New research led by scientists at the American Museum of Natural History and the Smithsonian's National Museum of Natural History reveals that the majority of dogs living today have low but detectable levels of post-domestication wolf ancestry that has likely shaped characteristics including body size, sense of smell, and personality traits. The study, published today in Proceedings of the National Academy of Sciences, suggests that this newly uncovered gene flow may help give unique advantages to dogs' survival in diverse human environments. Among their findings: post-domestication wolf ancestry exists in a wide range of dog breeds, from large Shiloh shepherds to the tiny chihuahua.
"Modern dogs, especially pet dogs, can seem so removed from wolves, which are often demonized," said the study's lead author Audrey Lin, a Gerstner Postdoctoral Scholar in Bioinformatics and Computational Biology at the American Museum of Natural History. "But there are some characteristics that may have come from wolves that we greatly value in dogs today and that we choose to keep in their lineage. This is a study about dogs, but in a lot of ways, it's telling us about wolves."
Dogs evolved from an extinct population of gray wolves under human influences during the late Pleistocene, about 20,000 years ago. Although wolves and dogs live in the same geographic regions and can produce fertile offspring, hybridization is rare. And with few exceptions of intentionally crossbred wolves and dogs, there is little evidence of gene flow between the groups after dog domestication separated their gene pools.
"Prior to this study, the leading science seemed to suggest that in order for a dog to be a dog, there can't be very much wolf DNA present, if any," Lin said. "But we found if you look very closely in modern dog genomes, wolf is there. This suggests that dog genomes can "tolerate" wolf DNA up to an unknown level and still remain the dogs we know and love."
The researchers explored historical dog-wolf gene flow using more than 2,700 published genomes from the National Center for Biotechnology Information and the European Nucleotide Archive of wolves, breed dogs, village dogs, and other canids spanning the late Pleistocene to the present. They found that almost two-thirds of breed dogs have wolf ancestry within their nuclear genome from crossbreeding that occurred around 1,000 generations ago. In addition, all of the genomes analyzed from village dogs—free-roaming dogs that live in or near human settlements—carry detectable wolf ancestry.
Czechoslovakian and Saarloos wolfdogs, which were purposefully bred through hybridization with wolves, had the highest levels of wolf ancestry, between 23-40 percent of their genomes. Among breed dogs, the most "wolfy" were the great Anglo-French tricolour hound (between 4.7 and 5.7 percent wolf ancestry) and the Shiloh shepherd (2.7 percent wolf ancestry). While the Shiloh shepherd originated from breeding efforts with wolfdogs or other recent dog–wolf hybrids to create healthier, more family-friendly shepherd dogs in the US, the origin of the extensive wolf ancestry in Great Anglo-French tricolour hounds—the most common hound in modern France—is unknown and unexpected. The Tamaskan, a "wolfalike" breed that originated in the UK in the 1980s from selecting huskies, malamutes, and other breeds with the goal of producing a wolf-like appearance, has about 3.7 percent wolf ancestry.
The researchers found several patterns among the data: wolf ancestry is higher among larger dogs and in those bred for certain types of work, including Arctic sled dogs, "pariah" breeds, and hunting dogs. Terriers, gundogs, and scent hounds have the least wolf ancestry, on average. While some large guardian dogs have high wolf ancestry, others, like the Neapolitan mastiff, bullmastiff, and the St. Bernard, have no detectable wolf ancestry. Wolf ancestry is also found in a wide range of dog breeds outside of these correlations, including in the tiny chihuahua, which has about 0.2 percent wolf ancestry.
"This completely makes sense to anyone who owns a chihuahua," Lin said. "And what we've found is that this is the norm—most dogs are a little bit wolfy."
The research team also compared how often personality terms are used by kennel clubs to describe dog breeds with the highest and lowest levels of wolf ancestry. The descriptor most associated with low wolf-ancestry breeds was "friendly," followed by "eager to please," "easy to train," "courageous," "lively," and "affectionate." In contrast, high wolf-ancestry dogs are more often described as "suspicious of strangers," as well as "independent," "dignified," "alert," "loyal," "reserved," and "territorial." Other descriptors, including "intelligent," "obedient," "good with children," "dedicated," "calm," and "cheerful" occurred with similar frequency in both groups of dogs. The team stressed that these traits are biased assessments of breeds' behaviors, and it is not known if wolf genes are directly responsible for these characteristics, but this finding opens paths for future research in dog behavioral science.
In addition, the study uncovered important adaptations that dogs have accessed through wolves, including: enriched wolf ancestry at olfactory receptor genes in village dogs, who depend on the ability to sniff out human food waste; and the distribution of a Tibetan wolf-like gene that helps Tibetan mastiffs tolerate low oxygen conditions in the Tibetan Plateau and the Himalayas.
"Dogs are our buddies, but apparently wolves have been a big part of shaping them into the companions we know and love today," said study co-author Logan Kistler, curator of archaeobotany and archaeogenomics at the National Museum of Natural History. "Through the years, dogs have had to solve all kinds of evolutionary problems that come with living with humans, whether it's surviving at high altitude, searching for their next meal as they freely roam a village, or protecting the herd, and it seems like they use wolf genes as part of a toolkit to continue their evolutionary success story."
Other study authors include Regina Fairbanks, from the University of California, Davis; Jose Barba-Montoya, from the American Museum of Natural History; and Hsiao-Lei Liu, from the National Museum of Natural History and University of Stockholm.
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