Different species of dogs ?

[blue_cristal]

It is very unlikely that a Chihuahua could successfully mate with a Great Dane. And sexual isolation is one of the criteria that separate species.

 

Are dogs of different breeds so different to each other that they have become different species ?

[JHAQ]

Dont confuse species with breeds . All modern dogs of any type are fundamentally interfertile ( and of the same species ) even if size differences preclude "normal " copulation . One could say breed differences are the first step in speciation but the same could be said for different human races -- all of whom are also interfertile .

[blue_cristal]

Dont confuse species with breeds.

 

I do not need to confuse. Certainly there must be a line , beyond which, a race become a new species.

 

Therefore this fuzzy line would be confusing itself ( no need for conceptual confusion ).

 

All modern dogs of any type are fundamentally interfertile ( and of the same species ) even if size differences preclude "normal " copulation .

 

Any sexual impossibility, being it mechanical or physiological, can cause species isolation.

 

One thing is being fertile through artificial insemination and another entirely different is being fertile by natural sexual interaction.

 

One could say breed differences are the first step in speciation but the same could be said for different human races -- all of whom are also interfertile .

 

Well, as far I know, human races are not so different that they are prevented to mate between each other and reproduce.

[Paralith]

Any sexual impossibility, being it mechanical or physiological, can cause species isolation.

 

The reason why reproductive isolation causes speciation is that it blocks the exchange of genes between species. Now even though a chihuahua may not be physically capable of mating with a great dane, genes can still be passed from one to another through intermediary matings. This is similar to the idea of a ring species - both sides of the debate can be reasonably argued. (http://en.wikipedia.org/wiki/Ring_species) Dogs probably aren't the best example to argue species concepts with though, because their breeding is so carefully controlled by humans. If all the breeds were let loose in the wild to do their thing, we can't be entirely sure what would happen to the extreme breeds. Most dogs will mate with whatever female dog they can manage with, and aren't choosy about breed, so after time the chihuahua and great dane breeds could possibly have a great comingling of genes.

[goingtothedo]

"Species" is kind of a fuzzy term, even Darwin thought so. He went to some considerable lengths in The Origin of Species to spell out that some well qualified parties may consider a particular set of individuals as species and another equally well qualifed consider the same individuals to be varieties of a species or races.

 

His point was that varieties are, to use his phrase "incipient species". Left to go on in the same track they may well become established as fully fledged species incapable of breeding with each other. But should circumstances draw the groups together again they will merge back into one amalgamated species.

 

A better definition of species than individuals that can mate with each other is perhaps individuals who will tend to mate with each other, but even this definition is fraught with rocky shores and wayward currents.

 

In the end, "species" is an artificial term, handy for cataloging, but to be approached with caution who dealing with real living entities.

[geoguy]

"Species" is kind of a fuzzy term, even Darwin thought so. He went to some considerable lengths in The Origin of Species to spell out that some well qualified parties may consider a particular set of individuals as species and another equally well qualifed consider the same individuals to be varieties of a species or races.

 

His point was that varieties are, to use his phrase "incipient species". Left to go on in the same track they may well become established as fully fledged species incapable of breeding with each other. But should circumstances draw the groups together again they will merge back into one amalgamated species.

 

A better definition of species than individuals that can mate with each other is perhaps individuals who will tend to mate with each other, but even this definition is fraught with rocky shores and wayward currents.

 

In the end, "species" is an artificial term, handy for cataloging, but to be approached with caution who dealing with real living entities.

 

Excellent post . In paleontology we sometimes rue the day that Linnaeus introduced binomial species/genus taxonomy...not because it is flawed in itself but because it has been take too literally as a biological clasification rather that one of taxonomy (your mention of cataloging).

 

As with any term is science , 'species' must be defined when used in general use....or have an accepted definition within a particular zoological discipline...sometimes as refined as that accepted among a particular family of beetles, etc.

 

We were classifying some rugose corals and the criteria for a genus was having a visible feature distinct from another....and a species within that genus was the difference within that particular sfeature. 99% of species out of the millions named in literature have no have no record of sexual compatibility. Reproduction might be 'assumed' but many species, especially those of the tens of thousands of beetles, moths and so on actually have two named species...one for male and one for female. Their species names are based strictly on morphology and the species only combined together if, in the rare event, someone take the time to study them in detail.

