Million-year-old DNA sheds light on the genomic history of mammoths.
By: Tom van der Valk, Patrícia Pečnerová, David Díez-del-Molino
Summarized by: Amanda Gaskins, a senior at the University of South Florida studying geology and astronomy. After she graduates, she plans on continuing her education and obtaining her master’s degree in Geological Oceanography, where she hopes to find ways to combat the effect of global warming on coral reefs. In her free time, she loves to spend time in nature and read mystery novels.
What data were used? A team of scientists made paleogenetic (i.e., studying the DNA preserved in fossils) history by extracting what turned out to be the oldest genome data from the molar teeth belonging to three different mammoth species.
Methods: To reveal the age and makeup of the mammoth’s genetic data, the authors isolated the DNA from molars found in the Siberian permafrost. Fortunately, the cold temperatures of Siberia reduced the effects of DNA break down throughout time. From there, they used methods that maximized the restoration of short fragments of DNA. The authors utilized biostratigraphy, a branch of stratigraphy that involves correlating and assigning the relative ages of rock strata by using the fossil fauna captured within them, in order to gain an idea of when the mammoths lived. They did this by correlating the fossil remains found at the Siberian site with fossils at locations where absolute dates are available. Moreover, in order to observe how these species of mammoths adapted to their cold environment in Siberia, the authors compared the genomes of the woolly mammoth descendants with those of the ancient specimens.
Results: Through their experiments, the authors were able obtain ages for each of the three mammoths under speculation; each mammoth specimen is discussed here using a nickname given to them by researchers. The youngest of the mammoth group, nicknamed Chukochya, lived approximately 680,000 years ago. By examining the nuclear DNA that is contained within every cell nucleus of a eukaryotic organism, the team was able to construct a phylogenetic (evolutionary) tree (Figure 1) and discovered that Chukochya actually shares a common ancestor with the wooly mammoth. This confirms the hypothesis that Chukochya was a representative of an early form of the woolly mammoth. Adycha is the second-oldest mammoth of the group, whose life span aged back 1.34 million years ago amidst the early Pleistocene. It lived before Chukochya but is an ancestor to the woolly mammoths. The oldest mammoth of the bunch was dubbed Krestovka, with mitochondrial genome (DNA found only in the mitochondria in the cell) dating confirming that it roamed the earth 1.65 Mya in the early Pleistocene.
Why is this study important?: This study provides an excellent example of the potential that ancient paleogenomics have to help uncover the mysteries of evolutionary processes like speciation, in which populations evolve and develop into distinct species. Not much research has been done on deep-time paleogenomics with respect to speciation, as it would require a sample with a long range of genome time sequences, ranging at least a million years old, which the vast majority of fossils do not preserve. The previous oldest genomic data on record was recovered from a horse specimen dating back only 780-560 thousand years ago. The experiment also gives insight on the potential of utilizing DNA as a component of biostratigraphy to help correlate the ages of the rocks and fossils contained within them.
The big picture: Overall, this study shed light on the evolution of mammoths while breaking records in paleogenomic history by uncovering the most ancient DNA sample ever analyzed, pushing our knowledge of genomics all the way back into the Ice Age. The ideas and methods displayed in this experiment will be beneficial in future studies regarding temporal data.
Citation: van der Valk, T., Pečnerová, P., Díez-del-Molino, D. et al. Million-year-old DNA sheds light on the genomic history of mammoths. Nature 591, 265–269 (2021). https://doi-org.ezproxy.lib.usf.edu/10.1038/s41586-021-03224-9