As I understand it, bright colors like red or orange are usually considered to be a ‘warning sign’ indicating the potential to be poisonous in many species of frogs and snakes. Why is this the case? Wouldn’t a poisonous species be better off camouflaged than being visible to its predators??
You could argue that the bright colors help to scare off predators, but then what would stop non-poisonous species from evolving the bright colors as well? What keeps the display ‘honest’??
And what comes first in the evolutionary process, being poisonous or being brightly colored?
Nothing prevents nonpoisonous species from using bright colors to “pretend” to be poisonous. Two examples which immediately come to mind are the king snake, which closely mimics the poisonous coral snake in its coloration, and the viceroy butterfly, which mimics the mildly toxic monarch butterfly.
Camouflage is good for animals for animals which don’t need to move around much, but for animals which need to hunt actively, bright colors allow it to go about its business and still remain relatively safe.
It’s a guess, but I imagine the evolution went down something like this:
Some animals developed venom.
There was less selective pressure in these animals to keep skin in dull colors. If you’re an animal that can win almost every fight, the quality of your camos doesn’t make much difference to survival.
Other animals without an instinctive fear of brightly colored critters began winning Darwin awards.
Selective pressure in favor of brighter colorings. This causes poisonous animals to become even more garish, and as Q.E.D. points out there are a few mimics too.
Why mimics aren’t more common? I’ll admit that I don’t have a great answer to that. Perhaps it is also unwise among non-humans to make threats where you can’t deliver.
Of course, many poisonous animals are camouflaged.
You would have to take every example on a case by case basis, since in every case the animal in question developed its coloring as a response to a specific environmental pressure. In the case of a brightly colored poisonous creature, it may simply be that in that specific situation, camouflage was less effective against local predators than “Warning colors,” so the animal evolved to be brightly colored.
Many types of fish, for instance, have to seek out food sources in such a way as to make camouflage a less-than-deal solution, since a fish in open water is pretty much out in the open and many of their potential diners can see them easily; in that situation, far better to display bright colors to say “Back off, pal. I know you can see me, but I’m poisonous.” Conversely, a poisonous animal that CAN camouflage itself effectively usually will. Most rattlesnakes are pretty hard to see; even though most have specific striping patterns, the great majority are brown, black or green in accordance with local conditions, so they can still hide quite effectively. Look at this picture of an Eastern Diamond Rattler. It would be easy to miss this guy.
There would not be any universal truth; the evolutionary rationale would always be local and species-specific.
I would suspect that being brightly colored goes hand-in-hand with being poisonous. It doesn’t help to be poisonous if you are still likely to be eaten. Sure, you may kill you whatever eats you, but that doesn’t help you out much. Thus, the fact is usually (though not always) advertised up front. This is why mimicry (the technical term for such is Batesian mimicry – mimicry by more palatable species of less palatable ones – by the way) works, and has evolved.
Incidently, the term for such distinctive coloration in association with a repellent defense of whatever sort is aposematism. Some thoughts on the evolution of aposematism can be found here. Note also that aposematism is a defensive measure, not an offensive one. Organisms which rely on toxins to catch or subdue prey (e.g., rattlensakes) typically do not advertise the fact. Those organisms which do not wish to eaten are the ones which typically have the associated markings. The markings thus serve as the primary defense (deterring attackers beforehand), with the toxin acting as a secondary defense, should a predator be determined. Batesian mimicry, then, similarly relies on the coloration as a primary defense, but lacks the associated secondary defense.
Sorry I don’t mean to nitpick but it should be noted that * poisonous * typically describes things which are dangerous to eat, * venomous * refers to things which are are capable of injecting toxins.
Of course it’s a very blurred line. Snake meat is very good to eat, while snakes themselves are likely to poison any animal attempting to make a meal of one.
