Reading back, I can see that interpretation - now I understand the basis for your response. I did not mean to imply anything about ancestral forms.
Many of the responses here, notably those of the well-grounded** Blake **and Colibri, sound like gospel. This is the way it is. I’d be interested in knowing what we have that passes for evidence of these assertions? How do we know, for example, that the Viceroy butterfly mimics the Monarch? Is that the only explanation of their similar phenotypes? How do we know that the ability to produce venom preceded the development of coloration in coral snakes, for instance?
This paper sheds some insight on that: The viceroy butterfly is not a batesian mimic (abstract only available from that link, unless you wish to pay for the full article). The conclusion is that the viceroy is actually a Mullerian co-mimic with the monarch.
I would suggest this paper: Coral Snake Mimicry: Does it Occur? (.pdf doc). The conclusion?
Note that many of these examples have been debated in scientific circles for some time. What Blake and Colibri are presenting is the current state of knowledge for these animals. They aren’t just implying “this is the way it is”, just because.
The Viceroy Limenitis archippus was originally thought to be a Batesian mimic, but as it turns out is a bad-tasting Mullerian mimic.
As you can see, the Viceroy differs drastically in coloration from other members of the genus Limenitis in the US, which are mostly black and white or blue and white. This type of coloration is probably ancestral for the genus. This implies there was some selective force that drove this change in coloration in the Viceroy.
Some of the best evidence for mimicry is that the Viceroy’s color pattern differs in different parts of its range in coordination with the distribution of other species of models.
Where the range overlaps the Monarch, the subspecies of the Viceroy resembles that species.
However, in Florida the Viceroy occurs with the Queen Butterfly,and the subspecies there is quite different, and resembles the Queen instead of the Monarch.
This kind of coordinated variation between species is very common in butterflies, and actually is one of the lines of evidence that led Bates to propose mimicry in the first place.
Some of the most spectacular examples are found in the genus Heliconius. In this image, note that the butterflies in the left column belong to several different species in the genus Melinaea, while the ones on the right are all different subspecies of a single species of Heliconius that occur in the same areas as the species on the left.
It may sound like that because we are summarizing the results of one hundred and fifty years of research on the subject in a few sentences. The evolution and genetics of this phenomenon is a very active area of research today.
All of the other members of the family Elapidae (which includes cobras, mambas, kraits, etc) are venomous, which indicates this is the ancestral condition for the group. This implies that coral snakes, which are just one group in the family, developed their coloration after venom evolved.
Several points - remember, as others have pointed out, that animals don’t “evolve colors or patterns”. What happens is that nature cranks the gene randomizer, and any little change in an individual that creates an advantage - shape, size, color, appendage form, ec - will result in more of that individual’s genes surviving.
So once a species begins to taste bad, if they start to lose their camoflage by random action, it may turn out not only to be not be a bad thing, but if they become recognizable - it’s a good thing.
There’s a scientist in Russia who spent 40 years growing “tame” foxes. Each generation, he culled the ones that were most aggressive to humans. Toward the end, not only did they look like dogs, but they started to get pelt features like a silver blaze on the forehead. The implication here is that distinctly disadvantageous features, like cammo failure, can arise spontaneously. It’s environmental pressure that limits the likelihood of that trait surviving. With the protection and feeding from man, you can grow bright white poodles, or calico and siamese cats, etc.
Interesting - I wonder if anyone has done a test to see if their natural predators instinctively recognize the warnings from poisonous “meals”, or if they each one have to learn the hard way? Birds especially ahve a lot of instinctive learning; and I wonder how educatable some lower-on-the-food-chain animals are?
Also - do wasps or bees mimic each other? I’ve often thought the similar coloration and the similarity of their defence (stingers) is such that wasps are just lazy cousins who figured out there are easier meals than going from flower to flower for a small mouthful of sugar?
There is some experimental evidence for innate recognition of warningly colored prey in birds, although learning plays a role too.
It is generally considered that the yellow-and-black patterns found in many stinging bees and wasps are cases of Mullerian mimicry. (And, since many wasps are fierce predators on other insects, I wouldn’t consider them lazy cousins.)
Would someone mind explaining in a little more detail how the bright colors come to be? I understand that for the group, the combination of toxicity and bright colors is benificial. The death of one brightly colored frog teaches a preditor not to eat others from the group. But if the most brightly colored frogs are more likely to be eaten (by predators who have not learned they are toxic), they are less likely to pass on the bright colored trait. Where is the advantage for the individual to be brightly colored?
Generally speaking, they aren’t eaten. They are unpalatable, and the predator can tell that as soon as he gets the critter in his mouth (that is, after all, the intent of the poison they are advertising). Thus, they are typically spit out, and continue on their merry way, often none the worse for wear. Sure, they could just stick with being unpalatable, but then you’d have every Tom, Dick and Harry trying to eat you, which can get pretty old. Thus, the colors serve as a first line of defense: “I am very bad tasting, so just look elsewhere.” If the predator didn’t get the memo, then the second line of defense - the actual poison - lets them know that, yeah…shoulda looked elsewhere.
