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Author Topic:   All species are transitional
Mammuthus
Member (Idle past 4549 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 226 of 246 (256206)
11-02-2005 10:50 AM
Reply to: Message 225 by NosyNed
11-02-2005 10:42 AM


Re: Animal Examples?
Which mice? I am not aware of any mammals that can form hybrids with novel ploidy that go on to reproduce asexually and then at some point, sexually. Mice on an island could speciate sympatrically but it would have nothing to do with sudden changes in ploidy like in plants or frogs. So mammals would never face that situation.

Are you thinking of ring species?


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NosyNed
Member
Posts: 8837
From: Canada
Joined: 04-04-2003


Message 227 of 246 (256213)
11-02-2005 10:55 AM
Reply to: Message 226 by Mammuthus
11-02-2005 10:50 AM


Sylas again
Gee, this reminds me we haven't seen him for ages :(.

Message 35

And from a link in
Message 42

quote:
A recent (13 January 2000) report in Nature describes a study of house mouse populations on the island of Madeira off the Northwest coast of Africa. These workers (Janice Britton-Davidian et al) examined the karyotypes of 143 house mice (Mus musculus domesticus) from various locations along the coast of this mountainous island. Their findings:

* There are 6 distinct populations (shown by different colors)
* Each of these has a distinct karyotype, with a diploid number less than the "normal" (2N=40).
* The reduction in chromosome number has occurred through Robertsonian fusions. Mouse chromosomes tend to be acrocentric; that is, the centromere connects one long and one very short arm. Acrocentric chromosomes are at risk of translocations that fuse the long arms of two different chromosomes with the loss of the short arms.
* The different populations are allopatric; isolated in different valleys leading down to the sea.
* The distinct and uniform karyotype found in each population probably arose from genetic drift rather than natural selection.
* The 6 different populations are technically described as races because there is no opportunity for them to attempt interbreeding.
* However, they surely meet the definition of true species. While hybrids would form easily (no prezygotic isolating mechanisms), these would probably be infertile as proper synapsis and segregation of such different chromosomes would be difficult when the hybrids attempted to form gametes by meiosis.



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Mammuthus
Member (Idle past 4549 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 228 of 246 (256224)
11-02-2005 11:09 AM
Reply to: Message 227 by NosyNed
11-02-2005 10:55 AM


Re: Sylas again
Hi ned,
Thanks for the clarification. But I see a difference in this case compared to the plant example I gave. Let me see if I can clarify.

quote:
The different populations are allopatric; isolated in different valleys leading down to the sea.
* The distinct and uniform karyotype found in each population probably arose from genetic drift rather than natural selection.

The mouse populations with different karyotypes are separated. It is quite possible their karyotypes changed after they speciated i.e. not the direct cause. In the plant example, we are talking about the generation of an individual or group of individuals (from the same meotic event) that have a new ploidy and cannot mate with the parent stock within a single population. They then mate either with each other (if more than one are present) or reproduce asexually until they can mate sexually. All within one population and within a single generation.

Second, the mouse example is also reduction of chromosome numbers as opposed to complete changes in ploidy as can be seen in plants with complete duplication of the genome i.e. from diploid to triploid, tetraploid etc. Sometimes, even karyotypically different animals can still produce fertile offspring. They would have to test this assumption "these would probably be infertile as proper synapsis and segregation of such different chromosomes would be difficult when the hybrids attempted to form gametes by meiosis".


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NosyNed
Member
Posts: 8837
From: Canada
Joined: 04-04-2003


Message 229 of 246 (256267)
11-02-2005 1:38 PM
Reply to: Message 228 by Mammuthus
11-02-2005 11:09 AM


Not the best example
I agree this isn't the example I was after but it is at least related.

Wilson mentions that animals also speciate through polyploidy and I was after real examples. He doesn't supply any details.

This message has been edited by NosyNed, 11-02-2005 01:38 PM


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Omnivorous
Member (Idle past 1041 days)
Posts: 3808
From: Adirondackia
Joined: 07-21-2005


Message 230 of 246 (256276)
11-02-2005 2:31 PM
Reply to: Message 229 by NosyNed
11-02-2005 1:38 PM


Re: Not the best example
I ran across a proffered example last night--I believe it was bivalves. I'll see if I can find it again.
This message is a reply to:
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robinrohan
Inactive Member


Message 231 of 246 (256398)
11-02-2005 11:20 PM


polyploidy
Anybody got a nice plain definition of "polyploidy"?

