Seeing genes in space & time: the evolution of neutral and functional genetic diversity using woolly mammoth

点击翻译按钮获取中文摘要

Understanding how a population changes through time is critical to understanding the broader picture of species evolution and extinction. By examining the dynamics of population change, we can explore how, as a result of changing competitive pressures and habitats, species distributions alter through time and space. Populations can increase or decline, or differ in their levels of migration and immigration. Although it is theoretically possible to directly observe these processes, the time span across which observations would be necessary renders this all but impractical. Fortunately, direct observation is not the only way to infer changes occurring in populations, because all of these processes leave traces in the genetic diversity of a species. By sequencing pieces of genetic information of a species (DNA) from a large number of individuals within a population, it is possible to shed light on the dynamics of species going back hundreds of thousands of years. When analysing data from modern populations, data may be insufficient to acquire the full picture of past population change - any information from populations no longer around today will be lost. A far more powerful approach is to directly sample the genetics of past populations. This approach uses ancient DNA: DNA that survives trapped in tissue such as hair and bone dating back to ~120,000 years. Research in ancient DNA has shown that the dynamics of Pleistocene populations were more complicated than had been initially inferred from modern data alone. Critically, the Pleistocene is a period which covered a series of large changes in climate, and a detailed examination of Pleistocene population dynamics may shed light on how species respond to the effects of climate change.However, there are difficulties arising from the decay of DNA over time, which leaves relatively few bones that can be successfully sampled, and results in short pieces of DNA, problematic for analyses. One upshot of this is that most ancient DNA studies to date have relied on an abundant, short loop of DNA called mitochondrial (mt) DNA. However, mtDNA is only passed down through the maternal line, and cannot provide any information on the paternal lineage. Sequencing a large number of dated bone samples for longer sequences of both mtDNA, and DNA from the cell nucleus, would shed light on both male and female evolutionary history, and provide a much better insight into how animal populations have changed over the last few hundred thousand years.The woolly mammoth, an icon for both the Pleistocene and species extinction, is an ideal species in which to study how animals may be affected by climate and environmental change. Moreover, by examining genes that may be favoured during times of climate change, such as those involved in hair growth or cold adaptation, it will be possible to investigate any differing patterns in the DNA between these and more 'neutral' genes, helping us to better understand both the demographic and adaptive processes taking place in these populations.Recent progress has made such a project possible. Using new high-throughput technologies for analysing DNA, in combination with methods to locate the specific DNA fragments of interest, we can now rapidly and efficiently analyse thousands of units of DNA code from hundreds of fossil remains, allowing us to infer what happened to populations in the past.