Science: How do glass frogs become transparent?

The glass frog is a strange creature
that lives in the rainforests of the Americas.
They are usually nocturnal and sleep on leaves during the day, with their green skin blending in with the leaves
.
Surprisingly, their abdomen is transparent and their bones and organs are clearly visible
.
This adaptability masks the silhouette of glass frogs, making it difficult for predators to spot them
.

A new study suggests that this "stealth behavior" of glass frogs is accomplished by hiding almost all of their red blood cells in their unique liver
.
The study, led by scientists at the American Museum of Natural History and Duke University, was published Dec.
22 in
the journal Science.

This work could lead to new research related to blood clots, as glass frogs pack and transport about 90 percent of their red blood cells to the liver each day, but somehow avoid the production
of blood clots.

Co-corresponding author Jesse Delia, a postdoc at the American Museum of Natural History, said: "There are more than 150 species of glass frogs in the world, but we are only just beginning to understand the way they interact with the environment, some in ways that are really incredible
.
”

Transparency is a commonly used form of camouflage in aquatic animals, but is rare on land
.
For vertebrates, becoming transparent is difficult because their circulatory system is full of red blood cells
that interact with light.
Previous studies have shown that ice fish and eel larvae achieve transparency
by not producing hemoglobin and red blood cells.
But according to the results of the new study, the glass frog used a different strategy
.

Carlos Taboada, from Duke's Department of Biomedical Engineering, said: "Glass frogs overcome this challenge by hiding red blood cells
.
They almost pause their respiratory system during the day, even in high temperatures
.
He is also the corresponding author
of the study.

Researchers at Duke University have used a technique called photoacoustic imaging, which uses light to induce sound waves to propagate
through red blood cells.
This allows researchers to map the location of individual cells while the glass frog sleeps, without the need to use contrast agents or other surgical procedures
.
This is particularly important for this study, as the transparency of glass frogs can be disrupted
by activity, stress, anesthesia, and death.

The researchers focused on a special glass frog (Hyalinobatrachium fleischmanni).

They found that the glass frog in the resting state removed nearly 90 percent of the red blood cells from the blood circulation and wrapped them in the liver, which contained reflective guanine crystals, resulting in a two- to three-fold
increase in transparency.
Whenever glass frogs need to become active again, they transport red blood cells back into the bloodstream
.
At this point, the light absorbed by these cells destroys transparency
.

In most vertebrates, the aggregation of red blood cells can lead to dangerous blood clots
in the veins and arteries.
However, glass frogs do not develop blood clotting, which raises a number of important questions
for biological and medical researchers.

"This is the first in a series of studies documenting the hyaline physiology of vertebrates, and it promises to stimulate biomedical work to harness the extreme physiology of these frogs to achieve new goals in human health and medicine," Delia said
.

Original search

Carlos Taboada, Jesse Delia, Maomao Chen, Chenshuo Ma, Xiaorui Peng, Xiaoyi Zhu, Laiming Jiang, Tri Vu, Qifa Zhou, Junjie Yao, Lauren O’ Connell, Sö nke Johnsen.
Glassfrogs conceal blood in their liver to maintain transparency.
Science, 2022; 378 (6626): 1315 DOI: 10.
1126/science.
abl6620