Is your dog frightened by a plastic bag flapping in the wind? When a stranger comes to the door, is he barking, hiding or looking for you? Does he hunt squirrels?
A study that combined 46,000 answers to these and other questions with DNA sequences from more than 4,000 dogs — including domestic and wild dogs — identified genetic variants linked to characteristic dog behaviors.
It’s a Herculean effort to unravel the complicated genetics woven through hundreds of years of dog breeding, and to catalog the genetic changes — many of which are involved in neurodevelopment — behind the behavioral characteristics of different breeds.
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“There are about 350 recognized dog breeds in the world, and each is a different story,” says geneticist Elaine Ostrander of the US National Human Genome Research Institute in Bethesda, Maryland, and author of the study, which is published on December 8 in Cell1. “You can’t just herd them like you would with humans.”
Each of these unique stories has left its mark on the genomes of specific breeds. Some breeds are heavily influenced by a particular male who did well at a dog show and whose semen was frozen and widely distributed. Others might have been influenced in a different way: for example, the populations of some large breeds of dogs declined dramatically during times of war or famine, when there was not enough food to sustain them. Sometimes breeders then mixed different canine lines in an attempt to reintroduce lost characteristics into the remaining population.
The complexity of these stories makes it difficult to trace the genetic origins of behavioral traits, so Ostrander and his colleagues decided to do away with conventional breed categories and instead use DNA sequences to group dogs into genetic lineages. . The team analyzed the DNA of nearly 4,300 dogs, including 2,800 purebreds covering 226 officially recognized breeds. The approach – which also included DNA from mixed-breed dogs, semi-wild dogs and wild canids from four continents – yielded ten distinct lineages.
From there, Ostrander and his colleagues turned to behavioral surveys collected from owners of more than 46,000 purebred dogs to map behavioral traits across bloodlines. Members of the terrier line, for example, tended to show predatory and aggressive behavior towards other dogs, while small dogs tended to be nervous.
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An analysis of DNA sequences associated with these behaviors has identified a number of variants linked to the development of the nervous system. For example, variants common in sheepdogs – bred for their herding instincts – have highlighted a molecular pathway involved in forming connections between nerve cells. Previous studies have shown a link between two genes involved in this pathway and the behavior in which female mice herd their young tightly, suggesting herding may have evolutionary roots in maternal actions to protect offspring.
The findings are an exciting advance in understanding relationships between canine lines, says geneticist Elinor Karlsson of Chan Medical School at the University of Massachusetts Worcester. Earlier this year, Karlsson released data showing that breed is a poor predictor of a dog’s behavior.2.
“It’s been a real struggle in canine genetics,” she says. “It’s starting to go beyond the idea of comparing one breed to another and really looking at how the behavior matches the ancestry of the dogs.”
This study focused on small changes in DNA sequences, such as single letter changes and small DNA deletions or insertions. According to canine geneticist Adam Boyko of Cornell University in Ithaca, New York, future studies could look at other forms of genetic variation, such as larger deletions or rearrangement of chromosomal segments.
As such studies continue to map the genetics underlying dog behavior, it is hoped that the results can inform research into neurodiversity and the biological basis of human behaviors, Boyko says. “It gives human researchers the ability to start generating hypotheses that you might not otherwise have in the absence of this big model.”
Since dogs and humans often share a home, such studies could be helpful in understanding how environment shapes disease risk. “At the end of the day, dogs and humans are probably more similar to each other than they are different, if you look at the whole spectrum of animal evolution,” says Karlsson. “We can totally understand each other for most things.”
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