[goingtothedo]

Yes, it is too easy to take a handy mental toolkit and impose that onto the real world out there.

 

I rather liked the tale of the lawyer who argued that evolution could not be true because it would mean that in the transition from one species to another, it would mean that somewhere along the generations, a mother would give rise to an offspring who was not the same species as herself.....

 

Kind of a temporal version of a ring species I suppose

[blue_cristal]

Yes, it is too easy to take a handy mental toolkit and impose that onto the real world out there.

 

I rather liked the tale of the lawyer who argued that evolution could not be true because it would mean that in the transition from one species to another, it would mean that somewhere along the generations, a mother would give rise to an offspring who was not the same species as herself.....

 

Yet it can be true in some cases like in the occurrence of polyploidy.

[goingtothedo]

Please tell me more

[goingtothedo]

Sorry just looked it up and reminded myself what polyploidy is (I've little formal education is this area; just a deep interest and a lot of reading). Yes, it happens particularly in plants doesn't it; multiplication of sections of the genome.

 

So when that arises in an individual, how does it go about breeding? i.e. finding an appropriate partner? Must it multiply vegetatively to produce other individuals to get a compatible match?

[blue_cristal]

Sorry just looked it up and reminded myself what polyploidy is (I've little formal education is this area; just a deep interest and a lot of reading). Yes, it happens particularly in plants doesn't it; multiplication of sections of the genome.

 

Not really. It is the multiplication of the entire set of chromosomes.

Here is the wikipedia definition:

"Polyploidy is the condition of some biological cells and organisms manifested by the presence of more than two homologous sets of chromosomes. Polyploid types are termed according to the number of chromosome sets in the nucleus: triploid (three sets; 3x), tetraploid (four sets; 4x), pentaploid (five sets; 5x), hexaploid (six sets; 6x) and so on."

 

 

So when that arises in an individual, how does it go about breeding? i.e. finding an appropriate partner? Must it multiply vegetatively to produce other individuals to get a compatible match?

 

Plants usually can have both sexual and asexual reproduction. Therefore a new Polyploidal mutant plant could reproduce asexually. Additionally some plants have both masculine and feminine sexual organs so they can auto-fertilize themselves.

 

Polyploidy is less frequent in animals. However a new Polyploidal mutant animal can produce a progeny through parthenogenesis where there is no need for male fertilization.

[geoguy]

Polyploidy is less frequent in animals. However a new Polyploidal mutant animal can produce a progeny through parthenogenesis where there is no need for male fertilization.

 

Most of North America's species of whiptail lizzards reproduce this way. The individuals are all female.

[goingtothedo]

Most of North America's species of whiptail lizzards reproduce this way. The individuals are all female.

 

Really? So are they all genetically identical? In effect, clones?

[blue_cristal]

Really? So are they all genetically identical? In effect, clones?

Not necessarily. In average there are some dozens of new mutations added to each individual.

[blue_cristal]

Some of the latest scientific estimates show that on average, humans have approx 175 new mutations per diploid genome per generation.

 

http://www.genetics.org/cgi/content/full/156/1/297

 

That means that although we may be still similar enough to our parents species to be considered as members of their species, we carry new mutations and new recombinations ( reshuffling of genes ) of existing mutations that potentially could start a new species.

 

Therefore each one of us is potentially a bridge between two different species.

[bombus]

Some of the latest scientific estimates show that on average, humans have approx 175 new mutations per diploid genome per generation.

 

http://www.genetics.org/cgi/content/full/156/1/297

 

That means that although we may be still similar enough to our parents species to be considered as members of their species, we carry new mutations and new recombinations ( reshuffling of genes ) of existing mutations that potentially could start a new species.

 

Therefore each one of us is potentially a bridge between two different species.

 

Through evolutionary history, the point where one species becomes another is often pretty arbitrary. This is even true of higher taxons. Mammals, for example, are separated by paleontologists from mammal-like reptiles by the dentary squamosal jaw articulation. This 'line in the sand' was, I think, more-or-less made-up.

[lucaspa]

It is very unlikely that a Chihuahua could successfully mate with a Great Dane. And sexual isolation is one of the criteria that separate species.

 

Are dogs of different breeds so different to each other that they have become different species ?

