Reindeer moss has more sex than expected

In northern Canada, the forest floor is covered with reindeer moss. They look like a moss made of small gray branches, but they are stranger: they are compound organisms, a fungus and algae that live together as one. It is a large part of reindeer diets, hence the name, and the forest depends on moving nutrients through the ecosystem. They also have, at least in parts of Quebec, much more sex than scientists expected. In a new study in the American Journal of Botany, researchers found that the reindeer mosses they examined had unexpected levels of genetic diversity, suggesting that the lichens did more no-mix with each other than scientists would have guessed.

“We were surprised because this species of reindeer moss has always been considered a clonal species that reproduces asexually,” says Marta Alonso-García, the paper’s lead author and a postdoctoral fellow at the Université-Laval of Quebec. “It does not follow the expected pattern.”

Reindeer mosses swing both ways: they can sexually reproduce through spores, or they can clone themselves asexually. When fungi reproduce sexually, they send out root-like structures to a neighboring fungus and exchange genetic information when they touch. They then release spores, single cells that contain genetic material, that move and spread on the wind. When they land, they begin to grow and produce a new baby fungus that is genetically different from its parents. In asexual clone production, on the other hand, a piece of the entire lichen (fungus and algae), called the thallus, is cut off and regrowth into an entire organism that is genetically identical to its parent.

The two methods of reproduction have different advantages. “Sexual reproduction is very expensive,” said Felix Grewe, co-director of the Field Museum’s Grainger Bioinformatics Center and co-author of the study. “You have to find your mate, it’s harder than reproducing asexually. But many organisms do it, because if you have this combination and blending of genetic traits, you can eliminate negative mutations in the long run among other benefits.”

The researchers were studying reindeer mosses (Cladonia stellaris) to learn their genetic patterns. “We used DNA sequences to pull apart the genetic relationships between populations of this lichen,” says Alonso-García. “We tested whether individuals from Northern Quebec (Hudson’s Bay) were genetically different from those from the South (Parc National des Grands-Jardins, two hours from Quebec City). At the same time because of the important role in the colonization process after a fire we evaluated the genetic diversity of the wheat alongside a sequence of fires. ‘

Lightfish can reveal a lot about how wildfires affect ecosystems. “Wildfires are the most important disturbance in the northernmost forests in the world, and they play an important role in determining the distribution and composition of plant communities,” says Alonso-García. “In eastern North America, four consecutive vegetation stages are generally identified after a fire. During the first phase, lichens and mosses colonize the burned surface. Subsequently, the soil is covered with hill and horn mosses. The landscape remains mostly uniform for about 20 years until the advent of fruit mosses replacing the previous vegetation. Cladonia stellaris arrives the last one, usually three or four decades after the fire. “By studying genetic variations in reindeer mosses, the researchers hoped to learn how lichen recolonizes an area after a fire.

To study the DNA of the lichen, the researchers made samples of lichen and extracted their DNA. But lichen presents an extra challenge in this process, because it consists of a fungus and an algae (or a type of bacteria that perform photosynthesis) that live together. “That means all the DNA is put together, we have one pool that contains fungal DNA and algal DNA,” says Grewe. “We need to carefully filter and sort the order that reads bioinformatics.” The main body of a lichen consists of the fungus, so the researchers wanted to focus on the DNA of the fungal component. By comparing the pool of DNA with existing genomes, the researchers were able to select the DNA belonging to the fungus, and they were able to compare the fungal DNA of reindeer lichens from different areas of Quebec.

What they found was surprising: in general, there was far more genetic variation in the lichen than the researchers expected, and this suggests hanky-panky. “It is a common assumption that these reindeer lichens reproduce mainly asexually because there is little evidence that they produce spores, but now the genetic data show all this diversity, and this leads to the assumption that it may be some form of sex, says Grewe.

“We expected lichens from northern Quebec to be more similar than those from Parc National des Grands-Jardins. However, our results indicate constant migration of C. stellaris between populations throughout eastern North America,” says Alonso -García. . “Contrary to popular belief, we have actually found many reproductive structures in the species and these structures are formed after sexual reproduction.”

But while the lice appear to be more genetically mixed than expected, the researchers also found that the new lichens that emerge after a forest fire are genetically similar to those that were there before. It was counter-intuitive – the idea was that the small cloned crusts would be destroyed in a fire and that the repopulation of lice would grow from tracks coming from other areas on the wind. “In terms of the genetic diversity of the species after fires, we found no differences in four consecutive phases. This was also surprising, because the time since the last fire increases the probability that clonal fragments have successfully reached the sites, which is the genetic diversity. increase, “says Alonso. -García.

In addition to revealing the hidden sex life of reindeer moss, the study could also have implications for forest conservation. “We have learned that time since the last fire does not necessarily mean more genetic diversity. Therefore, conservation strategies in boreal forests must take this into account,” says Alonso-García. “The protection of an area should not be based solely on its age. This is very important because funding is usually limited, so we cannot carry out conservation activities throughout the forest.” In short: if conservation scientists want to protect forest areas with genetically diverse corn populations, the age of the forest is not the only indication of diversity.

Grewe adds the importance of bioinformatics in learning how organisms relate to each other. “It is amazing that today we can have such a detailed view of the evolution of populations using bioinformatics,” says Grewe. “This is another great example of how advances in sequencing technology enable us to learn in more detail than ever before about the evolution of an organism.”

---

---