Speciation - what exactly is it?

[shadron]

I found a page that I think answers the question that I posed in the OP, its in Understanding Evolution: History, Theory, Evidence, and Implications by R. G. Price:

http://www.rationalrevolution.net/articles/understanding_evolution.htm

The answer is that I was right, and Eos was right and William Parcher and Kuroyume and Raze and Biomorph are all right. It makes the following points:

- Linnaean species is a wrong concept and should be shelved, but is, unfortunately so woven into biology that such an excision will be very traumatic.
- Biological species are different from Linnaean; too bad they share the same word. This definition is much better but still has problems of ambiguity, transposition and attempting in general to make a gray situation black and white.
- Boundaries separating interspecies breeding include:
Pre-mating boundaries:

• Geographic isolation
• Mating preferences (organisms choose mates based on certain characteristics, such as color, song, size, smell, etc.)
• Physical incompatibility of sex organs (penis does not pair with vagina, etc.)
• Different mating schedules (different timed release of gametes among things like corals, plants, etc.)

Post-mating boundaries include:

• Different numbers of chromosomes
• DNA from one parent is not able to fully pair with other parent DNA during fertilization and mitosis

The article is much, much longer than just this one small section ("Species and Speciation"), and it has a ton of biology in it, easily enough, I think, for a 3 sem-hour college course on evolution, and may well be just that. I plan to take a week or so to look through it thoroughly. There are some spectacular (and gruesome) photos and lots of discussion in areas such as religion, social darwinism and creationist trickery.

I found it, BTW, from one of Dr. Adequate's skepticwiki pages, so thanks for that, Dr. A.

Appropos to the last few postings, look up also the Cama, a cross between a llama and a dromedary camel.

 

[Taffer]

I am a bit of a dilettante in biology. I've read Asimov in my earlier years, watched innumerable videos by Ken Miller, Aron Ra, cdk007, and others, and read lots of articles. I'd like to find out whether my notion about speciation is correct.

Species are usually defined as groups of animals who can interbreed and produce potent offspring. At the chromosome level, I presume it means that no critical genes have moved their site from one place to another on the chromosomes, and chromosomes have neither fused nor split apart. It seems to me that simple movement of a gene site would not itself be a problem, since it likely doesn't make much functional difference where on a chromosome a gene is located, but that gene shuffling between the mother's and father's chromosomes would make a hash of genes which have moved sites, rendering the proteins created from those sites to be inappropriate for the jobs they were intended to fulfill, and rendering offspring unviable, or at a minimum, sterile (what exactly is the mechanism for that, and why should it seem to be the result of a "close" match, BTW?).

Is there any good materials on the internet that explain how speciation occurs at the genetic level? Thanks for your help.

The issue is that the concept of a species in biology is an artificial category which often fits, but doesn't always. Things are easy when we deal with fairly large animals, but start looking at bacteria and plants, for example, and things start to become slightly more arbitrary.

A perfect example: A native New Zealand bird, the Black Stilt (Himantopus novaezelandiae) is taxonomically a separate species from the Pied Stilt (H. himantopus), but readily hybridizes with it to such an extent that this behaviour is threatening the black stilt's existence. Should we consider them a single species, or two separate species?
Another example is that of the mule, wherein sometimes female offspring of a male horse and a female donkey can, rarely, be fertile. Are they different species most of the time? All of the time. Never?

While the above examples are not the most controversial (both are explained by a species definition which simply states that most offspring be infertile), you get the idea.

Concerning the genetic modes of speciation, there is more to it than chromosomal number, etc. You mention that a gene's location should have no affect, but quite the contrary. The human genome, for example, has recently been shown to be fractaline in nature. In this case, the physical location of a gene can directly affect its regulation. Not to forget the affects of epigenetics, in which genomic imprinting directly affects the viability of the offspring.

Basically, biology, and genetics in particular, are really complicated.