Ok, can you go a step farther? - I can’t see a primitive animal coming across a dead cousin and saying to himself, “Jeez, Ernie ate one of those bright snakes a couple of hours ago. I imagine that I better not eat one, because it caused his death, so it might cause mine, too.” What would be a better, more realistic script that could explain how animals have learned not to eat those snakes?
A couple things. First of all, as has been mentioned, warning colors and patterns are often generalized over many species. The combination red/black or yellow/black is very widespread as a warning signal throughout the animal kingdom, being found in snakes, frogs, wasps, bees, butterflies, and many others. So a mutant frog with a yellow-black pattern might be avoided by predators whether or not it was toxic (which is how Batesian mimicry evolves in the first place).
Secondly, warning coloration can evolve by kin selection. If all the tadpoles in an egg mass share the same mutation for bright coloration, once they change into froglets one being eaten could protect all his siblings.
First, if animals die when they eat a toxic animal, that could cause selection for innate recognition of that warning coloration. Animals that automatically avoid toxic animals would never die from eating them, and so would be more likely to pass that trait on to offspring. As I mentioned above, there is some experimental evidence for innate recognition of warning patterns in birds.
Secondly, many animals aren’t toxic enough so that they kill predators, but are merely distasteful. In such a case the predator survives, but may teach its offspring or flock mates to avoid such prey in the future. (This is most likely in the case of birds and mammals.)
Plus, it is likely that a predator’s first encounter with one of these toxic forms occurs when the predator is still a juvenile - perhaps not yet experienced enough for a kill. So in the process of learning how to deal with prey, it can make the association that “brightly colored = bad tasting, therefore avoid”, without anyone having to die.
I don’t think there are many animals that have that sort of reasoning power over time. It’s possible they’d notice if the other animal almost immediately became sick.
However, not eating bright colored things could still be learned behavior, transmitted from a mother or other older caretaker animal to her young. Either the young only learn to eat things that Mom teaches them to hunt, or Mom actively dissuades them from stalking the brightly colored ones.
I don’t understand this point at all. How do you suppose the predators share this information among themselves, or from one generation to the next? It’s not as if they compile notebooks that they pass around saying ‘Something that looks like THIS is nasty to eat or poisonous’. Unless there is a mechanism by which this information can be acquired before the predator tries to attack the striped prey, then the striping confers no advantage whatsoever (although the toxicity may do).
I see a parallel here with some of the religious teaching that put me off religion. If we pray to Mr Deity and the sick person heals up, it’s proof that Mr Deity answers prayers. If the sick person doesn’t get better, it just wasn’t Mr Deity’s will. Well, hang on a minute, if all possible outcomes support the contention that Mr Deity exists, then none of them do.
Similarly here. If a toxic animal has bright markings, these are deemed to be some sort of ‘warning’ and this is supposed to be a wonder of the evolutionary process. But hang on… as others have pointed out… there are toxic creatures that are plain, camouflaged or brightly coloured, and there are non-toxic creatures that are plain, camouflaged or brightly coloured. So, any combination of traits is deemed to validate evolutionary theory.
I am not a creationist. I accept the truth of Darwinian evolution. I just wonder sometimes if we are asked to accept arguments that don’t quite add up.
You’re trying to put the cart before the horse, I think. No one is depending on mimicry to validate evolutionary theory, and neither mimicry nor its absence are evidence of evolution, per se. It’s just that we do happen to know about evolution, and we understand in principle that species and traits evolve due to selective pressures. When we observe traits, then, we can utilize the tools we have at our disposal to understand how various kinds of selective pressures caused those traits to evolve. This is a consequence of our understanding of evolution, *not *our evidence for it.
I’m surprised that you are having trouble with this idea. The mechanism is known as “learning,” which is very common in birds and mammals. An adult bird may learn that a certain kind of prey is distasteful by catching it, tasting it, and then spitting it out. It then will teach its offspring to avoid the same kind of prey when they encounter it together. In species with feeding flocks, individuals may teach even unrelated flock mates that certain kinds of prey are toxic or distasteful. In mixed species flocks, such information can even be passed on to members of other species.
Well, no, not “any” combination of traits. Of course, every animal has many other traits besides the ones that you have mentioned (including its general ecology, what kind of prey or food it takes, where it lives, etc), and these additional traits may help explain why some animals have gone one evolutionary route and others have taken another. Of course both Blake and I have vastly oversimplified things for the purposes of discussion on a messageboard. There are dozens of books and thousands of publications on this complex subject which examine why certain combinations of characters have evolved.
There are three methods, and they almost certainly interact…
One is that young animals learn by watching the old. This method is amazingly rapid amongst birds and mammals, and may be why warning colourations appear to be more common amongst animals preyed upon by birds an mammals.
