New York’s Central Park has a statue dedicated to him, and there’s even been a movie about him: a sled dog named Balto. Now he is the focus of a DNA study, 90 years after he died, to look at how he differs from current sled dogs.
The quick history of Balto
In 1925, this Siberian husky was part of an expedition in Alaska called the serum run, the goal of which was to bring life-saving medicine to young people in the remote town of Nome that were threatened by diphtheria.
The mission in horrendous blizzards conditions involved a series of sled dog teams transporting the anti-toxin relay-style from the city of Anchorage. Balto led the dog team that covered the last stretch of the grueling journey. There’s another dog, Togo who pulled the sled for 261 miles of the journey vs. 56 for Balto. Balto’s fame arose due to him being the dog who lead the last team on the last leg into Nome.
The dog died in 1933, and its mounted body has been on display at the Cleveland Museum of Natural History ever since.
“Balto’s fame and the fact that he was taxidermied gave us this cool opportunity 100 years later to see what that population of sled dogs would have looked like genetically and to compare him to modern dogs,” said Katherine Moon, a postdoctoral researcher at the University of California, Santa Cruz and the main author of the study.
Her team took skin samples from the dog’s belly and reconstructed its genome—the complete set of genes in an organism.
They compared this genetic material with that of 680 contemporary dogs from 135 breeds.
Contrary to a legend that held that Balto was half wolf—as suggested in an animated Universal Pictures film that came out in 1995—this analysis found no evidence he had wolf blood.
It turned out Balto shared ancestors with modern day Siberian Huskies and the sled dogs of Alaska and Greenland.
Zoom’s team also compared Balto’s genes with the genomes of 240 other species of mammals as part of an international effort called the Zoonomia Project.
This allowed researchers to determine which DNA fragments were common across all those species and have not therefore changed over the course of millions of years of evolution.
This stability suggests that these stretches of DNA are associated with important functions in the animal, and that mutations there could be dangerous.
The Details of the Study
The bottom line from the research was that Balto had fewer potentially dangerous mutations than modern breeds of dogs did, suggesting he was healthier.
The origins of the project actually go back a few years. Heather Huson, a champion sled dog racer turned Cornell University animal geneticist, was giving a talk at a meeting of sled dog veterinarians when one of the vets in the audience wondered if it would be possible to extract and analyze DNA from preserved hide. He even had a potential study subject in mind — Balto, whose taxidermied body is displayed in a glass case at the Cleveland Museum of Natural History.
Huson was hooked on the idea. “I grew up on the stories about Balto,” she recalls. But she had no experience working with old DNA, “and I wasn’t going to screw this up,” she says. So she reached out to the ancient DNA research community. The path quickly led to Beth Shapiro, a pioneer in revealing the genetic secrets of extinct creatures like mastodons and of ancient humans in the field called paleogenomics. “I reached out to Beth, and she said, ‘We can do this,'” says Huson.
The researchers got a sample of Balto’s skin from the Cleveland Museum and extracted the dog’s DNA from the sample. Moonthen did the heavy genetic lifting in UC Santa Cruz’s high-tech ancient DNA lab, reading the code of Balto’s snippets of DNA enough times to cover his entire genome 40 times over.
Normally, scientists would learn about the genetics of a species in part by looking at genetic variations among different individuals. Balto was just one individual, though, so “the challenge was how to make a research project out of one dog,” says Huson. But the team had an ace up their sleeve. In addition to being able to compare the sled dog’s genome to the 240 mammals in the Zoonomia Project, they also could tap a genetic repository created by the Broad Institute’s Karlsson that has complete genomes of 682 dogs from a wide variety of breeds. “It’s an incredible dataset,” says Moon. Because of the information it contains “we know so much about dogs — what parts of the genome make them look the way they do or perform the way they do,” Moon explains. Or as Shapiro adds, the Balto project “was an opportunity to bring these two datasets together.”
There were plenty of other scientific nuggets in Balto’s DNA as well. Born in the kennel of famous sled dog breeder Leonard Seppala in 1919, Balto was descended from dogs imported from Siberia. “But one of the coolest things is how close Balto is to modern Alaskan sled dogs as well as to the Siberian husky,” says Huson. His genome shows a mix of ancestors, with fewer deleterious genes compared to modern purebred breeds like Siberian huskies and Alaskan Malamutes. His DNA is also rich in so-called tissue development genes, which are involved in functions like muscle growth, metabolism, and oxygen consumption. “That’s exactly what you would need in a working dog,” says Moon.
Yet the genetics also reveal Balto’s limitations. Sled dogs were originally bred for great endurance, but since Balto’s time, breeders added in more speed. “Balto might have been a tough sled dog with a lot of endurance, but he wouldn’t have been very fast,” says Huson.
In fact, sled dog experts know that Balto wasn’t actually the real hero of the lifesaving 1925 journey. That honor belongs to a dog named Togo, who led Seppala’s team on the longest leg of the 674 mile trek, an astonishing 264 miles (compared to Balto’s 53 miles on the final segment). “Balto was the 2nd string dog,” says Huson. Not being prime progenitor material, he was neutered, in contrast to Togo, “who is the dog — the foundation of a lot of sled dogs,” says Huson. So, the next step, she suggests, is getting a sample from Togo’s remains, now preserved in Nome, in order to reveal the next chapter in this canine genetic drama.
Source: Science Daily – April 27, 2023