by Did67 » 17/12/19, 10:34
Two or three things :
a) In the living, a strict parasite never eradicates its host. It would be his death announced!
b) But the basic scale of living things, the ultimate link, is not the individual, but the species. Such an individual may very well die - what am I saying, he MUST die. It is the question of the survival of the species that is at stake.
So mistletoe will not kill the apple tree on which it is is a possible interpretation. Doubtful to me ... (if it's a parasite)
Or the mistletoe will kill such a sick tree to finish it off and make room for another healthy apple tree to take its place is also in the logic of the living.
c) Above all, the boundary between autonomous species, parasite and symbiont is not clear. There is a kind of continuum. If sometimes it is clear (such a species is only parasitic, or strict symbiotic or autotrophic), there are plenty of intermediate situations.
One mycorrhizal fungus is a symbiont as long as the vegetable does not have enough phosphorus. But fertilize with soluble P, and it becomes parasitic from the point of view of the vegetable. Who will keep him back (or at least will no longer attract him).
Ditto for the fixing bacteria of the genus Rhizobium. In poor soil, they are welcome symbiotes for fabaceae. Who feed them, in exchange for nitrogenous substances. But let the soil get rich and they become a pest. We then find nodules that are no longer active (they are not red). The plant keeps its carbohydrates for it!
I think that for mistletoe, we are in this hemi-parasite situation. I know apple trees right next to my home that have had them for a long time. We have been there for 20 years.
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