Lichen: The Threesome

SCIENCE

Traditionally, scientists have likened lichen to a married couple. But a new study suggests a third partner contributes to their ecological domestic bliss. (Washington Post)

Learn all about lichens with our poem!

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• We love lichen here at Nat Geo. What is lichen? Read through our fun poem for some help.
  • Lichens are a huge group of composite organisms. (Composite organisms are simply organisms that are made up of two or more independent organisms.)
    • Lichens are made up of an alga or cyanobacterium partner (called the photobiont), and a fungus partner (called the mycobiont). The mycobiont provides the lichen with minerals (structure), water, and shelter, while the photobiont provides the lichen with nutrients through photosynthesis.
  • Find some lichens on the “circle of life” here. Try Bryoria tortuosa, one of the lichens in the new study.
  • Lichens are some of the most common organisms on Earth. They are found in scorching desert heat and ancient Arctic ice, at sea level and Alpine elevations, on bare rock outcrops and the trees and shrubs of dense forests. (Super-successful little organisms!)

 

• Lichens probably have the most famous symbiotic relationship in nature. What is a symbiotic relationship? What other organisms engage in symbiotic relationships?
  • Symbiosis simply describes two or more distinct organisms living together for the benefit of one or both. (It’s a contested term among biologists, but that’s a pretty standard definition.)
  • Symbiotic lichens “have an important place in biology. In the 1860s, scientists thought that they were plants. But in 1868, a Swiss botanist named Simon Schwendener revealed that they’re composite organisms, consisting of fungi that live in partnership with microscopic algae … This kind of mutually beneficial relationship was unheard of, and required a new word. Two Germans, Albert Frank and Anton de Bary, provided the perfect one—symbiosis, from the Greek for ‘together’ [sym-] and ‘living’ [bio-].”
  • Although the term was literally invented to describe the fungi-algae relationship among lichens, the natural world is full of symbiotic relationships.
    • cows and gut flora. A cow’s digestive tract is full of specialized bacteria and protozoa that allow the cow to digest plant material. The microbes get a suitable place to live and a supply of food. The cow gets energy from digesting the gut microbes and the fatty acids they produce.
    • corals and algae. Brightly colored algae live inside coral tissues. The coral provides the algae with a protected environment and compounds they need for photosynthesis. In return, the algae produce oxygen and help the coral to remove wastes.
    • clownfish and sea anemones. Clownfish live among the toxic tentacles of sea anemones. The clownfish protects the anemone from anemone-eating fish. In return, the stinging tentacles of the anemone protect the clownfish from its predators. (A special mucus on the clownfish protects it from the stinging tentacles.)

 

• How has the new lichen study “overturned our longstanding assumptions about the best-studied symbiotic relationship on the planet”?
  • In more than 50 species of lichens on six continents, there are actually three partners in the symbiotic relationship, not two. The third partner is another type of fungus, known as a basidiomycete yeast.

 

• After 150 years of lichenology and microscopy (great vocab words!), how did scientists miss the yeasty “silent partner”?
  • The yeast has great chemical camouflage. “Down a microscope, a lichen looks like a loaf of ciabatta: it has a stiff, dense crust surrounding a spongy, loose interior. The alga is embedded in the thick crust. The familiar ascomycete fungus is there too, but it branches inwards, creating the spongy interior. And the basidiomycetes? They’re in the outermost part of the crust, surrounding the other two partners … They’re embedded in a matrix of sugars, as if someone had plastered over them. To see them, [the lead researcher] bought laundry detergent from Wal-Mart and used it to very carefully strip that matrix away.”

 

• Is there anything else we can possibly learn about the lowly lichen?
  • Yes! And don’t call them lowly.
    • What does the yeast do? Mycologists (people who study fungi) are not at all sure how the yeast partner contributes to, or benefits from, the symbiotic relationship.
      • “[the yeast] may provide structural support in addition to producing protective chemicals”
      • “it’s possible that the basidiomycete influences the growth of the other fungus, inducing it to create the lichen’s stiff crust … ‘But really, we don’t know what they do,’” says one researcher.
    • How do lichens get together in the first place? Another researcher says “We now see that [lichens] require two different kinds of fungi and an algal species. If the right combination meet together on a rock or twig, then a lichen will form, and this will result in the large and complex plant-like organisms that we see on trees and rocks very commonly. The mechanism by which this symbiotic association occurs is completely unknown and remains a real mystery.”

 

TEACHERS TOOLKIT

Washington Post: Lichen is a famous biological partnership — but it might actually be a threesome

Nat Geo: Lichen It Already

The Atlantic: How a Guy From a Montana Trailer Park Overturned 150 Years of Biology (typically great read from Nat Geo contributor Ed Yong!)