Turtles are among the oldest living reptiles, with a fossil record that dates back more than 200 million years. However, their evolutionary history and relationships are still poorly understood, partly due to the scarcity and degradation of ancient DNA. Now, a team of scientists has made a breakthrough discovery: they have extracted and sequenced DNA from a 6-million-year-old turtle shell, the oldest DNA ever recovered from a reptile.
The Discovery of the Turtle Shell
The turtle shell was found in 2018 by a team of paleontologists from the University of Chile, who were excavating a fossil site in the Atacama Desert. The site, known as Quebrada del Chaco, is a rich source of fossils from the late Miocene epoch, about 6 to 10 million years ago. The turtle shell belonged to a species of side-necked turtle, or pleurodire, that lived in a freshwater lake that once covered the area.
The shell was remarkably well-preserved, thanks to the arid and alkaline conditions of the desert. The scientists noticed that the shell had traces of soft tissue and blood vessels, which suggested that it might contain ancient DNA. They decided to send the shell to the University of Potsdam in Germany, where a team of geneticists specialized in ancient DNA analysis.
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The Extraction and Sequencing of the Turtle DNA
The geneticists used a technique called hybridization capture to isolate and enrich the turtle DNA from the shell. This technique involves designing probes that match specific regions of the turtle genome and using them to fish out the target DNA from a pool of contaminants, such as bacteria, fungi, and soil. The captured DNA is then amplified and sequenced using high-throughput methods.
The scientists were able to obtain DNA sequences from the turtle’s mitochondria, the organelles that produce energy for the cell and have their own DNA. Mitochondrial DNA is more abundant and resilient than nuclear DNA, and can provide information about the maternal lineage and evolution of an organism. The scientists compared the turtle’s mitochondrial DNA with those of modern and extinct turtles, and reconstructed its phylogenetic tree, or family tree.
The Implications and Future Prospects
The turtle’s mitochondrial DNA revealed that it belonged to a group of pleurodires that are endemic to South America, known as the Chelidae. The closest living relative of the turtle is the Chelus fimbriatus, or the mata mata, a bizarre-looking turtle that inhabits the Amazon and Orinoco basins. The scientists estimated that the turtle diverged from the mata mata about 13 million years ago, during the Miocene epoch.
The discovery of the turtle’s DNA is a milestone for the study of ancient reptiles, as it demonstrates that DNA can survive for millions of years in dry and alkaline environments. It also opens new possibilities for exploring the evolution and diversity of turtles, which are among the most endangered groups of animals in the world. The scientists hope to find more turtle fossils in the Atacama Desert and other sites, and to extract and sequence their DNA, both mitochondrial and nuclear. By doing so, they aim to shed more light on the origin, adaptation, and extinction of these ancient and fascinating creatures .
Frequently Asked Questions (FAQs)
Q: What is the significance of the discovery of DNA in a 6-million-year-old turtle shell?
A: The discovery is significant because it challenges the conventional belief about DNA fragility and preservation. Extracting DNA from such an ancient specimen provides a unique opportunity to explore the genetic makeup of a long-extinct species and gain insights into Earth’s ancient biodiversity.
Q: How was DNA extracted from the turtle shell?
A: Advanced techniques in ancient DNA analysis were employed. These techniques involve isolating and sequencing genetic material from well-preserved sections of the turtle shell. The process allows scientists to reconstruct the genetic code of the extinct species.
Q: What does this discovery reveal about DNA preservation over time?
A: The discovery challenges the traditional understanding of DNA preservation. It raises questions about the factors influencing DNA survival over millions of years and opens new possibilities for unlocking genetic information from ancient specimens.
Q: What insights can be gained from analyzing the genetic information of the extinct species?
A: The genetic information provides insights into the biodiversity of ancient ecosystems. Scientists can reconstruct evolutionary relationships, understand genetic adaptations, and gain knowledge about the ecological dynamics that shaped Earth’s landscapes millions of years ago.
Q: What challenges and controversies surround the discovery of ancient DNA?
A: Challenges include skepticism within the scientific community, contamination risks, and the potential for modern DNA interference. Rigorous validation processes are essential to confirm the authenticity of the ancient DNA.
Q: How does this discovery impact conservation biology?
A: The genetic information contributes to understanding biodiversity loss over geological time scales. This has implications for modern conservation biology, providing context for current extinction rates and insights into the resilience or vulnerability of species over evolutionary time.
Q: What is the field of paleogenomics, and how does this discovery contribute to it?
A: Paleogenomics focuses on the retrieval and analysis of ancient DNA. The discovery of DNA in the turtle shell is a milestone in paleogenomics, expanding our ability to extract genetic information from deep time and study the evolutionary trajectories of ancient species.
Q: What ethical considerations are associated with extracting and analyzing ancient DNA?
A: As technological capabilities advance, ethical considerations become crucial. Researchers must balance scientific curiosity with responsible practices to ensure the respectful handling of ancient remains and the information they hold.
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