Why Do Some Dogs Have Extremely Long Lifespans?
New data analyzes the genetic code of some extremely elderly dogs.
Posted May 15, 2020
I remember when I was looking for my first Cavalier King Charles Spaniel. One dog expert advised me, "Those are very sweet dogs, but if you are looking for that particular breed you should know that they have a tendency to topple over and die at around 10 years of age. However, there is a local breeder who is trying to do something about that. She has been importing breeding stock from Australia and from France where some lines of the breed seem to have a longer life span. Dogs of that heritage are a little bit larger than the ones we typically see here in North America, which might affect how well they do in confirmation trials, since they are being shown in the 'toy group,' but they do live two to four years longer than the average Cavalier."
I took her advice and contacted that breeder. Ultimately the dog that I got, Wizard, lived to be almost 14 years, which is old for a Cavalier King Charles Spaniel. However, that age is nowhere near great longevity in a dog. The longest lifespan that can be reliably confirmed for a dog is 29 years and five months, and that was an Australian cattle dog named Bluey. There are reports that another Australian dog, a black and tan Kelpie named Maggie, made it to 30 years of age, although the paperwork supporting that was never filed.
The average lifespan of dogs has been generally found to be between 10 and 13 years. Any dog older than 20 years would be considered to be extremely long-lived. Researchers often refer to such elderly animals as "Methuselah dogs." This is after Methuselah, a biblical religious figure mentioned in Judaism, Christianity, and Islam. Methuselah lived until the age of 969, which makes him the longest-lived individual mentioned in the Bible.
We do know that there are a number of inherited physical factors that influence the life expectancy of dogs, including their size, the shape of their heads, their breed, and several other characteristics. So obviously, if we are going to look for the reasons why some dogs live so much longer than others, it will take us into the study of genetics.
Dávid Jónás, a research fellow at the Department of Ethology at Eötvös Loránd University in Budapest, Hungary, led a team of researchers who decided to completely sequence the DNA of two Methuselah dogs, both of mixed breed: Kedves, a 22-year-old female, and, Buksi, a 27-year-old male. By doing a complete genomic mapping, the researchers hoped that they might find genetic features that might explain their extended life span.
The fact that only two dogs are being tested in this experiment might not sound like much; however, this was a study of the entire DNA map of each of them, and the results were compared to the whole genomes of 850 dogs of average longevity. To give you an idea of just how much work is involved in this kind of study, try to recall the shape of the DNA molecule. It looks like a twisted ladder, and each rung of that ladder can vary in terms of chemical makeup and orientation. The most common type of genetic variations are single nucleotide polymorphisms, frequently called SNPs (pronounced “snips”), and each SNP represents a change in the structure of just one of these rungs in the DNA ladder. For these two canine genomes, the researchers observed approximately 4.8 million SNPs. Their findings then had to be compared to the existing databanks, since their working hypothesis was that it was the unique genetic variants found in these elderly dogs which were most likely to account for their long lives.
So what exactly do these genetic analyses reveal? Well, as you might imagine, it's a little complicated. The researchers found 472 genes which seem to matter. A number of these have to do with the functioning of the nervous system. Some of the genes are very similar to those found in humans which are related to the immune system, the triggering of inflammations, and also Alzheimer's disease.
Of particular interest were a set of genes that were related to gene transcription, translation, and regulation. These are important because the genetic material in an individual needs to be copied and transcribed into every new cell as the body grows and repairs itself. You can conceptualize this as requiring an internal Xerox machine for genetic material. If the glass plate on the Xerox machine becomes dirty over time, it will affect the accuracy of copies—and when it comes to genetic material, will ultimately affect how well the new cells can function. Successive bad copies of genetic material can result in new cells malfunctioning and ultimately a shortened life span, while good copies allow the body to keep chugging along.
These new research findings helped the investigative team develop a hypothesis for further research, hopefully with a larger sample of old dogs: "A crucial genetic requirement of extreme longevity lies within the fine-tuning (i.e. the superior calibration) of gene expression." In other words, what is required is the best possible genetic Xerox machine to produce clean and readable copies of DNA in new cells.
While this current study doesn't provide precise guidelines for how we can breed dogs with longer lifespans, it does highlight the areas in the genetic code that researchers should be looking at. This should simplify future research on canine lifespans, and, as an added benefit, perhaps even assist in our understanding of human longevity.
Because the clearest demonstration of the effects of genetics on the life span of dogs is their breed, you might find it interesting to take a look at a study which looks at the life expectancy of 165 breeds of dogs.
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Jónás Dávid, Sándor Sára, Tátrai Kitti, Egyed Balázs, Kubinyi Enikö (2020). A Preliminary Study to Investigate the Genetic Background of Longevity Based on Whole-Genome Sequence Data of Two Methuselah Dogs. Frontiers in Genetics, 11, 315, DOI=10.3389/fgene.2020.00315