Just you wait: big dogs tend to age more quickly than small ones, which might be attributed to differences in the chemical tagging of the genome.Credit: Jacob King/PA Images/Alamy
A chihuahua might be at a disadvantage in paw-to-paw combat with a Great Dane, but being little has its benefits. A sweeping analysis of dog breeds has found that small pooches tend to age more slowly than large ones, and that rogue ‘jumping genes’ that hop around the genome in big dogs might be to blame.
The study, published on 8 October in Science1, encompassed nearly 900 dogs representing about 120 breeds, and found that canine ageing is accompanied by changes in specific chemical groups that are added onto DNA. These marks on DNA, which can control gene activity, are part of a cell’s epigenome and the loss or gain of these groups is sometimes used as a biological marker of ageing.
Big dogs tend to accumulate epigenetic changes at a faster rate than small dogs do, the study found. Male dogs also amass these alterations faster than female dogs do, even if the male dogs had been neutered at a young age.
“It’s fascinating”, says Borbála Turcsán, who studies dog cognition and behaviour at Eötvös Loránd University in Budapest, and was not involved in the study. “It provides a molecular background for something we also observe at a behavioural level.”
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Some of the largest dog breeds, such as Irish wolfhounds, live for an average of ten years or less. This is in contrast to smaller breeds. Brianah McCoy, who studies ageing at the University of North Carolina at Chapel Hill, recalls her grandmother’s pet chihuahua: “That dog lived for like 20 years,” McCoy says. “And she was not nice.”
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McCoy, then working at Arizona State University in Tempe, and her colleagues are members of the Dog Aging Project, which has enrolled about 55,000 participants so far. Some of the dogs’ loyal humans periodically fill out surveys about their pet’s health and environment and submit blood samples.
To learn more about how breed and sex affect ageing in dogs, the team analysed the placement of chemical tags called methyl groups on the DNA of 894 dogs. They combined this with other data, including those from genetic sequencing.
The researchers then used this information to develop a molecular clock based on correlations between methylation patterns and chronological age. The resulting clock could predict a dog’s age to within a year on the basis of its epigenome. Those dogs whose epigenetic age was older than their chronological age also had a higher risk of dying in the next two years.
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