Register | Sign In


Understanding through Discussion


EvC Forum active members: 65 (9162 total)
5 online now:
Newest Member: popoi
Post Volume: Total: 915,821 Year: 3,078/9,624 Month: 923/1,588 Week: 106/223 Day: 4/13 Hour: 0/2


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   the phylogeographic challenge to creationism
mick
Member (Idle past 4987 days)
Posts: 913
Joined: 02-17-2005


Message 1 of 298 (262504)
11-22-2005 5:17 PM


The term "genetic structure" is used to describe the amount of genetic differentiation within a population of individuals. A population that is extremely homogenous, or that exhibits a continuum of polymorphic alleles distributed randomly across its members, has little genetic structure. On the other hand, a population that comprises a number of differentiated subunits (i.e. races, strains, varieties), or that exhibits a continuum of polymorphic alleles distributed nonrandomly across its members, is genetically structured.
When evolutionary biologists claim that macroevolution and microevolution are the same thing, they mean that the processes resulting in genetic structure within a species are the same processes that result in genetic structure between species.
"Spatial genetic structure" is genetic structure that results from differences in the geographic parameters experienced by spatially-separated populations. It is a consequence of straightforward microevolutionary processes. For example, in the middle ages it was rare for a person of Western-European descent to mate with a person of Asian descent. This is simply a consequence of the fact that it was difficult to travel from Europe to Asia in the middle ages. In the age of relatively easy international travel, the spatial genetic structure of human populations has been reduced, resulting in novel genetic and cultural combinations as seen in the Metis people of Canada (link to information on Metis people). The most simple example of spatial genetic structure comes from individuals asking themselves, "How far am I willing to travel in order to find a mate?"
As a microevolutionary process, the origin of spatial genetic structure is easily seen in natural populations. I've attached below a phylogeny built from the genetic sequences of members of the species Tamias amoenus (commonly known as the yellow-pine chipmunk). There is also a map showing where each genotype of this single species is located. I've added colour to the picture so that spatial structure is more obvious, and I've also attached a picture of Tamias amoenus so you know what animal I'm talking about.
reference
Tamias amoenus appears to exist as a spatially structured population. According to the map, the "purple", "yellow" and "red" clades are quite distinct from each other, while the "blue" and "green" appear to be overlapping, but not by very much. This is not surprising, because according to the phylogeny, the "blue" and "green" clades are closely related sister taxa. Given that this phylogeographic data represents variation within a species, and that creationists generally accept "microevolution", it should be possible for evos and creos to agree on the significance of the data. We can base our understanding of this data on the microevolutionary principles that Tamias amoenus arise from a single common ancestor and that the descendants of that ancestor have spread across the range, accumulating mutations along the way which have been preserved in each geographical region by heredity. For example, one reasonable hypothesis about the radiation of Tamias amoenus across north-west america is that the earliest members of the species crossed the rockies from the east or north (these are the yellow and purple clades) and established themselves in the Columbia, Clearwater and Highland mountains. They then split into two subpopulations, one moving northwest into the Cascades (the red clade) and one moving southwest towareds Sierra Nevada (the blue clade). Finally, members of the southern population travelled along the Snake River plain and populated southern-central regions from Oregon Highlands to the Beartooth Mountains. That is what the data suggests to me. And we're only talking about microevolution at this point.
Tamias amoenus is not at all unusual in exhibiting this kind of spatial genetic structure. Below are cladograms and distribution maps for black bears, Ursus americanus, and the shrew Sorex monticolus showing similar geographical clustering of genotypes.
reference
reference
The molecular evidence strongly suggests that population genetic structure in at least some mammalian species results from geographic isolation between subpopulations. Do we find similar patterns at levels of analysis above the species? Does the pattern hold at macroevolutionary scales?
Let's get back to the chipmunk, Tamias amoenus. Members of the genus Tamias easily hybridize with each other, and are probably not subject to reproductive isolation by incompatibilities in reproductive physiology. The closest related species to Tamias amoenus is Tamias ruficaudus. Here's a picture of ruficaudus on the left and amoenus on the right:
Although the pictures looks virtually identical, you might just be able to see that ruficaudus has a red/brown tail while amoenus has a black tail (it's not a photographic artifact). In general, amoenus has slightly darker pigmentation (compare the density of black stripes in the two pictures; but bear in mind that the apparent presence of a black stripe beneath the arm in amoenus but not in ruficaudus might just be unusual in this individual - I don't think that's a diagnostic feature). The two species are genetically distinct populations (i.e. true species) but they hybridize at low frequency in the wild.
Here's a molecular phylogeny based on sequences collected from amoenus and ruficaudus, along with a distribution map and drawings of the baculum (penis bone) of selected clades. The species involved are labelled (as crosses, squares, circles, etc) according to baculum morphology. The distribution of each clade is laelled as a greyscale colour. (This is a more complicated diagram, you will have to look at it for a little while).
larger version (may be easier to read)
reference
Geographic isolation appears to play a significant role in the maintenance of species-level genetic structure, just as it played a role in the maintenance of population-level genetic structure within Tamias amoenus. In the north, we have "clade 1", Tamias amoenus (shown in dark gray on the map, and as filled diamond and 'x' on the phylogeny). In the south, we mainly have "clade 3", Tamias ruficaudus (shown as filled or unfilled triangles on the phylogeny or as light gray on the map). In between these two groups, we have "clade 6" and "clade 5", recently-evolved clades that comprise subgroups of each species (Tamias ruficaudus simulans and Tamias amoenus canicaudus), and are likely the result of hybridization (between ruficaudus ruficaudus, ruficaudus simulans and amoenus canicaudus), and long-term migration from south to north. Areas of hybridization are labelled as "introgression zones". Again, this data is entirely consistent with the idea that Tamias amoenus and Tamias ruficaudus share a common ancestor, and that the descendants of that ancestor have spread across the range, accumulating mutations along the way which have been preserved in each geographical region by heredity. The fact that hybridization occurs in the regions of overlap shows that geographical distance is a major factor in structuring the populations of these species rather than intrinsic isolation by reproductive phsyiological incompatibility. However it seems at least plausible that there is some degree of local adaptation and that perhaps assortative mating helps keep the hybrid zones relatively limited in size.
Does the phylogeographic pattern persist within a genus? Let's stick with Tamias.
Here's a graphic showing the distribution of five "species groups" (which consist of closely related species which may be a single species but simply differentiated by spatial genetic structure). Again, we find that genetic distance and spatial distance are remarkably consistent. I have added pictures of each species group; from left to right: townsendii, merriami, minimus, amoenus.
larger image - may be easier to read
reference
So the basic microevolutionary process of spatial genetic structure originating from geographic distance appears to account quite well for distinct genetic groupings within species (amoenus), between species (amoenus and ruficaudus) and within a genus (amoenus, minimus, townsendii, merriami).
If you accept microevolution but reject macroevolution, how do you account for the spatial genetic structure of the Tamias genus without using microevolutionary processes? What non-microevolutionary mechanism prevents these easily-hybridizable species from collapsing into a single unstructured unit?
Mick
This message has been edited by mick, 11-22-2005 04:48 PM

