Phenotypic Plasticity and Speciation

[overtone]

The intent of the breeders, or lack of it in nature, has no bearing on the process of speciation.

Don't be silly. The intent of the breeder is the selection pressure in a domestic breeding program. It has everything to do with the results. The breeder wants a dog, they select for dog traits, they get a dog.

 

 

Because natural selection will never have variants among which to choose that will be as dissimilar as those produced by breeders. That is false. There is no limit to how dissimilar a naturally evolving organism can become from its distant ancestors, whereas a dog breeder is trying to develop, maintain, and establish, a variety of dog - it's an artificially limited range of variation, as well as being too recent and new to be expected to have created a new species of large mammal.

 

 

 

 

If the breeders' variants don't speciate (is that a word?), - -

How do you know they haven't? Dachshunds and Great Pyrenees are reproductively isolated, dissimilar in form and function, and quite likely to occupy different ecological niches if they ever successfully go feral. So they one step - going wild - from being different species.

 

The only reason a breeder's variant is not a step toward speciation is that the breeder prevents it. They want the best dog, not a halfassed sorta-hyena.

 

And that is why species stick around once evolved, as well - it becomes harder to benefit from a random alteration of the genome involved, so the evolutionary pressures will tend to maintain the species as is.

Edited February 3, 2015 by overtone

[starlarvae]

 

Not to mention that the domestic dog is the result of numerous independent domestication events, followed by long term and frequent gene flow with a variety of wild canine species. http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1004016#pgen-1004016-g004

 

Now, the most widely applied species concept in current science is the evolutionary species concept http://statgen.dps.unipi.it/courses_file/GdP/Papers/DeQueiroz_SpeciesConceptDelimitation_Syst.Biol.2007.pdf.

 

To paraphrase, this concept defines species as meta-populations which share a common and distinct evolutionary trajectory. Due to the complex nature of Canis lupus domesticus multiple origins, widespread gene flow with other species, dog breeds do not meet the criteria of the evolutionary species concept -moerover represent phenotypic outliers within a population, and generally would be rightly not considered to represent species.

 

As far as examples in nature, try social insects.

 

etc. Phenotypic variation is not synonymous with species diversity anywhere in nature. Dogs are not an exception.

 

How is your first reference relevant to contemporary dog breeds? The breeds in the chart in the OP haven't been engaged in gene flow behaviors with wolves or wild dogs. Breeders keep the breeds reproductively isolated. That's the point.

 

Social insects: If each caste could reproduce on its own, I suspect speciation would follow. But to cite non-reproducing castes in a species of insect misses the point. You can't get each caste to be reproductively isolated.

 

The bird example shows color variation. Do these variants cohabit in the same niche? If they've been subjected to the same selection pressures, why did they turn out so differently colored? Or, do the colors indicate gender within the species? If the latter, then this is a bad example, because neither gender could become reproductively isolated from the other.

 

The frogs: variation in color, but morphologically, allometrically not a whole lot of difference, nothing like that shown in the dog breed poster.

 

Phenotypic variation within a species PLUS reproductive isolation of each variant sets the stage for speciation in the standard understanding of speciation by selection.

[Arete]

 

How is your first reference relevant to contemporary dog breeds? The breeds in the chart in the OP haven't been engaged in gene flow behaviors with wolves or wild dogs. Breeders keep the breeds reproductively isolated. That's the point.

 

On an evolutionary timescale, they very very recently have engaged in gene flow with wolves and other canine species, as is evident from the article. The point is that using the evolutionary species concept, as described earlier, we can easily determine that dog breeds do not represent discrete metapopulations with independent evolutionary histories. As such its unequivocal that they don't represent species.

 

Social insects: If each caste could reproduce on its own, I suspect speciation would follow. But to cite non-reproducing castes in a species of insect misses the point. You can't get each caste to be reproductively isolated.

 

The statement you made was that no naturally occurring species has as much phenotypic plasticity as domestic dogs. Social insects, rather succinctly disprove that notion. Furthermore, a queen and a worker are actually genetically identical, and not all memers of "sterile" castes are sterile (e.g. around 1 in 10,000 worker bees are fertile http://www.jstor.org/discover/10.2307/2830426?uid=3739256&uid=2&uid=4&sid=21105246696821)

 

The bird example shows color variation. Do these variants cohabit in the same niche? If they've been subjected to the same selection pressures, why did they turn out so differently colored? ...The frogs: variation in color, but morphologically, allometrically not a whole lot of difference, nothing like that shown in the dog breed poster.

