Larger furry friends age faster at molecular level than small ones
How can a mini doggo live up to 14 years, when a big one only lives up to 10 years? Scientists finally solve the mystery and they say, it is all down to the DNA
READING LEVEL: ORANGE
Ever wondered why tiny furry friends live quite a lot longer than big muscular ones?
Turns out, the reason is hidden deep inside doggo DNA and scientists have finally solved part of this ageing mystery.
Few animals show the link between size and lifespan as clearly as dogs.
Within this one species, large breeds such as Great Danes* typically die younger than small ones such as chihuahuas*.
A new study shows the reason may lie in how DNA* changes as dogs get older. Across mammals, bigger species like elephants usually live longer lives than smaller ones like mice, but within a species that pattern can reverse.
Earlier comparisons across species linked certain biological mechanisms* to exceptional longevity*. But those are less suited to explaining differences among individuals within a species.
“We all know that big dogs usually don’t live as long as small dogs,” Arizona State University’s School of Life Sciences and Centre for Evolution Professor Noah Snyder-Mackler said.
“But we have not known whether their cells actually age faster, or whether they simply hit certain diseases earlier,” he said.
Prof Synder-Mackler is one of the authors of the study published in the journal Science.
To find out the answer, the researchers measured DNA methylation*, such as chemical tags that help control which genes are switched on and off.
Using age-related patterns in these tags, they built an epigenetic* clock that estimated a dog’s age with a median error of less than one year.
Analysing 1640 blood methylation profiles from 894 pet canines of various breeds, they found that larger dogs and male dogs showed signs of accelerated molecular ageing.
Dogs whose biological age appeared older than expected, based on their profiles, meanwhile faced a higher risk of early death.
“We found that large dogs show a faster-moving DNA methylation ageing signature in blood, and that this acceleration is especially strong in parts of the genome* that normally helps keep ‘jumping genes’ quiet,” Prof Snyder-Mackler said.
Jumping genes, also called transposable* elements, can copy and insert themselves into new spots in the genome.
LINE1s are a type of jumping gene normally kept silent by DNA methylation, but their activation has been linked to genome instability, which causes cancer and other age-related diseases.
In large dogs, “methylation at those regions appears to erode* more quickly with age, as if the genome is losing some of the tape or clamps that keep these mobile elements suppressed,” Prof Snyder-Mackler said.
This discovery suggests that the shorter lives of large dogs reflect a faster molecular ageing trajectory*.
“If large dogs simply died earlier after following the same molecular trajectory, we would look for late-life triggers of disease or mortality, but if parts of the ageing program move faster throughout adulthood, as our data suggests for the blood methylome, then there may be processes we can measure, follow over time, and potentially modify before disease appears,” the professor said.
DIFFERENCES BY SEX
The researchers also found differences between male and female dogs, largely on the X chromosome* — the sex chromosome that females carry in two copies and males in one.
There, LINE1 elements showed higher methylation in males.
Chromosomes are threadlike structures that carry genetic information inside cell nuclei.
“In our genome-wide analyses, the sex signal looked distinct from the body-size signal, so I would treat that as a separate biology that needs follow-up, rather than the same mechanism in disguise,” Prof Snyder-Mackler said.
The trade-off between large size and longevity may be a consequence of selective breeding rather than natural evolution.
Humans bred dogs to grow quickly and reach large adult sizes for tasks such as guarding, hunting and herding.
“If selection strongly favours rapid growth or large adult size before old age, late-life costs can come along for the ride,” Prof Snyder-Mackler said.
Previous explanations for why large dogs tend to have shorter lives focused on growth biology.
Researchers have also suggested that larger dogs may undergo more cell growth, develop more quickly or face a higher risk of cancer.
“Our study does not replace those ideas; it gives us a molecular layer downstream of body size,” Prof Snyder-Mackler said.
The findings raise the possibility that slowing molecular ageing could help extend healthy lifespan in larger dogs.
But lifespan is not governed by a single biological clock, according to the professor.
Large dogs would still face breed-specific risks, meaning that slowing molecular ageing would not turn a Great Dane into a chihuahua, in terms of lifespan, but could make one component* of its ageing trajectory less compressed*.
Minor edits have been made to this story for Kids News. Reuters reporting by Marta Serafinko in Gdansk; editing by Will Dunham.
WATCH THE VIDEO OF A GREAT DANE ON A PLANE
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GLOSSARY
- Great Danes: a large breed of dog historically kept for hunting
- chihuahuas: world’s smallest breed of dogs, it is named after Mexico’s largest state
- DNA: genetic information found inside cells of every living organism like people, other animals, and plants
- biological mechanisms: genetic material and internal processes in living organisms
- longevity: living for a long time
- methylation: a biochemical process involving chemical changes to DNA that affect how molecules act in the body
- epigenetic: the study of how cells control gene activity without changing DNA sequence
- genome: the complete set of genetic material or DNA in an organism
- transposable element: jumping gene, a part of DNA that can move or copy itself from one place to another
- erode: to gradually destroy or reduce something over time
- trajectory: the path, the course, or line of development over time.
- chromosome: a threadlike structure of nucleic acids and protein found in the cell nucleus carrying genetic information in the form of genes, passed from one parents to their children
- component: part of a larger whole, one element of a system
- compressed: squeezed, pressed into a smaller volume or space
EXTRA READING
How having a dog improves health
Koala-saving hero hound retires
Wolf pup clones: is this ‘de-extinction’?
QUICK QUIZ
- Which dog breed lives longer?
- What are jumping genes?
- Why do certain dogs live longer than others?
- Why is this study important?
- What tasks did humans breed dogs for?
LISTEN TO THIS STORY
CLASSROOM ACTIVITIES
1. Looking at a small sample
Make a list of 5 dog breeds with which you are familiar. They may be breeds you or family members have as a pet, breeds you have seen in a television show or movie, etc.
Use your research skills to find a reliable source that will provide you with the average size and lifespan for these breeds.
Arrange your list in size order.
Then arrange your list in lifespan order.
Do the size and lifespan in your small sample support the findings of the research in the study? Do you think this is a fair way to try to prove or disprove the findings? Explain your thinking.
Time: allow 30 minutes to complete this activity
Curriculum links: English, Science
Extension
When choosing a pet like a dog, owners might consider both their size and lifespan.
Make a list of other factors that you think are important to consider when choosing a pet.
Time: allow 10 minutes to complete this activity
Curriculum links: English, Ethical Understanding
VCOP ACTIVITY
I spy nouns
Nouns are places, names (of people and objects), and time (months or days of the week).
How many nouns can you find in the article?
Can you sort them into places, names and time?
Pick three nouns and add an adjective (describing word) to the nouns.