Replies to this message:
 Message 2 by jar, posted 11-22-2005 5:18 PM mick has not replied
 Message 3 by mark24, posted 11-22-2005 5:59 PM mick has not replied
 Message 5 by Yaro, posted 11-22-2005 6:14 PM mick has not replied
 Message 6 by robinrohan, posted 11-22-2005 6:17 PM mick has replied
 Message 15 by Omnivorous, posted 11-22-2005 11:24 PM mick has not replied
 Message 16 by Parasomnium, posted 11-23-2005 2:39 AM mick has not replied
 Message 17 by Mammuthus, posted 11-23-2005 5:56 AM mick has replied
 Message 181 by TimChase, posted 12-05-2005 10:50 PM mick has not replied

  
jar
Member (Idle past 395 days)
Posts: 34026
From: Texas!!
Joined: 04-20-2004


Message 2 of 298 (262505)
11-22-2005 5:18 PM
Reply to: Message 1 by mick
11-22-2005 5:17 PM


Promoted
Thread moved here by AdminJar

This message is a reply to:
 Message 1 by mick, posted 11-22-2005 5:17 PM mick has not replied

  
mark24
Member (Idle past 5196 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 3 of 298 (262513)
11-22-2005 5:59 PM
Reply to: Message 1 by mick
11-22-2005 5:17 PM


