This plant I am designing grows on earth, in locations where competition between plants is fierce, water is scarce and also nutrients in the soil are diluted. The dilution requires the plant roots to be developed at least in 1 cubic meter of ground to be able to sustain the plant life.

This plant has developed peculiar traits to succeed in this environments:

  • roots secrete a growth inhibitor, to prevent other plants to grow close
  • growth is fast in the first phase, to occupy the ground area until roots can sustain life. Then it slows down.
  • the plants growing in an area can synchronize the blooming and fructification on periods of 17 years, by means of chemicals secreted by the leaves.
  • the seed of the plant requires a bath in chloridric acid in order to develop (basically it has to go through the stomach of an animal)

In order to secure that seeds are spread away from the mother plant and to provide a boost of nutrients to the growing plant, the fruit of this plant is highly sweet, attracting animals from miles around thanks to smell. Once eaten the fruit releases, together with the seed into the stomach of the animal, a poison which stops peristaltic movements and kill the animal in 2-3 days. The rotting corpse will grant the growing seed the nutrients needed to develop the roots until the cubic meter mentioned above.

Is this a realistic mechanism?

  • $\begingroup$ The last point isn't necessary I think. If the fruit doesn't get eaten, why not let the seed try anyways? $\endgroup$ – DonQuiKong Apr 13 '17 at 8:15
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    $\begingroup$ it is to prevent the seed growing close to the mother plant (better no offspring than a competition mother-daughter) $\endgroup$ – L.Dutch Apr 13 '17 at 8:21
  • $\begingroup$ They wouldn't survive there without the nutrients, that problem solves itself and spares you from having to explain what the acid does $\endgroup$ – DonQuiKong Apr 13 '17 at 8:22
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    $\begingroup$ Not so much a comment on yours but another mechanism that may work is for the fruit to act as an aphrodisiac (/increases the release of attractive pheromones) - resulting in lots of offspring - but then if the seed (of the plant...) is inside the male after a few days it kills the animal and grows out from inside the rotting carcass. Lots of lovely nutrients yet it is still beneficial for the continuation of the genes so they wouldn't evolve not to eat the plant (if anything perhaps evolve to like it). $\endgroup$ – Lio Elbammalf Apr 13 '17 at 8:57

There is at least one plant in which the seeds and seed structures kill the animal which disperses them: Pisonia, aka birdcatcher trees.



These trees live on barrier islands with nitrogen poor sandy soil. Birds nest in them because birds like islands. The seeds are sticky and entangle chicks that run afoul of them.

enter image description here

this image found at http://hdpphd.blogspot.com/2014/04/capricornia-cays-survey-holiday-3-heron.html

Bogged down with seeds the chicks hop around for a bit then die, their hopping doing some dispersal and the carcasses fertilizing the seed.

As regards the prospects of an animal eating a fruit which will kill them, that is trickier and something I have not heard of. But not impossible. There would be very strong evolutionary pressure to not eat that fruit!

Re the anticompetition chemicals that happens not infrequently. Black walnuts are the one that comes to mind. http://hort.uwex.edu/articles/black-walnut-toxicity/ The bigger the tree the more poisonous the soil, but I think that is because under the tree is where the most nuts fall.

I could imagine a seed with a mechanism like the pisonia: it sticks to an animal and then gradually poisons it with something like curare (a paralytic neurotoxin). That lets the animal get a little distance. The soil in the immediate area of the dead animal will be pretty rich in the short term and that might be enough to discourage other seeds while your plant gets established.

  • $\begingroup$ I set the 17 years period between the fructification to "erase" memory of episodic survival to the poison. $\endgroup$ – L.Dutch Apr 13 '17 at 13:02
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    $\begingroup$ @L.Dutch: Natural selection does not depend on individual organisms remembering anything. Simply put, those animals who are attracted and eat the poisonous seeds leave less descendants that animals which don't. In time, most relevant animal populations will consist of individuals which don't find the poisonous seeds attractive. $\endgroup$ – AlexP Apr 13 '17 at 13:07
  • $\begingroup$ @AlexP, there are cicadas which reproduce with cycles of 13 or 17 years to reduce "reproductive resonances" with their predators. I was thinking of something similar, in this case for the victim. In case of an animal reproducing each year, I think 17 generations are more than enough to forget that "that particular plant killed your grand^17 father". $\endgroup$ – L.Dutch Apr 13 '17 at 13:15
  • $\begingroup$ The point is that they don't have to remember; it's actually irrelevant whether they remember or not. Natural selection simply does not work that way; it's simply that those organisms which due to some mutation (slightly off sense of smell, skewed sense of taste, whatever) are not attracted to the poisonous fruit will prosper. Not to mention that if a source of food is available something always evolves to eat it and not die. $\endgroup$ – AlexP Apr 13 '17 at 13:22
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    $\begingroup$ @AlexP is right. An example: a fruit eater with defective mutant gene for olfactory receptor corresponding to the volatile molecule this fruit uses. It would not find the fruit. The descendants of this animal would have much less local competition from conspecifics (as they had been poisoned) and this mutation would quickly spread. $\endgroup$ – Willk Apr 13 '17 at 22:39

Not if the fruit kills the animal that is supposed to distribute the seeds. Otherwise, this is not unlike seeds that only germinate after passing through the digestive tract of an elephant, for example. It is the poop rather than the carcass of the animal that provides nutrients.

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    $\begingroup$ This is a very good point, if you want the plant to be spread by animals then killing the animals that do so is not going to be an effective way to do that as they should soon learn to avoid eating it. $\endgroup$ – adaliabooks Apr 13 '17 at 10:21
  • $\begingroup$ Poop is an excellent source of nutrients. It has been used as a fertilizer since forever. Slowing down the digestion isn't a bad idea but just let them defecate further away. $\endgroup$ – Mazel Apr 13 '17 at 19:03

Perhaps to get around the animal evolving to not eat it you have the fruit be poisonous only some of the time. Perhaps 1/2 of the time it is reproducing it has lots of nice nutrients, but secretes laxatives after 2-3 days so the animal doesn't completely digest the seed. The other part of the time it kills the animal in 2-3 days and there is no way to tell the difference.

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