-- [ From: Scott Jordan * EMC.Ver #2.5.3 ] --
Dear Rich,
Do you recommend any particular books that delve into these biological
concepts? I realize that these are hardly new but perhaps you are aware
of a text that would be of help to the interesed layperson.
Thanks in advance,
Scott Jordan
-------- REPLY, Original message follows --------
> Date: Tuesday, 03-Feb-98 12:08 AM
>
> From: Worldwide \ Internet: ([log in to unmask])
> To: conch-l \ Internet: ([log in to unmask])
>
> Subject: Re: color and pattern variation
>
> Ross,
>
> Your explanation of variation seems to be related to natural selection
and
> frequency dependent selection, and are well taken. These biological
concepts
> were covered in the article I co-authored on the isolation and
evolution of the
> land shell genus Amphidromus in Indonesia [Am.Conch. June 1997 (on
Conch-Net:
> http://coa.acnatsci.org/conchnet/gold697.html )]. What I was
interested to
> know is whether the biological concepts which may influence variation
in land
> shells would also hold true for marine species?
>
> For instance, marine mollusks are often encrusted with marine
organisms, or
> periostracum which completely obscure color and pattern. Would
natural
> selection, or frequency dependent selection then apply to a group such
as the
> Cones where the periostracum obscures the color and pattern? Since
predators
> are not developing a search image of the color/pattern, would genetic
drift
> (described in the above article) be a more appropriate theory
explaining
> variation? -- e.g. Conus cedonulli shows extreme variation within one
> population. The Amphidromus article states that genetic drift tends
to
> eliminate variation within a population and increases differences
between
> populations. Confusing!
>
> Another instance where a species exhibits a great deal of color
variation
> within a population is Spondylus linguaefelis. It inhabits water deep
enough
> to filter out most of the warm color range that Ross refers to. Also,
the
> species is almost always encrusted with sponge and other organisms,
totally
> obscuring the color. Yet the species which lives its life anchored in
one
> position is found in a broad range of colors. Do these colors have
any
> function?
>
> So again, the question restated is, "Do the biological concepts
maintained for
> intra and inter-population variability of land snails like frequency
dependent
> selection, genetic drift, and the founder effect hold true for marine
species?
> Carol mentioned that she has not come across any specific mention in
the
> literature. Neither have I. Does anyone know of recent papers
related to
> these concepts? Gary? Tim? Others? Are there any easy answers?
Lot's of
> questions...
>
> Rich
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Richard L. Goldberg
> Worldwide Specimen Shells
> email: [log in to unmask]
> homepage: http://www.erols.com/worldwide
> ------------------------------------------------------------------
> "The shortest distance between two points
> is under construction." Noelie Alito
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
>
> At 05:32 AM 2/2/98 -0400, Mayhew wrote:
> >Did anybody see which way January went?? Talk about warp-speed time
> >travel!!
> >
> > A week or so ago, someone asked about the feature i admire
the most
> >about Mollusc shells: the incredible range of variation many
populations
> >exhibit, regarding color and patterns, especially in many of the most
> >common spp, and the most successful and diverse families, such as
> >Pectinidae, Neritidae, and of course Conidae. It is highly probale
> >that these spp and families BECAME so successful because of their
> >adaptability, which included their ability to blend in with their
> >visible surroundings whenever nessessary -ie, whenever predatory
> >pressure based upon color and/or pattern occurs. I believe that many
> >spp maintain a genetic "pool"
> >of visually-related variation, based partly upon past episodes of
> >visual predation which enhanced the relative survival rate of certain
> >colors and pattern-types, and partly upon simple genetic drift, which
> >often produces morphs of limited or no survival value (as in shocking
> >orange Nucella lapillus L., or violet Neptunea lyrata decemcostata-
> >beautiful from our perspective, but not corresponding to any feature
in
> >their environment that i have ever seen!). The more varied a given
> >species' pool of visual possibilities, the better their chances of
> >surviving in different portions of their total niche, if and when
> >visual predation becomes intense locally or regionally.
> >A "local" example would be Littorina obtusata L.. In situations where
> >crabs can easily pick them off their Fucus habitat, they are
> >marvellously camoflaged, being mainly green and pale yellow, these
> >being the colors of the blades and bladders of the algae they live
on.
> >In other localities, where crabs are less able to get at them, they
are
> >orange, black-striped, and a good variety of morphs or quite scarce
in
> >the crab-harrased populations.
> > Some of the variation we humans easily notice in sunlight,
with eyes
> >capable of differentiating many thousands of colors, hues, and
pattern
> >subteties, may be due to the differing visual charactaristics of the
> >bakground, the medium (air vs water of varying depth) the shell is
> >viewed in, as well as the visual capabilities of the relevant
> >predator(s): Water filters out certain wavelengths, and most marine
> >predators cannot distinguish as wide a range of colors as we can-
some
> >indeed are color-blind, and rely upon form, pattern, refleciveness,
> >etc., to discern their lunches from surrounding inedible materials.
> >So, what may look like very different colors and hues to our
discerning
> >eyes, may be nearly identical to the predator(s) which help determine
> >their relative frequencies by eating the inhabitants of the shells
> >they can more easily find. Likewise, some patterns may be just as
> >difficult for predators to discern as others which seem to us, under
> >very different circumstances, to be radically dissimilar (Neritidae
> >would seem to be masters at producing "visually-equivilant" patterns!
!).
> > Any other theories, or comments and critisisms on the ideas
above,
> >would be most welcome! -Ross Mayhew
> >(Schooner Specimen Theories)
> >
>
>
> >At 11:00 PM 1/27/98 -0600, Goldberg wrote:
> >Here's a topic for discussion. Color variation within a species has
always
> >interested me; both aesthetically and scientifically. Marine species
like
> >Pecten and Spondylus are prime examples. What are the accepted
theories
> >for particular marine species varying widely in color? Is it
adaptive
> >coloring? Genetic? Spondylus and Pectens are quite often encrusted
or
> >coated with marine growths which obscure the external coloring. So
> >adaptive coloring seems a less likely theory. A number of Murex,
Chitons
> >and other groups have species that also exhibit a wide range of
colors.
> >Color variation in land shells is often an adaptive characteristic.
What
> >about marine shells? Anyone takers?
> >
> >Rich
> >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >Richard L. Goldberg
> >Worldwide Specimen Shells
> >email: [log in to unmask]
> >homepage: http://www.erols.com/worldwide
> >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
-------- REPLY, End of original message --------
|
