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Scientists shear shrinking Soay sheep story

soay sheep.jpgThe strange story of shrinking Soay sheep on the island of St Kilda has resurfaced this week, with two of the research teams involved sniping at each other in the pages of the Royal Society’s Biology Letters journal.

Jake Gratten, of the University of Sheffield, and his colleagues take issue with the claim made in 2009 by Shane Maloney that climate change might be leading to a decline in dark sheep on the island.

First, some background. Back in 2008, Gratten was a co-author on a paper in Science which claimed to have solved the mystery of why larger, dark sheep are losing out to lighter, smaller sheep. Their large size should have made them more successful, but Gratten et al found that some of the genes that occur with a gene that leads to dark coats have negative impacts that outweigh the benefits of being bigger boned (see: Black sheep really are bad).

Then, in 2009, another team claimed that climate change was also playing a role. In their paper in Science they wrote being larger seemed to be just less useful now that global warming made the winters more survivable (see: Scotland’s shrinking sheep shocker).

Shortly after that, Maloney, of the University of Western Australia, and his colleagues added that the fact that the larger sheep were also darker meant their colour advantage (in terms of absorbing more solar radiation) was also less useful and therefore possibly involved in their declining dominance. (See: Global warming is shrinking your dinner.)

Still with us? Now Gratten’s group have issued a riposte to Maloney in a paper entitled ‘No evidence for warming climate theory of coat colour change in Soay sheep’. It does what it says on the tin, setting out problems in the statistical analysis used by Maloney and highlighting that the weather data used in his paper correlates better with increasing UK human population size than with Soay sheep coat colours.

“Given the scrutiny that climate change science is currently under…, attributing biological changes to global warming should surely require the highest standards of proof,” they write. “In this case, there is no evidence that warming climate is responsible for the decline in frequency of dark Soay sheep on St Kilda.”

Not so, says Maloney’s group. They stand by their theory, although admitting an error in calculation on one point, and say that a warming climate is still a plausible hypothesis for the decline in dark sheep.

“The field of climate change science being under close scrutiny should not hinder the free exchange of ideas,” they say. “We have presented a plausible hypothesis alternative to that of Gratten et al, and their recent comments do not persuade us to retract that hypothesis.”

Image: Simon Barnes via Wikipedia


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