RESUMO
Temporal genomic data hold great potential for studying evolutionary processes such as speciation. However, sampling across speciation events would, in many cases, require genomic time series that stretch well back into the Early Pleistocene subepoch. Although theoretical models suggest that DNA should survive on this timescale1, the oldest genomic data recovered so far are from a horse specimen dated to 780-560 thousand years ago2. Here we report the recovery of genome-wide data from three mammoth specimens dating to the Early and Middle Pleistocene subepochs, two of which are more than one million years old. We find that two distinct mammoth lineages were present in eastern Siberia during the Early Pleistocene. One of these lineages gave rise to the woolly mammoth and the other represents a previously unrecognized lineage that was ancestral to the first mammoths to colonize North America. Our analyses reveal that the Columbian mammoth of North America traces its ancestry to a Middle Pleistocene hybridization between these two lineages, with roughly equal admixture proportions. Finally, we show that the majority of protein-coding changes associated with cold adaptation in woolly mammoths were already present one million years ago. These findings highlight the potential of deep-time palaeogenomics to expand our understanding of speciation and long-term adaptive evolution.
Assuntos
DNA Antigo/análise , Evolução Molecular , Genoma Mitocondrial/genética , Genômica , Mamutes/genética , Filogenia , Aclimatação/genética , Alelos , Animais , Teorema de Bayes , DNA Antigo/isolamento & purificação , Elefantes/genética , Europa (Continente) , Feminino , Fósseis , Variação Genética/genética , Cadeias de Markov , Dente Molar , América do Norte , Datação Radiométrica , Sibéria , Fatores de TempoRESUMO
Prehistoric population structure associated with the transition to an agricultural lifestyle in Europe remains a contentious idea. Population-genomic data from 11 Scandinavian Stone Age human remains suggest that hunter-gatherers had lower genetic diversity than that of farmers. Despite their close geographical proximity, the genetic differentiation between the two Stone Age groups was greater than that observed among extant European populations. Additionally, the Scandinavian Neolithic farmers exhibited a greater degree of hunter-gatherer-related admixture than that of the Tyrolean Iceman, who also originated from a farming context. In contrast, Scandinavian hunter-gatherers displayed no significant evidence of introgression from farmers. Our findings suggest that Stone Age foraging groups were historically in low numbers, likely owing to oscillating living conditions or restricted carrying capacity, and that they were partially incorporated into expanding farming groups.
Assuntos
Agricultura/história , DNA Mitocondrial/genética , Variação Genética , Genoma Humano , População Branca/genética , DNA Mitocondrial/história , Genômica , História Antiga , Humanos , Países Escandinavos e Nórdicos , População Branca/históriaRESUMO
The major problems concerning ancient DNA studies are related to the amount of extractable DNA and the precautions needed to avoid contamination. From the very first step of the analyses, the DNA extraction, these problems must be confronted. There are several extraction methods available for DNA in ancient tissue; several of them are complicated and time consuming, and none of the methods have reached an acceptance level such that they are routinely used on a widespread basis. Here we investigate the efficiency of two methods, one based on magnetic separation of the targeted molecules, and one based on silica binding. The efficiency rate of these two on the material studied seems to be identical. The silica binding method has the benefit of relative simplicity, but the magnetic separation technique also has advantages. For example, it is possible to reuse the extract several times for different loci, and it is possible to concentrate all extracted DNA from one locus into one PCR.
