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Re: Growth inhibition (was APD V4 #328

Hello Paul,

A similar inhibition can be seen in Daphnia:

As the culture gets more dense, the reproduction rate slows down and
then stops completely, despite sufficient available food. At this point,
depending on the Daphnia strain, one of three things happens:

a) They produce ephippia
b) The culture crashes
c) The culture slowly thins out (the Daphnia die of old age?)

Often "a" is followed by "b", but not always.

There is even a (German) term for the excreted inhibitory substances --
"Hemmungstoffe". In some instances they can be removed/reduced by
filtering through activated charcoal.



> Date: Mon, 5 Jun 2000 23:29:34 -0700
> From: krombhol at teclink_net (Paul Krombholz)
> Subject: Re: hormonal (or other) inhibition
> In the '60s a man named Merill s. Rose did some fascinating experiments on
> inhibition in tadpoles.  He found that in an aquarium only one or two grew
> well, and the rest were stunted and did not eat very much, in spite of an
> abundance of food.  He found that the big ones produced something in the
> water that inhibited feeding in the rest.  Water from the tank with the big
> ones could be transferred to another tank, and it would inhibit tadpoles
> there, too.  The water lost its inhibitory properties if it was heated to
> over 50 degrees centigrade.  Interestingly, the inhibitory factor could be
> filtered out of the water with ordinary filter paper, indicating it was not
> something in solution, but particulate, possibly cells from the inhibitory
> tadpoles.  At that point, just when it was really getting interesting, the
> research ended.  A year went by, and then Professor Rose now working at a
> different institution, I think,  published a paper on something else,
> something dull and uninteresting.  Apparently the funding ran out for his
> tadpole research.  I have never had the time to find if somebody else
> continued that line of research.
> Paul Krombholz, in central Mississippi,where we got about 1.5 inches of
> rain yesterday and last night.