The lichen story and the guy who revised it

A story I wrote in July of last year described a huge change in our understanding of one of the best known cases of symbiosis: the view that a lichen is a symbiotic partnership between a fungus and an alga. That happens to be true—the alga photosynthesizes, producing food for the fungus, while the fungus provides support, water, and minerals for the alga. But there’s more.

The alga/fungus partnership was discovered in 1868 by the Swiss botanist Simon Schwendener, and it’s what all of us who took biology were taught—until last year. For that’s when a paper came out in Science by Toby Spribille et al. (see my summary of it here) showing that there was a third partner in the symbiosis: another fungus, but a basidiomycete (a group that includes yeasts) along with the well-known ascomycete (the two groups of fungi diverged about 400 million years ago),

A piece by Ed Yong in last year’s Atlantic, called to my attention by reader Hempenstein, tells how Spribille, raised in a trailer park in Montana, came to the discovery that overturned over 150 years of conventional wisdom.  It’s a cool tale, involving sequencing the genome of two lichens that seemed to involve the same species of ascomycete fungus but one of which appeared to contain basiodiomycete genes as well.  The failure to recognize this third partner in the relationship explains why scientists had encountered difficulties trying to make synthetic lichens by combining the constituent ascomycete and alga in the lab. They were simply missing a partner.

Of course Spribille wasn’t working by himself: there are 12 other authors on the Science paper describing the finding. And we’re not sure if all lichens have these three constituents: so far Spribille has found this situation to obtain in most of the “macrolichens”, but not all of them. And there are other groups of lichens that haven’t yet been examined. Finally, this whole revision may lead to a revision of what each of the partners provides for the others. Clearly the algal role is well defined, but what about the two types of fungi?

At any rate, the story shows the surprises that await us, and how easily long-established paradigms can change in an instant—especially now that we have the ability to sequence DNA. I’ll give just one excerpt from Yong’s piece, “How a guy from a Montana trailer park overturned 150 years of biology”. (I have to say that’s a bit clickbait-y given that Spribille did get a Ph.D. and did his work in a great lab (the McCutcheon group) working on symbiosis; and, moreover, it was a collaboration and not just the work of one guy.)

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 everywhere in that outer layer,” says Spribille.

Despite their seemingly obvious location, it took around five years to find them. They’re embedded in a matrix of sugars, as if someone had plastered over them. To see them, Spribille bought laundry detergent from Wal-Mart and used it to very carefully strip that matrix away.

And even when the basidiomycetes were exposed, they weren’t easy to identify. They look exactly like a cross-section from one of the ascomycete branches. Unless you know what you’re looking for, there’s no reason why you’d think there are two fungi there, rather than one—which is why no one realised for 150 years. Spribille only worked out what was happening by labeling each of the three partners with different fluorescent molecules, which glowed red, green, and blue respectively. Only then did the trinity become clear.

Here’s a photo from the science paper showing the yeasts:

f3-large1

(from paper): Figure from paper. (A) B. fremontii, with (B) few FISH-hybridized live yeast cells at the level of the cortex. (C) B. tortuosa, with (D) abundant FISH-hybridized cortical yeast cells (scale bars, 20 μm).

And the mysteries that remain:

“But really, we don’t know what they do,” says McCutcheon. “And given their existence, we don’t really know what the ascomycetes do, either.” Everything that’s been attributed to them might actually be due to the other fungus. Many of the fundamentals of lichenology will need to be checked, and perhaps re-written. “Toby took huge risks for many years,” says McCutcheon. “And he changed the field.”

31475686-flavoparmelia-caperata-macrolichens-stock-photo

A macrolichen. (Source here).

38 Comments

  1. Mark Reaume
    Posted January 17, 2017 at 1:59 pm | Permalink

    sub

  2. busterggi
    Posted January 17, 2017 at 2:00 pm | Permalink

    “how easily long-established paradigms can change in an instant”

    Gotta disagree – adding a third ‘partner’ to the relationship doesn’t invalidate the other two previously known ones. Its’ additional info but it doesn’t replace what was already known.

    • Gregory Kusnick
      Posted January 17, 2017 at 2:29 pm | Permalink

      It certainly calls into question some of what we thought we already knew, such as the role of the ascomycetes in the partnership.

    • Diane G.
      Posted January 18, 2017 at 1:21 am | Permalink

      Yeah, to me this seems fascinating but not revolutionary.

  3. Janet
    Posted January 17, 2017 at 2:25 pm | Permalink

    Wouldn’t it have been fun to be the one who made this discovery! How many more surprises are out there?

