Scotland's red deer are threatenedby a Japanese breed, Juliet Vickery reports. We have, as a nation, broadly welcomed Japanese investment in Britain but there is a growing feeling that one such investment should be banished from our shores. Like so many Japanese products it is smaller, more efficient and much more successful than its British counterpart. Its scientific name is Cervus nippon, its common name - sika deer.

Introduced from East Asia at the end of the last century for "decorative purposes", Sika deer have established themselves across Scotland and are now interbreeding with native red deer. Des Thompson of Scottish Natural Heritage, the Government's conservation body in Scotland, says: "If the spread continues there may be no pure red deer left on mainland Scotland within 30 to 40 years. The red deer is the true icon of wild places and a great magnet for tourists." He warns that swift action is required if Britain's "monarchs of the glen" are not to be "hybridised out of existence".

The highland economy is also at risk. About 20 per cent of Scotland's countryside is devoted to stalking interests, worth about Pounds 2 million a year. High prices are paid for the chance to shoot the "royal stag" - a male red deer bearing 12-pointed antlers.

Smaller than red deer, the sika's summer coat has white spots and a bright white rump patch. Red deer have no spots and a cream coloured rump patch. Hybrids exhibit a mixture of characteristics but after several generations of crossing are hard to distinguish from the pure breeds. It is only through genetic studies that the extent of sika in Scotland has become clear. If the rate of spread continues the only red deer left will be in captivity or tucked away on Hebridean islands.

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But does it matter? After all, red deer are themselves a mongrel race stemming from different introductions including some Wapiti from North America. Some would question whether "pure" Scottish red deer ever existed. Scientists at the Institute of Zoology, London are trying to find out through analyses of DNA samples from different red deer populations. "The major damage, in terms of genetic integrity [of Scottish red deer], has already been done," says Mike Bruford. "We have imported so many red deer that the indigenous population has probably already been lost".

So can anything be done to slow the hybridisation process? The Red Deer Commission will publish a deer management policy in the autumn, which is likely to include the establishment of "sika and hybrid-free zones". Dick Youngson, technical director of the commission, says: "On offshore islands like Lewis, Rhum and Islay, that don't have sika yet, we will be recommending that land-owners don't import sika or red deer from the mainland."

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Containing the sika on the mainland will be harder. "We will be calling for a tough policy on sika with heavy culling at the edge of current ranges. We need to control sika numbers such that they neither damage trees and crops nor spread outwards," he said. The Scottish sika deer population is estimated at about 13,500 and the annual cull is less than 3,000. Under the new Deer of Scotland Act, to be implemented this November, a cull of almost twice this is likely to be phased in.

There are still many aspects of sika biology and their hybridisation that are not understood. Why are sika spreading more rapidly in some areas than others? Scientists at Edinburgh University have started a three-year study, funded by the Natural Environment Research Council. The work will involve a study of DNA samples to find the genetic differences between different red and sika populations throughout Scotland. This will be combined with measurements of skeletal structures, particularly the skull and jaw bones. Differences in physical characteristics can then be linked to genetic differences to find whether, and how fast, the physical characteristics of hybrids are shifting towards those of sika.

The situation also provides a rare opportunity to study some exciting aspects of evolutionary biology. Nick Barton, a population geneticist at Edinburgh University, says: "For decades scientists have asked questions about what selection pressures act to keep two populations distinct. A hybrid zone like that between sika and red is equivalent to a natural laboratory where we can look at different mixes of genotypes and ask how they fare in the wild. Do some genes spread faster than others? If so which ones? What traits are being favoured and why? This in turn will allow us to address some of the fundamental questions about speciation."

But when it comes to supper-time, sika is definitely ahead in the stakes, Michael Mitchell, general manager of Mitchell Game Limited, the largest game dealers in Scotland, says: "Venison from sika is generally considered to have a much better flavour than that from red deer."

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