Subspecies versus breeds

[Haltlose]

What is a "subspecies" versus a "breed"?

 

A Wildcat (Felis silvestris), has five subspecies, but a house cat (Felis catus) doesn't have subspecies, but breeds.

 

For example, a siamese and a maine coon are very different in appearance and behavior, so why shouldn't they be considered subspecies?

 

Thanks for any help.

[bombus]

What is a "subspecies" versus a "breed"?

 

A Wildcat (Felis silvestris), has five subspecies, but a house cat (Felis catus) doesn't have subspecies, but breeds.

 

For example, a siamese and a maine coon are very different in appearance and behavior, so why shouldn't they be considered subspecies?

 

Thanks for any help.

 

The criteria for species and sub-species are not particularly strict and are open to interpretation. It tends to boil down to convenience if the truth be told. Some class Felis domesticus/catus as a sub-species of F. sylvestris, others don't.

 

Also, it would seem some divide F. catus into subspecies:

 

* F. catus anura - the Manx

* F. catus siamensis - the Siamese

* F. catus cartusenensis - the Chartreux

* F. catus angorensis - the Turkish Angora

[lucaspa]

What is a "subspecies" versus a "breed"?

 

A Wildcat (Felis silvestris), has five subspecies, but a house cat (Felis catus) doesn't have subspecies, but breeds.

 

For example, a siamese and a maine coon are very different in appearance and behavior, so why shouldn't they be considered subspecies?

 

Thanks for any help.

 

Haltose is correct in that the categories are not strict. This is what Futuyma says in Evolutionary Biology:

 

"Subspecies: A taxonomic term for populations of a species that are distinguishable by one or more characteristics, and are given a subspecific name (e.g. the spuspecies of the rat snake Elaphe obsoleta; se Figure 21 in Chapter 9). In zoology, subpecies have different (allopatric or parapatric) geographical distributions, so are equivalent to "geographic races;" in botany, they may be sympatric forms. No criteria specify how different populations should be to warrent designation as subspecies, so some systematists have argued that the practice of naming subspecies should be abandoned." pg 450

 

"Semispecies: Usually, one of two or more parapatric, genetically differentiated groups of populations that are thought to be partially, but not fully, reproductively isolated; nearly, but not quite, different species."

[angelpparker]

Please tell about subspecies" versus a "breed?

[lucaspa]

Please tell about subspecies" versus a "breed?

 

Once you get below the category of "species", there are several names that all try to categorize differences between groups within a species: variety, breed, population, subspecies, semispecies, and race. In addition to the 2 from Futuyma's texbook I posted above, here are a few more:

 

"Race: A vague, meaningless term, sometimes equivalent to subspecies and sometimes to polymorphic genetic forms within a population."

 

"Variety: Vague term for a distinguishable phenotype of a species"

 

None of the names are specific. Notice how Futuyma says of subspecies "No criteria specify how different populations should be to warrent designation as subspecies". Biologists today usually speak of "populations". In Darwin's day they used the term "variety". Breed seems to be equivalent to "variety" and is used, not surprisingly, by human breeders. Using artificial selection, breeders make "breeds". We are, of course, most familiar with breeds of housepets like cats and dogs. And we distinguish breeds by their appearance -- their "phenotype". Great Danes look different from St. Bernards look different from Labrador Retrievers look different from Cocker Spaniels, etc.

 

Subspecies has criteria like variety "populations of a species that are distinguishable by one or more characteristics" That's what variety and breed does. However, subspecies also includes, for animals, the idea that these populations are in different geographical areas: "In zoology, subpecies have different (allopatric or parapatric) geographical distributions". This might have been true of dogs in that some breeds were bred in particular geographical areas, such as the daschund in Germany. That geographical isolation is, of course, mostly no longer true. Neighbors have different breeds of dogs as pets.

 

For plants, a subspecies could be in the same local geographical area (since plants can't move and they may be isolated within a few discrete locations within the area).

 

But really, the bottom line is that the terms are so loose and ill defined that, for biologists, they are meaningless. Breed = subspecies = variety = race = biologically useless term.

 

The only term that has any meaning is semispecies. There you have partial reproductive isolation. Ring species such as the Arctic gull or the California salamander would have the individual populations be semispecies. Dogs today could (at least) be split into semipecies, since there are reproductive barriers between some of the breeds. Genetic data says dogs are 4 species.