    • Mark Sturtevant
      Posted January 17, 2017 at 6:41 pm | Permalink

      Exactly 3 more. Then we will have found all there is to know. 😉

      • Mark Joseph
        Posted January 18, 2017 at 9:56 pm | Permalink

        Kind of like Somerset Maugham’s three rules for writing a novel! 😉

    • Michael Fisher
      Posted January 17, 2017 at 11:17 pm | Permalink

      We have some big surprises in the world of single-celled organisms – especially in difficult places such as deep in the crust. I suspect that most of the biomass may be ‘hanging out’ underground below both land & sea bottom [just my personal opinion based on no learning 🙂 ]

      I was reading about bits of DNA that have been sifted from those regions I mention & it’s known there’s some single-celled creatures down there that are worldwide distribution, but nobody can point & say “there it is” – we have no samples of the actual organisms & it’s a tricky problem to match the two types of samples other than by grabbing everything & going from there. How do you do that & keep the creatures alive & comfortable?

  4. Hempenstein
    Posted January 17, 2017 at 2:31 pm | Permalink

    Make sure to read the Atlantic piece for the outline of Dr. Spribille’s journey after the trailer park part. Here’s the beginning of the relevant excerpt:

    “… He was raised in a Montana trailer park, and home-schooled by what he now describes as a “fundamentalist cult.” At a young age, he fell in love with science, but had no way of feeding that love. He longed to break away from his roots and get a proper education. …”

    All I can say is Bravo!

    • Posted January 18, 2017 at 11:49 am | Permalink

      It is cases like this which convince me that public education has to be one of our most important social projects.

      Imagine all the other innovators and thinkers that are left to languish because they too were in trailer parks with bad schools – cultic or otherwise.

  5. Barbara Radcliffe
    Posted January 17, 2017 at 3:02 pm | Permalink

    Having had a long term love affair with lichens I shall continue following this fascinating story!

    • Christopher
      Posted January 17, 2017 at 11:23 pm | Permalink

      I second that! A hand lens or a microscope and a bit of lichen makes for a pleasing afternoon, even if I’m still so uneducated that I can’t ID the species. In winter, after a rain or a snowmelt, they are like glowing jewels plastered on trees and rocks. I still remember feeling the thrill of teasing apart a lichen and peering at in under the microscope in my biology lab and seeing an ascus and the spores for the first time.

  6. Steve Pollard
    Posted January 17, 2017 at 3:12 pm | Permalink

    Thanks for this fascinating story. I was brought up on the two-way symbiotic picture, so the third dimension is an intriguing complication. I have nothing to add but kudos to Dr Spribille, and apologies to PCC(E) for not clocking my interest in the science posts more explicitly.

    • Mark Joseph
      Posted January 18, 2017 at 9:57 pm | Permalink

      Exactly. I’m checking in here to say that I’m reading (and loving) this science post!

  7. Posted January 17, 2017 at 3:22 pm | Permalink

    If this were posted on Facebook, I would lichen it.

    • Mark Sturtevant
      Posted January 17, 2017 at 6:44 pm | Permalink

      In England I think they pronounce it “litch-ens”, and so one would say
      “I would lick it”. Which, fortunately, is also funny.

      • Marilee Lovit
        Posted January 17, 2017 at 7:47 pm | Permalink

        Some lichens have a peculiar taste. I was in a field trip once where the instructor had us licking lichens on tree bark.

        • Christopher
          Posted January 17, 2017 at 11:26 pm | Permalink

          I’m sure the ones lower on a tree trunk, leg-high to a dog certainly have a peculiar taste…actually, now that I’ve said that, (and thought of the ones higher up watered by squirrels) I’ll have to lick one myself. It may sound odd, but I don’t usually explore the outdoors with my tongue, I’m more tactile-visual, but clearly I’m missing something.

          • Marilee Lovit
            Posted January 18, 2017 at 5:43 am | Permalink

            Other than taste, the tongue can feel differences in how smooth (glabrous) or rough (scabrous) a surface is, even better than fingers can. In a sedge class, different teacher from the lichen class, we also used the tongue test, for the leaf sheath. This teacher sometimes referred to the glabrous sedges as “smooth as a frog’s belly.” Never used toads in that comparison.

          • kieran
            Posted January 18, 2017 at 8:51 am | Permalink

            There are soil science techniques that involve putting dirt in your mouth. When I started in a lab I was still told to refrain from mouth pippetting

            • kieran
              Posted January 18, 2017 at 8:52 am | Permalink

              Also to identify certain species of grass you have to chew it and it produces a vanilla flavour

              • Marilee Lovit
                Posted January 18, 2017 at 3:21 pm | Permalink

                Sweet grass does that. Meaning Hierochloe odorata renamed Anthoxanthum nitens.

              • Christopher
                Posted January 18, 2017 at 4:39 pm | Permalink

                So that means crab grass tastes like…

        • Posted January 17, 2017 at 11:57 pm | Permalink

          Just don’t lick any toads.

