UMass Chan study shows canine behavior is only slightly influenced by breed

A UMass Chan Medical School study of more than 2,000 purebred and mixed breed dogs, published today in Science, suggests that behavioral traits in dogs are not breed specific. This means, for example, that a golden retriever is only slightly more likely to be friendly than another breed.

“Although ‘friendliness’ is the trait we commonly associate with Golden Retrievers, we have found that the defining criteria of a Golden Retriever are its physical characteristics – the shape of its ears, the color and quality of its fur, its size — not whether it’s friendly,” said lead author Elinor Karlsson, PhD, associate professor of molecular medicine at UMass Chan and director of the Vertebrate Genomics Group at the Broad Institute of the Massachusetts Institute of Technology and the University from Harvard. “Although genetics plays a role in any dog’s personality, a specific breed of dog is not a good predictor of these traits.”

Kathleen Morrill and Elinor Karlsson, PhD

Canine behavioral disorders are often proposed as a natural model of human neuropsychiatric disorders. Compulsive disorders, for example, are often observed to manifest similarly in humans and dogs. Thanks to the power of DNA sequencing technology and the close relationship between pet dogs and their owners who are able to describe in detail the behavioral traits of their dogs, association studies at the scale of the genome in dogs have the potential to identify unique genetic areas in the dog genome. this could lead to new insights into similar genes in humans. Karlsson and colleagues show that large-scale, genome-wide association studies in dogs can yield genetic loci associated with behavioral traits.

Genome-wide association studies are an approach used in genetics research to try to associate specific areas of variation in a genome that correspond to certain phenotypes. Taking whole genome sequences from hundreds of thousands of people with the same disease, for example, allows researchers to identify large areas of the genome that may be predictive or causative of specific diseases.

the Science the research, which included data from more than 18,000 surveys of owners of their dogs, as well as results from genome-wide association studies from canine DNA samples submitted by owners of dogs, identified 11 locations along the canine genome that were strongly associated with behavior: surprisingly, none were breed-specific.

“A dog’s personality and behavior are shaped by many genes as well as their life experiences. This makes them difficult to breed for,” Dr. Karlsson said. “For the most part, pure breeds are only only subtly different from other dogs. A golden retriever is only slightly more likely to be friendlier than a mixed breed dog or another purebred dog, such as a dachshund.

The history of the emergence of modern dog breeds is relatively short in terms of evolution, in contrast to the history of the domestication of dogs by prehistoric wolves. Genetic research places the transition from wolf to dog around 10,000 to 15,000 years ago. Humans only began intentionally breeding dogs 2,000 years ago when they were selected for professional roles such as hunting, guarding and herding. It wasn’t until the 1800s that humans began to consistently select dogs for the physical and aesthetic characteristics we now associate with modern “pure” breeds.

Yet modern dog breeds are often credited with characteristics and temperaments (bold, affectionate, friendly, trainable) that match their ancestral function (guardian, warden, or hunter). Similarly, the racial ancestry of dogs is believed to be predictive of temperament and behavior. DNA testing is marketed as a tool for dog owners to learn more about an animal’s individual personality. However, there are few genetic studies that attempt to map behavioral tendencies to ancestry or inherited genetic factors.

By combining genome-wide association mapping technologies with pet owner surveys obtained through Darwin’s Ark, an open-source database of owner-reported canine traits and behaviors, Karlsson and the first author Kathleen Morrill, a doctoral student in the Morningside Graduate School of Biomedical Sciences at UMass Chan, explored the complicated relationship between modern canine breeds and behavioral characteristics.

Karlsson, Morrill and their colleagues sought to correlate areas of the canine genome with certain traits or behavioral characteristics. Pet owners who participate in Darwin’s Ark provide scientists with DNA samples from their dogs, obtained from saliva. Researchers are performing whole genome sequencing on these samples to generate a robust genetic dataset for investigation. For this study, owners completed 12 surveys totaling 117 questions about their pet’s behaviors and physical traits. Combined, this data provides scientists with the basis for assessing the relationship between genetics and owner-reported behavior.

“Given a large enough sample size, genome-wide association studies are a really powerful tool for learning more about genetics,” Morrill said. “We only get this sample size by looking at all dogs, not just purebred dogs but also mixed breed dogs. We compare all of these DNA sequences by calculation to identify areas of difference and commonalities that might be of interest.

Karlsson and Morrill collected over 2,000 canine genome samples and 200,000 survey responses through Darwin’s Ark. Because of the powerful stereotypes that exist about dog behavior and breeds, Karlsson and Morrill designed the study to account for possible owner bias, in part by establishing standard definitions for reporting and assessing canine behavioral traits such as that submissiveness (a dog’s response to human direction), dog-human sociability (a dog’s comfort with people, including strangers), and toy-directed motor patterns (interest and interaction of a dog with toys), among others. The physical and aesthetic trait standards were based on those published by the American Kennel Club.

Behavioral data were analyzed through the breeds declared by the owners and the ancestries of the genetically detected breeds. The results of these tests, which included data from 78 breeds, showed that while breed explained minor variation in behavior, the contributions of breed were relatively small (9%). For some behavioral traits, such as toy-directed motor patterns, age was a better predictor of behavior: younger dogs were more likely to score higher in this category. Physical traits like coat color were more than five times more likely to be predicted by breed than behavioral traits.

Additionally, investigators failed to find any behaviors exclusive to a particular breed. Even among Labrador retrievers, which had the lowest propensity to howl, 8% of owners said their Labradors sometimes howled. Similarly, while 90% of greyhound owners said their dogs never bury their toys, three owners described greyhound dogs as frequent burials.

The researchers also exploited the genetic ancestry of highly mixed-breed dogs to test whether the behavior is hereditary in a breed-dependent way. In some cases, inherited behavioral traits such as submissiveness are a little more likely to correlate with race, even if mixed a few generations ago. In the case of purebred dogs, ancestry can make behavioral predictions a bit more accurate. For less hereditary and less breed-differentiated traits, such as how easily a dog is provoked by frightening or annoying stimuli, breed is almost useless as a predictor of behavior.

In all, Karlsson and Morrill identified 11 locations on the dog genome strongly associated with behavioral differences, none of which were breed-specific; and 136 others suggestively associated with the behavior. Genetic differences between breeds such as Golden Retrievers, Chihuahuas, Labrador Retrievers, German Shepherds and others have primarily affected genes that control coat color, fur length and other physical traits – much more than race differences affected behavioral genes.

“The majority of behaviors that we consider to be characteristics of specific modern dog breeds are most likely the result of thousands of years of evolution from wolves, to wild dogs, to domestic dogs, and finally to modern breeds,” said Karlson. “These inherited traits predate our concept of modern dog breeds by thousands of years. Each breed inherited the genetic variation carried by these ancient dogs, though not always at exactly the same frequencies. Today, these differences manifest by personality and behavioral differences observed in some dogs of the same breed, but not all.

Current articles related to UMass Chan:
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LISTEN: Elinor Karlsson explains how dog DNA helps human research

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