 

[biomorph]

The issue is that the concept of a species in biology is an artificial category which often fits, but doesn't always.

I'm having problems with your "artificial" tag.

Although there are what appear to be exceptions, I venture to say that the emergence, divergence and perhaps convergence of the non breeders perhaps brings about some crossbreds, occasionally that might be fertile for some generations too.

Probably over a more extended period, for example the drift of diverging breeds, within species, that are "close enough" to bear viable future generations of offspring
might be seen to be actually diverging. Or not.

Things are easy when we deal with fairly large animals, but start looking at bacteria and plants, for example, and things start to become slightly more arbitrary.

I'm not sure about that.

Maybe.

.

A perfect example: A native New Zealand bird, the Black Stilt (Himantopus novaezelandiae) is taxonomically a separate species from the Pied Stilt (H. himantopus), but readily hybridizes with it to such an extent that this behaviour is threatening the black stilt's existence.

that's not a plant, or bacteria. ahem...

See above re divergence , convergence etc. maybe

Should we consider them a single species, or two separate species?

Well, for this case measure the drift in the breeding pairs over enough time, and eventually you might see a drift, one way or another. There might be a very long period of stasis even, if conditions permit.

Another example is that of the mule, wherein sometimes female offspring of a male horse and a female donkey can, rarely, be fertile. Are they different species most of the time? All of the time. Never?

See above

While the above examples are not the most controversial (both are explained by a species definition which simply states that most offspring be infertile), you get the idea.

Yup, did I make sense, ? am wrong?

Concerning the genetic modes of speciation, there is more to it than chromosomal number, etc. You mention that a gene's location should have no affect, but quite the contrary. The human genome, for example, has recently been shown to be fractaline in nature. In this case, the physical location of a gene can directly affect its regulation. Not to forget the affects of epigenetics, in which genomic imprinting directly affects the viability of the offspring.

Basically, biology, and genetics in particular, are really complicated.

Yup, that is true.

several billion years of time to get that way, eventually..lol

 

[biomorph]

I found a page that I think answers the question that I posed in the OP, its in Understanding Evolution: History, Theory, Evidence, and Implications by R. G. Price:

http://www.rationalrevolution.net/articles/understanding_evolution.htm

The answer is that I was right, and Eos was right and William Parcher and Kuroyume and Raze and Biomorph are all right. It makes the following points:

- Linnaean species is a wrong concept and should be shelved, but is, unfortunately so woven into biology that such an excision will be very traumatic.

Yes, I'd agree, but the truth is worth the trauma, this science after all.

- Biological species are different from Linnaean; too bad they share the same word. This definition is much better but still has problems of ambiguity, transposition and attempting in general to make a gray situation black and white.

Yes. it's hard.

- Boundaries separating interspecies breeding include:
Pre-mating boundaries:

• Geographic isolation
• Mating preferences (organisms choose mates based on certain characteristics, such as color, song, size, smell, etc.)
• Physical incompatibility of sex organs (penis does not pair with vagina, etc.)
• Different mating schedules (different timed release of gametes among things like corals, plants, etc.)

Post-mating boundaries include:

• Different numbers of chromosomes
• DNA from one parent is not able to fully pair with other parent DNA during fertilization and mitosis

The article is much, much longer than just this one small section ("Species and Speciation"), and it has a ton of biology in it, easily enough, I think, for a 3 sem-hour college course on evolution, and may well be just that.

Um, yup. don't ask.....

I plan to take a week or so to look through it thoroughly. There are some spectacular (and gruesome) photos and lots of discussion in areas such as religion, social darwinism and creationist trickery.

I found it, BTW, from one of Dr. Adequate's skepticwiki pages, so thanks for that, Dr. A.

Dr A is a star...as usual

Appropos to the last few postings, look up also the Cama, a cross between a llama and a dromedary camel.

I will, however timespan is relevant.

As you rightly state, and can be observed often with reality, boundary conditions are the mother of invention.