 

I hope that helps. If you have more questions, don't hesitate to ask.

[CharonY]

Well, actually those classification are taxonomically meaningless, but are used as an ad hoc distinction in a variety of fields, usually focussing on one particular diagnostic or physiolgocal aspect like serovars, pathovars, biovars, etc.

They often lose their significance outside the respective fields.

[lucaspa]

Well, actually those classification are taxonomically meaningless, but are used as an ad hoc distinction in a variety of fields, usually focussing on one particular diagnostic or physiolgocal aspect like serovars, pathovars, biovars, etc.

They often lose their significance outside the respective fields.

 

CharonY, all the terms (serovar etc) you used apply to microbiology. Most people don't associate "breed", "subspecies", etc with microorganisms but with multicellular organisms, particularly plants and vertebrates. Do microbiologists also use the other terms? I haven't seen that in the (admittedly somewhat limited) microbiology literature I have encountered.

[CharonY]

Actually this is not limited to microbiology. In botany cultivars are often used. I am not aware of a similar typification in animals, which makes sense as they were not categorized as excessively as crops or diseases....

 

Subspecies are sometimes but rarely used in microbiology (afaik, but then I am not a microbiologist).

Mostly "strain" is used to designate certain lines. The same goes for (lab-) animals.

These are, however, usually clonal lines.

[lucaspa]

Actually this is not limited to microbiology. In botany cultivars are often used.

 

When looking up definitions I only saw the terms used in micro. Can you cite some papers where the term was used in botany? Thanks.

 

I am not aware of a similar typification in animals, which makes sense as they were not categorized as excessively as crops or diseases....

I'd say they were categorized more excessively.

 

Mostly "strain" is used to designate certain lines. The same goes for (lab-) animals.

These are, however, usually clonal lines.

 

In animals, "strain" is used for inbred lines, such as Holtzman or Sprague-Dawley rats. It can also be used for varieties generated by manipulation of ES cells that are then used to replace the ES cells in a blastocyst -- thus making a "man-made" animal. Thus, ROSA mice (that started out with the bacterial beta-galactosidase enzyme inserted into the genome and then the first ROSA were inbred) are a strain.

 

In micro, since reproduction is asexual, of course what you get are clonal lines. However, "strain" is usually used for family of clones (clones that are genetically similar) that are genetically distinct from other families. The species name, such as Escherichia coli, is more like a genus name for sexually reproducing organisms, with the strains being the "species" within that genus.

[CharonY]

Yes, clonal is the wrong term for animals, I slipped into cell bio lingo. I did mean inbred lines.

 

 

In micro as well as cell biology strains cannot easily be compared to species in animals as something as small as a single point mutation could be classified as a new strain (usually in conjunction with phenotypic change, as e.g. resistance).

 

Regarding cultivars it is a term mostly in agricultural contexts there are too many to name, but here is just the first one from a simple pubmed search:

 

J Integr Plant Biol. 2008 Jan;50(1):102-10.

Simple sequence repeat analysis of genetic diversity in primary core collection of peach (Prunus persica).

Li TH, Li YX, Li ZC, Zhang HL, Qi YW, Wang T.

 

I'd say they were categorized more excessively.

I would argue against that

 

Just to elaborate, historically classification into strains was often done by categorizing according to certain properties, or often simply according to different isolates. In that regard strains are a subcollection within a species. Regardless whether an organism propagates sexually or asexually, the basic unit of species cannot be changed by this matter (unless we define them anew in the light of a revised evolutionary framework, which has not been done yet).

 

However, in microbiology since quite a while strains are established as pure if all the members are clonal (genetically identical). So if you take a bacterial or fungal cell (or an immortalized higher eukaryotic cell for that matter) and mutate it, you create a new strain (or cell line). In higher eukaryotes, however, strains are not always clonal (established cell lines often are, though).

 

But as one can see, my point simply is that classifications on this level are mostly driven by pragmatism. Cells or organisms are given denominators just to distinguish them from other based on certain (arbitrary) properties, isolation methods, and/or genetic alterations.

[lucaspa]

In micro as well as cell biology strains cannot easily be compared to species in animals as something as small as a single point mutation could be classified as a new strain (usually in conjunction with phenotypic change, as e.g. resistance).

