Geosmin, Alien Rain, and Meat Fruit

A while ago I remember learning that humans are apparently really good at smelling fresh rainfall. I looked it up and ended up reading this article in the Smithsonian Magazine, attributing that smell to geosmin, a compound created by certain types of bacteria that attracts springtails (among other things). The article then describes how the bacteria and springtails likely evolved a symbiotic relationship in which the bugs eat the bacteria and then spread their spores (endospores? idk I'm not a biologist) like birds eating berries/fruit and dispersing their seeds.

This planted a couple ideas in my head.

First off, if we only know the smell of rain because of bacteria native to this planet, we probably wouldn't be able to smell it on other planets. Or maybe they'd have their own distinct scents for rainfall depending on what chemicals or microbes are present in the soil. Those theoretical microbes have all kinds of implications for the rest of an ecosystem. There's a lot of interesting worldbuilding stuff you could do with this as a starting point.

The second idea is kinda gross if you couldn't tell by the title of this blogpost. The article likened the springtails eating and then, uh, crapping out the spores of the bacteria to birds doing the same with fruit/berry seeds. We're pretty used to plants doing this and I guess it's not too crazy for bacteria to do weird stuff like this, but I'm pretty sure nothing in the animal kingdom functions like fruit. Yes, some parasites rely on their eggs being ingested but I'm talking about a symbiotic relationship between the fruit-bearer and the fruit-eater.

If you wanted to design an animal that bore fruit a simple option would be to make it a sessile creature that produces fruit-like growths that other creatures consume to help disperse its offspring. Like a giant anemone or something. But that's the easy option. Let's try something weirder.

Plants use fruit as a seed dispersion method because they can't move so our fruit animal needs to have its movement restricted somehow. I'm thinking it could be a fish (or other aquatic animal) that lives in lakes/ponds in a region that has a lot of disconnected bodies of water somewhat close by. You could just let the animal hop around on land like mudskippers to get to other lakes but that kinda goes against this alien fish thought experiment.

Anyways, these creatures would need their eggs to function like seeds, so they would have to resist stomach acids and also only become active in appropriate conditions. Animals already do both of these things using dormant eggs called cysts. Parasites such as tapeworms benefit from the stomach acid resistance while brine shrimp (aka sea monkeys) benefit more from staying dormant in dry conditions. Our creature's eggs might only become active if there's enough water present. If they're, uh, deposited in an existing body of water, great, they can start their lives immediately. If they end up on dry land they could remain dormant until rain washes them into a lake.

So that's the seeds of our animal fruit taken care of. What about the actual fruit proper? There's a number of things you could do for that. One option could be surrounding the eggs with some kind of edible membrane that attracts other animals. A more morbid approach could see the parent animal metamorphosize into the "fruit" while keeping the eggs in some internal compartment. If flounders can exist in real life then this alien fruit fish can do all kinds of wacky stuff if we want it to.

So, uh, now that we have this creature what do we do with it? It could be an interesting thing to throw at players in a survival situation in an RPG as a one-off creature. It could also be the basis for an entire lineage of weird fruit fish and the surrounding ecosystem if you're into speculative evolution. You could also design a culture that relies on these animals as a major food source, either as a tribal society or even an industrialized one with vast factory farms. The world's your oyster. Doubly so if you decide to make the creature a bivalve.