All sorts of cues can cause organisms to alter rates of growth, of shell
deposition, of metabolic rates and processes etc. These cues include both
chemical and mechanical. Evidence shows that organisms react to chemical
cues even if the predators themselves have been physically removed, for
example. All such changes in rates of growth and metabolic processes,
however, necessarily require that they fall in the organisms' 'plasticity
envelope'. Some parasites are able to effectively 'tweak' these envelopes
and cause all sorts of bizarre changes to infected organisms, including
growth aberrations, cessation of reproductive function and so on.
Alex

-----Original Message-----
From: Conchologists List [mailto:[log in to unmask]] On Behalf Of Pete
Krull
Sent: 26 March 2009 02:06
To: [log in to unmask]
Subject: Re: [CONCH-L] Crab Induced Snail Evolution in Our Generation?

Alan; can you or someone explain how a mussel shell can be induced to grow
thicker because a crab is chewing on it? obviously the mussel can't make a
conscious decision to do that. Is it the irritation that causes thicker
shell growth? If so then captive mussels could be induced to grow thicker
shells by scraping them with a file?

I understand how a colony of mussels could, over generations, grow thicker
shells because of this type of predation but i can't grasp how a single
organism can perform that feat. pete krull

-----Original Message-----
From: Conchologists List [mailto:[log in to unmask]] On Behalf Of Alan
Kohn
Sent: Wednesday, March 25, 2009 7:48 PM
To: [log in to unmask]
Subject: Re: [CONCH-L] Crab Induced Snail Evolution in Our Generation?

Alex Menez's comments are quite correct, accurate and helpful. The term
adaptation can apply both to change in an individual organism or in a group
(population or species). The jargon term "phenotypic plasticity" is often
applied to the former (the case described for Nucella), to distinguish it
from genetic change. The latter typically does involve genetic change over
time, i.e. evolution.

Alan

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