news

한어Русский языкEnglishFrançaisIndonesianSanskrit日本語DeutschPortuguêsΕλληνικάespañolItalianoSuomalainenLatina

Many people like fireflies. Their appearance often means a good ecological environment and a romantic atmosphere.

Photo provided by Firefly interviewee

It is one of the few terrestrial organisms that can emit light. After a long period of evolution, the "purposes" of firefly light have included courtship behavior, confusing and trapping prey, and intimidating predators.

But why do fireflies glow in the first place, and why did they evolve this ability in the first place?

Previously, a theory widely accepted in academia was that the ancestors of the Firefly family originally evolved fluorescence as a warning signal of toxins in the body, telling predators: I am poisonous!

However, a recent study published by Zhen Ying's team, a researcher and doctoral supervisor at the School of Life Sciences of Westlake University, overturned the above theory by reconstructing the evolutionary history of toxins in fireflies.

The related paper was published online in PNAS Nexus, a sister journal of the Proceedings of the National Academy of Sciences of the United States of America, with the title "Firefly toxin lucibufagins evolved after the origin of bioluminescence".

On August 4, Researcher Zhen Ying and the first author of the paper, postdoctoral fellow Zhu Chengqi, were interviewed by The Paper.

Didn't fireflies originally glow to serve as a toxin warning signal?

The cardiotonic steroid LBGs toxin is the only toxin found in multiple firefly genera.

"We conducted tests based on the firefly toxins of six of the eight subfamilies of fireflies today, and integrated previous data. We found that fireflies that can independently synthesize LBGs toxins are limited to a single subfamily," Zhu Chengqi told The Paper.

Although some fireflies in North America also have this toxin, this is caused by eating other fireflies that contain LBGs toxins.

In other words, only one subfamily of fireflies can autonomously synthesize LBGs toxins.

So, does the theory that fireflies evolved the ability to glow in order to show "I am poisonous" still hold true?

By comparing the similarities of gene sequences across the entire genome, the researchers determined with a high-confidence phylogenetic tree that the appearance of firefly toxins was later than the appearance of fluorescence.

Their research found that fireflies that can independently synthesize LBGs can only be traced back to the common ancestor of the Lampyridae subfamily, which is far later than the time when fluorescence first appeared in the Lampyridae family.

This shows that even if the "I am poisonous" luminous signal theory is true, it is not the reason why fireflies originally evolved the ability to glow.

On July 20, 2024, in Suizhou, Hubei, the Baopu Valley Scenic Area located in the Tongbai Mountains at the junction of Henan and Hubei provinces and the source of the Huaihe River ushered in the firefly viewing period. After nightfall, thousands of fireflies flickered and danced in the grass and forests, decorating the real version of a midsummer night's dream, attracting many tourists to check in and watch fireflies. Visual China Data Map

So, what was the original cause of the glow? Zhen Ying's team explored the historical environmental background of the evolution of fluorescence in Lampyridae.

Based on the molecular clock theory and three fossil calibration points, Zhen Ying's team estimated the time of the evolution of fluorescence and LBGs toxins. "If you want to estimate the absolute historical time, you need to use fossils with time information for calibration." Zhen Ying told The Paper that fossil evidence can be used as a better time scale, and combined with the species tree, it can be used to estimate the time when historical events occurred.

Through research, they estimated that the fluorescence of the branch to which fireflies belong appeared about 180 million years ago in the Jurassic period.

During this period, after the mass extinction event closely related to the Toarcian Oceanic Anoxic Event, the oxygen content in the atmosphere continued to rise from a historical low.

At the same time, the substrate of the fluorescence reaction, luciferin, has been shown to act as an antioxidant.

Therefore, Zhen Ying's team proposed a new hypothesis: the reason why the ancestors of fireflies originally evolved the ability to emit light may be to cope with the oxidative stress caused by the increasing oxygen content and the hot and dry environment. They evolved luciferin, an antioxidant, to "ignite" and consume excess oxygen free radicals and eliminate the toxic effects of excessive reactive oxygen on cells, and fluorescence may have originally been just a byproduct.

This hypothesis still needs more evidence to be verified.

Why aren't fireflies killed by the toxins in their own bodies?

Why don't fireflies with toxins in their bodies be killed by their own toxins?

Through molecular dynamics simulation and sodium-potassium pump activity experiment comparison, Zhen Ying's team found that fireflies that can independently synthesize LBGs toxins have accumulated mutations in their own ATPα proteins, which affects the binding of toxins to them. This makes them tolerant to LBGs toxins.

But there may be other mechanisms that help fireflies "check and balance" the toxins in their bodies. This is also one of the questions that Zhen Ying's team wants to answer in the future.

Zhen Ying told The Paper that firefly toxins are cardiotonic steroid toxins, which can affect heart contraction and blood pressure and have great medical value. This includes digoxin, a drug that has already appeared on the market. Currently, most of these compounds are chemically synthesized or biologically extracted, and their biosynthetic pathways have not been fully analyzed.

Biosynthesis can reduce environmental impact, lower costs, and even improve the quality and safety of drugs.

"We are also interested in analyzing the biosynthetic pathway of firefly toxins," said Zhen Ying.