Glass frogs turn transparent by hiding red blood cells in their livers, scientists find

A glass frog had transparent skin (Getty Images/iStockphoto)

Amphibians like glass frogs turn transparent while they sleep – and now scientists have figured out how.

The creatures hide 90% of their red blood cells in their liver, which is covered with a mirror, so their eyes, bones, and internal organs become all that is visible.

Despite this, they manage to avoid getting a massive clot, and when they wake up, blood rushes back through their bodies.

Study author Dr Sönke Johnsen of Duke University in the United States explained: “Whenever glass frogs want to be transparent, which is usually when they are in resting and vulnerable to predation, they filter almost all red blood cells from their blood and hide. in a mirror-covered liver, somehow avoiding creating a huge blood clot in the process.

“Whenever frogs need to become active again, they pull cells back into the bloodstream, giving them the metabolic ability to move.”

The creatures – which live in the southern United States, Central America, the Caribbean and northern South America – are nocturnal animals that sleep upside down on translucent leaves the color of their backs .

They can be nearly impossible to spot when awake as they are only a few inches long and are most active at night when their green skin helps them blend in with the surrounding grass and leaves.

However, they become true masters of camouflage when they sleep.

While many sea creatures, including icefish and eel larvae, can turn transparent or change their skin color, this skill is far less common on land. Glass frogs do this to make it harder for predators to spot them.

Red blood cells in the circulatory system prevent most animals from becoming transparent.

These cells absorb green light well, which is the color of light normally reflected by plants and other vegetation.

In return, the oxygen-rich red blood cells reflect red light which makes the blood and circulatory system very visible, especially against a bright green leaf.

Glass frogs are one of the few terrestrial vertebrates that can turn transparent, which has been of particular interest to researchers, but few have understood the process so far.

The glass frog's translucent legs make its silhouette less recognizable by predators and harder to spot (Getty Images/iStockphoto)

The glass frog’s translucent legs make its silhouette less recognizable by predators and harder to spot (Getty Images/iStockphoto)

For the study, the team focused on a particular type of glass frog called hyalinobatrachium fleischmanni.

Researchers traveled the world to collect glass frogs and performed imaging tests on them.

They used them to produce optical models that proved that animals could become transparent by pushing red blood cells out of their vessels.

The team suspected that the cells were stored in one of the frog’s internal organs which are encased in a reflective membrane.

They explained that for a transparent animal, its biology was “surprisingly” difficult to decipher.

Experts from across the United States had to help the team navigate it.

Study author Dr Jesse Delia, who now works at the American Museum of Natural History, explained: “If these frogs are awake, stressed or under anesthesia, their circulatory system is full of red blood cells and they are opaque.

“The only way to study transparency is if these animals are sleeping happily, which is difficult to achieve in a research lab.

“We were really banging our heads against the wall for a solution.”

However, the team discovered an imaging technology called photoacoustic microscopy (PAM) which they used to make the discovery.

This process involves projecting a safe laser beam of light into tissue, which is absorbed by molecules and converted into ultrasound waves.

These sound waves are then used to create detailed biomedical images of the molecules. The imaging tool is non-invasive, quiet and sensitive.

Professor Junjie Yao, who specializes in PAM technologies at Duke, explained: “The red blood cells themselves provide the contrast, as different cell types absorb and reflect different wavelengths of light.

“We could optimize our imaging systems to look specifically for red blood cells and track the amount of oxygen flowing through the frog’s body.”

During the study, the frogs slept upside down in a Petri dish, which is similar to how they would sleep on a leaf. The researchers then shined a green laser on them.

The red blood cells in the frog’s body absorbed the green light and emitted ultrasound waves, which were then picked up by an acoustic sensor to track their location.

The team now wants to examine the process by which they manage to store so many cells in their liver to learn more about human vascular health.

Dr Delia added: “This is the first in a series of studies documenting the physiology of vertebrate transparency, and it will hopefully stimulate biomedical work to translate the extreme physiology of these frogs into new targets for human health and medicine.”

The findings were published in the Journal of Science.

Leave a Reply

Your email address will not be published. Required fields are marked *