In northern Canada and the Russian tundra, the forest floor is covered with deer lichens. Even though they
"We were surprised because this species of deerlichens have always been thought to reproduce asexually,” says Marta Alonso-García, lead author of the paper and a researcher at the University of Quebec at Laval.
Deer lichens develop in both directions:they can be reproduced sexually through spores, or they can be cloned asexually. When fungi reproduce sexually, they direct structures that look like roots towards a nearby fungus and exchange genetic information when touched. They then release spores, individual cells containing genetic material, that travel in the wind and disperse. When they land, they begin to grow and produce a new fungus that is genetically different from their parents. On the other hand, with asexual clonal reproduction, a part of the entire lichen (fungus and algae), called the thallus, is pinched off and grows into a whole organism that is genetically identical to its parent.
The two reproductive methods have different advantages.
“Sexual reproduction is very expensive.You have to find your partner, it's more difficult than asexual reproduction. But many organisms do this because sexual reproduction allows them to weed out negative mutations in the long term."
Felix Grewe, co-director of the Field Museum's Grainger Center for Bioinformatics
Researchers have studied the lichens of the reindeer(Cladonia stellaris) to learn about their genetic structure: “We used DNA sequences to reveal the genetic relationships between populations of this lichen,” says Alonso-Garcia. "We tested if the samples from northern Quebec (Hudson Bay) are genetically different from those found in the south (two hours from Quebec)."
In addition, lichens can tell a lot about how wildfires affect ecosystems.
“Forest fires are the most serious in terms ofdamage incidents in boreal forests, and they play an important role in the distribution and composition of plant communities,” says Alonso-García. —In eastern North America, after a fire, four successive stages of vegetation are usually distinguished. At the first stage, crustose lichens and mosses colonize the scorched surface. Subsequently, the soil is covered with cup-shaped and horny lichens. And then after 20 years, fruticose lichens appear, replacing the previous vegetation.”
To study lichen DNA, researcherscrushed lichen samples and extracted their DNA. But an additional problem with lichens is that they are made up of fungi and algae that live together. “This means that all the DNA is mixed together, we get one pool that contains the DNA of the fungi and the DNA of the algae,” says Greve. The bulk of the lichen is made up of fungi, so the researchers wanted to focus on the DNA of this fungal component. By comparing the pool of DNA to existing genomes, the researchers were able to isolate DNA belonging to the fungus and then compare the DNA from lichen fungi from different parts of Quebec.
It turned out that lichens had a lot more genetic variation than the researchers expected.
“The general assumption was that thesedeer lichens mostly reproduce asexually because there was little evidence that they produce spores. Now, the genetic data shows all this diversity, and this leads to the assumption that it may be some form of sex, ”says Greve.
“In fact, we have discovered a variety of reproductive structures across species, and these structures are formed after sexual reproduction,” Alonso-García concludes.
At the same time, after a forest fire, new lichens that arise are genetically similar to those that were before.
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