When an asteroid hit Earth 66 million years ago, it unleashed mass mortalities all over the planet. The most famous victims were the dinosaurs, but also early birds, insects and other life forms were hit. The collision caused ash clouds to block the sun and cool the planet's temperature. However, a recent study in Scientific Reports shows that some species of lichens ̵
"We thought that lichens would be negatively affected, but in the three groups we looked at, they seized the opportunity and diversified quickly," said Jen-Pang Huang, the newspaper's first author, a former postdoctoral fellow at Field Museum now at the Academia Sinica in Taipei. "Some lichens make sophisticated 3D structures like plant leaves, and these fill the niches of plants that have died out."
The researchers were interested in studying the effects of mass extinction on lichens after they had read an essay on how the asteroid strike also caused the extinction of many species of early risers. "I read it on the train and thought:" My God, the poor lichens, they must have suffered too, how can we understand what happened to them? "Says Thorsten Lumbsch, lead author of the study and the Field Museum Curator of Lichenized Mushrooms.
You've seen lichens a million times, even if you have not noticed. "Lichen is everywhere," Huang says, "when you walk in the city, the rough or the gray Places that you see on rocks or walls or trees are the usual crusting lichen. Sometimes they look like chewing gum on the floor. And if you go to another city. "Untouched forest, you can find orange, yellow and vivid violet colors – lichens are really pretty." They are what scientists call "symbiotic organisms" – they consist of two different life forms, who share a body and work together. They are a partnership between a fungus and an organism that can photosynthesize and gain energy from sunlight – either a tiny algae plant or a special kind of blue-green bacterium. Mushrooms that contain fungi and mold are on their own branch on the tree of life, separate from plants and animals (and actually closer to us than to plants). The main task of mushrooms is to break down decomposing material.
During the mass extinction 66 million years ago, plants suffered because the asteroid's ash shielded the sunlight and lowered its temperature. But mass mortality seemed like a good thing for mushrooms – they do not rely on sunlight as food and just need a lot of dead stuff, and the fossil record shows an increase in fungal spores at that time. Since lichens contain a plant and a fungus, scientists wondered if they were adversely affected like a plant or a fungus.
"We had originally expected that lichens would be negatively affected because they contain green things that need light," says Huang.
To see how lichens were affected by mass extinction, scientists had to become creative – there are not many fossil lichens from that time. But while the researchers had no lichen fossils, they had many modern lichen DNA.
By monitoring the growth of fungi in laboratory environments, scientists generally know how often genetic mutations occur in fungal DNA – how many times a letter in the DNA sequence is accidentally reversed during the DNA copying process. This is called the mutation rate. And if you know the mutation rate when comparing the DNA sequences of two different species, you can generally extrapolate how long ago they had a common ancestor with the same DNA.
The researchers fed DNA sequences from three families of lichens into a software program that compared their DNA and figured out what their pedigree would look like, including estimates of how long ago it was before it branched out into the groups we did see today. They substantiated this information with the few lichen fossils they had 100 and 400 million years ago. And the results indicated a lichen boom after 66 million years, at least for some of the leaf-weaving families.
"Some groups did not show any change, so they did not suffer from or benefit from the changes in the leaf lichen boom," says Lumbsch, who alongside his work on lichens is the Vice President of Science and Education in the field. "Some lichens died out, and the leaf larch trees filled these niches, and I was really happy to see that not all lichens suffered."
The results underscore how profoundly the nature we know today was shaped by this mass extinction. "If you could look back 40 million years, the best-known groups in terms of vegetation, birds, and fungi would be more like what you see today than they were 70 million years ago," says Lumbsch. "Most of what we see in nature today has come after the dinosaurs."
And as this study shows how lichens responded to mass extinctions 66 million years ago, it could shed light on how species respond to dinosaur mass extinctions. Planet is currently underway. "Before we lose the biodiversity of the world, we should document it because we do not know when we need it," says Huang. "Lichens are environmental indicators – a simple biodiversity study allows us to assess air quality and air pollution."
Apart from the potential impact on understanding environmental impact and mass extinction, researchers point out the way in which the study deepens our understanding of the world around us.
"It's fascinating to me, because that would not have been possible without large molecular datasets, which would have been impossible ten years ago," says Lumbsch. "It's another piece of the puzzle to understand what's going on in nature around us."
"We expect many patterns from studying other organisms, but fungi do not follow this pattern, mushrooms are crazy," says Huang. "They are really unpredictable, very diverse, very funny."
Individual lichens can have up to three mushrooms, as studies show
When the dinosaurs died, the lichens thrived (2019, June 28)
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