The secret of sheep breeds is getting smaller and smaller

The new study shows that warmer winters are making Scotland's wild Soay sheep increasingly smaller, despite the natural evolutionary benefits that should have helped the species grow larger.

The new study provides evidence that climate change is the reason for the decline in the size of wild sheep living on the island of Hirta in Scotland, according to scientists' first report in 2007. The study believes that, due to the effects of climate change, the survival conditions on Hirta Island are becoming easier, which means that low-growth, slow sheep are more likely to survive. over winter compared to the past. This, together with the newly discovered 'young mother sheep effect', whereby young sheep will produce smaller baby animals, explaining why the average size of sheep on the island is reduce.

The theory of classical evolution suggests that over time, the average size of wild sheep will increase, as larger animals tend to adapt, survive and reproduce better than small individuals, and females often have the same characteristics as their parents. However, for Soay sheep in Hirta, a remote island in Saint Kilda Islands, Scotland, the average body size has decreased by about 5% over the past 24 years.

The warmer winter is making Scotland's wild Soay sheep increasingly smaller, despite the natural evolutionary benefits that should have helped this species to grow bigger. (Photo: iStockphoto)

The team analyzed data on body size and life history, including important milestones in the life of a sheep Soay Island Hirta over the past 24 years. They found that the sheep on the island did not grow as quickly as before, and that the smaller sheep were able to survive and grow better. This reduces the average size of sheep populations in general.

Professor Coulson said this is a consequence of warmer and shorter winters born under the impact of climate change, meaning that sheep do not need to gain much weight in the first months to qualify exist until it is 1 year old like before, when the winter is colder and more severe.

He explained: 'In the past, only large, healthy sheep and healthy lambs who achieved the necessary weight gain in the first summer could cope with Hirta's harsh winter. But now, due to the effects of climate change, grass - the food source of this species - is available for many months of the year, and survival conditions become easier, so even sheep retardation is still possible. This means that small, weak sheep are increasingly taking up larger proportions in the population. "

The research results show that the decrease in average body size in Hirta island sheep is primarily an ecological response to environmental changes over the past 25 years; Natural evolutionary changes are only part of the very small reason for this phenomenon.

In addition, the team also discovered that the breeding age of female sheep affects the size of the offspring. They found that little females of less than five years of age were incapable of producing later offspring when they reached their childbearing age would reach the size of their current mother. This 'young mother sheep' effect has not been included in previous analyzes of natural selection, which partly explains why Hirta sheep do not follow the development forecasts made by biologists. .

'The young mother's sheep effect explains why Soay sheep does not become bigger than we are expected,' concluded Professor Coulson. 'But it's not enough to explain why they're even getting smaller. We believe this is due to climate change. Both of these plus factors have defeated the natural selection process that we still expect. '

The study was conducted in collaboration with scientists from Leeds, Cambridge, Edinburgh and Stanford universities. Funding is funded by the UK Natural Environment Research Council (NERC).

Refer:

Arpat Ozgul et al.The Dynamics of Phenotypic Change and the Shrinking Sheep of St.Kilda.Science, July 3, 2009