While that chihuahua might seem about as similar to a wolf as a shrub is to a mighty redwood tree, some small breeds like the tiny, big-eared chihuahua have some wolf ancestry.
New research published today in the journal Proceedings of the National Academy of Sciences (PNAS), finds that the majority of dogs living today have low but detectable levels of post-domestication wolf ancestry. These genes have likely helped shape multiple characteristics, including personality traits, sense of smell, and body size. This newly discovered gene flow may have given canines a unique survival advantage in human environments.
“Modern dogs, especially pet dogs, can seem so removed from wolves, which are often demonized,” study co-author Audrey Lin from the American Museum of Natural History in New York City, said in a statement. “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.”
Man’s best friend
About 20,000 years ago (the late Pleistocene), dogs evolved from a now extinct population of gray wolves that came under human influence. Wolves and dogs that live in the same geographic regions can produce fertile offspring.
However, hybridization—interbreeding between two animals of different species—is considered rare. With a few exceptions of intentionally crossbred wolves and dogs, there is little genetic evidence of gene flow between these 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.”
Diving into the wolf-dog gene flow
In this new study, the team explored historical dog-wolf gene flow using over 2,700 published genomes from wolves, breed dogs, village dogs, and other canids from late Pleistocene up to the present. Almost two-thirds of breed dogs have wolf ancestry within their complete genome from crossbreeding that occurred roughly 1,000 generations ago. Additionally, all of the genomes analyzed from free-roaming dogs that live in or near human settlements called village dogs carry detectable wolf ancestry.
Czechoslovakian and Saarloos wolfdogs have the highest levels of wolf ancestry. These breeds were purposefully bred through hybridization with wolves and modern dogs have wolf ancestry in 23 to 40 percent of their genomes.
Among breed dogs with a well documented lineage, the dogs with the highest amount of wolf ancestry are the Anglo-French tricolour hound (between 4.7 and 5.7 percent wolf ancestry) and the Shiloh shepherd (2.7 percent wolf ancestry). The Shiloh shepherd originated from breeding efforts with wolfdogs or other recent dog–wolf hybrids, with the goal of creating healthier, more family-friendly shepherd dogs in the United States. However, the origin of the extensive wolf ancestry seen in the Great Anglo-French tricolour hounds is unknown.
The Tamaskan, a breed that originated in the United Kingdom during the 1980s by selecting genes from huskies, malamutes, and other breeds, has about 3.7 percent wolf ancestry.
Critical leftovers
Several patterns emerged from this nearly 20,000 years of dog data. Wolf ancestry is higher among larger dogs and in those that are bred for certain types of work. These include Arctic sled dogs and hunting dogs.
On average, terriers, gundogs, and scent hounds have the least wolf ancestry. While some large guardian dogs have high wolf ancestry, others including 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 chihuahuas. They have 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.”
Those leftover wolf genes may also be responsible for some important adaptations. Village dogs who survive on their ability to sniff out human food show enriched wolf ancestry in their olfactory receptory genes. The distribution of a wolf-like gene also helps Tibetan mastiffs tolerate the 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,” added study co-author Logan Kistler from the National Museum of Natural History in Washington D.C. “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.”
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