 

These are subjective judgments of phenotypic variation, and thus worth little - I have no idea you can tell the frogs have the same body size from that photo, for e.g. as it's actually wrong - they vary in body size, toxicity and mating call http://onlinelibrary.wiley.com/doi/10.1046/j.1439-0310.2003.00863.x/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2007.03479.x/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false http://link.springer.com/article/10.1007/s10886-006-9034-y#page-1.

 

The point is, that many naturally occurring populations display a wide variety of phenotypic variation within populations across an extremely wide variety of parameters. You can't single domestic dogs out and make a sweeping comment about their phenotypic variation.

 

Phenotypic variation within a species PLUS reproductive isolation of each variant sets the stage for speciation in the standard understanding of speciation by selection.

 

This is again, incorrect. See cryptic species and hybridization.

 

The standard definition of a species under the evolutionary species concept, as previously stated, is a meta-population with an independent evolutionary history. Monophyly, reproductive isolation, phenotypic distinction, etc are all indicators of that evolutionary history, but not definitive of it. See previously cited Dq Quieroz paper.

Edited February 3, 2015 by Arete

[overtone]

 

 

The bird example shows color variation. Do these variants cohabit in the same niche? If they've been subjected to the same selection pressures, why did they turn out so differently colored?

Very often a given, strong, selection pressure will admit of two of more workable but mutually exclusive responses - migrating vs hibernating, say, or fight vs sneak mating. One of the more common pressures is predation by visual identification, which can and often does lead to wide variation in shape and color within a given species of insect. There is also sexual selection for variety rather than single trait - in bird song, in multiple mating species, etc - and outbreeding by choice, which requires identifying genetic strangers.

 

And so forth. Evolutionary theory is a profound advance in our analytical capabilities and comprehension - well worth your learning, some day.

[starlarvae]

 

It's been pointed out that you have cherry-picked an example that would be exceedingly bad illustration of speciation, because dog breeding is all about removing variation from a sub-species. You don't allow for any mutation to accumulate that would serve to allow a species to evolve.

 

If you want an actual example of how speciation could occur, why not go and look at actual known examples of evolution in action? Rhagoletis flies, for example.

http://evoled.dbs.umt.edu/lessons/speciation.htm

 

So instead of breeding out differences as we do with dogs, we see an example of genetic differences accruing in nature.

Unless you can point to some valid rule that says there's a threshold, i.e. a certain amount of variation always leads to separate species, this is a non-argument.

 

The distinctions you draw among and between species and sub-species seem awfully arbitrary. Dog breeding is about removing variation from a sub-species, you say. Well, maybe it's about creating novel sub-species. Look again at the chart in the OP. The enormous variability within the species -- that is, from sub-species to sub-species -- is the result of selective breeding. Within a sub-species, variability will be relatively small -- IF the sub-species is reproductively isolated. That's how breeders create sub-species.

 

Consider the flies in your example -- the two types became reproductively isolated (or, at least became genetically distinguishable) because of their preferences for the different kinds of trees. The reproductive isolation of variants is all we're talking about. Each kind breeds with its own kind. If the flies display less phenotypic variability than do the breeds of dogs (do they differ phenotypically in ways other than feeding behavior?), then why the fly speciation but no dog speciation? (You don't actually say that there was a speciation event with the flies, but you seem to imply it.)

 

As for breeding out differences from dogs, look again at the OP chart. Don't you see lots of differences among the breeds?

 

Non-argument? I'm just noticing a case of reproductive isolation of sub-species (aka, breeds) in which the sub-species vary dramatically from one another in their phenotypes. That is supposed to set the stage for speciation. What's the missing ingredient?

[swansont]

The distinctions you draw among and between species and sub-species seem awfully arbitrary. Dog breeding is about removing variation from a sub-species, you say. Well, maybe it's about creating novel sub-species. Look again at the chart in the OP. The enormous variability within the species -- that is, from sub-species to sub-species -- is the result of selective breeding. Within a sub-species, variability will be relatively small -- IF the sub-species is reproductively isolated. That's how breeders create sub-species.