See chaos theory for example maybe.

glad to have been of help, even if only a little.

 

[Taffer]

I'm having problems with your "artificial" tag.

Why?

Although there are what appear to be exceptions, I venture to say that the emergence, divergence and perhaps convergence of the non breeders perhaps brings about some crossbreds, occasionally that might be fertile for some generations too.

Probably over a more extended period, for example the drift of diverging breeds, within species, that are "close enough" to bear viable future generations of offspring
might be seen to be actually diverging. Or not.

I have to admit, I have no idea what you're saying. If you're saying that sometimes related species can breed and sometimes they can produce fertile, then I agree.

I'm not sure about that.

Maybe.

.

When bacteria can gather DNA from completely unrelated species, and when they do not reproduce sexually, it becomes difficult to rely on our limited definition of species.

that's not a plant, or bacteria. ahem...

See above re divergence , convergence etc. maybe

What? It doesn't matter how this came about, only that the phenomenon exists, and it challenges the traditional view of a species.

Well, for this case measure the drift in the breeding pairs over enough time, and eventually you might see a drift, one way or another. There might be a very long period of stasis even, if conditions permit.

I am beginning to see the problem is one of language. In evolutionary biology, drift refers to genetic drift, not a change in relatedness between two species. Also, divergence and convergence are related to evolution, in the latter case specifically the evolution of the same phenotype by unrelated species.

See above

Yup, did I make sense, ? am wrong?

My point was not to post concrete proof that species do not exist, only to point out that certain phenomena can challenge the traditional species characterization. I even admitted as much, by giving a possible explanation for the very phenomena I presented as examples.

 

[biomorph]

Why?

Hard to say....but no big deal..

I have to admit, I have no idea what you're saying. If you're saying that sometimes related species can breed and sometimes they can produce fertile, then I agree.

Yes, my point being that at the boundary of interspecies breeding fitness, is where I think most of the few exceptions occur.

I'm postulating some speculative reasons for these uncommon, perhaps what appear to be violations of a real definition of a species.

i'm probably not making that clear., perhaps it is irrelevant to this discussion.

When bacteria can gather DNA from completely unrelated species, and when they do not reproduce sexually, it becomes difficult to rely on our limited definition of species.

Yes. I agree.

What? It doesn't matter how this came about, only that the phenomenon exists, and it challenges the traditional view of a species.

Sorry, I've got the perspective that it adds to the "traditional" view, I guess...

I am beginning to see the problem is one of language. In evolutionary biology, drift refers to genetic drift, not a change in relatedness between two species.

yes, if you like, I can go with that,.

However genetic drift is a driver for the (divergence etc) in the two species you mention isn't it?

Also, divergence and convergence are related to evolution, in the latter case specifically the evolution of the same phenotype by unrelated species.

OK

My point was not to post concrete proof that species do not exist, only to point out that certain phenomena can challenge the traditional species characterization. I even admitted as much, by giving a possible explanation for the very phenomena I presented as examples.

You did, I merely tried to find where those challenges occurred, and if there were perhaps, in an evolved system of divergence, special conditions. I think that perhaps there are.

I think you have raised some interesting points, tho.

It is a very interesting subject..

 

[Taffer]

Yes, my point being that at the boundary of interspecies breeding fitness, is where I think most of the few exceptions occur.

Which is exactly my point. You cannot have clear categories without clear boundaries. The broad view is one of discrete species, but upon close examination there is a lot of grey in a world we would all prefer to be black-and-white.

I'm postulating some speculative reasons for these uncommon, perhaps what appear to be violations of a real definition of a species.

There is no "real" definition of species, because species is just a word, made up by humans. It is a category imposed on a area which is not discrete, but is a spectrum.

Think of the colours of the rainbow. There is a clear difference between blue and green, but it is impossible to find the exact border where blue stops being blue, and starts being green. This is like species in nature. The broad view allows for clear divisions, species, genera, etc, but it is at the boundaries where the natural system shows that it is a spectrum of relatedness.