 

Yes. At the least dogs are now a ring species. However, one paper says that, genetically, dogs are now 4 species:

 

3. C Vila` , P Savolainen, JE. Maldonado, IR. Amorim, JE. Rice, RL. Honeycutt, KA. Crandall, JLundeberg, RK. Wayne, Multiple and Ancient Origins of the Domestic Dog Science 276: 1687-1689, 13 JUNE 1997. http://www.idir.net/~wolf2dog/wayne1.htm

[lucaspa]

Some of the latest scientific estimates show that on average, humans have approx 175 new mutations per diploid genome per generation.

 

http://www.genetics.org/cgi/content/full/156/1/297

 

That's VERY high. Other studies have gotten similar numbers but it is AT LEAST 100x higher than for other multicelled animals.

 

That means that although we may be still similar enough to our parents species to be considered as members of their species, we carry new mutations and new recombinations ( reshuffling of genes ) of existing mutations that potentially could start a new species.

 

Speciation requires reproductive isolation. In fact, for sexually reproducing organisms, speciation equals reproductive isolation. Mutations alone do not provide this.

 

Therefore each one of us is potentially a bridge between two different species.

 

Uh, this is a common myth of evolution on internet boards, but it isn't true. Evolution doesn't work this way.

[lucaspa]

Through evolutionary history, the point where one species becomes another is often pretty arbitrary.

 

Because evolution happens to populations, the exact point where you have a new species is impossible to define. Take a transition and at generation 1 we have species A. At generation 10,000 it's obvious we have species B. But where in that transition you get a new species is impossible to pin down. Because of the gradual nature of evolution and reproductive isolation, you cannot say "at generation 5,000 we have species A and at generation 5,001 we have species B"

 

"This primitive configuration of pongid and hominid traits has led the discoverers and describers of these early Australopithecines to assign them to a new species. If the first Australopithecines to be discovered is properly Australopithecus africanus, the early ones, they suggest, should be Australopithecus afarensis. Not al scholars agree. I have to confess that, although I have had the opportunity to handle both the Ethiopian and the South African material with which it is being compared, and although I agree with virtually all of what its describers say in regard to its tendency to be more primitive in a series of traits, I am not convinced that the differences are pronounced enough to warrant separate specific recognition. ...

"Our disagreement is merely a matter of the assignment of names. This is based on the judgement of the individual scholars and is a trivial matter, but it does point up an issue of fundamental significance. In an evolutionary continuum, change occurs more or less gradually through time. At the early and late ends of such change, everyone agrees that different names are justified, but when one form slowly transforms into another without break, the point where the change of name is to be applied is a completely arbitrary matter imposed by the namers for their convenience only - it is not something compelled by the data." C. Loring Bruce, "Humans in time and space." In Scientists Confront Creationism, edited by LR Godfrey, 1983, pp. 254-255.

[lucaspa]

"Species" is kind of a fuzzy term, even Darwin thought so. He went to some considerable lengths in The Origin of Species to spell out that some well qualified parties may consider a particular set of individuals as species and another equally well qualifed consider the same individuals to be varieties of a species or races.

 

And WHY did Darwin do this? To show the transition of one species to another!

 

His point was that varieties are, to use his phrase "incipient species". Left to go on in the same track they may well become established as fully fledged species incapable of breeding with each other. But should circumstances draw the groups together again they will merge back into one amalgamated species.

 

This is the tug of war between disruptive selection and gene flow.

 

A better definition of species than individuals that can mate with each other is perhaps individuals who will tend to mate with each other, but even this definition is fraught with rocky shores and wayward currents.

 

In the end, "species" is an artificial term, handy for cataloging, but to be approached with caution who dealing with real living entities.

 

No, species are the ONLY "real living" biological entities. It's just that we can't come up with a precise definition for them because evolution is true. Because populations gradually transform from one species to another over the course of many generations, it is impossible to make a precise definition of species. Whatever definition one makes, there are going to be populations in transition that don't fit the definition.

 

The error is to think that this evolutionary reality means that species are not real.

[lucaspa]

All modern dogs of any type are fundamentally interfertile ( and of the same species ) even if size differences preclude "normal " copulation . One could say breed differences are the first step in speciation but the same could be said for different human races -- all of whom are also interfertile .

 

This has gone further in dogs. The biological species definition is:

"Species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups." Mayr.

