Breeders of purebred dogs select them largely for their looks. Golden retrievers are yellow and shaggy; basset hounds are short with long ears. But Alaskan sled dogs are selected to be fast, tough, and hard working. That's been enough to make them a distinct breed, according to a new genetic study.
When Heather Huson was growing up in Pennsylvania, her stepfather went to see a sled dog race and fell in love with the sport. "I started racing when I was 7," she says. Her family moved to upstate New York when she was a teenager because it had better snow. Now she's a graduate student in genetics at the University of Alaska, Fairbanks—but she's still interested in sled dogs.
Huson was interested in studying the genetics behind performance in her beloved animals. For this study, Huson visited eight kennels—four that specialize in distance races like the Iditarod, and four that specialize in sprints, races of 5 to 50 kilometers that last only a few hours. All of them use Alaskan sled dogs. Huson, who trained as a veterinary technician before graduate school, drew blood from a total of 199 dogs—"easier than trimming toenails," she says—and she or someone at the kennel ran each dog and scored its speed, endurance, and work ethic (i.e., how much of the run it was actively pulling as opposed to letting its teammates do the work).
Alaskan sled dogs seem like they shouldn't have much in common genetically. They look different—they can be long-haired or short-haired, floppy-eared or perky-eared, 13 or 30 kilograms. And though breeders of distance dogs tend to stick to other Alaskan sled dogs, sprint-dog breeders mix in other breeds, like English pointers, shorthaired pointers, and even greyhounds. But Huson found much more commonality than she anticipated.
To figure out which breeds the dogs were most closely related to, Huson analyzed microsatellites, small, repeating sequences of DNA. In earlier work, one of her co-authors had figured out patterns of microsatellites that identify each of 141 purebreds. Huson expected that sled dogs' microsatellites would group them with Siberian huskies or Alaskan malamutes, the breeds that were their most likely ancestors. But instead, they formed "their own little genetic group," she says—essentially a breed of their own, as unique as poodles or corgis. Although the microsatellite patterns of one sled-pulling mutt might include his pointer grandpa and Siberian forebears, most of the microsatellites represented the unique Alaskan sled dog pattern. "This is saying, 'Here's another genetic breed of dog, but they were selected for and bred based on performance,' " not on looks, Huson says. The study will appear online tomorrow in BMC Genetics.
Huson also determined which breeds brought different attributes to the dogs. Dogs with a lot of malamute and husky blood had more endurance; those with ancestors that were pointers and salukis were speedier.
Don't look for the Alaskan sled dog at the Westminster Kennel Club dog show anytime soon, though. The people who breed these dogs use them for work and have no particular interest in lobbying the American Kennel Club to recognize them as purebreds, Huson says.
The conclusion that sled dogs represent their own breed is unexpected, says evolutionary biologist Robert Wayne of the University of California, Los Angeles. "It was a bit of a surprise to find that they're distinct from everything else." The work, he notes, should lead the way to finding genes behind a variety of behaviors in these dogs, like the willingness to pull a sled.