I looked it up in a dictionary; unfortunately, I couldn't understand the definition.

ABE:

Apparently , in these circles, "polyploidy" is an everyday word, like "please" or "thank you."

"How was your day, dear?"

"Well, it was rather polyploidy, to be frank."

"I'm sorry to hear that."

"No problem. I'll get over it."

That sort of thing.

This message has been edited by robinrohan, 11-02-2005 10:35 PM


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Asgara
Member (Idle past 376 days)
Posts: 1783
From: Wisconsin, USA
Joined: 05-10-2003


Message 232 of 246 (256399)
11-02-2005 11:32 PM
Reply to: Message 231 by robinrohan
11-02-2005 11:20 PM


Re: polyploidy
haploid - one copy of chromosomes
diploid - two copies (think us)
polyploid - more than two copies

http://en.wikipedia.org/wiki/Polyploidy


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robinrohan
Inactive Member


Message 233 of 246 (256402)
11-02-2005 11:50 PM
Reply to: Message 232 by Asgara
11-02-2005 11:32 PM


Re: polyploidy
Like having triplets?
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nwr
Member
Posts: 5585
From: Geneva, Illinois
Joined: 08-08-2005


Message 234 of 246 (256404)
11-03-2005 12:06 AM
Reply to: Message 233 by robinrohan
11-02-2005 11:50 PM


Re: polyploidy
Like having triplets?

Not quite the same.

Your sperm are haploid, because they have only one copy of each chromosome.

Your regular cells are diploid, because they have two copies of each chromosome (one from your father and one from your mother).

If a cell had three copies of each chromosome, presumably that would be called triploid.

Mammals are normally all diploid (excluding reproductive cells). But some plants have separate haploid and diploid phases. I think some insects do that too, but my memory is hazy. Someone will probably correct me on the details.

The discussion was with circumstances where there can be more than two copies of each chromosome in cells.

By the way, I really liked the way you asked your question in Message 231. It was pretty funny.


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robinrohan
Inactive Member


Message 235 of 246 (256484)
11-03-2005 10:58 AM
Reply to: Message 234 by nwr
11-03-2005 12:06 AM


Re: polyploidy
The discussion was with circumstances where there can be more than two copies of each chromosome in cells

Thanks. I'll study it out.


"Turning out pigs for creationists makes me blue and blurry."--Brad McFall
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RAZD
Member
Posts: 19754
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 6.2


Message 236 of 246 (256567)
11-03-2005 6:33 PM
Reply to: Message 225 by NosyNed
11-02-2005 10:42 AM


Re: Animal Examples?
See several examples of speciation at

Speciation & hybridization (click)

V. "Instant speciation" via polyploidy etc.

Plants can speciate almost instantaneously by changing the ploidy (number of sets) of their chromosomes, accompanied by their ability to persist/disperse as "founders" via asexual reproduction. They spread vegetatively and don't necessarily have to deal with the problem of sexual reproduction for some time. In animals, less dramatically, a more rapid founder effect process (Mayr, 1942; Templeton, 1996) may sometimes be an alternative to the gradual process usually considered to dominate speciation in animals. On population genetics grounds, Slatkin (1996) argued for the potential importance of what is sometimes called "founder flush" speciation in the face of several dismissive reviews of the process. For animals, the major interest in "instant" speciation involves rapid divergence due to a few changes in major regulatory genes affecting development. Recently, however, a tetraploid rodent was discovered in South America (Gallardo et al., 1999). I suspect that few biologists would have considered this a possibility until it was reported.