The second is genetic. Quite simply any animal with an innate fear of the “pattern” of poisonous creatures will produce more offspring, which will share that fear. There is some pretty compelling evidence for example that grazing animals instinctively fear the smell of lion. This doesn’t need to be taught. That makes sense, since any young creature that didn’t hide as soon as it smelled lion wouldn;t have much chance to learn through other means. The same mechanism probbaly applie sot wanring colouration as well.
The third is individual trial and error. An animal that attempts to eat a poisonous creature will get ill and avoid that creature thereafter. Its young will also need to learn to avoid the creatures as the avoidance isn’t transmitted. However the outcome for the prey species is still the same. Within short order the most experienced predators will all be avoiding it.
To give some idea of how fast these work you need only look at what happened when marine toads were introduced to Australia around 50 years ago. Initially the populations of frog predators were decimated and their were fears of widespread extinctions. Today the predators in the initial release sites have all recovered and all either avoid the toads, or have learned mechanisms to render them harmless. But the toads are still spreading their range, and predators on the edge of the range are still being decimated. In the case of birds and mammals and probably crocodiles the avoidance ebehavior is almost certainly learned from observing adults. In the case of snakes and frogs it’s either genetic or due to individual trial and error. We know that at least in the case of one water snake it is trial and error, with juvenile snakes preying on the less toxic tadpoles, and after one meal making them sick they avoid that toad smell for the rest of their lives.
But regardless of what mechanism the predators use to learn avoidance, the main point remains: that the more distinct the prey is in appearance (or smell), the better the predator is able to distinguish it, and thus avoid it. If all poisonous prey animals were the same colour as their non-poisonous relatives then at some point predators would have to either take a chance and try everything, or else starve to death. So it’s in the prey’s interests to advertise their poisonous nature.
As others noted? As I noted, explicitly, with an explanation.
No organism is subjected to just one stress, so there is never just one optimal colour scheme. A single organism may have to deal with:
Overheating, in which case light colours are optimal.
Warming up on cold mornings, in which case dark colours are optimal,
Hiding from predators and prey, in which case camouflage is optimal.
Intimidating rivals and attracting mates, in which case flamboyant colours are optimal.
And that is a very short list. We could easily add another twenty or so factors that will change the optimal colouration pattern. And of course for poisonous creatures we also have to add on the ability to advertise their poisonous status, which compete with all of them.
So which colouration pattern predominates? Well that depends upon a range of factors including which mutations occur, which of these factors most influences survival and what other alternatives may exist.
So no, any trait doesn’t validate evolutionary theory. Rather it’s a simple fact that evolutionary theory has been validated, and we seek to establish which of these factor is at play. Colibri has already posted some papers on how we do this. If we suspect that camoflage is at play then we might place expose range of animals to a prey species, and see how close the prey gets before fleeing. If we suspect that warning colouration is important then we can expose them to predators and oberve the predator reaction. We can then paint the exact same animals different colours and repeat the experiment. The results of these trails will confirm of falsify the hypothesis.
Since evolutionary theory is already well established, we use that theory as the basis of our predictions. In exactly the same way that we might use the theory of gravity as the basis of a prediction about the motion of a spacecraft. We don’t need to re-confirm the theory every time we want to use it. Nor do we say that the Apollo flights validated Newton, except in the sense that they failed to falsify it.
Well that’s the thing. The arguments do add up. Modern Evolutionary theory predicts that any trait that has evolved multiple times must present some reproductive advantage. And when we test the bright colouration patterns of poisonous animals. Lo and behold it provides a reproductive advantage. In other cases toxic creatures don’t have bright colouration, and Lo and behold it provides a reproductive advantage as well, effective against different stresses. It all adds up perfectly, and it is all exactly as Darwin predicted.
If these traits didn’t provide any reproductive advantage, then it wouldn’t add up. If toxic animals were brightly coloured, and they were eaten just as frequently as their drab conterparts, then you could say it didn’t add up. Or if drab animals were no more capable of ambushing prey.
There are some examples of this in the world. The ridiculous speed of the pronghorn antelope, the colouration of the panda that Colibri mentioned. These traits don’t have any established evolutionary advantage, so we have t speculate on what may have caused them to develop. But such cases are rare, and on their own can’t invalidate the theory. They just remain unproven.
But as far as warning colouration goes, it all adds up perfectly.
The clearest definition of Natural Selection EVAH!
Thanks guys. Neither of these facts had occured to me.
I’ve seen some animal shows that have mentioned that some predators also avoid eating some animals due to their behavior. Even if the potential prey is not brightly colored, but seems to boldly walk out in the open, this can be taken as a sign that there might be a good reason this animal is not afraid.
I’m trying to think of animals in the Giant Panda’s range that would be powerful enough to consider predating it.
Brown bears and gray wolves, for a couple. In earlier times, possibly tigers and leopards. In the Pleistocene, predators like scimitar cats may have shared its range.