Right. Breeding is in place to remove variability that might otherwise accumulate and lead to speciation.

 

Consider the flies in your example -- the two types became reproductively isolated (or, at least became genetically distinguishable) because of their preferences for the different kinds of trees. The reproductive isolation of variants is all we're talking about. Each kind breeds with its own kind. If the flies display less phenotypic variability than do the breeds of dogs (do they differ phenotypically in ways other than feeding behavior?), then why the fly speciation but no dog speciation? (You don't actually say that there was a speciation event with the flies, but you seem to imply it.)

 

For that claim to have merit, you need a rule that says that x amount of phenotypic variability is a species boundary. Does one exist? I think the answer is no, but I'm not a biologist. My understanding is that species is a much more fluid concept.

 

The flies are represented as speciation-in-progress, often pointed to as a rebuttal to certain claims that evolution can't be observed.

 

As for breeding out differences from dogs, look again at the OP chart. Don't you see lots of differences among the breeds?

 

Non-argument? I'm just noticing a case of reproductive isolation of sub-species (aka, breeds) in which the sub-species vary dramatically from one another in their phenotypes. That is supposed to set the stage for speciation. What's the missing ingredient?

 

What's missing is a requirement that a certain amount of phenotype difference must lead to speciation. Which would probably be tied into a 1:1 mapping of genotype and phenotype, and good luck with trying to demonstrate that.

 

In The Third Chimpanzee (Jared Diamond), it's pointed out that two closely-related bird species, red-eyed and white-eyed vireos, differ genetically by 2.9%. Humans and chimps differ by only 1.6%. Which has a closer phenotype match?

 

Dog breeds have a tiny difference in their genetics — most of their physics differences are explained by just 7 locations on the genome.

http://www.livescience.com/8472-genetic-variations-separate-great-danes-dachshunds.html

 

Seems to me all you've done is separate some characteristics. If we lined up all of the tall, blond-haired blue-eyed folks and contrasted them with short people of some other skin tone, hair color and possibly a few other characteristics, would you have the same level of difference? We know that such differences in humans are due to very minor genetic differences, and do not represent different species

[starlarvae]

On an evolutionary timescale, they very very recently have engaged in gene flow with wolves and other canine species, as is evident from the article. The point is that using the evolutionary species concept, as described earlier, we can easily determine that dog breeds do not represent discrete metapopulations with independent evolutionary histories. As such its unequivocal that they don't represent species.

 

Recency of gene flow from wolves, etc. So what? Look at some of the goofier dog breeds. They've pretty much had any wolfiness bred out of them. What constitutes an "evolutionary history"? If length of time is the missing ingredient, then what exactly is it that time would accomplish? Reproductively isolate distinct sub-species? But that's exactly what the breeders have done.

 

The statement you made was that no naturally occurring species has as much phenotypic plasticity as domestic dogs. Social insects, rather succinctly disprove that notion. Furthermore, a queen and a worker are actually genetically identical, and not all memers of "sterile" castes are sterile (e.g. around 1 in 10,000 worker bees are fertile http://www.jstor.org/discover/10.2307/2830426?uid=3739256&uid=2&uid=4&sid=21105246696821)

Unless you're talking about phenotypically distinct sub-species (or castes) that can become reproductively isolated from one another, as dog breeds can, your example is not relevant.

 

These are subjective judgments of phenotypic variation, and thus worth little - I have no idea you can tell the frogs have the same body size from that photo, for e.g. as it's actually wrong - they vary in body size, toxicity and mating call http://onlinelibrary.wiley.com/doi/10.1046/j.1439-0310.2003.00863.x/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2007.03479.x/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false http://link.springer.com/article/10.1007/s10886-006-9034-y#page-1. The point is, that many naturally occurring populations display a wide variety of phenotypic variation within populations across an extremely wide variety of parameters. You can't single domestic dogs out and make a sweeping comment about their phenotypic variation.

Subjective judgements? Phenotypes are empirical. You can measure parameters. Height, length, weight, skull shape, leg shape, tail shape, fur thickness, color, pattern --- it's endless. Where in nature will you find such phenotypic variability as you will find in the dog chart? BTW, are the frog variants reproductively isolated from one another? If not, then the example is not relevant.

 

And your phrase, "independent evolutionary history" is not clear. Is it just another way of talking about reproductive isolation?

