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Fruit usually works in symbiotic relationship with animals by giving them food to take in and seeds to "deposit" elsewhere. But let's say you had a world where the dominant feeding method was liquivores. That means they inject their digestive fluids into their food and suck up the dissolved insides. How could fruit work then if the animals don't take solid matter inside? Is there anything besides attaching spurs like prickler bushes?

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    $\begingroup$ If that's the case then fruits probably wouldn't evolve in the first place. Fruits evolved because they could exploit the way in which most animals ingested food. If animals were primarily liquivores plants would adapt to exploit them that way, like how plants take advantage of (liquivorous) pollinators. Fruit as we know it wouldn't be selected for (and indeed, a fruitless world characterizes 2/3 of the history of life on land, so the world can exist without fruit). $\endgroup$ Feb 21, 2021 at 6:23
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    $\begingroup$ Valid point, but let's keep imagining. Someone could have another idea. $\endgroup$
    – Joe Smith
    Feb 21, 2021 at 6:26
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    $\begingroup$ Could the seeds start germinating on the outside of the fruit and move fast enough to climb onto the animal? $\endgroup$
    – thebjorn
    Feb 21, 2021 at 10:31
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    $\begingroup$ Biology is always a two-way street. The plants and animals being externally liquified would evolve to be more resistant to liquification (in the same way plants/animals are toxic to discourage being eaten) and there would be selective pressure against liquivores. Animals with more robust internal digestion would be needed to break down the tougher foods, and these might carry seeds. Thus the plants would select for seed carriers, just as the seed carriers select for yummy foods. $\endgroup$
    – DWKraus
    Feb 21, 2021 at 12:46
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    $\begingroup$ have you heard of nectar eaters. $\endgroup$
    – John
    Feb 21, 2021 at 15:42

4 Answers 4

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Hoards

nut hoard https://www.nps.gov/features/yell/slidefile/mammals/redsquirrel/Page.htm

https://en.wikipedia.org/wiki/Hoarding_(animal_behavior)

There are 2 main ways animals move seeds. OK 3 if you count those burrs that you discounted.

1: Eat fruit and poop out seeds.

2: Hide fruit / seeds with intent to eat them later.

In your world of liquivores, #2 works fine. Animals that find a fruit might want to eat it later, and so will stash the food in a place they can find it later. Maybe the animal comes back and eats it or maybe it doesnt. If it doesnt, the nut can germinate and grow. This is how squirrels plant trees. The squirrel intends to eat the nut, not grow a tree but some of the nuts go uneaten and so are planted by the squirrel.

""Fruits are juicy!" I can imagine the reader might object. "They do not store well!" I will remind the skeptical reader that in the proposed world

they inject their digestive fluids into their food

Fruits do not need to be juicy! They will be evolved to dry quickly and later reconstitute on injection of digestive fluids. This system would actually work better for the plants than hoarding of seeds which are at risk of being eaten. If nutrient rich reconstituted fruit were the object of the animal hoarder, the seed would be waste and would be left to germinate whether the animal returned to its hoard or not.

A fruit which rapidly dries also protects its nutrients against fungus and insects, neither of which disperse seeds. In the real world I am thinking of rose hips which by virtue of drying are available for animals all winter and into spring, but this is also true for other low-moisture berries. In the liquivore world this would be true for all fruits.

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    $\begingroup$ Very good. You really know how to think outside of the box $\endgroup$
    – Joe Smith
    Feb 21, 2021 at 18:28
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    $\begingroup$ @JoeSmith That’s almost an understatement, Willk is a local superstar in that department XD. I never tire of reading his answers $\endgroup$
    – Enthu5ed
    Feb 22, 2021 at 17:43
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Smaller seeds.

In the current world; Many seeds can survive stomach acids and come out the other end. In your world, they survive the acids, and are small enough to get sucked into the animal.

  • Animal injects acid into fruit. Fruit internals liquify but the skin doesn't.
  • Animal injects "straw" like thing to suck liquid fruit out.
    • The thicker the straw the better, as the less time it spends exposed and stuck to food, the less likely it is to be someone else's dinner.
  • Fruit seeds are tiny and fit into the straw, getting sucked into the animal.

One of two things:

  • Seed gets stuck in the animal. The animal has a way of cleaning any tiny solids out that gets stuck in its system (eg it "vomits" to backflush the system) and that results in the seed being distributed.
  • Seed gets stuck in the animal, and stays there. Animal eventually dies some long time later far away, in which case the seed is fertilised by the dying animal.

Seeds currently are tiny genetic packages with some starting energy and nutrients for the plants taking up the bulk of the size. In your world - get rid of much of that starting nutrients as possible and rely on the animals vomit, or body, to provide that.

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Strong seed walls

Plants have evolved fruits which are of very high water content and seeds are of tough wall. Animals inject their fluids, but the fluids don't harm the seeds. When the animals suck the fruit dry of all juices, the fruit shell dries off and later falls on its own. The seeds then get dispersed based on physical activities in the terrain.

Plants use other modes than dormant seeds

One can imagine more plants to be viviparous like Mangroves, not requiring seeds. Similarly the roots can be imagined to give birth to a network of plants on their own. Here, fruits serve the purpose of a plant waste bag (plants end up depositing minerals they do not need in fruit like structures).

Evolutionary behavioral traits in animals

Animals can't filter the seeds out and evolution teaches them to keep the more troublesome seeds that enter their feeding tube into one side of the mouth/separate cavity for some time before spitting it out. This could take inspiration from ownls regurgitating material they can't digest in form of pellets.

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How could fruit work then if the animals don't take solid matter inside?

The fruit is made by two layers: the outer one contains the seeds, the inner one the pulp which is then liquefied by the feeding animal.

Once the animal punctures the fruit, it "clamps" for a certain time to the appendix used by the animal and detaches from the plant. This makes it easier for the animal to feed, since the lunch will hold itself, and since the animal will be moving around will help spread the seeds away from the mother plant.

This can happen either because the feeder forcefully remove the fruit ending up launching it away or because the feeder moves away from the plant carrying the fruit with it.

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  • $\begingroup$ I feel thebjorn says what you're trying to much clearer and briefer. $\endgroup$
    – Joe Smith
    Feb 21, 2021 at 13:26
  • $\begingroup$ @JoeSmith, they are asking a clarifying question on something that is nowhere present in my answer. $\endgroup$
    – L.Dutch
    Feb 21, 2021 at 16:09

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