Mick,
Great post!
Mark

There are 10 kinds of people in this world; those that understand binary, & those that don't

This message is a reply to:
 Message 1 by mick, posted 11-22-2005 5:17 PM mick has not replied

Replies to this message:
 Message 4 by 1.61803, posted 11-22-2005 6:11 PM mark24 has not replied

  
1.61803
Member (Idle past 1504 days)
Posts: 2928
From: Lone Star State USA
Joined: 02-19-2004


Message 4 of 298 (262516)
11-22-2005 6:11 PM
Reply to: Message 3 by mark24
11-22-2005 5:59 PM


and the chipmonks were cute too.

This message is a reply to:
 Message 3 by mark24, posted 11-22-2005 5:59 PM mark24 has not replied

  
Yaro
Member (Idle past 6497 days)
Posts: 1797
Joined: 07-12-2003


Message 5 of 298 (262518)
11-22-2005 6:14 PM
Reply to: Message 1 by mick
11-22-2005 5:17 PM


Excelent post mick!
I have recently been looking for information like this. I second Mark24's POTM.

This message is a reply to:
 Message 1 by mick, posted 11-22-2005 5:17 PM mick has not replied

  
robinrohan
Inactive Member


Message 6 of 298 (262521)
11-22-2005 6:17 PM
Reply to: Message 1 by mick
11-22-2005 5:17 PM


So the basic microevolutionary process of spatial genetic structure originating from geographic distance appears to account quite well for distinct genetic groupings within species (amoenus), between species (amoenus and ruficaudus) and within a genus (amoenus, minimus, townsendii, merriami).
If you accept microevolution but reject macroevolution, how do you account for the spatial genetic structure of the Tamias genus without using microevolutionary processes? What non-microevolutionary mechanism prevents these easily-hybridizable species from collapsing into a single unstructured unit?
I don't get it. What does this show? That geographic distance accounts for speciation?

This message is a reply to:
 Message 1 by mick, posted 11-22-2005 5:17 PM mick has replied

Replies to this message:
 Message 7 by mick, posted 11-22-2005 7:55 PM robinrohan has replied

  
mick
Member (Idle past 4987 days)
Posts: 913
Joined: 02-17-2005


Message 7 of 298 (262554)
11-22-2005 7:55 PM
Reply to: Message 6 by robinrohan
11-22-2005 6:17 PM


Hi robin,
I'm not specifically talking about speciation (a supposedly macroevolutionary process). I'm talking about the genetic differentiation of populations (a supposedly microevolutionary process).
I'm trying to show that a microevolutionary mechanism ("i only mate with individuals I can access geographically, and my offspring will therefore have geographically-distinct karyotypes") can (at least in principle) be responsible for the genetic structure of populations, species and genera. In other words, microevoluationary processes can account for the maintenance of macroevolutionary structures (such as the genetic structure of Tamias).
I originally intended this thread to go into the ID forum. I invite people who believe in microevolution but reject macroevolution to explain how the spatial genetic structure of Tamias and other taxa is maintained, without making use of microevolutionary processes.
The genetic structure of populations within species (Tamias ameonus) and between species (the Tamias genus) is consistent with the idea of common descent and heritable genetic variation. For example if you get out an atlas you will be able to draw in geographic entities such as Snake River and the Northern Rockies, and see that the genetic delineation of populations both within and between species follow such entities precisely (I'll try to do this in a later post - at the moment I'm looking for a decent hi-res map of north america available online).
It would be interesting to know why macroevolution is supposed to be impossible, given that its phylogeographic patterns are 100% consistent with microevolutionary processes.
I'll post some maps tomorrow.
AS a side note, I believe that speiaction in Tamias has occured allopatrically due to geographic isolation, but that's not precisely what I want to talk about here.
Mick

This message is a reply to:
 Message 6 by robinrohan, posted 11-22-2005 6:17 PM robinrohan has replied

Replies to this message:
 Message 8 by robinrohan, posted 11-22-2005 8:05 PM mick has replied

  
robinrohan
Inactive Member


Message 8 of 298 (262557)
11-22-2005 8:05 PM
Reply to: Message 7 by mick
11-22-2005 7:55 PM


I'm trying to show that a microevolutionary mechanism ("i only mate with individuals I can access geographically, and my offspring will therefore have geographically-distinct karyotypes") can (at least in principle) be responsible for the genetic structure of populations, species and genera. In other words, microevoluationary processes can account for the maintenance of macroevolutionary structures (such as the genetic structure of Tamias).
OK, I get this. But didn't you say that these different species within the genus Tamias interbreed? How then can we call them distinct species? What's the rationale?

