I am waiting for some response as to vision-oriented mushroom eaters. You seem to be pretty nervous here while your explanation of mushroom coloration is unexplainable via natural selection (and what's more - it's even funny considering slugs as vision-oriented mushroom-eaters). And whats worse, you cannot in this case obscure it with another darwinistic mantra - "sexual selection"!
(There is no such thing as "sexual selection" in mushrooms kingdom, so you cannot use dialectical alchemical mix of "natutal selection" and "sexual selection" as you use it so creatively in explanation of the long neck of Giraffe etc...)
I'm a student of fungal biology, so I'll try to help you out here.
What you're saying isn't quite true; there is sexual selection in many fungi. The form it takes is quite different from that which we see in animals, however. Many fungi (particularly in the basidiomycota) have what are called mating strains. Depending on the clade in question, a given species can have as many as nine different mating strains. In order for these fungi to reproduce, the appropriate mating pair must find each other. There is even at least one genus, Armillaria, that takes advantage of this arrangement to parasitize certain members of an entirely different genus, Enteloma. The Armillaria effectively fools the Enteloma into "thinking" that its a compatible strain and then takes over the hapless basidiomycete, forming what is called an "abortive Enteloma," which looks nothing like either Armillaria or Enteloma. So there is sexual selection, but it takes place at the chemical level, not the visual level.
As to why mushrooms (and other fungi as well) have evolved particular colors, there's no single answer for that. It depends on what fungus we're talking about. For example, many coral fungi (Ramaria) produce bad-tasting chemicals that, as a side effect of their presence, can result in colors ranging from brown to purple to scarlet. Most fungi, by the way, are not preyed upon by primarily visual fungivores. Most things that eat fungi look for chemical signals, not visual ones, so color isn't a particular constraint. The bulk of animals that feed primarily on fungi are insects (particularly flies and beetles) and gastropods. A good example of how fungi put this to their advantage is found amongst the Phallales, or as they're affectionately called, the stinkhorns. Stinkhorn species come in all sorts of colors, from putrid slimy greens to beautiful orange and yellow, but what they all do in common is produce a slimy spore mass called gleba. They've evolved to smell like carrion, too, which attracts plenty of flies. The flies land on the gleba and get a little meal, then fly away with the spores stuck to their feet. When the gleba dries out, the spores fall off, and the flies are thus made into the primary vector for distributing the fungi. Color isn't important at all in this; a scavenger that uses visual cues quickly recognizes the fungus as not being food when it arrives after having tracked the scent. I've observed this behavior personally in raccoons in the southeastern United States.
But here's a good one for you, a consumer that does use visual cues: squirrels. Squirrels frequently eat members of genus Russula, even some (such as Russula emetica) that we humans find unpalatable. And which russula do they eat? Well, they seem to go after those that aren't necessarily colored brightly, but certainly those which contrast strongly against their background. It may well be that Russula spores can be spread in squirrel droppings; the aforementioned R. emetica, for instance, tends to be very bright red to pink. I've observed squirrels eating white russulas on numerous occasion as well, though I can't say for sure what species they were (as you may know, Russulas are very difficult to distinguish based solely on morphology). In answer to your question, then, we have to ask which fungi you're referring to, because Fungi is a kingdom with nearly as much diversity as that in animals and plants, so it's impossible to lump them all together. Estimates of the number of species run as high as 1.5 million, and we've barely scratched the surface in cataloguing them. For whatever reasons, we mycologists aren't exactly the rock stars of the biological world, so funding for everything we'd like to do all at once can be a bit on the lean side.
FYI, my own research involves looking at the relationship between one order of fungi, the Polyporales, and one family of beetles, the Tenebrionidae. It's just getting off the ground, but the plan is to map the phylogenetic distances within each taxon and compare them to see whether the two have conditioned one another's evolutionary history. The beetles form very tight, frequently one-to-one relationships, with the fungi, and the question arises as to what's going on there. I can tell you with great certainty, though, that these important fungal exploiters do not seek their prey by visual cues.
So, we do see natural selection in the fungi, and we do see sexual competition in some of them. Hope this clears some of your questions up.
