"Rodent centers are powerful tools in paleoecology," said Michael Tessler, postdoctoral fellow at the American Museum of Natural History, in a statement. "We wanted to see how we could use and expand this priceless resource to get an overview of life in America 1,000, 10,000, or even 30,000 years ago and measure how it has changed in the United States since then. "
Pack rats are nocturnal rodents that use plant material to build nests in dry caves. Your urine helps hold the nests together. This allows the nests to be preserved for tens of thousands of years, some dated before the last ice age.
Since pack rats have a limited food area, their centers consist of content that is representative of the local environment in the region. Time when the materials were collected. This could give us clues to previous environments and climates, the study says.
"Midden content is so well preserved that fragments of old DNA can be extracted and analyzed over thousands of years," said Rob Harbert, assistant professor at Stonehill College, in the statement. "They were used to identify an extinct sloth that has been preserved in southern Argentina, to tell us the history of bighorn sheep in California, and to provide evidence of papillomavirus infection at pack rates over the past 27,000 years."
Fossil middens across America could allow us to "genetically profile entire communities through time and space," added Harbert, but we must first improve the analysis of the data from the deposits – a key objective of the study.
The researchers analyzed DNA from 25-pack Rat Midden samples between the ages of 300 and 48,000, which came from the City of Rocks National Reserve in Idaho and the Guadalupe Canyon in northern Baja California, Mexico. The scientists focused on a DNA sequencing technique called a shotgun that randomly selects DNA fragments for sequencing. They found that pack rat centers, at 32,000 years of age, had recoverable DNA that matched the fossils found in the deposits.
Since the shotgun technique sequences random parts of DNA, researchers need a solid database to assign the sequences to an organism. If no data are available for this organism, they will either get the next match or no match. In addition to DNA degradation, this enabled the researchers to definitely only tune the DNA fragments at the family level and not at genus or species groups.
"As the cost of DNA sequencing continues to decrease and computing power increases, the prospects for using this technique will improve significantly," said Harbert. "Further research into the taxonomic composition of Middens could refine our understanding of the timeline of past climate change, species migration, and extinction, and this will better inform the study of the effects of current and future climate change."