  8. Posted January 17, 2017 at 4:11 pm | Permalink

    This work must have been done by creationists. After all, they always tell us that all evolutionary biologists do is sit around telling just-so stories and adulating Darwin. No actual sequencing, or any such.

    😉

  9. Michael
    Posted January 17, 2017 at 4:28 pm | Permalink

    Toby Spribille’s life looks like it would make a great miniseries. Netflix might be interested.

    • Hempenstein
      Posted January 18, 2017 at 12:27 pm | Permalink

      Something of the sort, anyway. There seems almost nothing online re. his early years beyond the “fundamentalist cult” in the Atlantic piece, but I did find this. Looks like he’s from the Missoula area, up on Flathead Lake. Per friends in Missoula, there are Hutterites up on the lake, and that combined with his German that per the Atlantic piece enabled him to get into U Gottingen, Hutterite seems a good guess, as someone else suggested I think when PCC(E) first posted on this (since it doesn’t seem to be here). From the Missoula News link here, it seems he has a strong bond to the area, returning every year, and so it might be a better descriptor to say that he came from an insular community.

      Some discomfort in the snooping, but isn’t that what scientists do in a sense?

  10. loren russell
    Posted January 17, 2017 at 4:30 pm | Permalink

    The story here, involving the hidden yeast partner is fascinating, but may not be the end of the story.

    Lichens, in the broad sense of a symbiosis involving one or more fungal and one or autotrophic partners.. are highly polyphyletic. The great majority of full-on lichens have an ascomycete as “dominant” — or perhaps, “architectural” fungal partner, but there are also basiomycetes in this role. In some cases, the association must be quite recent — for instance, in the agaric genera Omphalina [“little belly button”] and Xertomphalina [“dry little belly button”] where some species form lichen associations, and others are decomposers.

    The traditional school figure, 2-partner lichens are merely an entrée to the complexity of trophic symbiosis. If we look, we will find multitudes of such connections.

    • Michael Fisher
      Posted January 17, 2017 at 11:23 pm | Permalink

      I take your post as a challenge Loren 🙂

      I understood one in three terms that you used. I’m getting my online dictionary out & see if a light turns on for me

  11. Jonathan Wallace
    Posted January 17, 2017 at 5:26 pm | Permalink

    Fascinating! My knowledge of lichens is pretty basic but I love seeing them – both the brightly coloured crustose ones that paint ‘maps’ on rocks and the tufted or leafy ones that give trees (a least in unpolluted places)fantastic beards.

  12. Marilee Lovit
    Posted January 17, 2017 at 6:02 pm | Permalink

    The Science paper is not a free download. I appreciate Jerry’s posts both last year and this one. I am trying to learn more about lichens, and am lucky that so many live in my surroundings.

  13. Mark Sturtevant
    Posted January 17, 2017 at 6:39 pm | Permalink

    Completely cool, and a good example where taking a calculated risk can pay off big.

  14. Paul S
    Posted January 17, 2017 at 6:52 pm | Permalink

    Very cool. I’ve been fascinated with lichen for years. Admittedly my previous knowledge is from the 1958 Encyclopedia Britannica.

  15. jeffery
    Posted January 17, 2017 at 7:04 pm | Permalink

    I don’t see where Spribille was “taking huge risks”: of course, he would have lost the time and energy spent on his studies if his work hadn’t have panned out, but he would’ve ended up gaining something- at the very least, the knowledge that he was wrong and that what he suspected was true wasn’t the case. Was his career, or reputation on the line?. Sounds like another bit of “click-baityness” on Yong’s part, like Spribille was some kind of persecuted, “lone-wolf” scientist battling the forces of hidebound conformity. It was just science, guys!

  16. Ken Elliott
    Posted January 17, 2017 at 8:49 pm | Permalink

    I am lichen and fungi ignorant, but found this to be fascinating due to the paradigm shift that came about from Spribille and company’s dogged determination and subsequent discovery. Discoveries of this magnitude are quite rare, regardless of field, aren’t they? As any soccer fan knows, when that rare feat of skill and timing comes off in a match it is thrilling beyond description. I can’t imagine the level of sheer primal elation they must’ve felt, both immediately, and for days…..weeks afterward.

  17. Posted January 18, 2017 at 7:42 am | Permalink

    Very interesting article and posting. Thanks.

    “But really, we don’t know what they do,” says McCutcheon.

    But we do know: They are propagating their selfish genes.

  18. Posted January 18, 2017 at 11:52 am | Permalink

    Wow. What other examples of three-way symbioses are there?

  19. Jeff
    Posted January 19, 2017 at 4:37 am | Permalink

    Great, thanks. Motivated me to get a book on lichens.


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