I have been thinking about the Eggplant lately. It perplexes me. When I think of fleshy fruits, I try to think in terms of what reward they offer their animal dispersers. For most, it is sugars – from the mango (dispersed by large ruminants) to the blueberry (dispersed by small birds). This is easy to understand, because sugars are metabolically cheap for the plant to produce. Then there are those few, like avocados and their relatives, which provide lipids as the reward – more expensive from the plant’s point of view, but that is the cost of coevolving with a specialized disperser that requires that.
But the eggplant? It doesn’t have much of a nutritional profile. It doesn’t taste sweet-tart like a tomato, so it wouldn’t seem to attract dispersers who seek sugars. It doesn’t contain much lipid either. As I researched this further, I found that the eggplant was domesticated from the wild Solanum incanum (which some online sources amusingly misspell Solanum insanum, perhaps in reference to old folk beliefs that eggplant caused madness). It so happens I have an observation of it: Bitter Tomato, Okahandja, Namibia. But that brings me no closer to the answer, because that species is known as bitter apple, bitterball, or bitter tomato. What fruit eating animal would be attracted to bitter? Bitter flavors are psychologically thought of as associated with poison, so I cannot imagine a disperser for a bitter fruit.
Any ideas about the original disperser of the eggplant?
I’m guessing milkweed has some taste issues as judged by human taste receptors but monarch caterpillars are closely adapted to eating it. All sorts of things that are repellant to humans are resources for other species. In fact, all sorts of things that are toxic to humans are resources for other species, including nightshades.
I remember Okahandja with mixed feelings. Got my first ever speeding ticket there.
If that’s the case the nutritional value may not be so important, and even being as low as it is it may still be higher than the grass-based diets of those animals, and megafauna don’t need to be as concerned about toxins as smaller animals.
It’s also worth mentioning that wild avocados are extremely bitter, but are still vigorously sought after by wildlife, including the Andean Spectacled Bear. I tried eating some of the wild avocados when working on the conservation of the bears and found them to be utterly inedible, but the bears and other wildlife loved them.
This paper seems to be the one everyone is referencing when it comes to wildlife based dispersal of eggplants:
It depends on the species of Asclepias you are referring to, I’ve only ever tried A. syriaca, but a few sources claim other other species in the genus to be quite bitter. A. syriaca, on the other hand, is not bitter at all to humans (I eat it regularly, and have never known anyone else who does so and finds it bitter or otherwise unpleasant). I’m not saying the plant isn’t toxic, but it is maybe not as toxic as people are often led to believe and can be safely consumed with cooking and with some moderation (i.e. eating it in season, not every day of the year). This is not something unique to wild plants, as many domesticated crop species (nightshades, especially) require cooking to render them safe to consume.
It’s so hard to tell with domesticated plants bred for human consumption. The most extreme example, I believe, is Zea maise. It can trace it’s origin back to Teosinte, which looked more like wheat. Now, since it has been so highly modified, there is really no way for it to propagate without human intervention. Enclosed within a tight ‘wrapper’, only vertebrates which can find and eat it would remotely be able to disperse the seeds. I don’t know about eggplant, but the modern version may be undesirable to most fauna, in nutritional terms.
Curiously, last week during our condo Landscape committee walkthrough, we came across two large eggplants that someone discarded under a street tree. They’d appeared to have only been ~very~ slightly nibbled by the squirrels, no bird pecks, or other gnaw marks.
Probably birds; IIRC they’re not affected by solanaceous poisons, so it likely doesn’t taste bitter to them. A lot of fruits, especially red ones, are like that, with compounds that are toxic to mammals but not birds so that they get the right disperser.
Also, in a place like that, the water of the fruit alone might be a good attractant!
Now I’m confused. So many of these sources say Solanum insanum, but searching for that in Wikipedia brings up only the eggplant itself and S. incanum. Is the correct spelling (and meaning) really that contested?
This is not the only case I have seen on iNat disagreeing with other sources. The grapefruit, I have always known as Citrus X paradisi, which looks like it should be the correct spelling if it is “of paradise”; but on iNat, it comes up as Citrus X paridisi, with an “i” in place of an “a.” That doesn’t suggest any meanings to me.
Sorry if that was offensive. Human-dominated landscapes typically have trash… I just figured animals would go for high calorie trash over raw eggplants.
I wonder that you would assume there are chicken bones and greasy paper on the property.