Re: Doug Stemke's question in regard to switches in Conus

Developmental plasticity under the influence of a differing specific
environmental factor is in fact fairly well established for mollusks
and quite common across the whole phylogenetic spectrum. Such switches
have been almost totally ignored by most geneticists or dismissed as
rare developmental aberrations. Some definitive criteria for a true
phenoplastic switch are that: 1) an identifiable chemical, hormonal, or
tissue factor induces morphological change  during development; 2)
spreads rapidly within the P generation; and 3) may or may not show in
the F2 and later generations, depending on environment. It may also be
reversible in P, F2 or later generations. Moreover, such switch
mechanisms may be activated  by tissue or external factors at any
cellular level, ranging from the timing of homeobox gene expression, to
the modification of RNA transcripts after translation, to the assembly
of protein domains in the microsome, or even later in the inactivation
of protein domains during growth.

I searched through M. J. West-Eberhardt's, recent compendium of
research, "Developmental Plasticity & Evolution"  (Oxford Press, 2003),
where I find numerous references to such snail/mollusk research (pp.
307-362). A fairly typical example involved rearing Physa gyrina, or P.
heterostropha, in controlled pair groups in either water in which
crayfish co-existed or water in which fish but no crayfish co-existed.
Within the month, facultatively induced differences in shell morphology
appeared; i.e., snails exposed to shell-crushing fish predators showed
wide apertures and very much strengthened, rotund shells. Fish exposed
to crayfish predation, only, showed narrow-apertured, thin elongate
shells, with barricading teeth (crayfish feed from the inside of Physa
species).

Such phenomena are strongly suggestive of a phenoplastic switch. This
is one reason why I think the sooner we toss neo-Darwinian explanations
into the trash can, and focus instead on the environment in which a
species develops, the better we will understand the basis of
speciation. Study of DNA cannot help much here, because the real issue
is one of regulatory silencing of genes, RNA transcripts, or protein
domains by external factors. The genome, itself, may remain unchanged
throughout.

Burt Vaughan
Evolutionary Biology
WSU-TC

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