As to why more species don’t practice Batesian mimicry, the answer is failry obvious. The protective colouration only works as long as animals learn to asociate those colours with a poisoning event. If the number of non-toxic mimics reaches a critical level, it breaks down. Some predators will experience a meal from a ‘poisonous’ animal. From that they tend to learn what species are truly poisonous and which are mimics. The only way this system works is if the first few experiences every predator has is of a poisonous food source. If there are large numbers of mimics then the technique fails.
To paraphrase 9and hopefully clarify) what Blake is saying: The number of mimic species must be small relative to the number of true poisonous/venomous species, or else potential predators will likely catch and consume a mimic, and naturally survive the experiece before it attemts to catch and consume one of the ones that could kill it.
I’ll add to this. Mimicry is also uncommon because it comes at a price: if the species the animal is mimicking becomes extinct, the mimic species will shortly be wiped out as well once the predators realize that all the animals that look like it are safe to eat.
The mimics don’t look at any picture, they either die or they don’t. If there are so many of them that the predators have an incentive to distinguish them, then they die. The strategy fails.
Precisely. Evolution is an ongoing series of trial-and-error experiments, nearly all of which fail. Every now and again, however, a mutation occurs which proves beneficial and gives its possessors a slight advantage over other members of its species, and the mutation is passed on to susequent generations more frequently. The point is, organisms don’t “choose” a particular trait because it gives them an advantage; it’s more accurate to say that the trait gets passed on if it keeps the organism alive long enough to reproduce more than organisms lacking the trait.
I believe these are what are typically used on TV and in movies in place of corals. The mnemonic I heard once to distinguish the two is “Red by black, a friend of Jack. Red by yellow, kills a fellow.” So far, every ‘coral’ snake I’ve seen in a movie has had a red-black-yellow-black-red pattern.
Just so nobody gets too overconfidant, that menmonic works for the two North American species of Coral Snake.
But it does not work for some of the dozens of species of Latin American Coral Snakes. Just a heads up in case you’re visiting the tropics any time soon ;).
And I’ll add to this: Batesian mimicry must evolve in the presence of an existing poisonous species. There would be no selective advantage to looking like something which the local predators have never seen. Gobble up that brightly-colored bug and nothing happens…well, it won’t be long before the brightly-colored bug is itself extinct.
All of my other questions have been answered, but I still don’t understand the process by which the bright colorations could have evolved in the first place, regardless of whether or not the species is poisonous or whether the color change evolves gradually or suddenly.
Let’s say you’re member of a species of frogs that are all currently green. How is it to your advantage to be brightly colored, if you’re the only one that looks this way? All it would do is make you stand out to your predators, taking the genes that caused your distinctive coloration with you. There are costs, but no benefits.
I can see how aposematism can continue once it is already in place, but when it starts off there would be a ‘learning curve’ for predators to associate the bright colors with getting sick upon ingesting a particular species.
We’ll go with your frog example for the sake of simplicity. First of all there must already be a brightly-colored poisonous frog living in the forest alongside your green ones. The predators in the forest have already learned to avoid these brightly-colored ones, but know the green ones, if they can find them, are safe to eat. One day, one of the offspring of the green frogs is born with a brightly-colored spot on its body that happens to slightly resemble the coloration of the poision ones, just enough to give a predator pause before trying to catch it, giving it time to escape. This frog breeds and has offspring with the same coloration, and down the road aways, some of these offspring have a larger and more prominent patch of color and survive even better than their relatives. This process continues until we have a population of frogs with coloration that strongly resembles the poisonous species. You have to bear in mind that this process takes a long time, often many thousands of generations.
It makes perfect sense. If you’re a poisonous frog that looks like all the other nonpoisonous green ones around, you still might get eaten, since the predators can’t distinguish you from the nonpoisonous ones. If some of your kids are born with a patch of bright color through some random mutation, however, they may stand out more, but since they have a distinguishing characteristic that predators can identify, they have a very slightly higher chance of breeding than plain green ones, and pass on this trait in the manner I described above, until eventually you have a population of brightly-colored poisonous frogs that predators know to avoid.
Darwins Finch could probably explain this better than I, but I don’t see him around.