Your nearest Chihuahua may appear so distant in appearance to its wolf-like ancestors that they might as well be entirely different animals, but their cute veneer hides select genes that brought about their “toy-like” appearance—and if recent studies are anything to go by, they might actually be a link to their distant wolven past.
The study in question, which was published in the journal Current Biology, gathered their necessary data from the National Institutes of Health (NIH) through the institution’s National Human Genome Research Institute (NHGRI) Dog Genome Project (DGP), a citizen science project which focuses on the health and body structure in the domestic dog (Canis lupus familiaris) across all its breeds by having owners collect DNA samples of their pet dogs.
From there, the team of scientists responsible for the study located the genetic mutation responsible for small dog breeds like Chihuahuas and Pomeranians, and found them within the insulin-like growth factor 1 (IGF1) gene. Thing is, after cooperation with other researchers from England and Germany, the scientists there also found IGF1, but this time in 54,000-year-old DNA sourced from Siberian wolves (Canis lupus campestris). Additionally, the mutation can also be found in other living canids, like golden jackals (Canis aureus) and coyotes (Canis latrans).
“It’s as though nature had kept it tucked in her back pocket for tens of thousands of years until it was needed,” said senior author and NIH geneticist Elaine Ostrander, who specializes in dogs, in an official statement.
To be specific, the mutation lies near the IGF1 gene section of canine DNA, which when expressed can influence the body size of the dog as it grows up. Alleles, or variants of the gene, from dog parents can include either an extra cytosine (C) or thymine (T) base, which express a small or large body size respectively. Once a dog inherits two alleles of the gene from both its parents, it may then end up with different combinations of alleles: CC, CT, or TT.
The research team found a major correlation between these allele combinations and dog sizes: “CC” yielded small dogs like the aforementioned “toy” breeds; “CT” led to medium-sized dogs; and “TT” was strongly correlated with larger dogs.
“We were surprised to find the mutation and delighted to find that both variants [C and T] were present over 54,000 years ago,” Ostrander told LiveScience, noting how the same IGF1 mutation was found in both ancient Siberian wolf DNA and in the DNA of modern-day jackals and coyotes, which all possessed the CC allele combination (two copies of the C allele).
Ostrander and the team also noted that the petite nature of dog breeds around today would never have been achieved naturally, and was thus partially due to human domestication and breeding. Ostrander added to this by saying “[the] small allele was maintained at a low level for tens of thousands of years until it was selected on during or around the time of domestication.”
It must be noted, however, that the IGF1 gene is not solely responsible for dog body sizes; the gene joins a 20-strong list of genes that are known to express body size in canines, much like how hundreds of genes do a similar function in humans.
The team notes that future studies on the topic will include an analysis of the proteins produced by these special dog size genes to determine how they work together to create “big dogs, little dogs, and everything in between,” according to Ostrander.
(For more dog news, read about how their cute head tilts may be a sign of concentration and brain activity.)
References
- Baker, H. (2022, January 27). Gene mutation that helps make ‘toy’ dog breeds so small existed in wolves 54,000 years ago. LiveScience. https://www.livescience.com/small-dog-gene-found-in-ancient-wolves
- Cell Press. (2022, January 27). Gene mutation that makes dogs small existed in ancient wolves. EurekAlert! https://www.eurekalert.org/news-releases/940745
- Plassais, J., von Holdt, B. M., Parker, H. G., Carmagnini, A., Dubos, N., Papa, I., Bevant, K., Derrien, T., Hennelly, L. M., Whitaker, D. T., Harris, A. C., Hogan, A. N., Huson, H. J., Zaibert, V. F., Linderholm, A., Haile, J., Fest, T., Habib, B., Sacks, B. N., … Ostrander, E. A. (2022). Natural and human-driven selection of a single non-coding body size variant in ancient and modern canids. Current Biology, 0(0). https://doi.org/10.1016/j.cub.2021.12.036
