Echidnas blow snot bubbles to cool down | Science

Short-beaked echidnas may be one of nature’s strangest looking creatures. Resembling a pug-size hedgehog with the schnoz of an anteater, they are one of only five living species of monotreme, that rare mammal that lays eggs. They’re also encased in a coat of stiff spines and lack the ability to sweat—features that should kill them in the scorching deserts of Australia they call home.

Now, a team of scientists has discovered some of the strategies the echidna employs to stay cool. It blows snot bubbles and flexes its spine, scientists report today in Biology Letters, allowing it to shed heat in temperatures that can approach 40°C.

The find isn’t just a cool discovery, says Tahlia Perry, a zoologist at the University of Adelaide who was not involved in the new study—it could help scientists conserve these mysterious mammals, whose populations are declining in some areas because of habitat loss and vehicle strikes.

Echidnas use their elongated beaks and powerful claws to break apart termite mounds, slurping up the insects with their long, tacky tongues. When threatened by predators such as feral cats, they curl up into a ball like an armadillo.

Monotremes, which diverged from other mammals millions of years ago, are incapable of panting, sweating, or licking themselves to cool down. Short-beaked echidnas (Tachyglossus aculeatus), which live throughout the Australian continent, adopt a nocturnal schedule to avoid the searing summer heat. If they find themselves out during the day, they burrow underneath houses and occasionally take dips in birdbaths, rivers, or beaches, according to Perry, who runs Echidna CSI, a nationwide citizen science project that monitors wild echidnas.

Yet even with these strategies, researchers have concluded from lab studies that temperatures above 35°C should cook these prickly insectivores. However, field researchers have observed echidnas waddling around at temperatures of almost 40°C.

To determine how echidnas beat the heat, researchers used an infrared camera to record wild short-beaked echidnas that live in nature reserves near Perth, Australia. Over the course of 1 year, the scientists took infrared images of 124 of the animals, allowing the team to record their internal temperatures without having to capture them.

Observing these animals in the wild is crucial, as lab studies don’t always replicate the real world, says Stewart Nicol, a zoologist studying echidna physiology at the University of Tasmania who was not involved with the work.

In the infrared images the team collected, most of the echidnas’ bodies glowed shades of red, orange, and pink—signs of varying degrees of heat. But the tips of their beaks were usually a dark shade of navy blue.

This extreme thermal disparity is due to their snot. “When they get really hot, they start to blow mucus bubbles that break over the tip of their beak,” says lead author Christine Cooper, a zoologist at Curtin University.

As the snot evaporates, it carries away heat, making the beak almost 10° cooler than other parts of the echidna’s body. And because so much blood travels through the echidna’s elongated nose, Cooper says, the strategy helps cool the rest of its body as well.

Other animals also utilize such “evaporative cooling.” Storks and turkey vultures urinate on their legs to keep cool, for example, and kangaroos lick their veiny forearms to keep them moist.

But echidnas have an additional trick up their sleeves. Their spines, composed of hardened, hollowed-out hair follicles, act as insulation. When the creatures are cold, the spines lie flat along their back like a bristly combover, preventing heat from escaping. When hot, the spines stand up, allowing heat to dissipate. “It’s a really flexible insulation,” Cooper says.

The team also found evidence that some spineless areas of the echidna’s body, including its soft underbelly and the inside of its legs, allow heat to escape. If it gets chilly, it curls up into a ball to prevent heat loss from these areas.

In future studies, Cooper and her colleagues plan to model how much heat the echidna loses as its snot evaporates and its spines shift. That could help researchers forecast how this ancient group of mammals will fare in a warmer future, she says. “We’ve seen them running around in the field when it’s over 37° out,” Cooper says. “Now that we know the mechanisms behind their heat tolerance, we can model how climate change may impact them.”

Short-beaked echidnas may be one of nature’s strangest looking creatures. Resembling a pug-size hedgehog with the schnoz of an anteater, they are one of only five living species of monotreme, that rare mammal that lays eggs. They’re also encased in a coat of stiff spines and lack the ability to sweat—features that should kill them in the scorching deserts of Australia they call home.

Now, a team of scientists has discovered some of the strategies the echidna employs to stay cool. It blows snot bubbles and flexes its spine, scientists report today in Biology Letters, allowing it to shed heat in temperatures that can approach 40°C.

The find isn’t just a cool discovery, says Tahlia Perry, a zoologist at the University of Adelaide who was not involved in the new study—it could help scientists conserve these mysterious mammals, whose populations are declining in some areas because of habitat loss and vehicle strikes.

Echidnas use their elongated beaks and powerful claws to break apart termite mounds, slurping up the insects with their long, tacky tongues. When threatened by predators such as feral cats, they curl up into a ball like an armadillo.

Monotremes, which diverged from other mammals millions of years ago, are incapable of panting, sweating, or licking themselves to cool down. Short-beaked echidnas (Tachyglossus aculeatus), which live throughout the Australian continent, adopt a nocturnal schedule to avoid the searing summer heat. If they find themselves out during the day, they burrow underneath houses and occasionally take dips in birdbaths, rivers, or beaches, according to Perry, who runs Echidna CSI, a nationwide citizen science project that monitors wild echidnas.

Yet even with these strategies, researchers have concluded from lab studies that temperatures above 35°C should cook these prickly insectivores. However, field researchers have observed echidnas waddling around at temperatures of almost 40°C.

To determine how echidnas beat the heat, researchers used an infrared camera to record wild short-beaked echidnas that live in nature reserves near Perth, Australia. Over the course of 1 year, the scientists took infrared images of 124 of the animals, allowing the team to record their internal temperatures without having to capture them.

Observing these animals in the wild is crucial, as lab studies don’t always replicate the real world, says Stewart Nicol, a zoologist studying echidna physiology at the University of Tasmania who was not involved with the work.

In the infrared images the team collected, most of the echidnas’ bodies glowed shades of red, orange, and pink—signs of varying degrees of heat. But the tips of their beaks were usually a dark shade of navy blue.

This extreme thermal disparity is due to their snot. “When they get really hot, they start to blow mucus bubbles that break over the tip of their beak,” says lead author Christine Cooper, a zoologist at Curtin University.

As the snot evaporates, it carries away heat, making the beak almost 10° cooler than other parts of the echidna’s body. And because so much blood travels through the echidna’s elongated nose, Cooper says, the strategy helps cool the rest of its body as well.

Other animals also utilize such “evaporative cooling.” Storks and turkey vultures urinate on their legs to keep cool, for example, and kangaroos lick their veiny forearms to keep them moist.

But echidnas have an additional trick up their sleeves. Their spines, composed of hardened, hollowed-out hair follicles, act as insulation. When the creatures are cold, the spines lie flat along their back like a bristly combover, preventing heat from escaping. When hot, the spines stand up, allowing heat to dissipate. “It’s a really flexible insulation,” Cooper says.

The team also found evidence that some spineless areas of the echidna’s body, including its soft underbelly and the inside of its legs, allow heat to escape. If it gets chilly, it curls up into a ball to prevent heat loss from these areas.

In future studies, Cooper and her colleagues plan to model how much heat the echidna loses as its snot evaporates and its spines shift. That could help researchers forecast how this ancient group of mammals will fare in a warmer future, she says. “We’ve seen them running around in the field when it’s over 37° out,” Cooper says. “Now that we know the mechanisms behind their heat tolerance, we can model how climate change may impact them.”