Mirsoglasnomne (mirsoglasnomne) wrote,

Благостный симбиоз

Расчудесная книга про микробов вышла недавно на английском. Я не удержался, и дал её в апрельский Forbes. Идёт взахлёб, и scinquisitor несомненно её одобрит, когда тоже доберётся. Тут я, однако, приведу мнение учёных о симбиозе, который ни разу не благостный в принципе:

“We like our black-and-white narratives, with clear heroes and villains. In the last few years, I’ve seen the viewpoint that “all bacteria must be killed” slowly give ground to “bacteria are our friends and want to help us”, even though the latter is just as wrong as the former. We cannot simply assume that a particular microbe is “good” just because it lives inside us. Even scientists forget this. The very term symbiosis has been twisted so that its original neutral meaning – “living together” – has been infused with positive spin, and almost flaky connotations of cooperation and harmony. But evolution doesn’t work that way. It doesn’t necessarily favour cooperation, even if that’s in everyone’s interests. And it saddles even the most harmonious relationships with conflict.
We can see this clearly if we temporarily leave the world of microbes and think a little bigger. Take oxpeckers. These brown birds can be found in Africa, clinging to the flanks of giraffes and antelope. They’re classically viewed as cleaners that pick ticks and blood-sucking parasites off their hosts. But they also peck at open wounds – a less helpful habit that stymies the healing process and increases the risk “of infection. These birds crave blood, and they satisfy that craving in ways that either profit their hosts, or punish them. A similar dynamic goes on in coral reefs, where a small fish called the cleaner wrasse runs a health spa. Big fish arrive, and the wrasse picks parasites from their jaws, gills, and other hard-to-reach places. The cleaners get meals, and the clients get healthcare. But the cleaners sometimes cheat by nipping bits of mucus and healthy tissue. The clients punish them by taking their business elsewhere, and the cleaners themselves will castigate any colleagues that annoy potential customers. Meanwhile, in South America, acacia trees rely on ants to defend them from weeds, pests, and grazers. In return, they give their bodyguards sugary snacks to eat and hollow thorns to live in. It looks like an equitable relationship, until you realise that the tree laces its food with an enzyme that stops the ants from digesting other sources of sugar. The ants are indentured servants. All of these are iconic examples of cooperation, found in textbooks and wildlife “documentaries. And each of them is tinged with conflict, manipulation, and deceit.14

“We need to separate important from harmonious. The microbiome is incredibly important but it doesn’t mean that it’s harmonious,” says evolutionary biologist Toby Kiers.15 A well-functioning partnership could easily be seen as a case of reciprocal exploitation. “Both partners may benefit but there’s this inherent tension. Symbiosis is conflict – conflict that can never be totally resolved.”

14. Oxpeckers: Weeks, 2000; cleaner fish: Bshary, 2002; ants and acacias: Heil et al., 2014.
Weeks, P. (2000) ‘Red-billed oxpeckers: vampires or tickbirds?’ Behav. Ecol. 11, 154–160.
Bshary, R. (2002) ‘Biting cleaner fish use altruism to deceive image-scoring client reef fish’, Proc. Biol. Sci. 269, 2087–2093.
Heil, M., Barajas-Barron, A., Orona-Tamayo, D., Wielsch, N., and Svatos, A. (2014) ‘Partner manipulation stabilises a horizontally transmitted mutualism’, Ecol. Lett. 17, 185–192.

15. West, S.A., Fisher, R.M., Gardner, A., and Kiers, E.T. (2015) ‘Major evolutionary transitions in individuality’, Proc. Natl. Acad. Sci. U. S. A. 112, 10112–10119.
Tags: biology, books, science

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