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For millennia, the massive Tibetan mastiff has laid literal claim to the label "top dog."
The fierce breed, which boasts a lionesque mane and can reach 150 pounds, has long protected Himalayan flocks of sheep from Tibetan wolves and other predators lurking upward of 15,000 feet above sea level—heights no other canine can survive.
Prior - Research - Tibetan - Mastiff - Shortcut
Prior research suggests the Tibetan mastiff took an evolutionary shortcut by breeding with the Tibetan wolf, which had already adapted to the altitude by evolving more efficient hemoglobin: the protein that snares oxygen in the bloodstream and distributes it to organs.
The University of Nebraska–Lincoln's Jay Storz, Tony Signore and colleagues have now determined that sleeping with the enemy granted the Tibetan mastiff a hemoglobin architecture that catches and releases oxygen about 50 percent more efficiently than in other dog breeds. Signore reached the conclusion after testing the Tibetan mastiff hemoglobin against that of multiple domestic breeds, including Storz's own half-Great Pyrenees, half-Irish wolfhound.
Altitude - Problem - Oxygen - Signore - Researcher
"At altitude, the problem is taking in oxygen, because there's just less of it," said Signore, a postdoctoral researcher working in Storz's lab. "If you think of hemoglobin like an oxygen magnet, this magnet's just stronger."
The Nebraska researchers, who collaborated with colleagues at Qinghai University in China, already knew that the Tibetan mastiff's hemoglobin included changes in two amino acids—slight modifications to the structure of the protein—that are present in the Tibetan wolf but absent in all other dog breeds.
Engineering - Hemoglobins - Acid - Mutations - Team
By engineering and then testing hemoglobins that contained both amino acid mutations vs. just one or the other, the team discovered that both mutations are crucial to the adaptive change in hemoglobin performance. When either mutation was absent, the hemoglobin performed no differently than that of other dog breeds.
"There had been no direct evidence documenting that, yes, these two unique mutations have some beneficial physiological effect that...
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