All species are transitional

Half the problem is that there is no {line\delineation} but a gradual change over time that accumulates until at some point a person says "hey, that's different!"The other half the problem is that you do get two or more different populations that diverge, and at some point they stop interacting genetically: it could be due to {non-compatible sex} but it is more likely to be {non-desire} - they don't see the others as potential mates due to differences in appearances or behavior. The Asian Warbler ring species is a good example here.
http://www.zoology.ubc.ca/~irwin/Greenish%20warblers.htmlThe {non-desire} can be the shadow-line (sometimes crossed) and two species can co-exist with near similar genes but not actively breed - becoming less able to interbreed as time passes until another shadow line is crossed: sterile offspring (the donkey, zebra and horse). The final shadow line is crossed when breeding no longer produces living offspring.Even with population isolation there is not hard fast line but a period of transition.

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RebelAAmerican.Zen[Deist
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To me part of the problem is the concept itself. How isolated is isolated? Are we talking islands?Did you check the ring species article? Each variety occupies a distinct geological area and only overlap on the boundaries (and that is where hybreds occur). Are they isolated or just dispersed? When you get around to the end of the ring they behave as if isolated.Sometimes yes, it can be a distinct line: non-migratory birds on Hawaiian Islands are isolated from the mainland species they are (distantly) related to and always have been.Other times not so distinct. There are no clear "rules" here, because ultimately it is a totally artificial construction of human making.

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RebelAAmerican.Zen[Deist
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khakies?I'm shocked. are the cuffs rolled?

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RebelAAmerican.Zen[Deist
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You already included it: That is isolation by sexual selection, failure to mix genes.Where the gray fuzzy boundary lies is when the intermediately speckled still mate with both the unspeckled and the heavily speckled. This can still lead to some genetic flow between the two isolated populations but it is generations apart (carried by the lightly speckled ones)

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RebelAAmerican.Zen[Deist
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Lets look at it this wayWe have 4 groups based on genetic possibilitiesNN - non-speckled (both genes)
SS - darkly speckled (both genes)
NS - lightly speckled (one gene each)
SN - lightly speckled (one gene each)for all intents and purposes NS = SN so we can reduce this to 3 groupsNow assume thatNN mates with NN or NS but not SS
NS mates with NN or NS or SS
SS mates with SS or NS but not NNWe have isolation between NN and SS but not anywhere else in the population, so there is still some interbreeding between all others and still some genetic interchange between NN and SS by way of NS interactions.Note that NS is as large as both NN and SS combined, once S has become established in the population (which started as NN) AND in the absence of selection pressure to diverge.Is this a new species on day one of SS? Not really, because still breeds with a major (NS) portion of the population that is still part of the "old" species. It rather the beginning of the divergence.Final divergence is achieved when NS disappears due to sexual selection of NN for only NN {AND?\OR?} of SS for only SS.

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RebelAAmerican.Zen[Deist
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But can you guarantee that sexual isolation remains a dividing factor?Perhaps if a survival stress were applied to the area where the asian green warbler ring species overlaps that there would exist individuals that would interbreed even after having been sexually isolated.You could have transition back and forth.

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RebelAAmerican.Zen[Deist
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The sexual selection barrier may apply when the living is easy, but when times get tough the selection of mates may be less picky when survival is at stake.This was observed on the Galapagos Islands when two finch species interbred during a drought that did not interbreed before or after the drought.Line ... no line ... line ...

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RebelAAmerican.Zen[Deist
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What you are seeing is (usually male) sexual behavior with object less and less similar to potential mates due to a lack of better opportunities. This is one of the driving forces for the trend to regress species diversity in times of survival stress.Or it is in love with an image of the master.

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RebelAAmerican.Zen[Deist
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General lack of opportunity coupled with plentiful normal opportunity would by my assumption. When species are in survival stress they tend to move outside native territories looking for ones more like what they knew before, and this puts them into a position of more interaction with other species. On the Galapagos we have descrete islands so it is easy to focus on when the barriers are crossed.

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RebelAAmerican.Zen[Deist
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or that there is one kind: life.

a grief history of time?

or the camel\llama hybrid ... or the "liger" ...I was talking about the galapagos finches during the drought where some interbreeding was observed between {otherwise classified as different species} individuals.

See several examples of speciation at Speciation & hybridization (click)I think you were thinking of this tetraploid rodent - it's been discussed here before IIRCPage not found - My Kratom And Weed Blog
http://www.cricyt.edu.ar/...S/iadiza/ojeda/grecia%202000.htmenjoy{fix link - mixed ub with html}This message has been edited by RAZD, 11*03*2005 06:49 PM

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RebelAAmerican.Zen[Deist
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