我..无聊..翻译science网站上的短讯...
这是一桩有关绵羊变小的公案。
在遥远的苏格兰Hirta岛上，绵羊们正在变小，平均起来，过去24年里整整缩水了5%！这次问题可没有出在进化上。研究人员说，气候变化才是真凶。
Hirta绵羊的名字来自生养它们的遥远苏格兰小岛，属于Soay品种。身为最原始的驯养绵羊之一的Soay羊第一次抵达Hirta岛是1932年的事了。因为Hirta岛十分偏远，岛上的绵羊一直处在遗传隔离的状态：其他品种的绵羊没有被引进到岛上。于是这些绵羊成为了十分理想的科学研究对象。
2007年，科学家第一次报道了Hirta羊变小的现象。在伦敦Imperial College，领导这项研究的的生物学家Arpat Ozgul和他的同事分析了过去24年的绵羊体重数据。他们确认，Soay羊真的正在越变越小。而根据他们今天发表在science上的report，变小的原因是气候变化。
研究者注意到，在过去，Hirta岛上的绵羊在它们人生中的第一个夏天里大吃青草，为了渡过岛上典型的严冬做好体重上的准备。可是在过去的25年里，Hirta上的冬天又短又温和，相当反常。据此，Ozgul和他的同事提出，因为岛上的绵羊能在一年的更多月份里吃到鲜草，它们不再需要像以前那样夸张的增肥。还有一点就是，Hirta岛的严冬在过去不会放过年轻绵羊生下的小母羊，而现在它们有了生存的机会——可是因为它们的出生体重较低，它们怎么都长不到正常绵羊的尺寸。研究者说，这拖了整个居群平均尺寸的后腿。进一步的数学建模使得研究者们提出，自然选择在Hirta绵羊变小一事上几乎没有发挥什么作用。
来自UCLA的生态学家，同时也是进化生物学家的Malcolm Gordon，赞扬了这项研究。但是他认为还有其他机制在起作用。“岛上环境条件的改变可能使得绵羊食用植物的化学成分和营养价值发生了变化”，他说，也许这会让绵羊身材缩水。尽管如此，今天最后他还是说，气候变化大概仍是罪魁祸首。
Secret of Scotland's Shrinking Sheep Solved
By Nayanah Siva
ScienceNOW Daily News
2 July 2009
Call it the case of the shrinking sheep. On the remote Scottish island of Hirta, sheep have been getting smaller, shrinking an average of 5% over the last 24 years. Don't blame evolution, though. Researchers say climate change is the real culprit.
The Hirta sheep belong to a breed known as Soay, after the remote Scottish island where they arose. One of the most primitive forms of domestic sheep, Soays first came to Hirta in 1932. Because Hirta is a remote island, its sheep have remained genetically isolated, and no other sheep have been brought in for breeding. That's made Hirta's Soays ideal subjects for scientific study.
In 2007, scientists first reported that the sheep were smaller than they had been in the past. This prompted biologist Arpat Ozgul of Imperial College London and colleagues to analyze body weight data going back 24 years. The researchers confirmed that the Soays had indeed been getting smaller. And, as they report online today in Science, the reason appears to be climate change.
In the past, Hirta's sheep gorged on grass during their first summer, the team notes, piling on the weight in order to make it through the island's typically harsh winters. But over the past quarter-century, Hirta has had unusually short and mild winters. As a result, Ozgul and colleagues propose, grass has become available for more months of the year, meaning the Soay sheep do not have to bulk up as much. In addition, Hirta's harsh winters used to kill small ewes born to young mothers. But now these small ewes survive--and because of their low birth weight, they never get as big as normal sheep. That drives down the average size of the entire population, the team reports. Further mathematical modeling allowed the researchers to propose that natural selection has played little--if any--role in the shrinkage of the Hirta sheep.
Malcolm Gordon, an ecologist and evolutionary biologist at the University of California, Los Angeles, praises the study. But he says that other mechanisms may be at work. "Changing [environmental] conditions on the island ... [may] have led to changes in the chemical composition and nutritional value of the plant foods the sheep eat," he says, and that may have shrunk the sheep. Though at the end of the day, he says, climate change could still be the root cause.
Related Site
The Dynamics of Phenotypic Change and the Shrinking Sheep of St. Kilda
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