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Author Topic:   What is your favorite example of speciation?
Parsimonious_Razor
Inactive Member


Message 1 of 15 (94753)
03-25-2004 4:14 PM


When the subject comes up, as it seems to often what are your favorite examples of speciation being observed either with very strong fossil evidence or even observed in modern times?

Replies to this message:
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Denesha
Inactive Member


Message 2 of 15 (94756)
03-25-2004 4:19 PM
Reply to: Message 1 by Parsimonious_Razor
03-25-2004 4:14 PM


Hi Parsi,

I have numerous examples. Are fossil fishes good enough for our debate?

I currently study such events.

Denesha


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Parsimonious_Razor
Inactive Member


Message 3 of 15 (94757)
03-25-2004 4:28 PM
Reply to: Message 2 by Denesha
03-25-2004 4:19 PM


Ideally anything that I can get access to check out is great.

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RAZD
Member (Idle past 644 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 4 of 15 (94759)
03-25-2004 4:33 PM
Reply to: Message 3 by Parsimonious_Razor
03-25-2004 4:28 PM


foramins
try

http://www.cs.colorado.edu/~lindsay/creation/foram_article3.html


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist


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Quetzal
Member (Idle past 5111 days)
Posts: 3228
Joined: 01-09-2002


Message 5 of 15 (94910)
03-26-2004 8:33 AM
Reply to: Message 1 by Parsimonious_Razor
03-25-2004 4:14 PM


The family Tenrecidae of Madagascar are by far my favorite examples of speciation, well represented by fossil, subfossil and modern forms linked to an ancestral species in Africa AND a distantly related living species (Protomogale). Otherwise, species flocks of cichlids in East Africa or the ciscoes (Coregonus spp) of the US Great Lakes can do in a pinch.

If you want more glaring examples of "modern" transitionals - populations at the cusp of incipient speciation - I'd go with ring species like the Ensatina eschscholtzii group of salamanders in California, the green warblers (Phylloscopus trochiloides) of China, Tibet and Siberia, and of course the herring gulls (Larus spp) which has a nice "ancestor" species to go along with it (Larus smithsonianus), which species has the added advantage of being still extant. For a good review of the ring species discussion, see Irwin DE, Irwin JH, Price TD, 2001, "Ring species as bridges between microevolution and speciation", Genetica 112-113:223-243.

quote:
A demonstration of how small changes can lead to species-level differences is provided by ring species, in which two reproductively isolated forms are connected by a chain of intermediate populations. We review proposed cases of ring species and the insights they provide into speciation. Ring species have been viewed both as illustrations of the history of divergence of two species from their common ancestor and as demonstrations that speciation can occur in spite of gene flow between the diverging forms. Theoretical models predict that speciation with gene flow can occur when there is divergent ecological selection, and geographical differentiation increases the likelihood of speciation. Thus ring species are ideal systems for research into the role of both ecological and geographical differentiation in speciation, but few examples have been studied in detail. The Greenish warbler is a ring species in which two northward expansions around the Tibetan plateau have been accompanied by parallel evolution in morphology, ecology, and song length and complexity. However, songs have diverged in structure, resulting in a lack of recognition where the reproductively isolated forms come into contact in Siberia. Our analysis suggests that these differences could have arisen even with gene flow, and that parallel rather than divergent ecological changes have led to divergence in sexually selected traits and subsequent speciation.

That'll probably be enough to go on. If you'd like more discussion of why I think these examples are compelling, I'd be happy to expand on this answer (ad nauseum )


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Dr Jack
Member (Idle past 1344 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 6 of 15 (94911)
03-26-2004 8:48 AM
Reply to: Message 1 by Parsimonious_Razor
03-25-2004 4:14 PM


HeLa

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Denesha
Inactive Member


Message 7 of 15 (95541)
03-29-2004 2:25 AM
Reply to: Message 3 by Parsimonious_Razor
03-25-2004 4:28 PM


Ah yes, got it now! It's cladogenesis examples your seeking for.
If so, they are very rare to observe on fishes. I have one, and this is currently out for publication.
Most of my concerned fish speciations are "classic" gradual anagenesis.

Denesha


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MannyB
Inactive Member


Message 8 of 15 (95644)
03-29-2004 10:54 AM


I still think that Darwins Finches make an excellent demonstration of evolution. Different species have different beak shapes in order specialize on different food sources.

What is nice about this is that many of the species can hybridize. These hybrids are less well adapted than their specialized relatives and when climatic conditions are bad the hybrids are observed to die off faster.