Edited by Mike O Risal, : Didn't finish a sentence. Oops.
You're making several bad assumptions in this, so I hope I can continue clearing up some more of this.
There is great diversity in coloration of mushrooms and no darwnistic explanation of it. You have proved to the folks here what I had already known and what I had told them repeatedly - there were no vision-oriented mushroom eaters except squirrels. Consequently every attemt (Alan Fox) to explain such a color diversity as outcome of selective pressure is plasusible explanation only for hard-core believers of Natural selection as the source of evolution.
Coloration is still an outcome of several selective pressures, just not one particular pressure. For example, one of the many problems that fungi face is exposure to sunlight. Many of the colors we see in mushrooms are a reaction to that pressure; being brightly colored to white reflects light, preventing the fruiting bodies from drying out and/or spores from being damaged by radiation. Remember, when you're looking at a mushroom, you're only looking at a very small part of the overall organism, much like a flower on a plant. The rest of the organism is in the substrate, and without microscopic and/or genetic examination or other specific tests, you can't tell one mycelium from another except by inducing fruiting. We see a trait expressed in a particular organ facing a particular pressure that isn't expressed in the rest of the organism — a very good sign of a response to selective pressure, in fact. What you're doing here would be analogous to stating that humans face no selective pressure to be able to metabolize dietary sugar because we don't produce insulin in our skin.
I also gave another example of how a fungus evolved coloration as a response to predators, albeit not visual ones. The coloration (in Ramaria, e.g.) is a byproduct of accumulating chemicals to make it unpalatable to non-visual predators, which are still very much a problem for fruiting bodies that are produced above ground; note that macrofungi that produce fruiting bodies below ground (e.g., Gasteromycetes) never produce colorful fruiting bodies, because they face neither pressures from solar radiation nor from predators; being underground prevents the chemical signals which nonvisual predators use to home in on the fungi from finding them in the first place, so these fungi either haven't evolved the response or else are descendants from fungi that used to produce pigmented fruiting bodies but lost this trait when the energy cost involved became greater than the benefit in keeping it, and we can tell that this has occurred because of phylogenetic investigation. All of this is exactly in keeping with what evolutionary biology would predict.
I am talking mainly of mushrooms everybody can see in forest walking there - most famous - violet (as your mentioned Russula, Russula fragilis), - brown (Boletus reticulatus) - red (Amanita muscaria) - tigred (Amanita pantherina) - green (Russula virescens) - yellow (Cantharellus friesii) etc.
Even here, you're lumping together some very different groups. For example, Cantharellus, Boletus and Amanita are in an entirely different orders! Again, we'd still have to ask "Which fungi?" The three have very significant physiological differences and slightly different solutions to environmental pressures, including predation. There are no lethal species of Boletus or Canthatellus, for example, but many members of Amanita are quite deadly. Boletus, on the other hand, does produce some potent GI irritants in order to defend its fruiting bodies, and Cantharellus tends to have a strategy combining producing huge numbers of fruiting bodies and general inedibility (i.e., just being plain old trimitic and impossible to chew through).
It's another explanation - color as a side effect of development. No doubt there are chemicals responsible for coloration (pigments etc) but it should be shown that such pigments have also other role than "self-representation" of the given mushrooms.
I gave you at least one in my previous reply (being unpalatable), and now a second one (protection from solar radiation). Also, keep in mind that I didn't say that fungi have no visual predators other than squirrels, I said that overall, their most important predators aren't visually oriented. Deer will eat mushroom, and accounts of reindeer becoming intoxicated by Amanita muscaria are well-known, too. Again, we wind up having to ask "which fungus?" rather than making a generalization about an entire kingdom, or even a whole division.
As far as what you've said about snakes, it may be true that they arose as a secondary consideration, but the fact that they still have them is what's important to consider. It's absolutely not unusual to have a trait arise as a side-effect; in fact, a great many of them do. This doesn't preclude this "side effect" from being useful, and it certainly is no evidence against evolution. Again, I don't know whether or not its true of snakes in this particular instances, but I can say that we have several species of poisonous snakes here and I can certainly attest to the effectiveness of their camoflauge.
