Dog breeds tend to have signature traits: Border collies love to herd, greyhounds love to chase, and German shepherds make good guard dogs.
There’s a reason for that: Traits like these are highly heritable, according to a study of 101 dog breeds that identifies genetic differences in behavior.
The study , published Oct. 2 in the Proceedings of the Royal Society B, points to 131 genetic variants, and offers new evidence to support what scientists have long suspected: that some of the behaviors that help characterize breeds - a drive to chase, for example, or aggression toward strangers - are associated with distinct genetic differences among them.
"Dogs present a good model for understanding what portion of the variation in their behavior is attributable to differences in genetics, and how much to their environment and experiences," said Noah Snyder-Mackler , an assistant professor of psychology at the University of Washington and a co-author of the study.
Most dog breed diversity has arisen in the last few centuries. People have bred dogs for their looks, but the bulk of breeding efforts have taken aim at eliciting particular behaviors, said James A. Serpell, a professor at the University of Pennsylvania’s School of Veterinary Medicine.
"If you look at the evolution of the dog, selection has been primarily for behaviors: hunting behaviors, guarding behaviors, or giving companionship to humans," said Serpell, the study’s senior author.
What seems obvious - that genes can influence an individual’s behaviors - has not always been easy to support with evidence, in large part because behaviors are complex traits, the researchers said.Tendencies such as aggression, anxiety, or a compulsion to chase anything that moves are governed by many genes, not just one.
But dog breeds, being highly inbred, have allowed researchers to make progress in this area. Snyder-Mackler and the research team recognized that, if a dog breed is associated with a particular behavior that distinguishes it from other breeds, it might be easier to detect the genetic variants contributing to that behavior if that breed’s genome was compared to a host of others.
The team used data from C-BARQ, short for Canine Behavioral Assessment and Research Questionnaire, a survey that more than 50,000 dog owners have filled out about their pets. C-BARQ returned a result on 14 behavioral "factors" about each dog surveyed, giving a measure of traits such as stranger-directed aggression, excitability, energy level, and predatory chasing drive.
For this study, the researchers pulled 14,020 of those entries that included information about purebred dogs. To look for associations with genetics, they borrowed data from two earlier studies, together representing 5,697 dogs, for which 172,000 points in the genome had been sequenced.
They found that about half of the variation in the 14 measured behaviors across breeds could be attributed to genetics - a greater proportion than previous studies have found.
The traits with the highest rates of heritability - in other words, those that seemed to be most influenced by genetic factors rather than environmental ones - were behaviors such as trainability, predatory chasing, stranger-directed aggression and attention seeking. For these traits, genetics explained 60 to 70 percent of variation across breeds.
"These are exactly the types of traits that have been selected for in particular breeds of dogs," said Serpell. "So for trainability, you’re thinking of breeds like border collies that have to respond to human signals to accomplish complicated tasks; for chasing behavior you can think of something like a greyhound, which is innately predisposed to chase anything that runs; and for stranger-directed aggression you might focus on some of the guard dog breeds that are highly protective and tend to respond in a hostile way to unfamiliar people."
When the researchers looked for genetic variants associated with breed differences in the 14 C-BARQ traits, they found 131 variants tightly linked to these behaviors. Some were located in genes that have been implicated in influencing behavior, including in humans. But many were unknown and provide fodder for future study.
"This gives us an encouraging start and places to look," said lead author Evan MacLean of the University of Arizona. "We have ongoing projects where we’ve obtained genetic and behavioral data from the same individuals, so we’ll be able to dive deeper into some of these traits and variants to see if the patterns we found here hold up."
As a final step, the team looked to see where the genes in which key variants appeared were expressed in the body. Their analysis showed the genes were much more likely to be expressed in the brain than in other tissues.
The researchers’ results also leave plenty of room for individual differences and an animal’s environment in influencing behavior.
"It’s important to keep in mind that we looked at breed averages for behavior," Snyder-Mackler said. "We’re not at a point yet where we can look at an individual’s genome and predict behavior. Environment and training still has a very, very strong effect."
Bridgett vonHoldt of Princeton University was a co-author.