"Supersonic" Dung Cannons: Pilobolus oedipus

(N.B. This post was originally published with the erroneous ID of Pilobolus lentiger. Thanks to Malcolm Graves for catching my error and pointing out that, because of its double-walled spores, this is actually Pilobolus oedipus.)

 

My friend Ulli handed me a large Tupperware container. "A present," she said.  

A peak under the lid revealed a large pile of horse manure—always a nice gift for an organic gardener. But this wasn't just any horse manure, this was special horse manure: it had sprouted a massive colony of a dung-loving fungus called Pilobolus, also known as the Dung Cannon or Hat Thrower. 

Golden clusters of Pilobolus lentiger on horse dung.

Pilobolus species, (which, like the Spinellus and Syzygites I wrote about in my last post, belong to the order Mucorales), are impressive little coprophiles that, despite their smelly choice of substrate, are not only well-studied, but have even managed to hit the news as the "Fastest Living Thing on the Planet." 

Pilobolus species are usually the first coprophilous
fungi to produce fruit on herbivore dung.

Copriphilous fungi evolved to produce fruiting bodies in animal waste, and the way the spores that produce these fruiting bodies get into that waste is usually via the gut, which means the spores first need to be ingested. There's a problem with this scenario, though: herbivores shun their own, and others' excrement when they're grazing. Each animal, in fact, has its own well-defined "zone of repugnance." So how to get the spores far enough away from the dung to be eaten? Build a squirt gun, that's how—at least that's how Pilobolus species do it. And impressive squirt guns they are. Some are capable of expelling spores more than six feet (2 m) away, which, in human terms, would be like having a kid's water pistol that could hit a target 500 ft. (150 m) away.   

The spore capsules launched by Pilobolus species are coated
with a sticky material that glues them to nearby blades of
grass or, in this case, the wall of a plastic container.

Using only the normal, osmosis-generated pressure levels of fungi cells, Pilobolus spores are launched so fast that, until recent advancements in high-speed photography, the action was invisible to the human eye. Though the spore packets only reach maximum speeds of 25 meters per second, which isn't exactly shabby for something less than a millimetre in diameter, their acceleration is stupendous—up to 180,000 G! I witnessed this spectacular feat, or more accurately was its target, while trying to take close-ups of these tiny fungi. I felt a distinct ping! on my cheek, then another on my forehead, then another on my lip. It felt strange to be under attack by tiny missiles, stranger still to know that these missiles were probably being aimed at sunlight reflecting off my face.

Pilobolus oedipus

Structurally, a single Pilobolus consists of a long, thin sporangiophore that is expanded at the end into the subsporangial vesicle. The fluid-filled vesicle is capped by a black sporangium, or spore packet, with resistant walls. Orange pigments inside the sporangiophore act as light sensors which, in conjunction with the subsporongial vesicle that functions as a lens, allow the fungus to track light and angle towards it. In essence, Pilobolus have "eyes," eyes that aim for the brightest light around, the sun. Their aim is pretty amazing, too. You can place them in a dark box with a single pinhole of light and after a few hours you will find their spore capsules glued in a tight cluster around the pinhole. 

Some Pilobolus species, like my P. lentiger, also have rhythm. Not that they're dancers, (though maybe with time-lapse photography and a moving light source it might appear as if they're dancing—anybody?), but there's rhythm to their sporulation. When researchers placed them in either continuous light or continuous dark, sporangia were discharged almost continuously. But in a half-day-of-light/half-day-of-dark cycle, they consistently discharged sporangia most vigorously 6 hours after the light period began. 

Pilobolus oedipus spores are globose double-walled.

 The black sporangium with its load of spores—the missile part of 
Pilobolus—sits like a hat on top of the subsporangial vesicle.

The spore capsule easily ruptures under the weight of a cover slide.

The columellae that the sporangium sits on
before discharge are mammiform. 

I didn't realize until it was too late that my Pilobolus specimens had
been aiming sporangia missiles at the lens of my camera as well
as my face while I was photographing them outside, hence the
dark smudges on all my micro pics.

Reference & Resources:

Key and descriptions of Pilobolus species found in Brazil

Key and photos of British Pilobolus species
Mycoquebec's key to Pilobolus species 
Spores of a few Pilobolus species
Bruce, V. G., F. Weight, and C. S. Pittendrigh. 1960. Resetting the sporulation rhythm in Pilobolus with short light flashes of high intensity. Science 131:728–30.
"Spore Ballistics" with a nice little video of spores discharging set to music

Cornell Mushroom Blog post on the connection between Pilobolus and lungworm

Fun videos

The Fastest Living Thing on the Planet

18 hour time lapse of Pilobolus crystallinus (if only they'd moved the light around they would have been dancing!)

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A Poop & Scoop Ascomycete: Pseudombrophila porcina

Our puppy Ruby—now almost a year old—developed an interesting habit after the first snow last fall: she used her snout as a shovel to meticulously bury every one of her droppings. Okay with us. Out of sight, out of mind, as far as we were concerned. But when the big thaw happened a couple of weeks ago we ended up with a major yard and garden clean-up that had nothing to do with last year's plant matter. 

As happens, we missed a couple, and a few days ago I came across one of these strays. I was about to scoop it up with a shovel and toss it into the woods when I noticed something peculiar about it. It was polka-dotted. 

Sigh. 

I knew what I had to do—get out my loupe so I could closely inspect, yes, my dog's doodoo. This is the life of an ascomycetes freak. And here's what I saw, which, precisely because I've turned into an ascomycetes freak, was exciting:

Immature Pseudombrophila porcina on dog feces.

