<div data-thumb = "https://scx1.b-cdn.net/csz/news/tmb/2019/lichensarewa.jpg" data-src = "https://scx2.b-cdn.net /gfx/news/hires/2019/lichensarewa.jpg "data-sub-html =" Crustose Ophioparma Lichen Credit: (c) Matthew P. Nelsen, Field Museum ">
You probably saw a lichen, even if you did not notice. If you've ever wandered through the forest and wondered what the crusts on trees or rocks are, then those are lichens, a combination of algae and fungi that live together almost as if they were a single organism. And since they can grow on bare rocks, scientists thought that lichens were some of the first organisms that came from the water to the land, changed the planet's atmosphere, and paved the way for modern plants. A recent study in Geobiology extends this history by dipping deeply into the DNA of algae and fungi that form lichens, showing that the lichens have probably evolved millions of years after planting.
"When we look at modern ecosystems and see a bare surface like a rock, lichens often grow there and eventually plants grow," says Matthew Nelsen, lead author of the paper and a researcher at the Field Museum. "People thought the ancient colonization of land might have worked that way, but we see these lichens came into play later than plants."
Four hundred and eighty-five million years ago, Earth was very different from what we see today. Hardly anything lived on land. However, lichens can live in extreme conditions. They can grow on bare stones and break them down to create the soil for complex plants with roots ("vascular plants"). Scientists believed that lichens had to land before the vascular plants and made the environment more hospitable. But the work of Nelsen and his colleagues calls this timeline into question.
Nelsen did not want to disturb the status of lichens as one of the country's first colonizers. He was initially interested in finding out how the algae-fungus relationship that made up the lichens came about. If lichens could update their relationship status on Facebook, it would definitely be "complicated". They are a product of symbiosis, a relationship in which two species live together and both benefit. In this case, the algae ̵
1; or specialized blue-green algae called cyanobacteria – provide food, and the mushrooms wrap around and form a shelter. "The question of when lichens were formed and how often fungi developed the ability to build symbiotic relationships with algae has been controversial in the past," says Nelsen.
<div data-thumb = "https: // scx1. B-cdn.net/csz/news/tmb/2019/2-lichensarewa.jpg" data-src = "https: //scx2.b-cdn .net / gfx / news / hires / 2019/2-lichensarewa.jpg "data-sub-html =" Krustose Porpidia lichen growing on a rock Photo credit: (c) Matthew P. Nelsen, Field Museum ">
However, to determine exactly when lichens evolved, scientists needed to study the evolutionary history of the fungi and algae that make up them. The early fossil record of lichens is not very clear; It can be difficult to differentiate lichen fossils from other fossils, and all fossils that scientists know to be lichen are younger than the oldest complex plant fossils. The researchers used the available fossils to extrapolate the age of the pedigrees of lichen-forming fungi and algae. They compared these pedigrees with the age of fossil plants. The conclusion: Lichens have probably developed long after complex plants.
"Lichens are not as old as we thought they are, a younger, newer kind of symbiosis, and they have not covered the earth for a long time, there were plants and animals running around," says Nelsen.
The discovery of the lichen age makes it clear that the pattern of modern lichen on rocks in front of plants does not mean that lichens have formed before plants. "It provides a snapshot of what happened on earth in the depth of time and when some of these groups appeared," says Nelsen. And because growing lichens on the ground can make the soil moister, hold the soil in place and affect the type of nutrients present in the soil, we can gain a clearer picture of the world in which complex plants have evolved.  If we understand how Earth was hundreds of millions of years ago, we can examine how it has changed and gain more insight into the current state of our planet. For researchers, it's similar to the feeling you have when you learn about your family history from an ancestral DNA kit.
"It is changing our understanding of the early evolution of complex ecosystems on Earth," says Nelsen.
When the dinosaurs died, the lichens thrived
Lichen are much younger than scientists thought (2019, November 15)
retrieved on November 15, 2019
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