Glass Frogs: Clearing the Mystery of Clotting

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两只玻璃青蛙倒睡在一片叶子上,从叶子的上侧背光。这篇来自得克萨斯州皮尔兰米尔顿学院的 14 岁的莉亚·李 (Leah Li) 撰写的这篇文章是学习网络第四届年度 STEM 写作比赛的前 10 名获奖者之一,我们收到了 3,000 多份参赛作品。

Glass Frogs: Clearing the Mystery of Clotting

In a world where transparency is key, these amphibians wear their hearts on their sleeves. A quick glance at their translucent underbelly reveals the vital organ, pumping tirelessly among a network of bones and blood vessels seemingly suspended in a lump of gelatinous material. This odd sight is the glass frog, a creature whose extreme adaptation may be the key to preventing fatal blood clots in humans.

Jesse Delia, one of the researchers behind the discovery, was inspired while shooting images of glass frogs in Panama. When the frog fell asleep on the petri dish, the circulatory system, typically “red with red blood cells,” did something shocking: “It was colorless,” Carlos Taboada, a biologist at Duke University, said of the phenomenon. “It was insane. I had never seen anything like that.”

While transparency is not unique to glass frogs, most transparent organisms are aquatic due to the favorable reflection of light on water. The hemoglobin oxygen-transport system, responsible for an overwhelming majority of oxygen in blood, makes the red blood cells of vertebrates appear opaque, discouraging terrestrial creatures from adapting transparent camouflage. Against all odds, however, the glass frog became one of the few translucent terrestrial creatures.

To investigate how the glass frog did the impossible, Dr. Delia, Dr. Taboada and their colleagues monitored the transparency of 11 frogs during various activities such as sleeping, calling to mates and exercising. The study found that when asleep, the transparency of a glass frog increased by 34 to 61 percent compared to that of waking states. Using photoacoustic imaging, a technique that detects red blood cells, the team discovered that the liver stored a staggering 89 percent of the red blood cells in their body when sleeping, effectively hiding these opaque giveaways from the view of predators. This adaptation immediately seemed improbable — with so many cells packed into the small organ, how does the glass frog prevent clotting?

In humans, an abnormally high concentration of red blood cells increases the risk of blood clots, potentially deadly buildups of blood that block circulation. According to the Centers for Disease Control and Prevention, clotting kills 100,000 individuals annually and is the leading cause of death in pregnant or postpartum women and individuals with cancer (second to cancer itself), indicating the urgent need for the breakthrough that glass frogs may bring.

Currently, anticoagulants are used to prevent the blood from clotting, but — in the words of Richard White, an oncologist commenting on the study — scientists are hopeful that “[t]his seemingly basic observation about glass frogs leads to very clear implications for human health.” Through targeted research on the frog’s ability to contain dense concentrations of red blood cells without clotting, researchers hope to replicate the natural success of this amphibian to save the lives of millions.

While the glass frog certainly did not adapt the easiest camouflage, its unique ability to concentrate almost all of its red blood cells in the liver holds great potential for the future of anticoagulants. Glass frogs remind us that the greatest discoveries might be staring us in the eye — we just might be looking right through them.

Works Cited

Daniel, Ari. “The Astonishing Vanishing Act of the Glassfrog, Revealed.” NPR, 26 Dec. 2022.

“Erythrocytosis” Cleveland Clinic, 5 July 2022.

“Impact of Blood Clots on the United States.” Centers for Disease Control and Prevention, 9 June 2022.

Mueller, Benjamin, and Denise Grady. “AstraZeneca Vaccine and Blood Clots: What Is Known so Far.” The New York Times, 10 Apr. 2021.

Rhodes, Carl, et al. “Physiology, Oxygen Transport.” National Library of Medicine, 14 Nov. 2022.

Taboada, Carlos, et al. “Glassfrogs Conceal Blood in Their Liver to Maintain Transparency.” Science, 22 Dec. 2022.

Tamisiea, Jack. “Glass Frogs Become See-through by Hiding Their Blood.” Science, 22 Dec. 2022.