So not only can this show that several species are adapted to suit their particular ecological niche you can also show that hybrids are less well adapted. Because hybrids are less adapted you can also tentatively conclude that in the past less adapted ancesters evolved into better adapted species.

Hopefully I am making sense, though I'm not a trained biologist.

Also there are plenty of examples of plants adapting to high Lead concentrations next to roads and highways. In many cases the plants actually require high lead concentrations to thrive. This has started to reverse as many/most countries have banned lead additives in gasoline and the lead concentrations near roads has dropped.


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Denesha
Inactive Member


Message 9 of 15 (95867)
03-30-2004 4:43 AM
Reply to: Message 8 by MannyB
03-29-2004 10:54 AM


I think your "Lead plants" are evidence of adaptation but not yet speciation. Nothing needs to change in the genetic material.
It's similar with people living in high altitude currently, and are adapted but genetic is not concerned. I we are able to observe this for a long time AND the gene flow will be firmly cancelled between high mountain and "downstair people", you might see the first signs of a speciation uprising in a few hundred thousand years...

Speciation is long for human but short for the geologic time-scale.

Denesha


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MannyB
Inactive Member


Message 10 of 15 (95874)
03-30-2004 7:05 AM
Reply to: Message 9 by Denesha
03-30-2004 4:43 AM


Thanks for the correction. Are the Darwins Finches considered as speciation? I have read that hybridization occurs (and that hybridization in closely related bird species is common).

One definition that I have seen of what a species is of a population of living organisms that can only interbreed with itself. Clearly this definition is insufficient to account for the many organisms that can hybridize.


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Denesha
Inactive Member


Message 11 of 15 (95879)
03-30-2004 7:27 AM
Reply to: Message 10 by MannyB
03-30-2004 7:05 AM


Hybrids
Hybrids doesn't work very well. There is a discrepancy between both genetic material of the two species.
Classic natural hybrids exist. The Blasius newt is famous here.
In fact, it's just a hybrid, not a species.
If you prefer, a breeding misfit.

Have a look here:
http://www.darkwave.org.uk/~caleb/trispe.html

Denesha


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Quetzal
Member (Idle past 5111 days)
Posts: 3228
Joined: 01-09-2002


Message 12 of 15 (95904)
03-30-2004 8:57 AM
Reply to: Message 10 by MannyB
03-30-2004 7:05 AM


Hey Manny,

One definition that I have seen of what a species is of a population of living organisms that can only interbreed with itself. Clearly this definition is insufficient to account for the many organisms that can hybridize.

Your definition is correct (although most biologists add the caveat "in the wild"). Looking at the details of the biological species concept (BSC), however, shows that hybrids are, in fact, taken into consideration: the interbreeding criteria is a continuum, not a line drawn in the sand. Roughly, if gene flow between populations is reduced (to around <25% IIRC, although that is argued still), then the populations are considered non-interbreeding. A half dozen of Darwin's finch species produce known hybrids - but they're not considered "freely interbreeding", and most of the hybrids occur between three or four very closely related species (the Geospiza spp seem to be pretty promiscuous, for example). This isn't surprising with birds - isolation is pretty tough when you can fly from point A to point B without worrying about things like water barriers. In other species, the existence of a hybrid zone between populations is usually considered to be evidence of incipient speciation. Bottom line: it's a question of gene flow between populations, not so much whether or not the populations hybridize per se (obviously assuming viable hybrids).


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RAZD
Member (Idle past 644 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 13 of 15 (95939)
03-30-2004 11:08 AM
Reply to: Message 11 by Denesha
03-30-2004 7:27 AM


Re: Hybrids
Another "breeding misfit" I believe is the hybred of mule deer with white tail deer ... if I recall correctly, the mule usually avoids predators by jumping with all four feet (like antelope) while the whitetail usually runs. The hybred attempts both with mixed results.


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist


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NosyNed
Member
Posts: 8968
From: Canada
Joined: 04-04-2003


Message 14 of 15 (154911)
11-01-2004 2:32 PM
Reply to: Message 13 by RAZD
03-30-2004 11:08 AM


Bump for more specific examples.
It appears this thread died off without really being held to topic as well as it might.

Rusty has asked for examples.

Here is a long discussion of the issue at Talk Origins

http://www.talkorigins.org/faqs/faq-speciation.html

However, that may be a bit too much at once. I'll pull and example later if asked. I'd rather the real biologists discussed this.


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Steen
Inactive Member


Message 15 of 15 (157553)
11-09-2004 3:40 AM


My favorite has always been the ring-species.

  
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