I, lichen.

This fungal individual makes lots of complex structures, on which microbes live. So do you.

A lichen is an ecosystem. It consists of a multicellular fungus that provides the gross structure of the lichen, and a community of microbes that live in and on that structure, including photosynthesizers.

A human is an ecosystem. It consists of a multicellular animal that that provides the gross structure of the human, and a community of microbes that live in and on that structure. A human, unlike a lichen, generally cannot photosynthesize. 

We usually see humans as individuals, but lichens as ecosystems. In the last few years some scientists have advocating deep thought about humans as ecosystems. There has been very little deep thought about lichens as individuals.

Adventitious knowledge

Joseph Grinnell, eminent ecologist and zoologist of the early 20th century, and founding Director of the Museum of Vertebrate Zoology, where I was a graduate student, wrote some hilarious stuff. Google Scholar lists 376 publications in his name, most of which are actually by him, including foundational papers in niche ecology, bio-geography, museum science, and so forth. He took so many thousands of pages of detailed, elegant, highly legible, informative, rigorous, lyrical, systematic field notes that if I told you how many, I'd have to look it up again, and it is getting late here. And he is rightly revered as a founder and role model in the MVZ. But perhaps my favorite thing of all about Joseph Grinnell is his nearly forgotten, mildly disturbing, profoundly droll paper, "A Striking Case of Adventitious Coloration." I have no memory of how I first encountered this paper, other than that it was in my former life as an ornithologist at the MVZ. I have never come across another paper that cited it, and Google Scholar lists none. It is, at core, a mystery.

The whole story is available here. The first two sentences:

On February 8, 1920, I spent the afternoon with my family at a point in Moraga Valley, Contra Costa County, California, some five miles, airline, northeast of Berkeley. My son Willard undertook to exercise the shotgun for the purpose of securing some specimens of local birds such as happened to be needed at the Museum.

So ornately informal, so precisely vague, so informatively not-to-the-point, I am in love with this opening. No reputable journal would publish it these days, and that is a shame. He's storytelling, and quite well. The story strides on: Willard blasts a mated pair of Oak Titmice, both of whom have bright yellow breasts. Why bright yellow? Oak Titmice are grey, never yellow.  Grinnell rushes the five airline miles back to Berkeley, marches into the botany department with his dead birds, and tells them to figure out what kind of yellow pollen these birds have got on them. Not pollen, say the botanists. Grinnell marches into a mycology lab and tells them to figure out what kind of yellow spores his birds have on their breasts. Maybe slime molds, hard to tell, say the mycologists. Grinnell concludes that possibly bird feathers could be an important means of dispersal in slime molds! He finishes by pointedly mentioning that if anyone is interested, these two birds "and their loads of spores, constitute Nos. 40,391 and 40,392 in the bird collection of the Museum of Vertebrate Zoology." He publishes the whole thing in The Auk, and that is the end of that, for almost a century. A century, by the way, is how long Grinnell said some of the MVZ's specimens might have to wait before they would be put to some as yet un-imagined use. It has been 97 years.

Which brings me to that wonderful word in Grinnell's title, "adventitious." It means something on the order of "acquired by chance" which is how those titmice presumably got their yellow, and how I came to the knowledge that in a drawer in Berkeley two spore laden titmice waited.  What did I intend to do with this knowledge? Keep it in a drawer, until, perhaps after one hundred years, it proved valuable.

Now, I unexpectedly find myself with colleagues interested in spore dispersal ecology, and somebody mentioned spore dispersal via bird feathers. Which started me rummaging around in my dusty rusty musty gusty fusty drawers of ornithology, hunting for memory of birds with spores on them. All I remembered clearly was Willard undertaking to exercise the shotgun, but eventually (this morning) I found first memory, then paper, and shared both. And by afternoon my new mycology colleagues had requested access to Nos. 40,391 and 40,392 from my old ornithology colleagues at the MVZ, so that we can collect some of the long faded yellow dust. A little bit of molecular genetics wizardry (our lab is set up for sequencing DNA from dried fungal museum specimens) and we may finally be able to discover what made Grinnell's birds so yellow. If it is a new species of anything, we must surely name it after Willard.

Hyphum

I know a bit about a lot of organisms, but don't really qualify as an expert on any species. It is great fun planning experiments with people who know a lot about a particular organism. I can say, "if a hypha that is only 300 microns breaks in half, do you get two living 150 micron individuals, or two dead hyphae?" and get the immediate response, "The singular of hyphae is hyphum," followed by, "you would get two dead halves, so we don't have to worry about it." This way I can concentrate on designing the experiment and learn good Scrabble words.

EDIT: May 2nd 2017.
 The singular of hyphae is actually hypha. I just stumbled upon my own old blog post and said, "Whoa! That's wrong." I must have misheard that six years ago.

Jon Asks: 1

I've read that fungi are the only organisms that can degrade the longer-chain fibers in wood, such as lignin, and that without saprobic fungi the world would be blanketed in dead, undecayed trees. I see on Wikipedia that it is not literally true that no bacteria can degrade lignins, however, by Wiki's account, it does seem that no known bacteria are very good at it. (http://en.wikipedia.org/wiki/Ligninase) So why would that be the evolutionary case? Bacteria have evolved to break down pretty much everything else on the planet (roughly speaking), and wood has been around for something like 350+ million years. Why would they be such second-rate degraders when it comes to lignin?

This is an interesting question, but not one I can give a very satisfying answer to. Explanations of why something didn't evolve are always fairly speculative. Why no six legged tigers? Why no live-birthing birds? Why no Ents?

So why no lignin devouring bacteria? If they can do it poorly, why not well? Maybe it isn't worth their while to invest in that capacity, as they are always outcompeted by the fungi who can already do it? Maybe they can rely on the fungi to make the enzymes, and then they can just mooch. Perhaps the process of making the necessary enzymes requires separate cellular compartments, which bacteria lack. Maybe the necessary mutations just never occurred, and so couldn't be selected for. Certainly I don't know.