and since it doesn't amount to a large net evolutionary selector, it muddles
> through....
>
> - John
>
>
>
>



--
Dr. David Campbell
4830 University Blvd E H4
Tuscaloosa AL 35404
"I think of my happy condition, surrounded by acres of clams"

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