I'd obviously found a coprophilic fungus. A dung lover. But which one? There are lots to choose from, especially from the ascomycetes clan. "Lots" is a good thing—I don't know about everybody else but I like the idea of animal dung being broken down and returned to the earth as quickly as possible, and fungi are perfect for the job.

Immature Pseudombrophila look like tiny beads.

My find was clearly immature, so I got a couple of pieces of toilet paper and a pair of tweezers and brought a sample into the warm house where I dampened the paper. With this simple coaxing, two days later the tiny brown beads had turned into pale beige discs with furry exteriors. The biggest was about 2 mm across.

Mature Pseudombrophila porcina are still tiny.

A bit of digging got me to two very similar species in the genus Pseudombrophila that are both known to colonize herbivore and carnivore dung, P. porcina and P. merdaria. After reading an illuminating discussion about these two on Mycofrance, I went to the microscope. 

Pseudombrophila porcina spores.

The spores were smooth and the tips of the paraphyses were not inflated, so it looks like mine are Pseudombrophila porcina. 

I hate to say it, but as unpleasant as animal dung might be, for people like me it's still worth taking a closer look. 

References:

Pseudombrophila porcina on Mycoquebec
Pseudombrophila merdaria on Mycoquebec 
Ascomycete Fungi of North America: A Mushroom Reference Guide, Michael Beug, Alan E. Bessette, Arleen R. Bessette, University of Texas Press, 2014

Three “Fairy Pins”: Chaenotheca brunneola, Phaeocalicium polyporaeum, and Mycocalicium subtile

"Fairy Pins" growing on Phellinopsis conchata growing
on black ash (Fraxinus nigra).

I used to be able to count the number of hairs on a flea’s leg—with the naked eye. Not so much anymore. This age thing has got hold of me, has stolen the elasticity of the lenses of my eyes the same way it’s been slyly stealing elasticity from other parts of my body.

There’s no help for the rest of me, but for my fast-failing close-up vision, my new best friend is my loupe. Without this little magnifier I’d be lost. I’d have no idea if a mushroom’s stem was smooth or minutely velvety, or if its cap was finely hairy or tomentose.

These possible Chaenotheca brunneola 
are minute, less than 1mm long.

So when I brought home a new polypore I’d carved off a standing dead black ash—standing in 2 feet of snow, I might add—I used my loupe to have a close look at it. Pore surface pale yellow-brown with a blush of gray, small pores. Pileus black and cracked and partially covered in moss and algae, and…hey...what’s this? Black whiskers?! Nope, not whiskers, more like mini black matchsticks—and by "mini," I mean less than a millimetre long.

Though I’d never actually seen it, I was aware of the existence of a tiny black “Fairy Pin” fungus called Phaeocalicium polyporaeum that grows on old, often algae-covered polypores. So I looked it up. Turns out, though, that its substrate is limited to Trichaptum species, and my Fairy Pins were definitely not growing on a Trichaptum of any kind—more likely a Phellinus, specifically, Phellinopsis conchata. So what on earth were they?

Chaenotheca brunneola

It took a bit of detective work with the internet and a microscope to tentatively put a name to this serendipitous discovery: Chaenotheca brunneola.  

Spores of Chaenotheca brunneola(?)

Chaenotheca brunneola isn’t a simple ascomycete, as the Phaeocalicium is, but instead one that happens to live in partnership with a photosynthetic algae—in other words, it's a lichen. It has a shiny black stem, and a black head that usually has a fuzzy brown coating of spores. It grows most commonly on dead wood, of both conifers and deciduous trees, on lumber and fence posts…and, occasionally, on polypores. Cool. If that's what my collection is. Though mine have the expected globose spores, the heads are not shaped like pinheads; they're more elongated—like teeny weeny Trichoglossum. 

Phaeocalicium polyporaeum growing 
on Trichaptum biforme.

Phaeocalicium polyporaeum

Although I'm still not sure what these little guys are, they piqued my curiosity, so out I went into the snow again to look for old Trichaptum to see if any were hosting the Fairy Pin I'd already heard about, Phaeocalicium polyporaeum. 

Not fifty metres from my house, I found a tree covered head to toe in Trichaptum biforme. I inspected one with my loupe. Aha! There they were! I inspected more. Eighty percent were hosting Phaeocalicium. Who knew it would be so easy?

Phaeocalicium polyporaeum spores

Mycocalicium subtile grows on wood.

Mycocalicium subtile

But the story doesn’t end there. A day later I stumbled upon another bunch of Fairy Pins, these ones strewn along the length of a naked maple limb suspended above the snow. Assuming I’d simply found more Chaenotheca brunneola on its more usual substrate, I ignored the sample I’d brought home until I was about to photograph it a few days later. I got out my loupe expecting to see brown, fuzzy Chaenotheca heads. But that’s not what I saw. These ones had distinctly black heads that were quite large in proportion to their stems. I immediately plucked one off with my tweezers and squashed it under a slide cover, and—ta da—under the microscope it was clear that I’d found a third species.

Mycocalicium subtile spores

After more detective work, I found a third name, Mycocalicium subtile, another non-lichenized species like the Phaeocalicium. It grows on decorticated wood, usually in the open, hence its common name, "Snag Pin." Though I can't find any reference to this one ever colonizing old polypores, I did discover that there is yet another non-lichenized pin that does: Chaenothecopsis caespitosa. Since that Fairy Pin is as tiny as all the rest, the only way I'll ever find it is with my trusty loupe.

References:

Hutchison, L. J 1987: Studies on Phaeocalicium polyporaeum in North America. - Mycologia 79(5): 786-789

Lichens of North America, Irwin M. Brodo, Sylvia Duran Sharnoff, Stephen Sharnoff, Yale University Press, 2001, 828 pages, ISBN: 0300082495

John Plischke III’s Trial Key to Mushrooms That Grow on Other Mushrooms