RESUMO
Despite decades of research, the roles of climate and humans in driving the dramatic extinctions of large-bodied mammals during the Late Quaternary period remain contentious. Here we use ancient DNA, species distribution models and the human fossil record to elucidate how climate and humans shaped the demographic history of woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox. We show that climate has been a major driver of population change over the past 50,000 years. However, each species responds differently to the effects of climatic shifts, habitat redistribution and human encroachment. Although climate change alone can explain the extinction of some species, such as Eurasian musk ox and woolly rhinoceros, a combination of climatic and anthropogenic effects appears to be responsible for the extinction of others, including Eurasian steppe bison and wild horse. We find no genetic signature or any distinctive range dynamics distinguishing extinct from surviving species, emphasizing the challenges associated with predicting future responses of extant mammals to climate and human-mediated habitat change.
Assuntos
Biota , Mudança Climática/história , Extinção Biológica , Atividades Humanas/história , Mamíferos/fisiologia , Animais , Teorema de Bayes , Bison , DNA Mitocondrial/análise , DNA Mitocondrial/genética , Europa (Continente) , Fósseis , Variação Genética , Geografia , História Antiga , Cavalos , Humanos , Mamíferos/genética , Mamutes , Dados de Sequência Molecular , Dinâmica Populacional , Rena , Sibéria , Especificidade da Espécie , Fatores de TempoRESUMO
The causes of the late Pleistocene megafaunal extinctions are poorly understood. Different lines of evidence point to climate change, the arrival of humans, or a combination of these events as the trigger. Although many species went extinct, others, such as caribou and bison, survived to the present. The musk ox has an intermediate story: relatively abundant during the Pleistocene, it is now restricted to Greenland and the Arctic Archipelago. In this study, we use ancient DNA sequences, temporally unbiased summary statistics, and Bayesian analytical techniques to infer musk ox population dynamics throughout the late Pleistocene and Holocene. Our results reveal that musk ox genetic diversity was much higher during the Pleistocene than at present, and has undergone several expansions and contractions over the past 60,000 years. Northeast Siberia was of key importance, as it was the geographic origin of all samples studied and held a large diverse population until local extinction at approximately 45,000 radiocarbon years before present ((14)C YBP). Subsequently, musk ox genetic diversity reincreased at ca. 30,000 (14)C YBP, recontracted at ca. 18,000 (14)C YBP, and finally recovered in the middle Holocene. The arrival of humans into relevant areas of the musk ox range did not affect their mitochondrial diversity, and both musk ox and humans expanded into Greenland concomitantly. Thus, their population dynamics are better explained by a nonanthropogenic cause (for example, environmental change), a hypothesis supported by historic observations on the sensitivity of the species to both climatic warming and fluctuations.
Assuntos
DNA/genética , Fósseis , Ruminantes/genética , Animais , DNA/história , DNA Mitocondrial/genética , DNA Mitocondrial/história , Extinção Biológica , Variação Genética , História Antiga , Humanos , Dados de Sequência Molecular , Filogenia , Dinâmica PopulacionalRESUMO
We extracted DNA from 39 Danish aurochs specimens and successfully amplified and sequenced a 252 base pair long fragment of the multivariable region I of the mitochondrial control region from 11 specimens. The sequences from these specimens dated back to 9830-2865 14Cyr BP and represent the first study of genetic variation of Danish aurochs. In addition, for all specimens we address correlations between the ability to obtain DNA sequences and various parameters such as the age of the sample, the collagen content, the museum storage period, Danish geography and whether the specimens were found in an archeological or geological context. We find that aurochs from southern Scandinavia display a star-shaped population genetic structure, that is indicative of a local and relatively recent diversification from a few ancestral haplotypes that may have originated in the ancestral Western European population before migration northwards during the retreat of the glaciers. Scenarios suggesting several invasions of genetically distinct aurochs are not supported by these analyses. Rather, our results suggest that a single continuous migration northward occurred. Our findings also suggest, although with only limited support, that aurochs in Northwestern Europe underwent a population expansion beginning shortly after the retreat of the glacial ice from Denmark and had a stable population size until the population decline that must have occurred prior to extinction. The absence of haplotypes similar to modern domestic cattle in our aurochs suggests that introgression between these species must have been limited, if it occurred at all. We found that the successful recovery of genetic material for PCR amplification correlates with sample age and local geographic conditions. However, contrary to other studies, we found no significant correlation between length of time in museum storage or the type of the locality in which a specimen was discovered (archeological or geological) and amplification success. Finally, we found large variances in our estimates of collagen content preventing an evaluation of this as an indicator of preservation quality.