Re: News: Evolution is slowing snails down.

On May 13, 7:52 am, rokim...@xxxxxxx wrote:
On May 13, 5:59 am, Ye Old One <use...@xxxxxxxxx> wrote:





Evolution is slowing snails down
Matt Walker
Editor, Earth News

http://news.bbc.co.uk/earth/hi/earth_news/newsid_8043000/8043689.stm

Garden snails are evolving slower metabolisms.

Natural selection is favouring snails with reduced metabolic rates,
researchers in Chile have discovered.

It is the first time that evolution has been shown to select for this
trait in individuals of any species.

Snails with lower metabolisms are at an advantage because they have
more energy to spend on other activities such as growth or
reproduction, the researchers say in the journal Evolution.

Roberto Nespolo and Paulina Artacho of the Southern University of
Chile in Valdivia examined a long standing biological hypothesis known
as the "energetic definition of fitness".

"This predicts that animals that spend less energy will have more
surplus for survival and reproduction," says Nespolo.

Few studies have tested the idea, and three done on rodents could not
find any evidence it was true. "Ours is the fourth and the first to
demonstrate significant directional selection on metabolism," says
Nespolo.

Nespolo and Artacho measured the size of almost 100 garden snails
(Helix aspersa). They also gauged their standard metabolic rate (SMR),
by measuring how much carbon dioxide each animal produced while at
rest.

The standard metabolic rate is a measure of the minimal amount of
energy an animal requires to stay alive.

"Standard metabolic rate is the energy required for maintenance. In
other words, having less maintenance permits you to have more energy
for other activities, such as growth and reproduction. That's why less
metabolism represents higher fitness," says Nespolo.

After seven months, they recaptured the animals, collecting the empty
shells of those which had died.

Survival of the SMR

They found size did not predict which animals survived. But metabolic
rate did, with surviving snails having a metabolic rate 20% lower than
that of the snails that didn't survive.

And the lower each snail's metabolic rate, the greater its chance of
survival. That means that nature is selecting for snails that are more
energy efficient, says Nespolo.

Nespolo's and Artacho's study worked in part because of the snails
they chose to study.

Previous research examined metabolism in wild mice. But it's
impossible to know whether mice that disappear from a study have died,
or simply moved away. So it's difficult to accurately measure how many
mice survive year to year.

By studying garden snails living in purpose-built enclosures, Nespolo
and Artacho avoided this problem, as their snails did not move far and
left behind empty shells when they died.

"We could recover the dead because of their shells and because they
did not move more than a couple of metres each year," says Nespolo.

Snail's pace

The researchers now plan to answer the ultimate question: is having a
slow metabolism linked to moving slowly?

If it is, that means that snails are not only evolving to use energy
more slowly, but are increasingly moving at an even lower snail's
pace.

--
Bob.

The first thing that they should check is whether this is a response
to environmental toxins (human insecticides and pollution).  Lower
metabolism means that the snails have to ingest less of the pollutants
with their food and have more time to deal with the toxic chemicals
that they ingest so that they do not rise above lethal levels.

The investigators held the snails for seven months in three controlled
field enclosures "closely mimicking
the density and habitat of the original populations (i.e., enclosures
contained the same plants found at the collection sites)." Presumably
they did not apply insecticides or other toxins to the experimental
sites which were under their control.

.

Relevant Pages

  • Re: News: Evolution is slowing snails down.
    ... energy an animal requires to stay alive. ... metabolism represents higher fitness," says Nespolo. ... that of the snails that didn't survive. ... resistant celery by picking out the plants with the least insect ...
    (talk.origins)
  • Re: News: Evolution is slowing snails down.
    ... surplus for survival and reproduction," says Nespolo. ... energy an animal requires to stay alive. ... metabolism represents higher fitness," says Nespolo. ... that of the snails that didn't survive. ...
    (talk.origins)
  • News: Evolution is slowing snails down.
    ... Garden snails are evolving slower metabolisms. ... surplus for survival and reproduction," says Nespolo. ... They also gauged their standard metabolic rate, ... metabolism represents higher fitness," says Nespolo. ...
    (talk.origins)
  • Re: News: Evolution is slowing snails down.
    ... Garden snails are evolving slower metabolisms. ... Roberto Nespolo and Paulina Artacho of the Southern University of Chile ... The standard metabolic rate is a measure of the minimal amount of energy ... metabolism represents higher fitness," says Nespolo. ...
    (talk.origins)
  • Re: News: Evolution is slowing snails down.
    ... surplus for survival and reproduction," says Nespolo. ... energy an animal requires to stay alive. ... metabolism represents higher fitness," says Nespolo. ... that of the snails that didn't survive. ...
    (talk.origins)