SPECIATION? - - One Species turns into Six Chromosomal Races (amended)

(George Brooks) #1


The 2000 article [at bottom] has been superceded by this more recent one, which discusses newly formed “races” of mice, instead of species… [Below is the abstract.]

Chromosomal phylogeny of Robertsonian races of the house mouse on the island of Madeira: testing between alternative mutational processes.
Genet Res 2005 Dec 23;86(3):171-83. Epub 2005 Nov 23.
Janice Britton-Davidian, Josette Catalan, Maria da Graça Ramalhinho, Jean-Christophe Auffray, Ana Claudia Nunes, Elodie Gazave, Jeremy B Searle, Maria da Luz Mathias
Institut des Sciences de l’Evolution, UMR 5554, Laboratoire Génétique et Environnement, CC65, Université Montpellier II, France. britton@isem.univ-montp2.fr

The ancestral karyotype of the house mouse (Mus musculus) consists of 40 acrocentric chromosomes, but numerous races exist within the domesticus subspecies characterized by different metacentric chromosomes formed by the joining at the centromere of two acrocentrics. An exemplary case is present on the island of Madeira where six highly divergent chromosomal races have accumulated different combinations of 20 metacentrics in 500-1000 years. Chromosomal cladistic phylogenies were performed to test the relative performance of Robertsonian (Rb) fusions, Rb fissions and whole-arm reciprocal translocations (WARTs) in resolving relationships between the chromosomal races.]

I lifted this link out of a recent posting … I thought it was way too important to leave it hidden in that particular thread!

Island mice may evolve faster: From one species to six
By Bijal P. Trivedi
April 28, 2000

Janice Britton-Davidian spent several weeks in 1999 placing hundreds of mousetraps all over the semi-tropical island of Madeira and discovered what may be an example of “rapid evolution.” She caught hundreds of small brown mice that look pretty much alike but that are genetically distinct—a very unusual thing for such a small, geographically contained place. It normally takes thousands to millions of years for one species of animal to diverge to become two. On Madeira, one species may have evolved into six in the space of just 500 years.

Britton-Davidian, an evolutionary biologist at Université Montpellier II in Montpellier, France, showed that populations of Maderian mice have between 22 and 30 chromosomes, even though their ancestors, who first arrived with the Portugese in the 15th century, had 40.

Madeira is a rugged volcanic island with sharp black cliffs that block all but a few isolated rocky shores. Only a few small villages decorate the strip of coast. The Portuguese were first to inhabit the island, bringing with them the mice that Britton-Davidian so avidly seeks. As the Portuguese founded small settlements around the island, they inadvertently deposited small groups of mice at each stop. And, for the last five centuries, mountainous barriers have prevented these coastal colonies of rodents from commingling.

Britton-Davidian collected hundreds of mice from about 40 locations around the island and found six distinct populations. The common brown house mouse of Europe, presumably the ancestor of the Madeira mice, has 40 chromosomes, but the six families of Madeiran mice have between 22 and 30.

The current families of Madeiran mice are not short of genetic material. They have not lost any DNA. What happened is this: over time, some of the chromosomes fused together, packing more DNA into some chromosomes. Each of the six unique populations of mice on Madeira has its own special assembly of fused chromosomes. Each group of mice may now be its own species.

The diversity of fused chromosomes seems to have occurred in just 500 years, or between 1,500-2,000 generations of mice, says Britton-Davidian. Furthermore, the huge diversity in chromosomes has evolved solely from geographic isolation rather than adaptations to different environments.

“What is surprising is how fast this has taken place,” says Scott Edwards, an evolutionary biologist from the University of Washington, in Seattle. Based on fossil records of sea urchins and invertebrates, evolution of different species is thought to take thousands to millions of years. “But this is an interesting case because it may prove to be an extreme case of rapid speciation,” says Edwards.

Britton-Davidian wants to know whether these populations of mice have evolved into different species or whether they are on the cusp of speciation. A species is defined as a group of organisms that can mate and produce fertile offspring.

One of Britton-Davidian’s most surprising findings is that she and her colleagues found no mice that are hybrids among any of the six groups. “This might be because the hybrids are infertile or they may be less fit than the parents and unable to survive,” says Britton-Davidian. Other explanations could be that the groups have been geographically isolated and have not had the chance to mate, or that the mice “recognize each other as different and choose not to mate.”

Britton-Davidian has taken some mice from Madeira back to her lab in France and will try interbreeding the six populations to confirm whether the hybrid mice are infertile, which, if they are, would imply that the different groups were in the process of speciation. Her team will also observe the mice to see whether they show behavioral or physical differences.

. . .
Britton-Davidian, J. et al. Rapid chromosomal evolution in island mice. Nature 403, 158 (January 13, 2000).

Genome News Network is an editorially independent online publication of the J. Craig Venter Institute.
© 2000 - 2004 J. Craig Venter Institute.


Biological Information and Intelligent Design: evolving new protein folds

Thanks for posting it! Whenever I see announcements of direct observation of speciation, I think back to when my creation science experts told me that scientists had never seen evolution taking place and never would.

Evolution’s wonders are a major reason why I’m a Christian.


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(George Brooks) #4


Do you know how often mating pairs with dramatically different chromosomal structures produce fertile offspring?


