Jump to content

Phenotypic Plasticity and Speciation


Recommended Posts

 

Pick & choose from among a menu of definitions according to my purposes? That's weird science.

 

This link: http://en.wikipedia.org/wiki/Species#Definitions_of_species really is an eye opener. Is there any term outside of the biological sciences that is so problematic, any term whose definition is so wildly elastic?

 

Many. Say plasticity. What you mean in context of neurobiology is different from genetics, for example. The means and consequences of physiological plasticity are different from genomic. Or say "mechanics". What it means is quite different on the quantum vs the macro-level.

 

Language use is always context-driven. And as organisms have different modes of reproduction with different genetic consequences, it would not be very useful to put everything under the same umbrella. The need to establish context is especially important in complex systems, such as biological ones.

 

With regard to pick and choose, in a way this is why science has different branches. Different methodologies are needed to answer different questions. In terms of divergence of species you can (and sometimes have to) use morphological markers as genetic material may not be available. But obviously it would be silly to even try that for unicellular organisms.

Incidentally, this is why there is a need for specialization. It turns out nature is somewhat complicated.

Link to comment
Share on other sites

There is no such thing as a collective set of features that distinguishes any species of anything from any species of anything else.

 

Well said.

 

But if you try to sell a lumberman or firewood cutter the logging rights to an acre of mature, healthy, well grown woods dominated by this species: https://gobotany.newenglandwild.org/species/quercus/ilicifolia/ for the price of an acre of equivalently mature, healthy, well grown Quercus rubra, they will laugh at you. People with money on the line do not regard species distinctions as capricious and arbitrary whatsoever.

 

Leave it to financial interests distinguish species? why not? Who needs a panel of taxonomists?

Link to comment
Share on other sites

 

 

There is no such thing as a collective set of features that distinguishes any species of anything from any species of anything else.

Well said.

I was pointing out that you are for some reason being childish, stubbornly refusing to learn the basics of what you pretend to be asking about.

 

Leave it to financial interests distinguish species? why not? Who needs a panel of taxonomists?
The lumbermen hire the taxonomists in the first place - at least in those rare cases when the managers of serious logging operations had not learned some relevant taxonomy themselves.

The point was that anyone with an actual interest in the differences between different biological organisms of some overall kind, as opposed to a creationist troll who just wants to play stupid on somebody else's dime and site, has no problem recognizing the significance and value of the concept of species as taxonomists expert in the organisms of interest classify and label them. What you call capricious and arbitrary is for them investment grade information, the basic stuff they have to know.

Link to comment
Share on other sites

Admittedly, the critique of the definition of "species" took this thread far afield. The OP really had to do with reproductive isolation of sup-populations, each isolated group being subject to HIGHLY selective selection pressures at the hands of the dog breeders.

 

The point in the OP is that, given the morphological variation among dog breeds--much more extreme than would occur within a population in nature--why has there not yet been bred a non-dog? How does nature pull new species out of the much less pronounced variation that occurs in natural populations?

 

If the evolutionary account of speciation leans mainly on variation plus selection, then you can't contrive a situation more ripe for generating new species than that of dog breeding, yet no non-dog has emerged.

Link to comment
Share on other sites

 

 

The point in the OP is that, given the morphological variation among dog breeds--much more extreme than would occur within a population in nature--why has there not yet been bred a non-dog?
Not enough time, and no motive to do so.

 

Why would somebody who wanted to end up with something other than a dog set out to obtain the animal by breeding dogs? People breed dogs to get breeds of dogs. That is not mysterious.

Link to comment
Share on other sites

Not enough time, and no motive to do so.

 

Why would somebody who wanted to end up with something other than a dog set out to obtain the animal by breeding dogs? People breed dogs to get breeds of dogs. That is not mysterious.

 

 

The intent of the breeders, or lack of it in nature, has no bearing on the process of speciation. Reproductive isolation of subgroups, the various subgroups being subjected to differing selection pressures, should do it. How much morphological variation among reproductively isolated subgroups does speciation require? Even more than the breeders have produced? That would never happen in nature.

Link to comment
Share on other sites

 

And yet it seems to.

 

The "it" that occurs in nature is speciation. The theory behind the process is weak where it hinges on variation within a species, because nature can't match breeders' ability to produce morphological variants from a founding population. The dog breeds tell us that variation within a species can't have much to do with speciation. You can say that speciation via natural selection takes a long time, but what does all that time do besides reproductively isolate variant phenotypes?

Link to comment
Share on other sites

 

Natural selection can't be the primary mechanism of evolution.