What you've heard about the US isn't exactly true; gathering wild mushrooms is fairly popular on the West Coast and practically unknown in the South, but it does go on, although it's certainly not as important a part of culture here as in Europe, particularly in your part of the continent. Not that I mind; we're just coming out of season for Laetiporus sulphureus and coming into chanterelle season, and edible Pleurotis are plentiful most of the time (if one can get at them before the fungus gnats do). I don't mind not having too much competition; it's one less "selective pressure" I have to deal with myself!
Martin, I am beginning to think that there may be something amiss with your mind. As I have now said three times, you are lumping together entirely different ORDERS of organisms. It's not an "analogy." Asking why chanterelles have a color and then expecting Russula to have the same colors for the same reason is no different at all from asking why frogs have webbed toes and snakes don't. These are different organisms with different histories, and what you're trying to do here simply makes no sense at all.
Let me see if I can get this through your head. I have a hunch it won't work, but I'll give this one last try.
"Mushrooms" is a very general term referring to a particular arrangement of fruiting body on a narrow slice of an entire kingdom of life, Fungi. It's not even a term that can really be discussed in a narrow manner since, again, the arrangement has arisen independently in the course of the kingdom's history on no fewer than six widely spaced occasions. We can trace this because we can look right at the genes and see the changes by making mathematical comparisons.
You can't see why my explanations would be sufficient because, frankly, you don't know what you're talking about. You honestly don't. You're lumping together completely different organisms in an arbitrary manner and then asking me to explain why you are doing it. Nobody can do that, and if that's what you're expecting from somebody as a response, then you'll never get a satisfactory one.
Fungi don't "want" to express anything. They respond to simple stimuli, either negatively or positively. They don't think, they don't make decisions, they don't plan for a home in the tropics with a two-car garage. In making a statement like this, you're going yourself one step worse; you're trying to compare fungi with animals, particularly mammals. Even in those cases, though, your statements make no sense at all. Why would all members of a species "want" to be the same color? Why don't we see purple zebras and polka-dotted kangaroos? More to the point, why don't we see any blue chanterelles? A lack of self-expressive imagination? Truly, truly silly stuff. We can look at the phylogeny of the organisms in question and deduce evolutionary history from them that precludes blue chanterelles; they don't have the pathway to synthesize such pigments because they're not part of the ancestry. Perhaps some day there might be one, but there almost certainly never has so far. It's very, very simple, and doesn't require ascribing personality to fungus.
And yes, Martin, you should consider the color of hares as different from the color of wild pigs, because they are different animals that have evolved very different strategies to maximize their chances of passing on their genes. They also have ancestries that came from different places, which goes right back to the fungi again.
Traits don't change in the snap of fingers. Change, new pathways, happen gradually. This is exactly what we would predict, it's precisely what we see in the real world, and it's precisely what we can see into the deep past when we explore phylogeny. New fungal strains arise all the time. In fact, there's now a yellow variant of Pleurotus ostreatus that didn't exist a scant 50 years ago. It still lives in the same habitat as white Pleurotus, but it appears to be less susceptible to infestation by certain flies which are a major problem for its white counterpart. Note that I say "less susceptible" but not "immune." It didn't turn yellow to express its artistic side; it has to do with other changes to its morphology. Unless some other pressure harms it in continuing to do so, we can expect it to continue down its path... and it can coexist in the same area not only with visual predators, but even with the much more problematic chemically-directed predators. This is how fungi change over time. We know it happens because we can literally observe it happening as new strains arise.
So you go right on making these tremendous blunders of logic. Should you make them about fungi, I'll be there to clean them up. These are truly and deeply amateurish, illogical errors that reflect nothing that's an issue in reality. You asked a question, and you've gotten an answer from someone who has dedicated their life to studying these things and has been able to make predictions and produce results. If you want to live in a world that forces you to make statements that fungi want to express themselves through coloration, you go right ahead. Anybody who gives such a ridiculous statement any sort of credence deserves what they get... nothing.