When an asteroid smacked into the Earth 66 million years ago, it triggered mass extinctions all over the planet. The most famous victims were the dinosaurs, but early birds, insects, and other life forms took a hit too. The collision caused clouds of ash to block the sun and cool the planet's temperature, devastating plant life. But a new study in Scientific Reports shows that while land plants struggled, some species of lichens-organisms made of fungi and algae living together-seized the moment and evolved into new forms to take up the role of plants in the ecosystem.
"We thought that lichens would be negatively affected, but in the three groups we looked at, they seized the chance and diversified rapidly," says Jen-Pang Huang, the first author's paper and former postdoctoral researcher at the Field Museum now at the Sinica Academy in Taipei. "Some lichens grow sophisticated 3-D structures like plant leaves, and these ones filled the niches of plants that died out."
The researchers were interested in studying the effects of mass extinction on lichens after reading a paper about how asteroid strike also caused many species of early birds to go out. "I read it on the train, and I thought," My god, the poor lichens, they must have suffered too, how can we trace what happened to them? "" Says Thorsten Lumbsch, senior author of the study and Field Museum's curator of lichenized fungi
You've seen lichens a million times, even if you did not realize it. "Lichens are everywhere," says Huang. "If you go on a walk in the city, the rough spots or gray spots you see on rocks or walls or trees, these are common crust lichens. On the ground, they sometimes look like chewing gum. pristine forest, you can find orange, yellow, and vivid violet colors-lichens are really pretty. " They're what scientists call "symbiotic organisms" -they're made up of two different life forms sharing one body and working together. They are a partnership between a fungus and an organism that can perform photosynthesis, making energy from sunlight ̵
During the mass extinction, 66 million years ago, plants suffered from ash from the asteroid blocked out sunlight and lowered temperatures. But the mass extinction seems to be a good thing for fungi – they do not rely on sunlight for food and just need lots of dead stuff, and the fossil record shows an increase in fungal spores at this time.
"We originally expected lichens to be affected in a negative way because they contain green things that need light, "says Huang
To see how lichens were affected by mass extinction, scientists had to get creative-there are not many fossil lichens from that time frame.
From observing growing fungi in lab settings, scientists generally know how often genetic mutations appear in fungal DNA-how often a letter in the DNA sequence accidentally gets switched during the DNA copying process. That's called the mutation rate. And if you know the mutation rate, if you compare the DNA sequences of two different species, you can generally extrapolate how long ago they must have had a common ancestor with the same DNA
. they lichened into a software program that compared their DNA and figured out what their family tree should look like, including estimates of how long ago it was branched into the groups we see today. They boosted this information with the few lichen fossils they had, from 100 and 400 million years ago. And the results pointed to a lichen boom after 66 million years ago, at least for some of the leafier lichen families
"Some groups did not show a change, so they did not suffer or benefit from the changes in the environment, "says Lumbsch, who, in addition to his work on lichens, is the Vice President of Science and Education at the Field. "
The results underline how profoundly the natural world we know today was shaped by this mass extinction. "If you could go back 40 million years, the most prominent groups in vegetation, birds, fungi-they'd be more like what you see now than what you'd see 70 million years ago," says Lumbsch. "Most of what we see around us nowadays in nature originated after the dinosaurs."
And since this study shows how lichens responded to mass extinction 66 million years ago, it could shed light on how species would respond to mass extinction planet is currently undergoing. "Before we lose the world's biodiversity, we should document it, because we do not know when we'll need it," says Huang. "Lichens have environmental indicators-by simply doing a biodiversity study, we can deduce air quality and pollution levels."
Beyond the potential implications for understanding environmental impacts and mass extinctions, researchers point to ways the study deepens our understanding of the world around us
"For me, it's fascinating because you would not be able to do this without large molecular datasets." This would have been impossible ten years ago, "says Lumbsch. "Fungi are weird," says Huang, "We are expecting a lot of patterns from studying other organisms, but the fungi do not follow the pattern."
"They're really unpredictable, really diverse, really fun."
Individual lichens can have up to three fungi, study shows
When the dinosaurs died, lichens thrived (2019, June 28)
retrieved 28 June 2019
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