Humans have been selectively breeding dogs for thousands of years to perform tasks like guarding, hunting, and companionship. Research has investigated the links between the genetic influences on dog domestication or the genes underlying very specific historical dog roles, such as dogs that flush game out for their owner's hunts versus dogs that track and kill vermin on their own. Now researchers have investigated the genetics of behavioral traits that are seen in many different kinds of dogs.
Reporting in Cell, scientists assessed DNA from more than 200 breeds of dogs and almost 50,000 self-reported questionnaires from dog owners. This work has revealed many genes that are connected with the behaviors of certain breeds.
Senior study author Elaine Ostrander, founder of the Dog Genome Project at the National Human Genome Research Institute, noted that humanity's most successful experiment in genetics is the development of 350 dog breeds. Our survival has depended intimately on their ability to guard, herd, and hunt, she said.
People have also selected certain characteristics in dogs, such as how they look, which can complicate investigations of the genetics underlying behaviors, said first study author Emily Dutrow, a postdoctoral fellow at the National Human Genome Research Institute.
Whole-genome sequences from 4,000 dogs that were semi-feral, mixed-breed, and purebred were analyzed along with DNA from wild canines. The researchers found ten major genetic lineages that each corresponded to a breed of dog used for some task, such as protecting livestock. This suggested that there are common gene sets that are shared among dog breeds that are suited to similar tasks. he terrier lineage has breeds that have been used to catch and kill prey, and displays behaviors linked to increased prey drive, for example. Similarly, Pitbulls were originally bred for bull-baiting and bear-baiting, which were popular blood sports in England in the 19th century. Later, they were also used for dogfighting, although this practice is now illegal in many countries.
The behavioral tendencies were associated with major canine lineages, and the researchers found the genetic drivers underlying those behaviors with a genome-wide association study.
"We were particularly interested in livestock-herding dogs, who display one of the most easily defined breed-typical behaviors, characterized by an instinctive herding drive coupled with unique motor patterns that move herds in complex ways," said Dutrow.
Herding dogs were found to carry certain gene variants that are involved in axon guidance, which helps shape brain circuitry. These were highly enriched, along with genes that relate to social cognition and fear reactions.
"When you get a certain input or stimulus, the degree to which that creates a reaction in different parts of the brain shapes how we behave," said Ostrander. "So, if nerves within and between brain regions don't communicate in specific ways, then the behavior doesn't happen, and this is where axon-guidance genes come in to play."
A gene associated with sheep dogs, EPHA5, has also been linked to anxiety-like behaviors in animals, and could help explain why these dogs are so active and become hyper-focused on tasks. Humans and dogs may share "the same genetic toolkit," added Dutrow.
"After 30 years of trying to understand the genetics of why herding dogs herd, we're finally beginning to unravel the mystery," added Ostrander.
Sources: Cell Press, Cell