 

"Interfertile" is not necessary and is, in fact, the last stage in reproductive isolation. Below see a list of reproductive isolating mechanisms:

"Classification of Isolating Mechanisms

1. Premating or prezygotic mechanisms: Mechanisms that prevent interspecific matings.

(a) Potential mates are prevented from meeting (seasonal and habitat isolation)

(b) Behavioral incompatibilities prevent mating (ethological isolation)

© Copulation attempted but no transfer of sperm takes place (mechanical isolation)

 

2. Postmating or postzygotic mechanisms:

Mechanisms that reduce full success of interspecific crosses

(a) Sperm transfer takes place but egg not fertilized (gametic incompatibility)

(b) Egg fertilized but zygote dies (zygotic mortality)

© Zygote develops into an F1 hybrid of reduced viability (hybrid viability)

(d) F1 hybrid is fully viable but partially or completely sterile, or produces deficient F2 (hybrid sterility)"

Ernst Mayr, What Evolution Is pg 171

 

In terms of chihuahas and Great Danes, 1(b) and © operate, as well as 2(b). Male great danes have genital incompatibility with female chihuahas and perhaps male chihuahas with female great danes (the male chihuaha penis would not be long enough to deposit sperm where they could make it to the female great dane uterus). We also have the problem that, even if a male great dane does fertilize a female chihuaha, the female dies (as do the zygotes) because the fetuses are too large for her uterus.

 

You say "All modern dogs of any type are fundamentally interfertile". As far as I know, the relevant hybrid experiments have not been done. While we have "mutts", these are somewhat limited hybrids (dogs of approximately the same size) and it is not clear to me that hybrids of each and every breed is going to satisfy 2© and 2(d). If you have data that all breeds are still capable of interbreeding with every other breed and producing fully viable and fertile F1 and F2 hybrids, please let us know.

[blue_cristal]

 

Some of the latest scientific estimates show that on average, humans have approx 175 new mutations per diploid genome per generation.

 

http://www.genetics.org/cgi/content/full/156/1/297

 

That's VERY high.

 

It is high compared with old estimates. Since this latest measurement used more sensitive methods then probably this high estimate is more accurate.

 

 

That means that although we may be still similar enough to our parents species to be considered as members of their species, we carry new mutations and new recombinations ( reshuffling of genes ) of existing mutations that potentially could start a new species.

 

Speciation requires reproductive isolation. In fact, for sexually reproducing organisms, speciation equals reproductive isolation. Mutations alone do not provide this.

 

Why not ?

 

1) If the mutations are adaptive to a new niche, accessible to these individuals, this can start a process of insulation in relation to the parents’ species which, by additional new adaptive mutations or natural selection of existing alleles, can culminate with sexual isolation after a given number of generations.

 

 

2) If few individuals with new adaptive mutations ( or possessing an unusual combination of existing mutations [ alleles ] ) are accidentally transported to a new environment, geographically separated from the parents’ species, they can also start forming a new, allopatric, species through genetic drift.

 

 

Furthermore, I was talking generically and not specifically to sexual species. Some plants and few animals can became a new species in just one generation through a single huge genetic change ( polyploidy ). The new plants’ species could then proliferate through asexual reproduction or auto-fecundation. The polyploidic animals could reproduce through parthenogenesis.

 

And, although speculative, it is not impossible that an individual can start a new species by accidentally receiving a chunk of genes from a very different species through viral genetic transference which then happen to be adaptive to a new environment.

 

Therefore each one of us is potentially a bridge between two different species.

 

Uh, this is a common myth of evolution on internet boards, but it isn't true. Evolution doesn't work this way.

 

Why myth ?

 

When I said a “bridge between two species” it does not necessarily mean a bridge of just one step ( one generation ). The bridge can have as many steps or be as long as hundreds or thousands of generations under modifying selective pressures. Though, as I already said, it is not impossible speciation in just one generation in cases of polyploidy and, more hypothetically, through viral transference of an adaptive chunk of genes from one species to another.

[blue_cristal]

In an evolutionary continuum, change occurs more or less gradually through time. At the early and late ends of such change, everyone agrees that different names are justified, but when one form slowly transforms into another without break, the point where the change of name is to be applied is a completely arbitrary matter imposed by the namers for their convenience only - it is not something compelled by the data."

 

The evolutionary continuum is correct in the majority of cases.

But there are exceptions like polyploidy for instance, where the continuum changes abruptly .

