Monotreme Mucus Bubbles

In Greek mythology, Echidna was half-woman and half-snake. With Typhon, she birthed some of the most famous mythological monsters, including, according to various sources, Cerberus, Hydra, Chimera, the Nemean Lion, Sphinx, and Scylla.

When early naturalists encountered one of the planet’s strangest critters, they weren’t sure if it was a mammal or an amphibian, so they named it after one of the most prominent hybrid creatures (according to one etymological theory, at least).

Sculpture of Echidna by Pirro Ligorio from 1555

The echidna is a veritable oddity.

The four extant species of echidnas and the platypus are the world’s only monotremes. From the Greek words for “single” and “hole,” monotremes are classified as mammals, but they have one major difference from the rest of the hairy ones: monotremes lay eggs. The “hole” in a monotreme refers to the cloaca, which is a singular opening in animals that services the digestive, reproductive, and urinary tracts. Cloacae are very common in non-mammals, but extremely rare in mammals; most mammals have multiple orifices that specialize in different expulsions.  Perhaps 220 million years ago, monotremes diverged on the grand evolutionary tree from their fellow mammals. During that time, all but five species died out, leaving just a handful of critters that appear to be extremely bizarre relative to the rest of the kingdom.

A short-beaked echidna - photo by Fir0002

Is the creature above a hedgehog, an anteater, or a porcupine? Is it an ant-hedge-pine? Can it be any of those animals if it lays eggs?

As with many of the gnarliest, eccentric beasts, echidnas mostly live in Australia (some call nearby New Guinea home). This home base leads to another curiosity on the list of echidna oddities. Australia and New Guinea are hot places. The echidna is not built to withstand heat. Unlike most other entities, echidnas cannot sweat or pant to dissipate heat. Further, their spines act like a blanket – good for the cold, not so good for sweltering Australia. Lab studies suggest temperatures of 35°C (95° F) should spell lights-out for an echidna.

Australia quite often blows past 95° Fahrenheit. Yet, echidnas seem to have no problem foraging for insects across the continent. How do they manage to survive if they lack the traditional biology to cool themselves?

A new study reveals part of the magic: nasal mucus.

Researchers in Australia used infrared cameras to record the body temperatures of 124 different short-beaked echidnas as they went about their lives in a nature reserve near Perth. The results displayed something unexpected: the noses of an echidna were significantly cooler than the rest of the body, often 10° C. Because a lot of blood flows through the large schnoz, the temperature gradient allows the echidna to cool the rest of the body. As blood flows through the nose section, it cools and then returns to the hot body.

But the nose isn’t magically colder. As the lead scientist on the study, Christine Cooper, put it, “When they get really hot, they start to blow mucus bubbles that break over the tip of their beak.” When this substance evaporates, it disperses heat, sort of like a snotty sweat. Science notes that echidnas aren’t the only animal to use evaporative cooling in a weird way – storks and turkey vultures both urinate on their legs to employ evaporation, for example – but they seem to be the only species known to blow mucus bubbles for cooling.

Infrared image of an echidna - photo from Science/Curtin University

What a wild world.

A running nose isn’t just for sickness or allergy.

The researchers also discovered that the echidnas tend to spread their bellies onto cooler spots on the ground in order to chill themselves. Though these findings don’t mean echidnas are powerhouses when it comes to dealing with heat, they do elevate a critter scientists previously viewed as subpar in that arena.

Millions of years of evolution can craft some incredible methodologies.

Check out the short-beaked echidna blowing nose bubbles:

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