[overtone]

Non-argument? I'm just noticing a case of reproductive isolation of sub-species (aka, breeds) in which the sub-species vary dramatically from one another in their phenotypes. That is supposed to set the stage for speciation. What's the missing ingredient?

There isn't one. The stage is set for speciation.

 

What's your point?

 

 

 

 

Where in nature will you find such phenotypic variability as you will find in the dog chart?

Fungi, algae, several others. Like this: http://en.wikipedia.org/wiki/Pfiesteria_piscicidaor this: http://en.wikipedia.org/wiki/Gymnosporangium_juniperi-virginianae or this: http://en.wikipedia.org/wiki/Stem_rust

 

There are fungi that are officially identified as a sort of pair of species, so variable morphologically that their species designation is split into two parts with different scientific names, and only recent advances in genetic analysis and elucidation of life cycles have enabled us to identify those disparate morphologies as belonging to one coherent breeding and evolutionary population.

 

Edited February 10, 2015 by overtone

[Arete]

So what?

 

It would be helpful to your understanding if you read up on the evolutionary species concept.

 

Now, the most widely applied species concept in current science is the evolutionary species concept http://statgen.dps.unipi.it/courses_file/GdP/Papers/DeQueiroz_SpeciesConceptDelimitation_Syst.Biol.2007.pdf.

 

To paraphrase, this concept defines species as meta-populations which share a common and distinct evolutionary trajectory.

 

To go back to previously cited links, dogs, are resultant from multiple domestication events and a long history of gene flow with both each other and wild canine species. Therefore they do not have independent evolutionary histories. Ergo, under the evolutionary species concept, they could not be considered species.

 

Unless you're talking about phenotypically distinct sub-species (or castes) that can become reproductively isolated from one another, as dog breeds can, your example is not relevant.

 

I think you need to revisit the definition of phenotypic plasticity. If different morphotypes are distinct lineages, the phenotypic differences are not due to plasticity. Also, dog breeds are, at best partially genetically isolated at a prezygotic level. To try and claim that there is a postzygotic reproductive incompatibility would be false. The example holds - you cannot make the blanket assertion that dogs are more phenotypically plastic than all naturally occurring species - which is what you claimed, after all.

 

 

Subjective judgements? Phenotypes are empirical. You can measure parameters. Height, length, weight, skull shape, leg shape, tail shape, fur thickness, color, pattern --- it's endless. Where in nature will you find such phenotypic variability as you will find in the dog chart? BTW, are the frog variants reproductively isolated from one another? If not, then the example is not relevant.

 

1) Morphology can be empirical, however you use of it in previous posts is decidedly not so. If you make a clear statement like "dogs vary in body size/color/etc more than any other species" it can be quantified. By making a vague arm waving generalization about phenotypic variation without specifics leaves the judgement you make on other species entirely subjective, and thus rather worthless.

2) See previous examples, here's another in Mimulus

3) Again, you need to revisit phenotypic plasticity, as if each phenotype is a distinct lineage, the variation observed can no longer be termed to be plastic. Plasticity refers to the variety of morphotypes which arise from the same genotype, exposed to different environmental pressures. The dendrobatid frog populations shown in the previous photo are allopatrically distributed on islands.

 

 

And your phrase, "independent evolutionary history" is not clear. Is it just another way of talking about reproductive isolation?

 

It's been clearly explained previously and linked to. See above. Additionally, the presence or absence of reproductive isolation is not the be all and end all of species definitions. For e.g. about 25% of plant species can hybridize and to go back to canine species, coyotes and wolves can hybridize, but remain undisputed, distinct species.

 

Ultimately, what I think you're missing with the dog example is that the phenotypic distinction between breeds is at best, a precursor to speciation. Assuming the breeds are viable sub-populations within Canis lupus domesticus (which is debatable due to low effective population sizes and the need for human intervention) the separation between them and other dog breeds needs to persist long enough for them to develop characteristics which allow for unequivocal designation as an evolutionarily distinct metapopulation. At the time being, they haven't acquired enough of these traits - particularly at the genetic level to warrant most biologists in recognizing them as such.

Edited February 10, 2015 by Arete

[starlarvae]

Right. Breeding is in place to remove variability that might otherwise accumulate and lead to speciation.