[lucaspa]

It is high compared with old estimates.

 

No, it's pretty much in line with estimates done previously. It's high compared to other species. It is 120 times higher than the mutation rate in Drosophila. Over 100,000 times the mutation rate in E. coli!

 

Why not ?

 

1) If the mutations are adaptive to a new niche,

 

You just answered your own question: IF the mutations are adaptive. Mutations alone are not sufficient, you need selection.

 

There have been several experiments done to test the neutral theory of speciation, which basically says that new species happen because of mutations and then natural selection acts to make the new species different from the old. They have all found that mutation alone is not sufficient for speciation. Speciation results from natural selection. Since natural selection works on variations, it can produce new species from the variations generated by recombination without any mutations being involved.

 

accessible to these individuals, this can start a process of insulation in relation to the parents’ species

 

All the studies I have seen indicate that "insulation" -- whether geographic or lifestyle -- happens FIRST and not as a result of mutations.

 

2) If few individuals with new adaptive mutations ( or possessing an unusual combination of existing mutations [ alleles ] ) are accidentally transported to a new environment, geographically separated from the parents’ species, they can also start forming a new, allopatric, species through genetic drift.

 

Examples of allopatric speciation involve simply members of a species. They do not have, a priori, "new adaptive mutations". Rather, they are able to earn a living in the new area, but the adaptation comes AFTER they are there. And it is due to natural selection, not genetic drift. Yes, a few new traits can become fixed thru genetic drift, but I know of no case where speciation occurred this way. If you've got one from the literature, please share it. Futuyma in his textbook Evolutionary Biology discusses founder events -- where 2 of a species become isolated -- but even here the resulting changes are due to natural selection, not drift.

 

Some plants and few animals can became a new species in just one generation through a single huge genetic change ( polyploidy ).

 

As far as I know, even polyploidy does not result in a new species within a generation. The discussion of polyploidy always involves hybridzation and the papers I have seen requires several generations for the new genome to stabilize -- this stabilization resulting from crosses with the 2 original parent species and with others like itself.

1. Speciation in action Science 72:700-701, 1996 A great laboratory study of the evolution of a hybrid plant species. Scientists did it in the lab, but the genetic data says it happened the same way in nature.

2. Hybrid speciation in peonies http://www.pnas.org/cgi/content/full/061288698v1#B1

3. http://www.holysmoke.org/new-species.htm new species of groundsel by hybridization

4. Butters, F. K. 1941. Hybrid Woodsias in Minnesota. Amer. Fern. J. 31:15-21.

http://www.globalchange.umich.edu/globalchange1/current/lectures/speciation/speciation.html

"Alternative Models of Species Formation -- Hybridization and Polyploidy

In plants, new, reproductively isolated species may arise instantaneously, due to multiplication of the entire complement of chromosomes by a process known as polyploidy. This may occur as a result of hybridization, combining the chromosome sets from two parent species in a hybrid individual. If such hybrids turn out to be well adapted to environmental conditions, hybridization is a mechanism that produces new species.

Even if hybrids are unable to undergo sexual reproduction because their chromosomes do not sort out properly in meiosis, they may reproduce vegetatively. The total chromosome number also may double by combining the chromosome sets of a single species.

 

Of the 260,000 known species of plants, as many as half may have originated in this way. Many commercially important plants are examples of polyploidy (e.g. bread wheat, cotton, tobacco, sugar cane, bananas, potatoes). Polyploidy is an example of sympatric speciation defined as species arising within the same, overlapping geographic range. "

 

Gould has a paper on species by hybridization in land snails -- which means polyploidy. I often post the picture as an example of a series of transitional individuals between species. It is at the bottom of the post. That sequence did not happen within a single generation.

 

And, although speculative, it is not impossible that an individual can start a new species by accidentally receiving a chunk of genes from a very different species through viral genetic transference which then happen to be adaptive to a new environment.

 

If this is a sexually reproducing species (particulary animal), no, this won't work. If you are talking unicellular and asexual reproduction, then the distinction gets fuzzier of what exactly is a species at that point.

 

Why myth ?

 

1. Because your examples of single generation speciation don't work.

2. Because many species go extinct! Therefore individuals are not a bridge to a new species. Even if speciation is occurring, the individual spoken about could very well be one whose alleles are NOT used in the new species.