I’m about to get quite busy for the month of April which is great but I may have to slow the pace of my posting. This will probably be fine considering there hasn’t been a ton of responses to my posts, yet. I wanted to try to answer as many of the questions about lichens as possible. The photo above isn’t the best but it is the only example of a lichen I could find in my collection.
Lichens are a kind of text book example of symbiosis. Symbiosis means “living (bios) together (sym).” It is whenever two organisms form a relationship in which both benefit. Sometimes these relationships are necessary for the survival of one or both members and sometimes the organisms can live without them. In the case of lichens it is a relationship between a fungus and either a green alga or a cyanobacteria. These two kinds of organisms are both single-celled, photosynthetic creatures whose cells contain the same kind of chlorophyll as land plants’ chloroplasts.
Lichens acquire their food entirely through photosynthesis. So why do those little one-celled creatures need the fungus? They don’t. Most species of alga and cyanobacteria that are found in lichens can and do survive by themselves. But there is an advantage to forming a relationship with the fungus. Lichen-forming fungi produce a substance that speeds photosynthesis, making it a bit more efficient. They also absorb enough water for both the fungus and their photosynthetic friends so these cells don’t need to worry about getting water. It seems to be a very good advantage for the unicellular symbionts because many lichen-forming fungus species actually parasitize the chlorophyll containing cells.
They do not, however, tend to parasitize the trees they may be growing on. Most lichens use their growing surface simply as a substrate and do not have roots or other structures that take nutrients from below.
The coolest fact I found about lichens is that some species can live up to 4500 years. I don’t know what the life spans of most fungus are but that seemed pretty impressive.
It’s interesting how much parasitism, symbiosis and commensalism have already come up on the mycelial network. This is a perfect illustration of how the biological world is not set out in discrete parts but forms a web of interactions and relationships; it forms an ecology. What are some of your favorite examples of organisms living together (whether parasitically or not)?