Are you kidding? The dramatic within-species variability shown in the dog chart in the OP is the result of selective breeding.

 

For that claim to have merit, you need a rule that says that x amount of phenotypic variability is a species boundary. Does one exist? I think the answer is no, but I'm not a biologist. My understanding is that species is a much more fluid concept.

I think this thread already has established that the "species boundary" in a given case is decreed by a panel of taxonomists.

 

The flies are represented as speciation-in-progress, often pointed to as a rebuttal to certain claims that evolution can't be observed.

 

What's missing is a requirement that a certain amount of phenotype difference must lead to speciation. Which would probably be tied into a 1:1 mapping of genotype and phenotype, and good luck with trying to demonstrate that.

Phenotypic variation alone won't do it. You need reproductively isolated phenotypic variants. As the variants become more and more varied, at some point the taxonomists step in and pass judgement.

 

In The Third Chimpanzee (Jared Diamond), it's pointed out that two closely-related bird species, red-eyed and white-eyed vireos, differ genetically by 2.9%. Humans and chimps differ by only 1.6%. Which has a closer phenotype match?

 

Dog breeds have a tiny difference in their genetics — most of their physics differences are explained by just 7 locations on the genome.

http://www.livescience.com/8472-genetic-variations-separate-great-danes-dachshunds.html

 

Seems to me all you've done is separate some characteristics. If we lined up all of the tall, blond-haired blue-eyed folks and contrasted them with short people of some other skin tone, hair color and possibly a few other characteristics, would you have the same level of difference? We know that such differences in humans are due to very minor genetic differences, and do not represent different species

 

I'm not sure how important genomic/genotypic differences are, since the environment can select based only on phenotypes. It would be useful if some official panel of taxonomists made public their criteria for decreeing a new species (degrees of genetic difference, phenotypic difference, interbreeding, behavioral repertoire, etc. If you know of such, tip me off.

There isn't one. The stage is set for speciation. What's your point?

How much stage setting is required before the play begins? I guess we'll have to wait for the taxonomists to take their seats, first.

 

 

Fungi, algae, several others. Like this: http://en.wikipedia.org/wiki/Pfiesteria_piscicidaor this: http://en.wikipedia.org/wiki/Gymnosporangium_juniperi-virginianae or this: http://en.wikipedia.org/wiki/Stem_rust

 

There are fungi that are officially identified as a sort of pair of species, so variable morphologically that their species designation is split into two parts with different scientific names, and only recent advances in genetic analysis and elucidation of life cycles have enabled us to identify those disparate morphologies as belonging to one coherent breeding and evolutionary population.

The Wiki entries are interesting, but we have to be careful not to let phenotypically distinct castes (as with social insects) or life-cycle stages (as with metamorphosing creatures) count as phenotypical variants in the context of this thread, because such intraspecific variants, unlike dog breeds, cannot become reproductively isolated from one another.

[swansont]

Are you kidding? The dramatic within-species variability shown in the dog chart in the OP is the result of selective breeding.

 

But that's a separate issue. My point is a purebred stays a purebred because you eliminate variation. However, speaking to that other issue, I already posted a link which explains that the "dramatic" variation isn't really all that dramatic in terms of genetics. You are insisting otherwise, but it seems to me without anything to back it up.

 

 

I think this thread already has established that the "species boundary" in a given case is decreed by a panel of taxonomists.

And yet a few sentences later in your post you aren't sure this panel exists.

 

Phenotypic variation alone won't do it. You need reproductively isolated phenotypic variants. As the variants become more and more varied, at some point the taxonomists step in and pass judgement.

That's not how they judge, AFAIK, especially for extant species. I think you consider reproductive isolation, and the ability to produce fertile offspring. If the artificial barriers were removed, would different types of terriers mate? Would a terrier mate with a hound or a toy? Would they produce fertile offspring?

 

 

I'm not sure how important genomic/genotypic differences are, since the environment can select based only on phenotypes.

Some difference in phenotype does not prevent mating, but enough genotype difference prevents fertile offspring. Horses and donkeys producing mules, for example.

 

And again, the visual differences in dogs are not representative of all that much phenotype variation.

 

[Strange]

Are you kidding? The dramatic within-species variability shown in the dog chart in the OP is the result of selective breeding..

