Dark Jedi

Juat a cross-ref of related topics:

Speciation discussion on fertile Mules and Ligers:
<a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=58&t=001649" target="_blank">Here</a>

Doubting Didymus

That's a bit different. Speciation due to hybridisation is even greyer than speciation due to reproductive isolation, which is what we are talking about here.

Peez

pz,

There does not seem to be any point in pursuing this with you, so I will desist.

Peez

Peez

I disagree. Mere reproductive isolation is not evolution, let alone speciation or macro-evolution. If the change in beak size is entirely environmental, then the distinction between the populations would disappear as soon as the difference in environment dissapeared. That is, there has been no heritable change in either population. Thus, this is not evolution.

Take this a step further. There is a limit to how much change in beak size can occur entirely due to the environments that these populations experience. If we expose long-beak e-finches (environmental difference) to short-beak conditions, we get short-beak e-finches. If we expose short-beak e-finches to short-beak conditions, we get the same thing. Where is the evolution?

This is simply an example of phenotypic plasticity (environmental differences resulting in different traits from the same genes). In this particular example, the phenotypic plasticity might result in reproductive isolation, which may in turn facilitate independant evolution of the two groups. However, the groups are no more isolated than two population physically separated from each other (e.g. by a river). We do not consider macro-evolution to have occurred when a population is isolated by such a barrier.

Peez

Peez

My point was that, according to the definition given, a simple increase in population would be "evolution". I do not see this as meaningful, even looking at ‘group selection' models (it would be the equivalent to calling ontological weight gain "evolution" for evolution within a population). The distribution of a population would relate to group selection in a similar way that the home range of an individual would relate to evolution in a population. There is no doubt that these things would influence evolution, but defining evolution to include them would make "evolution" rather meaninglessness. I could demonstrate "evolution" just by showing that an individual's home range changed, or that a population size had decreased over the winter. We disagree there, given a rather loose definition of "gene". Fair enough, though I would not express it exactly that way myself. Still, the point is well-taken: evolution by some other mechanism (through non-nucleotide inheritance) is at least conceivable, but I have yet to see any indication that non-nucleotide evolution does take place. Of course not, no more than a cell with no ribosomes can express many phenotypes. Not at all. Let me put it this way: if a master gene-jocky was to change the wolbachia genotype without changing its phenotype (in one host animal), would there be any change to the wolbachia phenotype in the host's great-grandchildren? If this gene-jocky instead changed the wolbachia phenotype without changing its genotype (in one host animal), would there be any change to the wolbachia in the host's great-grandchildren? Because these gametes contain DNA. Barring maternal effects, what human traits are inherited outside of DNA? I am sorry, I did not mean to imply that you needed to make that kind of argument. I brought up the treatment of wolbachia relative to evolution in those articles only because I could find nothing there that suggested that wolbachia infection should be evolution. The fact that the author agreed was just meant to underscore that point, not as an appeal to authority. I don't see a problem with using a definition that is precise and includes non-nucleotide inheritance, I just don't see a burning need for it until it becomes an issue. Certainly I do not regard the allele-frrequency definition as merely appropriate to high school texts.

Peez

Peez

Excellent points. That group selection can occur, and that this selection might lead to evolution, are accepted by many evolutionary biologists. How often it actually does occur is more of an issue. Theoretical studies suggest that fairly restrictive conditions are necessary for group-selection to outweigh selection on individuals withing groups. Even if it does occur, evolution (as I define it) by group selection would result in a change in allele frequency (but in this case the allele frequency in the species would be changing, rather than in one population).

Peez

[ November 07, 2002: Message edited by: Peez ]</p>

KC

I think you need to revisit Mayr's Biological species concept:


BIOLOGICAL SPECIES CONCEPT

Dominant concept in evolutionary literature today, at least among zoologists.

Mayr (1940) defined species as "groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups." Dobzhansky (1950) defined species as "the largest and most inclusive ... reproductive community of sexual and cross-fertilizing individuals which share a common gene pool."

The most defining aspects of this concept are interbreeding among conspecific populations and reproductive isolation from non conspecifc populations. Morphological distinctness is not a criterion.

One major emphasis is that coexisting populations of separate "species" do not interbreed (reproductive gap between "good" species; non-dimensional concept). Thus, they are reproductively isolated from each other by reproductive isolating mechanisms (RIMs). Isolating mechanisms are a variety of means by which intraspecific reproduction is insured. They act by inhibiting different species from interbreeding successfully. Hence, RIMs define the limits of the gene pool of a species.

The second major emphasis is that species are viewed as representing the total collection of gene pools in all the demes of individual species (unlimited gene exchange among populations within a species; multidimensional concept).

Six tenets of biological species concept:

1. Species consist of populations, not unconnected individuals.

2. Species are defined by the reproductive isolation of populations, not by the fertility of individuals.

3. A species is a reproductive community.
Members of one animal species respond to one another as potential mates, and seek one another for the purpose of reproduction.

4. A species is an ecological unit.

Regardless of the type of individuals composing a species, it interacts as a unit with other species, with which it shares the environment.

