Natures wonders: lichens triple maybe quadruple partners (Introduction)

by David Turell @, Saturday, January 19, 2019, 00:05 (395 days ago) @ David Turell

There may or may not be complete symbiosis. There may be three or more partners that must be an algae and some fungi:

"Lichens can be found growing on bark, rocks, or walls; in woodlands, deserts, or tundra; as coralline branches, tiny cups, or leaflike fronds. They look like plants or fungi, and for the longest time, biologists thought that they were. But 150 years ago, a Swiss botanist named Simon Schwendener suggested the radical hypothesis that lichens are composite organisms—fungi, living together with microscopic algae.

" The very notion of different organisms living so closely with—or within—each other was unheard of. That they should coexist to their mutual benefit was more ludicrous still. This was a mere decade after Charles Darwin had published his masterpiece, On the Origin of Species, and many biologists were gripped by the idea of nature as a gladiatorial arena, shaped by conflict. Against this zeitgeist, the concept of cohabiting, cooperative organisms found little purchase. Lichenologists spent decades rejecting and ridiculing Schwendener’s “dual hypothesis.” And he himself wrongly argued that the fungus enslaved or imprisoned the alga, robbing it of nutrients. As others later showed, that’s not the case: Both partners provide nutrients to each other. (my bold)


"But without its alga, a lichen-forming fungus bears no likeness to a lichen. It’s an entirely different entity. The lichen is an organism created by symbiosis. It forms only when its two partners meet.

" But in 2016, Spribille and his colleague Veera Tuovinen, of Uppsala University, found that the largest and most species-rich group of lichens harbored a second fungus, from a very different group called Cyphobasidium. (For simplicity, I’ll call the two fungi ascos and cyphos).

" “The findings overthrow the two-organism paradigm,” Sarah Watkinson of the University of Oxford told me at the time. “Textbook definitions of lichens may have to be revised.” But some lichenologists objected to that framing, arguing that they’d known since the late 1800s that other fungi were present within lichens. That’s true, Spribille countered, but those fungi had been described in terms that portrayed them as secondary to the main asco-alga symbiosis. To him, it seemed more that the lichens he studied have three core partners.

"But that might not be the whole story, either.

"Look on the bark of conifers in the Pacific Northwest, and you will quickly spot wolf lichens—tennis-ball green and highly branched, like some discarded alien nervous system. When Tuovinen looked at these under a microscope, she found a group of fungal cells that were neither ascos nor cyphos. The lichens’ DNA told a similar story: There were fungal genes that didn’t belong to either of the two expected groups. Wolf lichens, it turns out, contain yet another fungus, known as Tremella. (I've reported this discovery before)


"It’s an exciting discovery, says Erin Tripp, a lichenologist from the University of Colorado Boulder, but it’s still unclear what Tremella is actually doing. Most likely, she argues, it’s an infection, albeit a very widespread one. The alternative is that Tremella is a core part of the lichen. “This would, of course, be very exciting,” Tripp says, but to demonstrate that, the team would need to try to reconstitute wolf lichens with or without Tremella or, alternatively, use gene-editing techniques to disable the fungus and check how the lichens respond. “Without this sort of experimental approach, it seems premature to suggest that Tremella represents a third, fourth, or whatever-th symbiont.”


“'Language matters a lot when dealing with these organisms,” Spribille, now at the University of Alberta, adds. “If we set up our language so that our definition of a lichen is fixed, and these other elements are extrinsic, we’re setting ourselves up to find that they’re extrinsic.” He thinks that researchers should move away from “the imperative of classification” and the compulsion to shoehorn organisms into fixed buckets. He suspects that the relationships between all the components of a lichen are probably highly contextual—beneficial in some settings, neutral or harmful in others.

"That’s a lesson other scholars of symbiosis should also heed. There’s a tendency to categorize the bacteria within an animal’s microbiome as good or bad, as beneficial mutualists or harmful pathogens. But such labels imply an inherent nature that likely doesn’t exist. The same microbes can be benign or malign in different contexts, or perhaps even at the same time. Biology is messy—as are lichens."

Comment: The major point of this article is that Darwin championed the idea of evolution through conflict, struggle, and the ability to survive. The point of the article is that much of life shows cooperation and that conflict may not be that important. Evolution can certainly mean each step is designed for survival as obviously must happen or there would be no evolution. Viewed this way, since there is no proof survival is the driving force, it must be taken as a weak argument. And puts natural selection as a concept in a tenuous position. It can only exert its influence on what is presented by evolving forms. Like survival, it cannot be seen as driving evolution.

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