 

Are you kidding? Breeders make sure that their animals remain within the breed standard.

 

I think this thread already has established that the "species boundary" in a given case is decreed by a panel of taxonomists.

 

Of course. It is a human concept. There are no God-given "kinds", despite what creationists tell you.

[starlarvae]

I think you need to revisit the definition of phenotypic plasticity. If different morphotypes are distinct lineages, the phenotypic differences are not due to plasticity. Also, dog breeds are, at best partially genetically isolated at a prezygotic level. To try and claim that there is a postzygotic reproductive incompatibility would be false. The example holds - you cannot make the blanket assertion that dogs are more phenotypically plastic than all naturally occurring species - which is what you claimed, after all.

 

If they're of distinct lineages, then the differences might be due to plasticity PLUS genomic variation. The variation referenced in the OP was intraspecific variation. How far back into ancestry do you go to determine "distinct" lineages, anyway? Second cousin twice removed?

 

"postzygotic reproductive incompatibility" ? I don't think I said or implied that. On the contrary, I assume that with artificial insemination, any two dog breeds could be interbred. I still would like to see an example of a species naturally as plastic as dogs --- an example that does not cite castes or life-cycle stages or genders as distinct phenotypes within a species, because such variants cannot be reproductively isolated.

 

 

1) Morphology can be empirical, however you use of it in previous posts is decidedly not so. If you make a clear statement like "dogs vary in body size/color/etc more than any other species" it can be quantified. By making a vague arm waving generalization about phenotypic variation without specifics leaves the judgement you make on other species entirely subjective, and thus rather worthless.

2) See previous examples, here's another in Mimulus

3) Again, you need to revisit phenotypic plasticity, as if each phenotype is a distinct lineage, the variation observed can no longer be termed to be plastic. Plasticity refers to the variety of morphotypes which arise from the same genotype, exposed to different environmental pressures. The dendrobatid frog populations shown in the previous photo are allopatrically distributed on islands.

Arm waving? If anybody knows of a study that compares species by degree of plasticity, quantified, I would like to see.

 

Mimulus, so far as I can determine, is a genus designation, and so we would expect it to encompass broader phenotypic variability than would a species.

 

I think you're right about typical usage of "plasticity", but if you substitute "phenotypic variability" or "morphological variability" or something like that, is doesn't change the point made in the OP.

 

 

 

[overtone]

I'm not sure how important genomic/genotypic differences are,

You mean you don't know what you are talking about? We know.

 

since the environment can select based only on phenotypes.

Select what?

 

Do you understand what an act of selection, in standard Darwinian theory terms, selects? Seriously - that's a basic bit of knowledge that you need to post on this topic. Do you have it?

 

 

 

 

It would be useful if some official panel of taxonomists made public their criteria for decreeing a new species (degrees of genetic difference, phenotypic difference, interbreeding, behavioral repertoire, etc. If you know of such, tip me off.

You have been linked, repeatedly, to explicit examples of taxonomic description of species, right here. The criteria used to "decree" those species, as with any formally proposed taxonomic classification, are all laid out for you on the page. Go read them, follow the links to others, Google for yourself, and so forth. You've been barraged with such stuff here, piled, enough to keep you busy for a year.

 

 

How much stage setting is required before the play begins? I guess we'll have to wait for the taxonomists to take their seats, first.

You mean the people who know what they are talking about? Yes, you will have to rely on the verdicts of people who know what they are doing. Either that or study up and learn something - watch the play, read the script, etc - for yourself.

 

 

The Wiki entries are interesting, but we have to be careful not to let phenotypically distinct castes (as with social insects) or life-cycle stages (as with metamorphosing creatures) count as phenotypical variants in the context of this thread, because such intraspecific variants, unlike dog breeds, cannot become reproductively isolated from one another.

You obviously didn't read any of those links.

 

I chose them partly because they were examples of intraspecific variation that could, in fact, become reproductively isolated - may even, in some cases, have become so already. (There is serious discussion among fungi taxonomy experts as to exactly when some of these self-reproducing 1N and 2N forms of many fungi deserve to be given their own species names) . You asked for examples of declared, taxonomically formal species with phenotypic variation comparable to the domestic dog's, and I handed you several with links to more - so your request is met, completely and conveniently for your immediate edification.

 

Move on.

Edited February 12, 2015 by overtone