Re: News: Evolution is slowing snails down.

On May 15, 12:26 am, "[M]adman" <ad...@xxxxxxxxxxx> wrote:
rnor...@xxxxxxxxx wrote:
On May 14, 8:34 pm, John Vreeland <john.vreel...@xxxxxxxx> wrote:
On Wed, 13 May 2009 10:59:34 GMT, Ye Old One <use...@xxxxxxxxx>
wrote:

Evolution is slowing snails down
Matt Walker
Editor, Earth News

Could higher metabolism be a symptom of a pathology, such as an
infection?

A parasite might well raise your CO2 consumption.

The usual mechanism for such a phenomenon in mammals is by raising the
body temperature.  But that doesn't happen in snails.

How do parasites raise body  temperature?

Is it similar to a fever that fights a virus?-

You asked perfectly reasonable questions of science that deserve a
straight answer.

Parasites do not really raise body temperature -- your immune system
does that in response to the parasitic infection. Many bacteria
produce pyrogens, substances that the body detects and causes a change
in the "set point" for your internal thermostat. Other pyrogens are
produced by phagocyte cells of the immune system. Whatever the
source, when the thermostat is reset higher, you tend to feel chilled
and your body responds by shivering, a way of making your muscles use
a lot of energy without doing physical work and so producing a lot of
heat, and by other methods of "non-shivering thermogenesis" which
produce heat. All these involve increasing the metabolic rate but
converting the food energy into heat rather than useful energy. (I
would argue that producing heat when you are cold is a very "useful"
thing to do, and should not be considered "wasteful".) There are non-
metabolic ways of increasing your temperature, too, like shunting
venous blood from superficial veins close to the surface to deep
veins. However the increase in temperature also directly increases
metabolic rate since all biochemical reactions run faster as the
temperature increases. It is not just parasitic diseases that cause
fever, the immune system reacts to all sorts of insults (the strangely
appropriate technical term).

The exact value of fever is somewhat controversial, but the elevated
body temperature does enhance immune system function and so helps
fight the disease. Some pathogens are also quite temperature
sensitive and don't do well at elevated body temperatures. In other
words, some fever is useful so don't be too quick in using aspirin or
other NSAIDs merely to reduce your temperature. However the fever can
also rise so high as to be dangerous in itself and then, of course,
you must bring down the temperature.



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