subject: Climate change shifts sheep shape
posted: Mon, 19 Mar 2007 02:40:24 -0000

Climate change shifts sheep shape

Climate change could have an impact on animal evolution and ecology,
scientists believe.

A 20-year study of Scottish sheep found weather patterns were driving
changes in body shape and population size.

Harsh winters led to larger sheep, which brought about changes in
population size, yet in milder winters this effect was not seen.

The team says the study, published in the journal Science, is the
first to connect these different factors.

"Until now, it has proven really quite difficult to show how ecology
and evolutionary change are linked, but we have developed a way to
tie them together," said Tim Coulson, an author of the paper and a
scientist at Imperial College London.

Dr Coulson and colleagues did this by examining a population of Soay
sheep on the island of Hirta in the Outer Hebrides.

"The reason we looked at these sheep is they have been studied in
enormous detail. Where they live is like a natural laboratory - it is
a really simple system - there is just sheep and grass on the
island," Dr Coulson explained.

Reproductive success

The scientists looked at data recorded since 1985, analysing sheep
population sizes and body measurements.

"To determine how ecology influences evolution and vice versa, an
important step is to be able to see how population dynamics are
influenced by traits such as body size or eye colour that are, in
part, controlled by genes."

The researchers discovered body size was linked to animal numbers:
when lots of large sheep came into the population, the numbers tended
to fluctuate quite widely, possibly because body size is linked to
reproductive success.

But the researchers also discovered the sheep's body size was in turn
influenced by their environment.

"We used a measure of how bad the winters were in Scotland, and this
has been changing over the duration of the study," said Dr Coulson.

During the harsher winters in the 1980s, the data showed big sheep
were genetically favoured, he said.

"But over the years, winters have been getting a little bit better;
and as winters have got better, we have found there is not as much
natural selection for large animals as we saw in the past, as there
is less advantage to being big."

He said the study revealed how environmental factors were driving
evolutionary and ecological change, and predicted that as the climate
changed, and winters became less frequently harsh, the sheep would
get smaller and the population size would be more stable.

"People have argued for a long time that climate change is leaving an
ecological legacy, but we have shown it will leave an evolutionary
legacy too," he added.

* Origin: [green life] revolution through evolution -

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