Lichen Life Will Find a Way

By: Bristol

This article is about why lichens are amazing. You may be familiar with lichens as those crusty circular patches on rocks, greenish tufts on tree branches, or trailing wispy tendrils like witches hair and Methuselah's Beard. They are stationary little flourishes on the landscape, scarcely noticeable.

Ragbag lichen from Puget Sound region of Washington

Lichens are a unique example of symbiosis, or a partnership, between a fungus and an algae. But how does that actually work?

Each individual lichen is composed of fungal filaments, or hyphae, which make up the actual structure. The specific fungi that are found in lichens are called lichenized, and are not found naturally outside of their lichen form. This is because lichenized fungi cannot survive without their partner, or photobiont. A photobiont is an organism that uses sunlight and air to make food, usually in the form of sugars or alcohols. In lichens, the photobiont is either an algae or cyanobacteria (usually an algae). These live interspersed among or sandwiched between two layers of fungus.

Witch's hair lichen from Prince William Sound, Alaska

Within the structure of a lichen, the fungus shelters and nurtures the algae cells, capturing water and air-borne nutrients for both of them. But it also forces the algae to give up a disproportionate amount of sugars (Some 70-80%). Their symbiosis is almost more of a parasite-host situation. This relationship, however, has enabled both organisms (or one composite organism) to survive a vast array of habitats and situations.

Unknown lichen from Prince William Sound, Alaska

Lichen diversity is concentrated in northern latitudes, around the Canadian border for those of us in North America. The Arctic alone has 1,750 species, and there's at least 250 species in the Antarctic. They can lie dormant and inert for long periods of time, and spring into life again when conditions improve (because of this they grow extremely slowly, from 1-4 mm to 9 cm per year). These hardy organisms have even survived outer space. A sample of elegant sunburst lichen was placed outside the Space Station in 2005 for 14.6 days, blasted with solar radiation and numbing cold, not to mention zero atmosphere and zero gravity. We humans last effectively no time before our lungs explode and we freeze horribly. The lichen was completely fine. In 2013 a lichen was placed in space for the next 1.5 years, and most of it (70%) remained viable (this is great support for the theory of Panspermia, which postulates that life came to earth from elsewhere in the universe, likely in the form of something hardy and indestructible, like lichens. Or waterbears).

Fishbone beard lichen from Puget Sound region of Washington

There's another reason I think lichens are pretty cool: They are an excellent example of one of my favorite biology quandaries. How do we define individuals and species? This probably sounds boring. Bear with me.

Life on this planet is like a fluid entity, constantly changing and evolving over time. Lineages break off and flourish, or go extinct, never to arise again. Some groups of organisms diverge only to rejoin thousands of years later.The overall goal of all life on this planet is to continue existence, in any way possible. And it’s really only static from the point of view of a short-lived organism, like ourselves. Over geologic time, separating groups of organisms into species makes no sense at all.

Wolf lichen in California

Lichens illustrate why this concept often doesn’t work even over shorter time periods. Why? Well, defining an individual lichen is tricky. The composite organism of fungus and algae is already two different species that together make one form. But there are a mere handful of photobiont species that are found in lichens, and thousands of lichen species. For example, of 1,750 arctic lichen species, there are only about 150 different species of photobionts associated with them. This means that many lichens use the same algae or cyanobacteria. Also, the algae can usually be found surviving outside the lichen, while the lichenized fungus cannot. For these reasons, lichens scientific names are the same as the fungus species. This is weird because each fungus is able to associate with more than one photobiont species at once, and even with different ones in different places. And these different partners can produce very different-looking lichens. Which still share the same scientific name because they involve the same fungus.

Green shield lichen from Hawk Ridge, Minnesota

In general, we tend to consider a species to be a group of organisms that can breed successfully. But we have gray areas. A couple more examples of creatures that don’t fit our neat species categories:

Canis lupus familiaris, specifically an Alaskan husky named Fiddle.

Dogs are all considered one species:

Canis lupus familiaris. And all along the size range, they can interbreed. But if you

take the extreme ends, say a Great Dane and a chihuahua, they could not breed naturally. Where do we draw the line?

A Western Gull on the Columbia River, Washington.

Another example of this is arctic gulls. In

a ring around the north pole are a series of gull species. Each of these can interbreed with its neighbor species, but when it comes full around and meets again, the two species have become too different to breed. So at which point are they really different species? (Note: there is some recent controversy on this subject, and if you're interested check out this scholarly article or this blog post which both explain further.)

Last one: Polar bears and grizzlies. They diverged from a common ancestor around 100,000 years ago, give or take. Right now, climate change is drastically altering the habitat that polar bears need. Melting sea ice is forcing them to move to survive. And in doing so, they are interacting with brown, or grizzly, bears. The hybrid bears, called pizzlies, are perfectly viable. Over time, the two bear species may very well merge, effectively breeding the polar bear species into extinction. They were really only separated by habitat needs.

The system of categorizing species works pretty well, on the whole, for us and our 80-year time scale. But if you step back, the gray areas are everywhere. There really isn't a perfect way to categorize life, and I find this both frustrating and fascinating. Lichens, as a composite organism, are an amazing example of the endless plasticity and fluidity of life, and one that you can find right outside your front door. Next time you go for a walk or a hike, be on the lookout for these hardy little gray-green life-forms. Ponder the iconic words "life finds a way", and how they relate not only to the terror-lizards, but to the humble lichen.

British Soldiers, Puget Sound region of Washington