I think you were thinking of this tetraploid rodent - it's been discussed here before IIRC

http://www.intl-pag.org/pag/8/abstracts/pag8374.html
http://www.cricyt.edu.ar/INSTITUTOS/iadiza/ojeda/grecia%202000.htm

enjoy

{fix link - mixed ub with html}

This message has been edited by RAZD, 11*03*2005 06:49 PM


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

RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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Brad McFall
Member (Idle past 3107 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 237 of 246 (265422)
12-04-2005 10:25 AM
Reply to: Message 94 by Brad McFall
10-18-2005 7:13 AM


Re: Brad's Justification of the term Missing Link

Click to enlarge


Click to enlarge


Click to enlarge


Click to enlarge

www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=5&t=102&m=37#37 -->www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=5&t=102&m=37#37">http://www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=5&t=102&m=37#37
www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=7&t=46&m=2#2 -->www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=7&t=46&m=2#2">http://www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=7&t=46&m=2#2
etc searching "genes for horns"

This message has been edited by Brad McFall, 12-04-2005 10:25 AM


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SuperNintendo Chalmers
Member (Idle past 3908 days)
Posts: 772
From: Bartlett, IL, USA
Joined: 12-27-2005


Message 238 of 246 (274191)
12-30-2005 12:42 PM
Reply to: Message 1 by Parasomnium
10-04-2005 9:48 AM


What we need to realise is that we are trying to impose an arbitrary system of discrete divisions on a continuous set of elements. With species it is no different. If you translate the example of the numbers to species, you can imagine a continuous sequence of intermediates from any ancestor you'd care to start with, right up to yourself. You are the same species as your parents, and they the same as theirs. At the other end of the line, the ancestor you started with is the same species as its offspring, and they are the same species as their offspring.

But if you went back far enough in the lineage so that the ancestor you start with is a tree-dwelling primate, then obviously this ancestor is not the same species as you. There must be transitionals. But wherever you look in the lineage, locally you cannot pinpoint any real transitions. That's because the transition takes place all over the lineage. Each and every one of your ancestors is a transitional. And if you have children or plan on having them, you are a transitional yourself.

Great, Great post. I think the problem is what we are really talking about are population groups. All members of a population group (at least for sexually reproducing animals) are always of the same species. There is no such thing as species A giving birth to species B. There are only population groups which change over time and may also split up. So a population group is always the same species... and in fact, like Para said, Species is a just an arbitrary classification we use when looking back over time at various population groups.

I liked to use the analogy of the aging process (not perfect, but I think it illustrates a good point). There is never a point in your life when you wake up and say, "wow yesterday I was a child and now I am an adolescent". However, when you look back at your life you do say, "X happened when I was a child" and "Y happened when I was an adolescent". However, in reality every single instant of your life is a different step in the aging process.

I've heard many people bring up the example of dogs and how they have never speciated even though we've been breeding them for thousands of years. Do we actually know this (I really don't know the answer here)? How do we know that present day dogs could breed with dogs that lived 15 or 20 thousand years ago? They may very well be a different species using that definition


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Faith
Inactive Member


Message 239 of 246 (274193)
12-30-2005 12:56 PM
Reply to: Message 238 by SuperNintendo Chalmers
12-30-2005 12:42 PM


There are only population groups which change over time and may also split up. So a population group is always the same species... and in fact, like Para said, Species is a just an arbitrary classification we use when looking back over time at various population groups.

The problem with this whole idea is that whenever you split a population group, each new group, while developing new forms, loses some genetic potentials, so the idea that there can be continuous open-ended change is an illusion. Over time the processes that split populations {ABE: and produce new phenotypes} also reduce genetic diversity, which ultimately reaches a point where no further change is possible. It sounds good but it doesn't work. I believe this natural limit to change is the definition of a Kind. Yes, supposedly mutation counteracts this effect, but I think that's mostly a matter of blind faith too.

This message has been edited by Faith, 12-30-2005 01:07 PM


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Coragyps
Member
Posts: 5377
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 240 of 246 (274196)
12-30-2005 1:10 PM
Reply to: Message 239 by Faith
12-30-2005 12:56 PM


Over time the processes that split populations also reduce genetic diversity, which ultimately reaches a point where no further change is possible.

This is blind assertion on your part, Faith. You have no data to back it up whatsoever - you can't identify where that "point" would be. Biologists, on the other hand, have whole library shelves full of examples of these splits preserved in the genes and morphology of all sorts of organisms.


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