 

Possibly, but I haven't seen it. Bacterial resistance to antibiotics involve more than a single pont mutation. Keep in mind that a single point mutation in the hybrid fertility genes can render a population of sexually reproducing animals a new species, too.

 

However, as I have seen "strains" presented in seminars in micro, there are a cluster of genetic differences, not just one.

 

Regarding cultivars it is a term mostly in agricultural contexts there are too many to name, but here is just the first one from a simple pubmed search:

 

J Integr Plant Biol. 2008 Jan;50(1):102-10.

Simple sequence repeat analysis of genetic diversity in primary core collection of peach (Prunus persica).

Li TH, Li YX, Li ZC, Zhang HL, Qi YW, Wang T.

 

I would argue against that

 

The early anatomists, such as Owen, worked mostly with animals and studied the various phenotypic differences quite extensively. As just one example, look at the study of cirripedia by Darwin: The Lepadidae; or, pedunculated cirripedes. [Vol. 1], The Balanidae, (or sessile cirripedes); the Verrucidae. [Vol. 2], A monograph on the fossil Lepadidae, or, pedunculated cirripedes of Great Britain. [Vol. 1] , and A monograph on the fossil Balanidae and Verrucidae of Great Britain. [Vol. 2].

 

Just to elaborate, historically classification into strains was often done by categorizing according to certain properties, or often simply according to different isolates. In that regard strains are a subcollection within a species. Regardless whether an organism propagates sexually or asexually, the basic unit of species cannot be changed by this matter (unless we define them anew in the light of a revised evolutionary framework, which has not been done yet).

 

Historically, assignment of species names in microbiology was done on phenotypic characterizations. As you know, all bacteria within the rods and sphere in light microscopes look pretty much the same. Thus, historically, we are stuck with the species name referring to a wide range of genetic variability. It's not that the basic unit of biology and evolution isn't the species, it's that the guys who first assigned categories of "species" on the microbiological level did not have the tools to distinguish species and, instead, gave the name "species" to what should properly be genera or even higher taxa -- based on the genetics.

 

However, in microbiology since quite a while strains are established as pure if all the members are clonal (genetically identical).

 

Again, in the seminars I have attended, strains are established as similar genetics, not identical. What you have is a descended family of clones: first one clone and then that clone has variations among it's clonal descendents.

 

So if you take a bacterial or fungal cell (or an immortalized higher eukaryotic cell for that matter) and mutate it, you create a new strain (or cell line). In higher eukaryotes, however, strains are not always clonal (established cell lines often are, though).

 

Even cell lines are not clonal. For instance, if you go to American Type Culture Collection and get cell lines, they are not clonal. Instead, most of them are established from particular tumors from particular individuals. But genetic analysis of cancer cell lines shows quite of a bit of genetic variability within the line. Not as much as within the original tumor, but still quite a bit.

 

To get "clonal" in cell lines, you must do additional manipulation. The most common is "limiting dilution" where you dilute the cell suspension so that you have odds of plating slightly less than 1 cell in the volume you are using for that particular cell culture well. Usually you use a 96-well plate and dilute the cell suspension so that you have about 0.8 cells per 100 ul, and then plate 100 ul per well. You then look on day 1 and eliminate any well that has more than one cell in it (this is very tedious work, BTW). Each well is a clone.

 

An alternative method is to insert a known DNA sequence via a retrovirus, still do the limiting dilution, and then use restriction enzymes to identify the insertion of the DNA sequence. This really is just a fancy way to confirm your limiting dilution.

 

But as one can see, my point simply is that classifications on this level are mostly driven by pragmatism. Cells or organisms are given denominators just to distinguish them from other based on certain (arbitrary) properties, isolation methods, and/or genetic alterations.

 

And I would partially agree with this point, but I would add that the original species designation was arbitrary based on the properties that could be observed under light microscopy. Therefore what we call "species" in microbiology is actually a genus or higher taxa when we get down to looking at the genetics. The real species are the "strains" of bacteria. So when we see a new strain of E. coli that can live in apple juice, what we have really seen is a new species formed.

 

Regarding cultivars it is a term mostly in agricultural contexts there are too many to name, but here is just the first one from a simple pubmed search:

 

J Integr Plant Biol. 2008 Jan;50(1):102-10.

Simple sequence repeat analysis of genetic diversity in primary core collection of peach (Prunus persica).

Li TH, Li YX, Li ZC, Zhang HL, Qi YW, Wang T.

