Adaptive reasoning behind poisonous animal being colorful

It seems a common theme in nature that some of the brightest, most unusally colored animals and plants are poisonous - and nature documentaries usually say that this is to warn other animals that it is poisonous or otherwise bad to consume.

What are the logistics of this, exactly?

Does the poisonousness develop before, after, or concurrently with the change in color patterns?

Are other animals supposed to know instinctively that colorful animals and plants should be avoided? Or is it a matter of them eating one, getting sick, and then having the vivid colors stick out in their mind so that they don’t go after similarly colored plants/animals in the future?

If being brightly colored is such a survival advantage, wouldn’t many species eventually mimic this adaptation even if they didn’t develop the poison to go along with it? Does this actually happen?

Is this something that happens with both animals that are poisonous (or otherwise dangerous) to eat, animals that have the ability to inflict a poisonous attack without being consumed, or both? In the latter case, wouldn’t it be enough to simply have the ability to strike out at potential predators without advertising it, and in the process, making yourself more visible?

In general, I’m trying to figure out how an animal goes from being non-poisonous/non-colorful to poisonous/colorful. Can you describe the process for me?


Well, it’s common enough there’s a term for it: Batesian mimicry

The combination of being poisonous and sending off a warning of it is called aposematism and an attempt to describe how it evolves is here but even that doesn’t directly address your specific question.

My thought would be that the poisonous characteristic develops first, perhaps initially just by happenstance. Once an animal is mildly adversive to eat then predators begin to avoid it and then the prey has a selective advantage if easier to identify and more adversive.


The latter.

See Sailboat’s reply.

Both, although more common in the former. The reason being that animals that have to bite can still be eaten, so for them there remains a trade off between camouflage and deterrence. Many opt for camouflage.

If you strike out you waste protein in the act of striking and in the venom produced. In addition you waste time that could be much better spent fucking or feeding. So ideally you want any potential predators to move on as soon as they see you, before you are even aware they are there.

An animal develops toxins through whatever process. That is beneficial in its own right since they will cause many predators to release the animal before they kill it. The predators then learn to avoid animals that look like that. The animals then have an evolutionary advantage if they exaggerate the features that the predators have learned to avoid. So for example many snakes have a banded pattern as camouflage. If predators learn to avoid banded snakes then the more conspicuous the bands, the less chance of being attacked. And as the poisonous snakes become more conspicuously banded predators will learn to avoid conspicuous bands and so the system enters a positive feedback loop. Eventually you end up with snakes with bright red and black bands.

The really short answer to the question “why are poisonous animals colorful” is probably that the animal gains no advantage from its poisonous nature if it is eaten or mortally wounded by what it’s trying to protect itself against. It can only pass along its genes (and perpetuate its properties) if its potential predators can somehow be signalled that it is dangerous, so bright colors that stand out and possibly shock the potential predator tend to survive, on average, more than nondescript ones. A bit of evolution takes place on the part of predators, too, since the ones that don’t recognize poisonous prey (either poisonous stings or poisonous to eat) preferentially die off relative to those that don’t try to eat the poisonous prey. Some of this might be a learning curve, if the predator survives a bad encounter with a stinging prey, or a really bad stomach ache from eating poison prey, but if the poison prey actually kills the predators by either method, then the others aren’t going to learn from its example.

Certainly is with some real-world predator/prey relationships. In the case of birds vs the caterpillars of the Cinnabar Moth, juvenile birds often need to learn the association by trying to eat one.

There are various routes, as has been mentioned. Venomous snakes first acquired venom in order to subdue their own prey. Some have remained cryptic, some like rattlesnakes are visually cryptic but have an auditory warning system, while coral snakes and others have acquired bright warning coloration.

The black-and-white pattern of the Giant Panda may be warning coloration. The panda is relatively slow-moving and appears as if it might be defenseless, but has very powerful jaws and teeth for eating bamboo. The coloration may signal potential predators that it is not as harmless as it looks.

Many animals that contain toxic chemicals don’t manufacture them themselves but get them from their food. For example, Monarch Butterflies obtain cardiac glycosides from the milkweeds they eat as caterpillars. The milkweeds themselves produce the glycosides to prevent caterpillars from eating them, but there are almost always a few herbivores that manage to evolve a way to defeat plant defenses. And then it’s efficient to sequester the plant defensive compounds and use them for their own defense. Once this happens, warning colors may develop.

Likewise it now seems like toxic amphibians like the poison-dart frogs obtain toxic compounds, or at least their precursors, from the ants and mites they eat.

Batesian mimicry has already been mentioned. This is when a harmless species comes to resemble a harmful one. There is also Mullerian mimicry, in which two or more harmful mimics come to resemble one another. The idea is that, if predators have to sample a few individuals in order to learn a warning pattern, each species will benefit by sharing the same pattern, since that will minimize the number of individuals sacrificed in each species.

This can result in the evolution of complex “mimicry rings” of many species that share the same pattern, including both Mullerian and Batesian mimics.

Mimicry extends to other features besides color pattern. Many harmless insects, including beetles, moths, true bugs, and others resemble stinging ants or wasps.

I tend to look at this in the reverse.

Poisonous animals are colorful because they never needed to evolve the camoflage coloration patterns to survive as a species.

That doesn’t make any sense. Why would they be colourful and patterned by default?

Certainly, only poisonous creatures have any chance of reproducing in large numbers despite drawing attention to themselves, and the attention that is warranted is because they are poisonous, so more brightly colored poisonous creatures outlive and out-reproduce their competition.
ETA: I’ve oversimplified.

Demonstrably wrong. The ancestral forms of many species with warning coloration have dull or cryptic coloration. Similar kinds of warning coloration has evolved convergently many times in unrelated species.

It’s really only a survival advantage if there are already colorful, poisonous critters nearby. The key is that the coloring is a defensive adaptation; it only works as a defense if the predator already “knows” that “color = bad”. If a population evolved the color first without the poison to back it up, then the predators would instead realize that “color = food”. Further, if the number of non-poisonous, but colorful, species were to become too great, then the color ceases to act as a suitable deterrent; a predator will be less likely to associate the color with a bad meal choice.

Poison dart frogs bred (and, obviously, fed) in captivity are non-poisonous.

Interesting. I did not realize that.

What about the black widow spider? Is the red violin-shape a similar deterrant to the coloring of frogs (etc.)?

Exactly. The copperhead virtually disappears in dead leaves.

Interestingly, the Copperhead and Cottonmouth both vibrate their tails in their defensive displays (possibly to make noise by rustling dead leaves). This may have been the ancestral behavior that led to the evolution of tail rattles in the related rattlesnakes.

I don’t think this demonstrates anything.

Not every red or yellow marked critter in the world is poisonous and not every poisonous critter in the world is marked.

But you’re the expert here, I’m just a theorist.

All I’m saying is that a critter that evolves bright markings randomly had better have something going for it to keep it from becoming a choice prey. Brightly colored critters that happen to be poisonous have a better chance for survival as a species than those that are made of whatever the local predators think of as bacon.

But every bright colored critter in the world has something going for it that allows it to continue to exist despite the lack of camoflage. Be it poison, living in a colorful environment or just living in a place where there are no predators.

An example of a critter mimicing a poisonous counter part:

Scarlet king snake mimics the Coral Snake.

Probably because you don’t know much about evolutionary theory.

Who said they were?

No, you’re not a “theorist.” You are just speculating in the absence of much knowledge of the subject.

That’s not at all what you said originally. You implied that the ancestral form was brightly colored, and “never needed to evolve camouflage patterns.”

A classic example of Batesian mimicry. Ancestral forms of both were most likely dull colored.