However genetic drift is a driver for the (divergence etc) in the two species you mention isn't it?

No. Genetic Drift refers to the change in allele frequency in a population over time due to random chance and sampling bias. Genetic drift does drive evolution, but it is not sufficient by itself for evolution to occur in a sufficiently large population. Selection is still required; genetic drift may influence speciation in an isolated population with no migration, however.

You did, I merely tried to find where those challenges occurred, and if there were perhaps, in an evolved system of divergence, special conditions. I think that perhaps there are.

The issue is not if there are special conditions, but that it exists at all. If the traditional distinction of a species truly reflects relatedness in nature, than these situations would never happen.

It is a very interesting subject..

Agreed!

 

[blutoski]

It seems to me that if there is such a thing as a species, and the normally they cannot breed together, then there must be some fundamental (genetic?) reason for it.

Usually. But sometimes they don't interbreed because of geographic isolation.

The species may be able to produce viable offspring if they meet, say, in a zoo or on an ethnocline. (eg: tigers and lions are seperate species from India and Africa respectively, but may interbreed in the Middle East or in the Bronx zoo)


The definition of species is a human system. Like the definition of a planet. Pluto is what it is, and tigers are what they are. How they categorize is up to us.

 

[blutoski]

All in all, my point though, was that everything is genetically determined, and species are classified by traits that are genetically determined. Genes are involved whether a different species can breed or not.

Ultimately, but genetic differences don't always mean genetic incompatability.

Another example is birds that live in different parts of a tree (high vs low branches, or trunkward vs perimiter). They don't breed with those who live in a different part of the tree.

However, if you move them to an environment with no tree, they interbreed without complaint.

The genetic difference only manifests a speciation in certain environments. In other environments, they could be considered the same species. In this case, genetic difference is necessary but insufficient.

Alternatively, if the only reason for distinction is geographic separation, there is no genetic difference, so it's not even necessary for these limited cases.

 

[Mojo]

It seems to me that if there is such a thing as a species, and the normally they cannot breed together, then there must be some fundamental (genetic?) reason for it.

Basically just that they are not genetically similar enough to be able to interbreed. All this is a bit circular, because the basic definition (or at least, one basic definition) of a species is a group of organisms that can successfully interbreed.

But the term "species" is a bit nebulous. What we see today as "species" are a snapshot of a population. If we were to come back in a few million years we might well see populations descended from current species that wiould qualify as a new species, but it would never be possible to pinpoint exactly when one species became another.

ETA: check out "ring species".

 

[kuroyume0161]

Basically just that they are not genetically similar enough to be able to interbreed. All this is a bit circular, because the basic definition (or at least, one basic definition) of a species is a group of organisms that can successfully interbreed.

But the term "species" is a bit nebulous. What we see today as "species" are a snapshot of a population. If we were to come back in a few million years we might well see populations descended from current species that would qualify as a new species, but it would never be possible to pinpoint exactly when one species became another.

ETA: check out "ring species".

Exactly my point about 'first human'. Apply what you said about 'coming back in a few million years...it would never be possible to pinpoint exactly when one species became another' to what I said about hominid speciation towards humans.

There seem to be two types of species designation here:

1) These are the categories that we use to deem individual species at this point in time - current extant biological organisms.

2) These are the categories that we deem individual species in evolutionary terms - extinct or ancestral organisms only evident from fossils.

The first is a bit more 'black and white' (and even then, not really). The second is just opening a can of worms - especially when one is attempting to delineate species in discrete ways under conditions of evolution and speciation which are not discrete. In other words, taking a snapshot makes it easy to employ our categorization system. But when trying to use it over a very long time period of changing organisms, it pretty much fails - not totally, but there are great rents in its applicability. Even Paleontologists still argue over which cladistic representations best represent classification and relationship: monophyletic, paraphyletic, or polyphyletic - and how they should be employed.