 

The "too many" are 2996 of which 52 are reviews. However, I accept the point: cultivar is used in agriculture. I am curious: what type of PubMed search did you run? When I ran ones using "cultivar, plant" or "cultivar, agriculture" this was buried over 100 items into the search. What search terms did you use?

[CharonY]

Lucaspa, I have not yet found the time to read your whole post. Just the top:

Possibly, but I haven't seen it. Bacterial resistance to antibiotics involve more than a single pont mutation. Keep in mind that a single point mutation in the hybrid fertility genes can render a population of sexually reproducing animals a new species, too.

 

Most spontaneous resistant strains arise from single point mutations within their ribosomal genes. They get classified as a new strain, accordingly.

 

Cultivars is a commonly used denominator. I am kinda surprised that you have not heard from it. It is also to my knowledge exclusively used for plant classification. A simple search should yield around 3k hits. But if you read the M&M section of papers including agricultural relevant plants you will very often find something like e.g. Medicago sativa cultivar something, which does not get displayed in the search. Sometimes it is omitted, though technically it is incorrect. I am gonna read your post sometime when I get back from the lab.

___________________________________________

 

I have posted a lengthy reply in this second part here, but the browser crashed. So here a quick version.

 

Historically, assignment of species names in microbiology was done on phenotypic characterizations. As you know, all bacteria within the rods and sphere in light microscopes look pretty much the same. Thus, historically, we are stuck with the species name referring to a wide range of genetic variability. It's not that the basic unit of biology and evolution isn't the species, it's that the guys who first assigned categories of "species" on the microbiological level did not have the tools to distinguish species and, instead, gave the name "species" to what should properly be genera or even higher taxa -- based on the genetics.

 

First, early microbiologist made taxonomy based on phenotype (as you correctly point out) which, however does not merely include morphology. In any case, modern bacterial taxonomy is now almost exclusively based on genome-genome hybridization and 16srRNA analyses. In other words, purely genetics. This makes your point:

 

And I would partially agree with this point, but I would add that the original species designation was arbitrary based on the properties that could be observed under light microscopy. Therefore what we call "species" in microbiology is actually a genus or higher taxa when we get down to looking at the genetics. The real species are the "strains" of bacteria. So when we see a new strain of E. coli that can live in apple juice, what we have really seen is a new species formed.

rather moot. If the new bacterium in apple juice has the same 16srRNA then it is still E. coli, even if it gained a few genes. One should add that an astonishingly high number (at least from what I heard, again, I am not really a traditional microbiologist) of older classifications were verified by the new methods.

 

Again, in the seminars I have attended, strains are established as similar genetics, not identical. What you have is a descended family of clones: first one clone and then that clone has variations among it's clonal descendents.

 

And again, to distinguish modified cells you give them different strain names, once you establish the differences. There might be a difference in how strains are presented in seminars and how they are designated in real life (though they should not), however this only underlines my point, namely that such distinction are made for practical reason, not for taxonomical ones.

Mind you, pure cell lines might at some point undergo mutations that you are not aware of, but until they surface somehow you treat them as if they were the original strain.

 

If you conduct genetic studies one has to be able to pinpoint precisely with what kind of cells you did your work with. As in microbial genetics you almost exclusively work with clonal cells, each deviation warrants a different strain name. During my graduate time I created roughly 40-50 site specific mutants in two different bacterial species (and created a new transfected plant cell line, though the grad student supposed to get a clonal line out of it apparently let it die....). Each mutant received a different strain name in the form of e.g. Genus spec Tu-121.

 

As eukaryotic cell lines are often not pure the designation of a cell line is not equivalent (but in some cases can be) as strains for bacteria. Then again, int theory different cell lines can be derived from the same individual, resulting in two different cell lines with essentially the same genetic makeup (in terms of sequence, at least). Mice or rat strains (inbred or hybrids) on the other hand do have yet other rules of naming (including a designation of lab and in case of hybrids from which strains they were derived from) and so on. In other words for each distinct organism the rules for naming something below the species level are different and usually set up by rather different nomenclature committees. In the end they are only there to be able to pinpoint unequivocally with what you are working with. In cases where it is easily possible (e.g. in bacteria) the designation can be ultraprecise (genetically) in other (e.g. mice strains) the variations can be rather large.

Edited August 11, 2008 by CharonY
multiple post merged