Why do dogs vary more in size than any other mammal species on the planet? The answer lies in ancient wolves, specifically in the IGF1 gene and its mutation.
Researchers identified IGF1 in 2007 as a gene with a major role in the size variability of domestic dogs, but efforts to identify the responsible gene mutation had been unsuccessful.
Ancient dogs, which were domesticated from wolves over the past 30,000 years, varied in size. But the current large differences in size - the largest breeds are up to 40 times larger than the smallest - emerged in the past 200 years.
Researchers analyzed the genomes of more than 1,400 dogs, including ancient dogs, wolves, coyotes and 230 modern dog breeds. They identified two variants in a section of DNA that are involved in controlling levels of the protein IGF1, a powerful growth hormone.
Across all breeds, dogs with two copies of one variant tended to weigh less than 15 kilograms, while two copies of the other version were more common in dogs weighing more than 25 kilograms. Dogs with one copy of each variant tended to be medium-sized,
But which came first? The Mastiff or the Chihuahua?
Researchers believe that the gene linked to small dogs is, evolutionarily speaking, much older than the gene found in large dogs. It's not clear when the large-bodied version evolved. Researchers found that an ancient wolf that lived in Siberia 53,000 years ago carried a copy of this version.
In the past, the prevailing view among scientists was that small body size was likely related to relatively new genetic changes, possibly unique to domestic dogs, and the latest research is turning that whole story upside down.
The researchers warn, however, that knowledge regarding the size of dogs is still fragmentary and they do not refer to a mutation that makes a wolf have the body of a Chihuahua but to a slow genetic process with small variations.
Source: Scientific American
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