Using records of large mammal populations in the Urals to decipher the timing and effects of global climate change.

目前解释全球气候变化影响的尝试依赖于对格陵兰岛、南极洲和北大西洋等地的冰和沉积物岩心的分析。然而，尽管这些记录非常详细，可以追溯到75万多年前，但它们实际上是周围地区海面温度的代用记录。因此，很难从海洋表面温度转移到理解陆地动物和植物如何受到这些记录中明显变化的影响。从晚更新世（约180- 12000年前）的大型动物骨骼中提取的古代DNA提供了一种全新的方法，可以获得详细的基因记录，了解种群是如何随着环境条件的变化而变化的（例如，灭绝、被取代或迁移到其他地方）。乌拉尔山脉在海拔相对较高的地方碰巧有一组很好的洞穴，里面有成千上万保存完好的动物骨头，这些动物在晚更新世时期居住在这个地区。我们已经证明，从这些骨头中提取DNA是可能的，通过碳定年，可以确定DNA序列的年代，并计算出种群中断的时间。通过研究几个不同的物种（在这个例子中是马、驯鹿、狼和棕熊），我们可以广泛地调查整个生态系统，并寻找许多物种在遗传结构上发生重大改变的时间。这意味着一个重大的（生态系统范围内的）事件，而主要的原因可能是气候变化。我们的初步数据表明，在遥远的欧洲和阿拉斯加/加拿大的动物种群中，可以同时看到重大的变化，这表明全球（或至少是半球范围）的事件是负责的。虽然动物的DNA让我们能够确定事情何时发生变化，以及种群迁移或灭绝的程度，但它并不一定能确定这种躁动的原因。为了调查这个问题，我们将检查来自骨骼起源的同一洞穴的沉积物（土壤）样本。牛津大学最近的研究表明，土壤中含有动物的DNA，尤其是过去占据某一地区的植物的DNA，可以提供不同时期植被的范围和类型的图片。洞穴沉积物对这种形式的研究特别有用，因为它们通常具有良好的地层学（从年轻土壤到年老土壤的稳定进展），并且保存在相对完整的状态。通过检查植被记录，并将它们与动物种群进行比较，我们应该能够确定在大动荡时期发生的植物变化，也许还能知道为什么某些物种灭绝而另一些物种幸存下来。然后，我们将把植被和动物种群的变化与物理冰和沉积物记录联系起来，试图确定这些记录中的信号如何与对地面的影响联系起来。有趣的是，一些动物的灭绝似乎与所谓的海因里希事件的气候波动有关。海因里希事件是指大西洋上的淡水似乎改变了洋流。陆地上短暂而剧烈的气候变化可能不会轻易地在物理记录中表现出来，因此有必要改变我们解释它们的方式。这些信息对于更好地了解过去的气候变化以及预测当前趋势（如全球变暖）的未来影响至关重要。

Current attempts to interpret the effects of global climate change hinge on the analysis of ice and sediment cores from places such as Greenland, Antarctica and the North Atlantic. However, while these records are very detailed and go back more than 750,000 years into the past, they are effectively a proxy record of the temperature of the sea surface in surrounding areas. Consequently, it is difficult to move from sea surface temperatures to an understanding of how land animals and plants are affected by the changes apparent in such records. Ancient DNA recovered from bones of large animals from the Late Pleistocene (c. 180-12,000 years ago) provides a completely new way to obtain detailed genetic records of how populations have changed through time (eg by becoming extinct, being replaced, or migrating elsewhere) as environmental conditions change. The Ural mountains happen to have an excellent set of caves at relatively high altitude, which contain thousands of well-preserved bones of the animals who occupied the area through the Late Pleistocene. We have shown that it is possible to extract DNA from these bones, and by carbon dating them it is possible to date the DNA sequences and work out when the population disruptions occur. By studying several different species (in this case horse, caribou, wolf and brown bear) we can survey broadly across the ecosystem and look for times when many species undergo major alteration in their genetic structure. This would suggest a major (ecosystem wide) event, and a prime candidate for the cause would be climate change. Our preliminary data suggests that major alterations can be seen at the same time in animal populations as far apart as Europe and Alaska/Canada, suggesting that planet-wide (or at least hemisphere-wide) events are responsible. While the animal DNA allows us to identify when things change, and to what extent populations move around or go extinct, it doesn't necessarily identify the cause of such agitation. To investigate this issue we will examine sediment (soil) samples from the same caves that the bones originate from. Recent work at Oxford have shown that soils contain DNA from animals and especially plants that occupied an area in the past, and can provide pictures of the range and type of vegetation at different times. Cave sediments are particularly useful for this form of study because they often have good stratigraphy (steady progression of younger to older soils down through the ground), and are preserved in a relatively intact state. By examining the vegetation records and comparing them to the animal populations, we should be able to identify what plant changes are occurring in periods of major upset, and perhaps why certain species are becoming extinct while others survive. We will then relate the changes in vegetation and animal populations to the physical ice and sediment records, to try and identify how signals in these records can be related to effects on the ground. It is already very interesting that several animal extinctions seem to relate to climatic fluctuations known as Heinrich events, when fresh water sheets on the Atlantic appear to alter current flows. It is possible that short sharp climatic alterations on land may not be readily apparent in the physical records, and it will be necessary to modify the way we interpret them. This information is critical for a better understanding of past climatic change, and in order to predict the future effects of current trends such as global warming.