To find out the age of dolphins, ask about their poop

This article originally appeared on Hakai Magazine, an online publication about science and society in coastal ecosystems. Read more stories like this at hakimagazine.com.

Darling. Guano. Manure. Poop. Everyone makes it, and scientists love it because once you get past the smell, feces can be a wealth of information.

Scientists already use scat to monitor the health of endangered species, such as killer whales. Otter feces, meanwhile, are helping scientists understand how important this is nutrients move through marine and terrestrial food webs. And in a new studyscientists outline another excellent use of poop: to non-invasively determine the age of bottlenose dolphins in the Indo-Pacific.

Researchers have several ways to calculate the age of marine mammals, but these techniques can be quite drastic. One of these involves capturing a marine mammal, extracting its tooth and measuring the growth layers of the dentin, a bit like counting the rings on a tree. Another strategy, known as an epigenetic clock, is to look at how the animal’s DNA has changed over its life by a process called methylation. This usually requires a skin sample, which scientists collect with a rifle or crossbow.

Although tooth extraction is largely safe, it does come with the risk of infections and other health problems. It is also stressful for the animal, as is the loss of skin tissue. Stressing animals can change their health or behavior, as well as scientists’ understanding of the animal’s natural ecology, says Genfu Yagi, the lead author of the new study. studywho is receiving her PhD from Mie University in Japan.

“Therefore, there is a need for non-invasive methods for age estimation,” Yagi said by email.

The solution? Collect crap instead.

Studies published in 2019 and 2020 found that the epigenetic clock technique used to calculate the age of animals from skin samples also works with fecal samples. But those researchers took samples chimpanzee And Japanese macaque feces. Would it work on marine mammals, Yagi wondered?

And so, between 2014 and 2021, he and his colleagues went diving for dolphin feces around the Japanese island of Mikura-jima. Their goal? A population of Indo-Pacific bottlenose dolphins which has been continuously studied since 1994 – and whose ages are already well documented.

Believe it or not, Yagi says swimming through dolphin doo-doo isn’t as dirty as it sounds.

“Dolphin feces look like a smoke screen, with several small clumps,” says Yagi. “The odor is not unpleasant and is more like a fishy odor than the typical odor associated with human or pet feces.”

Back in the lab, the scientists confirmed that measuring the fecal samples through DNA methylation rates is an accurate method for estimating the dolphins’ ages. Their work shows that the poo-based process is just as reliable as invasive methods – a first for marine mammals.

Steve Horvath, a geneticist at the University of California, Los Angeles, invented the epigenetic clock technique and first tested its effectiveness for calculating people’s ages in 2011. “I think the article is very innovative,” he says.

Although the method still needs to be refined and developed (for example, Yagi’s tests did not work well in lactating female dolphins), Horvath believes that epigenetic dating using feces can be used in a range of animals. “It could be very valuable for endangered species,” he says.

Poop, what can’t it do?

This article first appeared in Hakai Magazine and is republished here with permission.