Shih tzus, malteses, chihuahuas and other small dogs all have a common ancestor: the Middle Eastern gray wolf.
About 12,000 years ago, the small, domesticated canines diverged from gray wolves native to the areas in the Fertile Crescent, according to a study by a UCLA alumna published last week in Science, a premier scientific journal.
Melissa Gray, a former graduate student of ecology and evolutionary biology at UCLA, and her adviser, Robert Wayne, analyzed a specific variation present in the gene most responsible for reduced growth in lap dogs.
“We found that there was a great similarity in the genetic variance of Insulin-like Growth Factor-1 found in gray wolves in the Middle East and dogs,” said Gray, who is currently a postdoctoral fellow at the University of Wisconsin-Madison.
This specific variation in the gene is virtually absent in large dogs, or those more than 30 kilograms. However, all dogs weighing less than 9 kilograms possessed this unique mutation, she said.
“We wanted to know which wolf population had the closest gene variation to small dogs,” said Wayne, a professor of evolutionary biology at UCLA.
The experiments led the scientists to the specific gray wolf that still resides mainly in the regions of Iraq and Israel. However, larger dogs may have originated elsewhere.
According to Gray, the mutation that differentiated small dogs from larger dogs occurred early in dog history, but most likely after their divergence from wolves and their domestication.
“Hunter-gatherers liked this small size for whatever reason, so they selected for (the trait) by breeding the small dogs,” Gray said.
The study was based on the findings of a 2007 study exploring the size variation in dogs. The study concluded that IGF-1 was the prominent factor in determining the size of a canine, defined as a dog-like carnivore.
“The important thing to understand is that (IGF-1) is not the only gene that regulates body size,” Gray said. “But it is the one that results in either really large or really small dogs.”
Overall, Wayne’s lab focuses on the study of the Canidae family, which includes more than 35 species of animals such as dogs, foxes, wolves, coyotes and jackals. He conducts experiments to understand the genetic differences among the species and analyzes the dog genome in particular.
“Dogs were one of the first mammals with a complete genome, which was published in 2005,” Wayne said. “In the future we can sequence entire genomes of individual dogs and learn more about their behaviors.”
The findings of this study may help scientists understand both dogs and humans better, Gray said.
“Domesticated dogs are a great model species for biomedical research and medicine,” she said. “What we know about IGF-1 can be used to study obesity or cancerous growths.”
Overall, studying dogs can lead to beneficial findings in the future, Wayne said.
“We (humans) share a lot of genetic diseases with them,” he said. “Some of the greatest gene therapy was pioneered in dogs, so there are many things we can do with this information.”