This message is a reply to:
 Message 7 by mick, posted 11-22-2005 7:55 PM mick has replied

Replies to this message:
 Message 9 by mick, posted 11-22-2005 8:28 PM robinrohan has replied

  
mick
Member (Idle past 4987 days)
Posts: 913
Joined: 02-17-2005


Message 9 of 298 (262564)
11-22-2005 8:28 PM
Reply to: Message 8 by robinrohan
11-22-2005 8:05 PM


robinrohan writes:
OK, I get this. But didn't you say that these different species within the genus Tamias interbreed? How then can we call them distinct species? What's the rationale?
Members of speciose genera of rodents frequently do not fulfill the requirements of the biological species concept. But the BSC is based on the idea of gene flow, and since gene flow between populations within a species is almost always more than 0% and is always less than 100%, I think it is reasonable to consider the BSC as a gradient rather than as a binary classification system. It is usually operationalized as a binary system, but that is simply the most conservative view of "species" that we can have when we do experiments.
Although there might be some debate about whether amoenus and ruficaudus are "true species" according to the BSC, there is no doubt that the level of genetic diversification within Tamias is similar to that within other genera. Their species status is established on the basis of diagnostic systematic traits an on cladistic analysis. There hasn't been enough research to know whether hybrids of each species (or species group) suffer a reduction of fitness.
Hybridization in mammals is actually extremely common (and much more common in amphibians and birds, where hybridization not between genera but between families is not unheard of). More pertinent than the BSC is the genetic structuring of sympatric populations and the nature of "introgression zones". Life's just a big tree, after all.
Mick
in edit: you can find examples of inter-family hybridizations at http://www.bird-hybrids.com (I don't have time to search for them for you, but I guarantee they are in there)
This message has been edited by mick, 11-22-2005 08:37 PM

This message is a reply to:
 Message 8 by robinrohan, posted 11-22-2005 8:05 PM robinrohan has replied

Replies to this message:
 Message 10 by robinrohan, posted 11-22-2005 8:51 PM mick has replied

  
robinrohan
Inactive Member


Message 10 of 298 (262574)
11-22-2005 8:51 PM
Reply to: Message 9 by mick
11-22-2005 8:28 PM


Divergence
(By the way, it was a great post. I forgot to tell you that. I'm not criticizing it, just asking ignorant questions.)
So an example of a "microevolutionary process" would be geographic distance. You have a group of chipmunks and some of them wandered off and started their own group, which after awhile became a variant. Overtime it became a new species or semi-species.
Now creationism says that microevolution occurs as you stipulated, but it also says it never advances any further. (Why it would not advance any further is a mystery to me. It seems to me it would almost have to).
What your example shows us is that these variant races of chipmunks, or different specie, or however we wish to label them, get "maintained." They don't over time get all mixed up together again and become like they were before this separation happened, right?
But I would not think that creationism would be concerned with maintenance of the status quo but with further divergence.

This message is a reply to:
 Message 9 by mick, posted 11-22-2005 8:28 PM mick has replied

Replies to this message:
 Message 11 by Brad McFall, posted 11-22-2005 9:44 PM robinrohan has replied
 Message 18 by mick, posted 11-24-2005 12:31 PM robinrohan has not replied

  
Brad McFall
Member (Idle past 5033 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 11 of 298 (262579)
11-22-2005 9:44 PM
Reply to: Message 10 by robinrohan
11-22-2005 8:51 PM