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(Chris Falter) #6

Since Mme. Britton-Davidian said she was going to continue her research after 2000, I thought it would be good to check the literature. Indeed, she published the following result eleven years later:

Overall, the reproductive assays indicated that these C4-carrying hybrids were not sterile but showed an approximately 50% decrease in fertility compared to homozygous parental mice.

So the Madeira mouse sub-populations have advanced far along the path to speciation in just 500 years, but have not yet reached the point of no return.

IMO, Britton-Davidian’s findings seem highly consistent with the theory of evolution.

(George Brooks) #7

The article is what, 15 years old? Maybe they have confirmed more of the facts by now… I’ll give it a look-see…

(Chris Falter) #8

Looks like we were posting comments simultaneously. :smiley:

(GJDS) #9

No matter what the result, evolution is always proven!!!?? This is blatant - the hypothesis was clearly stated - if they reproduced, or if they did not reproduce - by definition. What sort of science are you people advocating?


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(Chris Falter) #11

Well, I said it was highly consistent with evolution, not that it proved evolution. :wink:

Secondly, population genetics shows that viability differences far smaller than 50% between alleles can cause dramatic shifts in allele frequency in short numbers of generations. I don’t have the exact numbers in front of me; if they are important to you, I’ll see what else I can dig up for you. Given that observation from population genetics, a 50% reduction in viability would result in the almost certain disappearance of an allele in short order, especially if that allele is found in very few individuals.

In the case under discussion, the C4-carrying hybrids were not even found in any individuals on the island of Madeira; they were only produced in Mme. Britton-Davidian’s lab. Thus it seems eminently reasonable to conclude that in the conditions prevailing on the island of Madeira, the 6 different sub-populations will indeed continue to diverge from one another.

Does that make sense? Did I miss anything?

Thanks, and have a great day!

(GJDS) #12

I am not looking for something you have missed, but rather point to the way the observations are discussed. If I were performing an experiment with similar variables, I would naturally begin by stating my hypothesis (if they breed, one result, if not, another).

But on a more interesting topic, just how can I use a control that eliminated conceivable variables (just for the sake of discussion I will list some in no specific order or importance: lab conditions as opposed to natural conditions, specific ecological niches that may be related to differences in nature, but absent in the lab, how would I equate variations with time, diet, etc etc).

I am not interested in a lengthy debate on pop genetics, and will gladly accept such methods as valid - but I will insist that the data and observations are able to withstand scrutiny in the light of claims made.

(Henry Stoddard) #13

It would be to know what they have learned since then. In any case, I believe the article is still of great interest.

(George Brooks) #14


So much text … so much heat …

Like I said, I’ll see if there have been any further developments on the Island mice…

In the meantime … here’s a BioLogos link on the topic:

“What seems to have happened is that, over time, the mice spread out across the island and split into separate groups. Madeira is a rugged volcanic island with crags and cliffs. So it makes sense that this would have been easy to do. There were many isolated corners for the mice to occupy. Over time, random mutations occurred—some chromosomes became fused together.”

“Now, In order to reproduce successfully, both parents must have the same number of chromosomes. So when a population develops a chromosome fusion, suddenly that group cannot mate with the other members of its species. It becomes a brand new species. That’s exactly what happened on Madeira. And because of this phenomenon, 6 new species evolved from just 1 or 2 in an extremely short amount of time.”


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(George Brooks) #16


For someone who intends “no heat” … you have a peculiar notion of building fraternal bonds.

“Blah, blah, blah” … it’s like listening to my nasty ol’ Aunt Rose … always so full of vinegar … Frankly, Eddie, it’s exhausting. Sometimes one vague sentence expressing a general tone is better than a bucket full of precisely crafted criticisms.

I’ll get back to you when I have some more details…


What you are missing is that EVEN IF no speciation had YET taken place, evolutionary processes nevertheless continue to change allele frequencies in populations over time. I do realize that evolution-opponents will continue to imagine an undefined “barrier” which somehow “prevents microevolution from becoming macroevolution”, they will never get around to defining that barrier because it doesn’t exist. Meanwhile, I will continue to praise God for the amazing evolutionary processes he created. They are wondrous to behold.

Of course, I am NOT saying that you do or don’t believe in the micro-evolution vs. macro-evoluion mambo (as The Sensuous Curmudgeon blogger calls it.) That’s irrelevant. That type of argument and thinking nevertheless arises wherever and whenever denial of evolutionary processes arises on the Internet. My post is in reaction to the ARGUMENTS, not the individuals who may have brought those arguments to mind.

Potholer54 has a great video where he points out that even Kent Hovind acknowledges that scientists are observing the development of a new species of rabbit. Hovind simply chooses to call the process anything but evolution. And because evolution of species is observed so regularly, recent decades have seen the emergence of the “evolution within KINDS” argument. When the unseen obstacle to evolution beyond species boundaries became impossible to maintain, they retreated to a barrier to evolution beyond KINDS.

We are all at liberty to praise God for different things. And every time I observe evolutionary processes at work, I am impressed by God’s omniscience and omnipotence. I have no reason to deny the works of God.


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(George Brooks) #19

I agree completely with this statement.


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