By Jody Bourton
Earth News reporter
Trouble in the glen? A sika deer stag runs with red deer hinds
Scotland's wild red deer are changing shape due to breeding with a foreign species, a new study has found.
Researchers previously found Japanese sika deer, brought to the country in the 19th Century, have bred extensively with native deer.
It was unclear then how crossbreeding would affect the species.
Now research by some of the same scientists shows that hybridisation is causing red deer to become smaller and sika deer to become larger.
The scientists warn that a new type of deer may emerge which will have serious implications for the future of both deer species.
The study, published in the Journal of Animal Ecology, was carried out on the Kintyre Peninsula in Scotland by a international team of researchers from Scotland, New Zealand and Australia.
'Mongrel of the glens'
Sika deer (Cervus nippon) occur in many of the habitats in Scotland that the native red deer (Cervus elaphus) lives.
Although it was already known that sika crossbreed with red deer, it was thought the overall impact on the native species was low.
The two species differ greatly in appearance: red deer are larger than sika, usually standing 30cm taller at the shoulder.
Red deer stags can also grow antlers with 12 points or more but sika antlers rarely exceed eight points.
Despite the fact that sika are smaller in size, the two species can mate giving birth to hybrids that are fertile.
At present hybrids are a rare occurrence, with scientists estimating that between 0.01 to 0.02% of deer in most areas where the species overlap are hybrids.
However, it has been found that in some areas as many as 40% of deer are of mixed breed.
Such crossbreeding may permanently alter wild deer on Scotland's mainland, some researchers fear.
The scientists used genetic analyses and measurements of deer anatomy to obtain their results.
The new research reveals for the first time that hybridisation is causing a decrease in weight for red-like hybrid females, and an increase in weight for sika-like female and male deer.
'Red-like' and 'sika-like' deer are considered to be red or sika deer respectively, but at some point in their ancestry have crossbred showing traces of hybridisation in their genes.
It is also changing the shape of the jaws of both variants.
Legislation already exists to protect the red deer on many of Scotland's islands from crossbreeding with sika deer, but mainland red deer remain at risk.
Even though the hybrid deer may not gain any selective advantage from being a crossbreed, hybridisation may continue, researchers warn.
"The new finding is a concern because intermediate-sized animals may not be so choosy who they mate with, leading to further hybridisation," says Professor Josephine Pemberton from the University of Edinburgh, who's lab undertook the research.
Prof Pemberton also explains that the change in size may affect the species' ecology, for example what each eats and when females breed.
"It is possible that a new type of deer with new ecological impacts will emerge," Prof Pemberton says.
"To date, it has not been clear what the practical effects of hybridisation on Scottish red deer are," she says.
"Our research fills this gap in knowledge and suggests that 'the mongrel of the glens' is a real possibility."