Re: Divergence
In
http://EvC Forum: What to do with Brad? (Yet another Brad McFall topic) -->EvC Forum: What to do with Brad? (Yet another Brad McFall topic)
the NPR Science Friday
Page not found - Science Friday
Flatow brought up this issue with respect to the bird flu. Eldredge said that creationists will concede that bird flu might some time "evolve" into a human strain. Niles said we would not even think this if evolution did not occur BUT and here it comes, Flatow THEN said, something like, "but IDers will make a difference between micro and macro evolution". What was the evo, response - well, Niles said what you did. He asserted that evolution was like "ripples on a pond" it goes in circles and never stops. The implication was that there is no stoping micro into macro evolution. Niels Eldredge used the word "break". He said evolution has no breaks.
After thinking about this I thought this morning that in truth these evos had not thought about the process hard enough. I can write a sentence next which might be a true "law of nature." If it is then it would enable one to show determinant breaks.
The sentence is, Brad said, "There is a direct correlation between causal acyclic graph representations of macrothremodynamic thermostats and parent to offspring ratios per clade."
Now if this is true it would also have something to say about spatial patterns of speciation statistically. I am not prepared to engage Mick on this, so I hope my interjection is not taken badly.
From this perspective I can see indeed that a creationism reply is suffiently outside Alvin and his yellow submarine band, but to be fair, I would have to engage Mick not at my hyper velocity but his more paced and deligthful posts.
This message has been edited by Brad McFall, 11-22-2005 09:50 PM

This message is a reply to:
 Message 10 by robinrohan, posted 11-22-2005 8:51 PM robinrohan has replied

Replies to this message:
 Message 12 by robinrohan, posted 11-22-2005 9:51 PM Brad McFall has replied
 Message 14 by Belfry, posted 11-22-2005 10:07 PM Brad McFall has replied
 Message 19 by mick, posted 11-24-2005 12:59 PM Brad McFall has replied

  
robinrohan
Inactive Member


Message 12 of 298 (262582)
11-22-2005 9:51 PM
Reply to: Message 11 by Brad McFall
11-22-2005 9:44 PM


Re: Divergence
"There is a correlation between causal acyclic graph representations of macrothremodynamic thermostats and parent to offspring ratios per clade."
Well, that certainly clears things up.

This message is a reply to:
 Message 11 by Brad McFall, posted 11-22-2005 9:44 PM Brad McFall has replied

Replies to this message:
 Message 13 by Brad McFall, posted 11-22-2005 9:53 PM robinrohan has not replied

  
Brad McFall
Member (Idle past 5033 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 13 of 298 (262584)
11-22-2005 9:53 PM
Reply to: Message 12 by robinrohan
11-22-2005 9:51 PM


Re: Divergence
Sorry, that's all I got (now).

This message is a reply to:
 Message 12 by robinrohan, posted 11-22-2005 9:51 PM robinrohan has not replied

  
Belfry
Member (Idle past 5086 days)
Posts: 177
From: Ocala, FL
Joined: 11-05-2005


Message 14 of 298 (262585)
11-22-2005 10:07 PM
Reply to: Message 11 by Brad McFall
11-22-2005 9:44 PM


Re: Divergence
Brad McFall writes:
Niels Eldredge used the word "break". He said evolution has no breaks.
After thinking about this I thought this morning that in truth these evos had not thought about the process hard enough. I can write a sentence next which might be a true "law of nature." If it is then it would enable one to show determinant breaks.
Is it possible you (or Eldredge) meant "brakes?"
If not, can you explain "breaks?"
... I ask, aware from my lurking that I tread into murky waters...

This message is a reply to:
 Message 11 by Brad McFall, posted 11-22-2005 9:44 PM Brad McFall has replied

Replies to this message:
 Message 51 by Brad McFall, posted 11-27-2005 8:05 PM Belfry has not replied

  
Omnivorous
Member
Posts: 3978
From: Adirondackia
Joined: 07-21-2005
Member Rating: 7.3


Message 15 of 298 (262601)
11-22-2005 11:24 PM
Reply to: Message 1 by mick
11-22-2005 5:17 PM


Mick, I'm mightily impressed--and with the only rodent I can tolerate to boot.
If mark had not already nominated, and Yaro seconded, I would do either: but "Thirded!" has a dull, plopping sound...
Remarkable presentation. Thank you.

This message is a reply to:
 Message 1 by mick, posted 11-22-2005 5:17 PM mick has not replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024