I believe it was Russ Jensen who once told me that he noticed some
molluscan species exhibited extreme characteristics at the end of a
geographical range.  What he was referring to in particular was Chicoreus
spectrum in Puerto Rico, the northern-most end of the species' range.  In
P.R. the shells he, and later I found while scuba diving were of
extraordinary hues, depth and variation of color, much as they are found in
the southern-most end of the range.
 
Cypraea tigris (schilderiana) in Hawaii, the northern-most range for that
species, grows to be larger and more inflated, than almost anywhere else in
its range.  Water temperatures, or other environmental influences may cause
these extreme colors or sizes to develop.
 
Could the same be true for the population of Nucella lapillus that you
describe?  Is this the northern-most end of the range for the species?
Just a thought.
 
Rich
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Richard L. Goldberg
Worldwide Specimen Shells
email:  [log in to unmask]
homepage:  http://www.erols.com/worldwide
 
"Historians will have to face the fact that natural selection
determined the evolution of cultures in the same manner
as it did that of species."   Konrad Lorenz
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 
At 04:05 PM 2/3/98 -0400, Mayhew wrote:
>Rich:  Two of the concepts you refer to- the founder effect and genetic
>drift, may account for  variation patterns in two interesting  Nova
>Scotia populations i have observed: The Neptunea l. decemcostata on
>Brown's Bank (off SW N.S.),  are far more often a beautiful shade of
>violet, than any other population i have seen or heard of
>(unfortunately, this pigmentation is nearly impossible to preserve- it
>fades in alchohol, and on exposure to light.  Interestingly enough, it
>seems to penetrate the entire thickness of the shell, instead of being
>surficial).  Also, the frquency of albinism is considerably higher in
>this population.  This unusual morphic disribution could have resulted
>from the "founder effect": a die-off, following which the survivers
>and/or reintroductions contained an unusually high percentage of the
>apparently recessive albinistic and violet pigmentation alleles.  I know
>of no environmental factors which could accout for these observations,
>and am also surprised that such an interesting  occurance is seemingly
>absent from the literature (i've looked!!).
>        At a locality near Halifax, the Nucella lappilus is riotously
variable-
>far beyond what could be explained by "frequncy-dependant selection", in
>my opinion.  Also, the relative frquencies of the population seem to
>shift semi-ramdomly from year to year.              Both could be
>exlained,at least partially, by genetic drift, enhanced by a natural
>tendancy towards mutation in the genes controlling  pigmentation in the
>species. (although the apparent yearly frequency shifts are more
>probably the result of very incomplete viewing  of the population- each
>time i visit, i probably see only 20-25% of the beasties in the local
>gene pool.)
>
     -Ross M.
>
     Schooner Specimen Shells.
>
>