This is the largest analysis so far of ancient dogs in the Americas. The findings appear in the Journal of Human Evolution.
An 11,000 – 16,000 year association with humans makes dogs a promising subject for the study of ancient human behaviour, including that of migration, said University of Illinois graduate student Kelsey Witt, who led the new analysis with anthropology professor Ripan Malhi.
As dogs have travelled with humans to every continent, they can potentially serve as an excellent proxy when studying human migration history. Analysis of ancient dog remains is often permitted, unlike humans “because living populations who are very connected to their ancestors in some cases may be opposed to the destructive nature of genetic analysis,” Witt said.
Like previous studies of ancient dogs in the Americas the new one focused on the dogs’ mitochondrial DNA, which is easier to obtain from ancient remains than nuclear DNA and, is inherited only from the mother. This means mitochondrial DNA offers researchers “an unbroken line of inheritance back to the past,” Witt said. However, the new study included a much larger sample of dogs than had been analysed previously, as well as incorporating results from earlier work.
The researchers sequenced a portion of the mtDNA HVR of 42 pre-Columbian dogs from three sites. Molecular anthropologist Brian Kemp of Washington State University provided new DNA samples from ancient dog remains found in Colorado and British Columbia, and the Illinois State Archaeological Survey (ISAS) provided 35 samples from a site in southern Illinois known as Janey B. Goode, near present-day St. Louis. The Janey B. Goode site is located near the ancient city of Cahokia, the largest and first known metropolitan area in North America. Occupation of the Janey B. Goode site occurred between 1,400 and 1,000 years ago, the researchers said, while Cahokia was active from about 1,000 to 700 years ago.
Dozens of dogs were ceremonially buried at Janey B. Goode, suggesting that people there had a special reverence for dogs. While most of the dogs were buried individually, some were placed back-to-back in pairs.
In Cahokia, dog remains, sometimes burned, are occasionally found with food debris, suggesting that dogs were present and sometimes were consumed. Dog burials in Cahokia during this time period are uncommon.
Diversity and relatedness
As previous studies had done, the Illinois team analysed genetic signals of diversity and relatedness in a special region (the hypervariable region) of the mitochondrial genome of ancient dogs from the Americas. University of Iowa anthropology professor Andrew Kitchen contributed significantly to this analysis.
The researchers found four never-before-seen genetic signatures in the new samples, suggesting greater ancient dog diversity in the Americas than previously thought. They also found unusually low genetic diversity in some dog populations, suggesting that humans in those regions may have engaged in dog breeding.
In some samples, the team found significant genetic similarities with American wolves, indicating that some of the dogs interbred with or were domesticated anew from American wolves.
Arrival in the Americas
But the most surprising finding had to do with the dogs’ arrival in the Americas, Witt said.
“Dog genetic diversity in the Americas may date back to only about 10,000 years ago,” she said.
“This also is about the same time as the oldest dog burial found in the Americas,” Malhi said. “This may not be a coincidence.”
The current study, of only a small part of the mitochondrial genome, likely provides an incomplete picture of ancient dog diversity in the Americas. “The region of the mitochondrial genome sequenced may mask the true genetic diversity of indigenous dogs in the Americas, resulting in the younger date for dogs when compared with humans,” Malhi said.
More studies of ancient dogs are planned, the researchers said, and Witt has already sequenced the full mitochondrial genomes of 20 ancient dogs to test this possibility, the researchers said.
Source: Past Horizons: http://www.pasthorizonspr.com/index.php/archives/01/2015/study-of-ancient-dogs-in-the-americas-suggests-migration-10000-years-ago