NEW YORK (GenomeWeb) – An international research team reconstructed 35 mitochondrial genomes and discovered that there was a single major dispersal event in non-African populations and a previously unknown population turnover in Europe during the end of the Pleistocene era, approximately 55,000 years ago.
As they reported today in Current Biology, the researchers generated 35 new pre-Neolitihic European mtDNA genomes, almost tripling the number of such genomes available for research purposes. To do this, they extracted mtDNA fragments from bone powder drilled from teeth and bone samples from late-Pleistocene hunter-gatherers. The fragments were reassembled using high-throughput sequencing on an Illumina HiSeq. The 35 mtDNA genomes were combined with 20 previously published ancient European mtDNAs, and their combined data were put through various modeling scenarios.
"There has been a real lack of genetic data from this time period, so consequently we knew very little about the population structure or dynamics of the first modern humans in Europe," senior author and Max Planck Institute for the Science of Human History researcher Johannes Krause said in a statement.
DNA from this time period is often heavily degraded, which is why "it's easier to get mitochondrial DNA," Max Planck researcher and study author Adam Powell told GenomeWeb. The trick, he explained, is finding good sources for mtDNA, which are hard to come by.
Present-day Asians, Australasians, and Native Americans carry both M and N mtDNA haplogroups, while present day Europeans almost completely lack lineages of the M clade, the researchers wrote in their paper. These different spatial distributions and estimates of the time of the most recent common ancestor of these two ancestral clades have been interpreted by some researchers as evidence of an early spread of modern humans carrying haplogroup M into Asia, followed by a later non-African diffusion of the N clade.
However, this study found that three hunter-gatherers from Belgium and France, dating between 35,000 and 28,000 years ago carried mtDNA haplogroup M. This led the team to propose an alternative dispersal model where there was a rapid and single dispersal event across Eurasia, with Asia being reached first. Western Eurasia would have been settled after haplogroup M was lost, leaving no trace of that ancestry in European settlers.
The researchers also determined that there was a previously unknown population bottleneck in Europe that occurred at the end of the Pleistocene, the last glacial period. This population turnover seems to have resulted in loss of haplogroup M in Europe. While they can't be sure, the researchers speculated that this may have been influenced by climatic events.
Powell, Krause, and their colleagues hope to expand on their research of this time period, but their plans are largely dependent on their ability to obtain more sources of mtDNA, Powell added.