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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