I'm a little worried that having plants sending signals to soil bacteria to produce ammonia without releasing the associated sugars and nutrients that legumes do, might put evolutionary pressure on those soil bacteria to stop reacting to those signals, potentially harming legume crops if that non-reactive soil bacteria proliferates.
I’m not sure if I’m following you correctly. If a non-reactive strain is evolved, by definition it will be unable to establish itself in the plant nodules, and that niche will still be occupied by reactive, symbiosis-capable bacteria. Besides, the signal for ammonia production, rhizopine, is actually a sugar-like compound.
I don't think you can just "by definition" reality like that. Sure, the non-reactive strain won't be called a symbiotic partner, by definition. But that doesn't poof the bacteria out of existence.
That said, I think you're correct about not being so concerned. If the symbiotic relationship was so exploitable, it'd probably be a great evolutionary advantage to do so. The signal being a sugar itself, as you note, doesn't surprise me.
> But that doesn't poof the bacteria out of existence.
By “definition” I meant “the rhizopine signaling pathway”, implying that no pathway → no symbiosis. Of course that signal insensitive strains or species can exist. It’s a symbiote and not a parasite, after all.
It makes sense. Same thing happens with antibiotic resistance, for example. It costs them energy and nutrients to develop and maintain resistance capabilities. Previously resistant bacteria may become sensitive again if exposure to the antibiotic ceases. The logic is they will be wasting energy duplicating and expressing useless DNA and proteins whose only purpose is dealing with antibiotics that are no longer present, so getting rid of them increases fitness because it frees up resources for other purposes.
Totally happens even with insects. The biotech industry started using BT genes (a fungus which takes care of corn ear worm) in GMO corn. Previously, BT was an organically approved pesticide, carefully applied by growers according to guidelines which made sure the target pest did not develop resistance. But with the genes making the nasties continually = BT all the time = excellent evolutionary driver = cases of resistant corn ear worm appearing. Biotech reaction: "we will just think of something new and keep doing it!" ref: https://entomologytoday.org/2018/10/23/problems-driving-resi...
> Previously, BT was an organically approved pesticide, carefully applied by growers according to guidelines which made sure the target pest did not develop resistance.
Excuse me, I'll just be over here laughing so hard I can't breathe.
In terms of possibility: some adaptations, whether these or others that we can't predict, will occur eventually; evolution doesn't stop.
In terms of how long it'll take: evolution is slow in terms of number of generations per organism, but it's relentless. The more widely any modification is deployed, the more interactions there are, and the quicker in terms of time some adaptation will occur; and, once an advantageous adaptation does occur in one place, seed dispersal will allow it to spread quickly.
As an example that I single out because I read about it recently in the delightful "Lives of weeds" by Cardina (https://www.cornellpress.cornell.edu/book/9781501759000/live...), the adaptations of plants to deal with the "irresistible" Round-Up pesticide are highly improbable, but there were trillions of chances, and so it didn't take long for them to develop; and, once developed, they spread very quickly.
