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

----- Original Message -----
From: "Alex Menez" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, March 25, 2009 11:57 AM
Subject: Re: [CONCH-L] Crab Induced Snail Evolution in Our Generation?


> An example of adaptation, i.e. the process of evolutionary modification
> which results in improved survival and reproductive efficiency. This can
> encompass any morphological, physiological, sensory, developmental or
> behavioural character.
> (Remember this is not the same as Adaptive Radiation which is the
> diversification into different ecological niches by species derived from a
> common ancestor, and requiring longer timeframes. Examples include the
> Hawaiian honeycreepers, Darwin's finches and the cichlid fishes of the
> great
> lakes of Africa).
>        Very similar findings to those about which this thread is concerned
> have been made with crabs and mussels, the latter thickening in shell
> within
> very short periods of time:  the Asian shore crab invaded the eastern
> coast
> of the U.S. about 15 years ago and began foraging on the native blue
> mussel,
> which, at the time, had no defences against the exotic, aggressive crab.
> The
> blue mussel responded to the crab's presence by building up a thicker
> shell
> over the course of a few months. I think some people are surprised by how
> quickly these changes can occur, and that they occur within individuals in
> response to environmental pressure (i.e. the crabs in this case). We are
> not
> thinking about evolution over generations, but changes based on the
> organisms' plasticity, which is in any case genetically determined, and
> will
> be expressed dependent on a whole range of factors. This expression is the
> phenotype, i.e. what we see in the animal. Because mollusc shell
> morphology,
> thickness, and so forth is relatively plastic, changes can occur quickly.
> And think of this happening with plants (where rapid change tends not to
> be
> that surprising).
> These variations can be acted on by Natural Selection... but that's a
> whole
> new discussion!
> Alex
>
> -----Original Message-----
> From: Conchologists List [mailto:[log in to unmask]] On Behalf Of
> Allen Aigen
> Sent: 25 March 2009 16:06
> To: [log in to unmask]
> Subject: Re: [CONCH-L] Crab Induced Snail Evolution in Our Generation?
>
> Not bad science as much as incomplete science.  It seems that they came up
> with a hypothesis to explain the change in average size of mature shells,
> without following up to prove it correct or not.  Has any one read the
> original, or know the authors to see if the article accurately reflects
> their findings?
>
> Allen Aigen
> [log in to unmask]
>
> ---------- Original Message ----------
> From: Pete Krull <[log in to unmask]>
> To: [log in to unmask]
> Subject: Re: [CONCH-L] Crab Induced Snail  Evolution in Our Generation?
> Date: Wed, 25 Mar 2009 10:47:41 -0400
>
> This sounds like bad science to me. If the crabs eat smaller specimens
> that
> means they would be eating mostly young snails, depleting that part of the
> population. There would then, possibly, be more food available for the
> remaining snails which might grow larger because they are eating more.
> This
> is not adaptation but a change in the environment. pete krull
>
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