I have argued similar points at time - my primary mechanism for evolution was the incorporation of endogenous retroviruses into the genome. (Look up "Virolution".) Then there is natural selection applied (secondary).

Link to comment
Share on other sites

I have argued similar points at time - my primary mechanism for evolution was the incorporation of endogenous retroviruses into the genome. (Look up "Virolution".) Then there is natural selection applied (secondary).

yeah, natural selection can at most tune the piano, It can't compose the melody.

 

 

Why? Because you can't (won't?) understand it, so it must be wrong?

Because natural selection will never have variants among which to choose that will be as dissimilar as those produced by breeders. If the breeders' variants don't speciate (is that a word?), there's no way nature can speciate based on selection among variants. Nature's primary source of new species must be something other than natural selection.

Link to comment
Share on other sites

yeah, natural selection can at most tune the piano, It can't compose the melody.

 

Because natural selection will never have variants among which to choose that will be as dissimilar as those produced by breeders. If the breeders' variants don't speciate (is that a word?), there's no way nature can speciate based on selection among variants. Nature's primary source of new species must be something other than natural selection.

You're saying this based on what?

 

It still sounds like you're treating speciation as something that happens, and suddenly you have a new species. That's not how it works.

Link to comment
Share on other sites

Careful with that one. The retroviruses transfer their own DNA along with DNA from other species. It is the latter which is of real value as it has undergone different selective pressures than our own.

A retrovirus that jumped the species barrier and then becomes endogenized. Have you seen examples of that?

Link to comment
Share on other sites

A retrovirus that jumped the species barrier and then becomes endogenized. Have you seen examples of that?

 

Many of the ones incorporated into our genome predate ourselves as a species, so I'm not sure how to answer that one. HIV probably has the best chance for something more recent occurring.

 

Bacteria are another means by which horizontal transfer can occur.

Link to comment
Share on other sites

 

Many of the ones incorporated into our genome predate ourselves as a species, so I'm not sure how to answer that one. HIV probably has the best chance for something more recent occurring.

 

Bacteria are another means by which horizontal transfer can occur.

Agreed all viruses from time to time jump species barriers, but you said it took with it stuff from the previous species. Let's see what?

 

The retroviruses transfer their own DNA along with DNA from other species

It was the DNA from other species that intrigued me. Has HIV still got DNA from the previous host associated with it? It wouldn't be so hard to tell where it originated (from what previous species), if it did carry this DNA marker longer term.

Link to comment
Share on other sites

 

What is your evidence for that?

And why would it matter?

Look again at the dog chart in the OP. Where in nature will you find that degree of variation within a species?

It matters if you argue that phenotypic variation correlates with variable reproductive success. If big variation among reproductively isolated subgroups of a species doesn't create new species (as is the case with dog breeds), then small variation won't do it.

Link to comment
Share on other sites

Look again at the dog chart in the OP. Where in nature will you find that degree of variation within a species?

 

There may be plant species with similar variations. But why is that relevant?

 

If big variation among reproductively isolated subgroups of a species doesn't create new species (as is the case with dog breeds), then small variation won't do it.

 

 

Small variations can and do create new species. For example dogs and wolves.

 

You have been given a many other examples of speciation. They all involve small changes.

Link to comment
Share on other sites

 

The "it" that occurs in nature is speciation. The theory behind the process is weak where it hinges on variation within a species, because nature can't match breeders' ability to produce morphological variants from a founding population. The dog breeds tell us that variation within a species can't have much to do with speciation. You can say that speciation via natural selection takes a long time, but what does all that time do besides reproductively isolate variant phenotypes?

 

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

 

Rhagoletis flies are native to North America. Their original, native host plants are hawthorn trees. Apple trees were introduced in North America more than 300 years ago, and they grow in the same habitats as hawthorns. Now, some flies use apple trees instead of hawthorns as their host plants. Experiments have shown that flies have a strong genetic preference for the tree (apple or hawthorn) on which they were found, and that mating takes place on the host plant. Because flies specialized for apples may never encounter/mate with flies specialized for hawthorns, this is a situation in which sympatric speciation can occur. Has it? Are the flies on apples genetically distinct from the flies on hawthorns? In turns out that flies that use apples are genetically different from the flies that use hawthorns.

 

 

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

Look again at the dog chart in the OP. Where in nature will you find that degree of variation within a species?

 

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.

Link to comment
Share on other sites

 

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.

 

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.

 

termitetypes.jpg

 

Eclectus parrots

Eclectus2WBPa_AcB260.jpg

 

Poison dart frogs (Dendrobates pumilio)

mark-moffett-strawberry-poison-dart-frog

 

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

Edited by Arete
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.