5. A species is a genetic unit.

A species consists of a large, intercommunicating gene pool, and individuals are temporary holding vessels of a portion of the gene pool. A species is a community of gene pools in demes of each individual species. This aspect allows integration of population genetics into questions regarding speciation.

6. Species are determined on the basis of distinctiveness rather degree of difference.

From:

<a href="http://www.tulane.edu/~eeob/Courses/Heins/Evolution/lecture6.html" target="_blank">Species Concepts</a>

You are assuming the environment changes before other genetic changes can accumulate between the populations to PHYSICALLY prevent successful hybridization. That is possible and in fact, in some finch populations in the Galapagos, hybridization is occurring at enough of a rate to slowly bring the two once-distinct populations towards panmixia. But so what? Prior to extensive genetic analysis, species were classified primarily by morphological means. The Galapagos finches were certainly classified that way originally by John Gould. What matters is, at one point in time these populations came to differ enough that genetic exchange between them became almost nil, which qualifies as speciation, and as macroevolution. Whether they became differentiated significantly from a genetic standpoint is irrelevant. Whether they remain that way permanently is irrelevant as well.

The relevant questions here remain, regardless of your example, whether or not the conditions result in reproductively isolated communities, and that the isolation is being driven by the morphological differences.

True, but we would consider macroevolution to have occurred if we tried to get individuals to mate with individuals from acrosss the river and they did not when brought together, which is what we see in the finches.

Cheers,

KC

[ November 07, 2002: Message edited by: KCdgw ]</p>

Peez

I don't think so . I am quite familar with it, note that Mayr is careful to specify "actually or potentially interbreeding natural populations" (my emphasis). Just because two populations are geographically separated from each other does not make them separate species, because they could still potentially interbreed if they came into contact. When a group of white-tail deer are isolated on an island, we do not consider them a new species. It is only after these populations can no longer even potentially interbreed that we consider them separate biological species. There is an excellent discussion in Biology, Sixth Edition (Campbell and Reece, 2002, Benjamin-Cummings) pp. 465-466, but any good introductory biology text book should cover this. I do not follow you here. Typically, we expect that geographic isolation allows independant evolution that may lead to speciation. That does not make geographic isolation in itself speciation or even evolution. Rather, it is (often) a precondition for speciation. This does not surprise me, nor does it contradict anything that I have stated. Of course, and they often still are. No, I disagree. The population of white-tailed deer on the island are completely isolated reproductively from other white-tailed deer, but they are still the same species. You seem to be arguing that every time a group of organisms is prevented from reaching another group from the same species, we should then consider them separate species. I don't see this as a useful definition. I disagree. Simply puting some cats in a locked room does not make them a new species.[/quote]Whether they remain that way permanently is irrelevant as well.[/quote]I do not disagree here, though it seems unlikely that completely different species could evolve to become so similar as to be the same species. You seem to be ignoring the issue that I raised. Do you think that it is irrelevant that "evolution" and "speciation" as you describe it is always reversable, never results in changes greater than phenotypic plasticity allows, and has no reason to be adaptive? If we put the two populations in the same environment with plenty of time, and they do not interbreed (successfully), then speciation would be considered to have occurred. If you consider that to be macro-evolution, then macro-evolution would have occurred. However, if you put them together and come back after a few generations and find that they are interbreeding (successfully), then speciation (and macro-evolution) has not occurred.


Peez

RufusAtticus

Doubting Didymus,

That's because nothing I am saying is controvercial, I'm just extending evolutionary definations as new evidence and thinking demands.

I'm not correcting the voice of your phrase, but rather the tense.

Because speciation is usually considered to have occured when two mendelian populations have become reproductively isolated due to physical differences.

Well, wolbachia infection is perminant. The only known cases of it being lost happened either with treatment with antibiotics or the rare chance that an ova is formed without any wolbachia.

Of course, population ranges are passed on to future generations. Although, I'm not quite sure how well speciation would preserve population ranges. Obviously there are geographical constraints, but they varry alot with respect to the taxon.

Peez,

Isn't that true with your defination too? A change in population size will change the allele frequencies in the gene pool.

No. There would be no effect on the hosts' phenotype.

Yes. There would effects on the hosts' phenotype. See; the host's phenotype evolves only when the wolbachia's phenotype evolves. Otherwise there is no change from the hosts' point of view.

Language, culture, etc.

~~RvFvS~~

[ November 10, 2002: Message edited by: RufusAtticus ]</p>

Doubting Didymus

So you are saying that the reproductive isolation must be due to traits of the isolated populations? That sounds sensible, but are you sure there are no exceptions?

Ooooo... Tricky. Like I said, species is an extremely slippery term. Neither of us should be expressing much confidence when we say 'X is or is not a species'. I think most of us can agree that a heritable wolbachia infection should be considered part of evolution (except Peez, who is more Dawkinsian than Dawkins ). The only question left, given our set of definitions, is where we are going to set the scale of the evolutionary 'unit'. I would be setting it at the genes of the parasite. Where would you set your unit? at the level of the parasite itself?

It's a tricky question, isn't it? And there is sod all consensus in the scientific community for us to go on, as well. I tentatively agree that the next generation 'inherits' the population distribution, but I am in the same boat as you when considering species inheritance. That is, both uncertain and skeptical.


Oho! Now you're talking!