Hi Nora,

I can vouch for your statement of polar bear skin being black...had the sad duty
of making a taxidermy mount of "Kuma" from Como Park Zoo in St. Paul. MN...vandals
ended her 20 years by dropping a chunk of concrete onto her head from the top of
her enclosure...spent my childhood watching her...

On the subject of albinism, has anyone else collected any stripeless Allogona
profunda? Would the lack of stripes make it albinistic, or merely
stripeless...hmmm...

Ken Zentzis
Wichita, Kansas

NORA BRYAN wrote:

> Nice summary Paul
> A further note on polar bears - their fur is actually translucent and hollow
> like a straw.  Their skin is black!  The combination is a strategy to gather
> warmth from the sun. This is not really shell-related, I guess (at least they
> swim a lot in the ocean so it's sort of ocean-related, and shells are in oceans
> too, so that's my pathetic link to being shell-related).
>
> Nora (natural history fan, lacking a bit..OK a lot  in the shell department)
> Calgary, Alberta
>
> "Monfils, Paul" wrote:
>
> > Looking at albinism in mammals and trying to apply those observations to
> > molluscs is probably not a valid approach.  In mammals, albinism is
> > relatively simple, at least in concept.  There is one major pigment involved
> > - melanin - which is responsible for most of the color seen in mammalian
> > skin, hair, eyes, and some of the color in certain internal organs.
> > Mammalian albinism is the inability to synthesize melanin, probably due to
> > the absence of a particular enzyme involved in melanin formation.  No enzyme
> > - no melanin - no color.  The concept at least is simple, even if some of
> > the genetic pathways causing the condition are fairly involved.  However,
> > where multiple pigments are involved, possibly controlled by multiple genes,
> > the situation becomes more complex, as Tom's reptilian examples illustrate.
> > To use another herpetological example, our local green frog has two skin
> > pigments, a yellow one and a blue one, which blend to create the appearance
> > of green.  This is a different situation from plant leaves, which look green
> > because of a single, actually green pigment.  Sometimes an individual frog
> > lacks the yellow pigment.  Result - a blue frog.  Now, ordinarily we
> > wouldn't refer to a blue frog as an albino.  Yet, the frog has exactly the
> > same genetic condition as an albino mammal - the genetic inability to
> > produce a single pigment.  So, how do we define albinism?  Is it an actual
> > genetic aberration, or only its visible outward manifestation?  If we use
> > the general definition "a genetically mediated inability to produce normal
> > pigmentation" then the blue frog is an albino.  If we define albinism as the
> > inability to produce any pigmentation at all, then it must be a far more
> > complex phenomenon in multipigmented animals than it is in mammals.  This is
> > particularly true in molluscs, where the shell and the soft parts may have
> > different pigmentation, each having multiple pigments controlled by
> > different genes, and created by diverse biochemical processes.  For this
> > reason, I would have to disagree with a couple of statements in Tom's last
> > paragraph.  Since the shell pigments may be different from the soft tissue
> > pigments both in composition and in synthesis, I don't think there is
> > necessarily any reason to expect that the "animal" in an albinistic shell
> > would also be albinistic.  If both shell and soft parts were albinistic,
> > that would indicate that either (1) the shell pigments and tissue pigments
> > were similar, or (2) that a more complex cause was operating, quite possibly
> > multiple causes, acting independently.  Also, I don't subscribe to the
> > theory of environmental causes.  It is true that albinism tends to be more
> > prevalent in certain localities.  However, the fact remains that most of the
> > individuals in a given locality are not albinistic, even though they are all
> > subjected to the same environmental factors.  Of course it could be argued
> > that certain individuals might have genetic predispositions to certain
> > environmental stimuli; but a more likely explanation for localized
> > concentrations of albinism (or other genetic traits) is inbreeding within
> > the localized population.  Albinistic mammals and birds don't last long in
> > nature, and are consequently very rare, due to two factors - greater
> > visibility to predators and susceptibility to skin and especially eye damage
> > from ultraviolet radiation.  In molluscs, these factors are minimalized
> > since (1) an aquatic habitat filters out harmful UV rays (more or less,
> > depending on depth), and most mollusc shells are opaque, even when
> > unpigmented, and (2) most of their predators do not depend on eyesight to
> > find them.  Therefore, albinism could quickly become commonplace in a
> > confined, inbreeding population of molluscs, even if it is a recessive
> > trait.
> > We should keep in mind that "albinistic" means more than just "white".  It
> > means lacking pigmentation by virtue of a specific genetic cause.  Polar
> > bears are white.  They are not albino.  They do not have a genetic inability
> > to produce melanin, as shown by the presence of melanin in their eyes,
> > mouths, inner ears, and internal organs.  The same is true of most white
> > domestic cats and dogs.  However, it is possible to have a true albino cat
> > or dog, or presumably an albino polar bear, in which there is no melanin
> > anywhere, because they are incapable of producing it.  In other words, when
> > a normally white species produces an albino individual, it is not as obvious
> > as when an albino appears in a normally pigmented species.  So, when a shell
> > dealer offers an "albino" specimen, the terminology is useful for describing
> > what the shell looks like, but it doesn't necessarily describe an actual
> > albino.  This is especially true of a species like Cypraea tigris, which
> > shows a range of color from pure white to pure black.  If an all-white C.
> > tigris is an albino, what is a specimen which has only two or three spots on
> > an otherwise white shell?  Dealers commonly refer to such sparsely-spotted
> > specimens as "semi-albino" or "near albino", which again is decriptively
> > useful, but probably not technically accurate.  On the other hand, an
> > all-white Strombus with a colored aperture might well deserve the
> > designation "semi-albino", or to be more accurate, "selectively albino".  In
> > other words, its loss of pigmentation may well be due to true genetic
> > albinism, but not all of its pigments are affected.
> > Lastly, someone inquired about the difference between "albino" and
> > "albinistic".  The difference is strictly grammatical - they do not refer to
> > different conditions.  "Albino", though we commonly use it as an adjective,
> > is technically a noun.  "Albinism" means a genetically mediated inability to
> > produce normal pigmentation.  "Albino" means an individual which exhibits
> > albinism.  "Albinistic" is the associated adjective.  So, an albinistic
> > individual is an albino, and vice versa.  And, technically we should speak
> > of "albinistic shells", not "albino shells".  But common usage often
> > prevails.
> > Paul M.