Speciation events

[Paul C. Anagnostopoulos]

I was chatting with an acquaintance the other day about evolution. He's kind of a fence sitter on the question of speciation. He said that he would be more convinced if there was an observed example of speciation, in the wild, that involved one or a few point/small mutations. Most of the examples cited involve some kind of polyploidy or similar macro-mutation.

I suggested that he might have to be patient, because finding small inter-species mutations in the wild is difficult, and we've only had the capability to analyze such mutations for a few years. I asked him what he thought about such speciations observed in the lab, but as usual, he wasn't convinced by that argument.

I've poked around a bit. I found this interesting paper:

http://ib.berkeley.edu/courses/ib160/Coyne_Orr98.pdf

Does anyone have any examples or additional useful information?

~~ Paul

 

[arcticpenguin]

There's an underlying difficulty in that 'species' is a poorly defined term. When does variation pass from 'variety' to 'species'?

Drosophila are probably your best bet, as covered in the link you posted.

The timeframe of evolution is generations. So it will be more visible in organisms with shorter generation times.

Bacteria diverge all the time, but are so casual about exchanging DNA that it might be difficult to point to a speciation event. Also, they are not visible except through a microscope, so species analysis would probably be done through biochemical or genetic means.

Drosophila are fairly complex organisms, much more so than bacteria or nematodes, so it would be easy to observe physical or behavioural effects of evolution.

No, I don't have any specific examples to cite.

 

[SteveGrenard]

For interesting accounts on theories of speciation, why not try the following authors and/or their works?

E.O. Wilson: The Diversity of Life
(Norton)


G. Ledyard Stebbins: Processes of Organic Evolution
(Prentice Hall)

Michael L. Arnold: Natural Hybridization and Evolution
(Oxford)


This last reference makes a powerful case for hybridization in
sexually reproducing animals as a tool for speciation over non-geologic time scales (e.g. in a human lifetime, for example)
I am not so sure bacteria, per se, "exchange DNA" and speciate that way. They reproduce by binary fission and most notably evolve characteristics such as antibiotic resistance as a result of
selection pressures.

 

[arcticpenguin]

[I am not so sure bacteria, per se, "exchange DNA" and speciate that way. They reproduce by binary fission and most notably evolve characteristics such as antibiotic resistance as a result of
selection pressures.

Allow me to clarify. I meant that bacteria may speciate through natural mutation and selective pressure, but that their ability to assimilate DNA might interfere with the ability to detect any speciation event.

For that matter, bacteria do also pick up new traits from DNA assimilation, and antibiotic resistance (for example) can be passed from one species to another. When the accumulation of new traits results in a nnew 'species' is a judgment call.

 

[Dymanic]

Speciation has been observed in the plant genus Tragopogon, but unfortunately the offspring is tetraploid. Disqualifying speciation by hybridization and polyploidy is going to make this guy hard to persuade. Sounds like he wants to see it in vertebrates. One thing that makes observing that kind of speciation in the wild difficult is the amount of time required. Not everyone agrees on this, but five to fifty thousand years is frequenty cited as being the minimum. And as AP pointed out, there is still the fuzziness of the term 'species.

We had a thread on this a while back

 

[SteveGrenard]

I agree external assimilation of DNA CAN cause genetic changes in bacteria and result in new strains or serotypes. In 1928 Griffith discovered "transformation," which is the assimilation of external DNA by bacteria.

Non-virulent R strain bacteria were transformed into S strain bacteria when they were mixed with dead S types. It is questionnable whether these are strains, races or serotypes of the original organism or entirely new species in the sense that the original poster asks. Experiments on a lab bench are difficult to confirm under natural circumstances and, of course, do not always or necessarily occur.

Avery then separated and purified the macromolecule components of the S strain bacteria and mixed them with the R types. He concluded DNA was the transforming substance.

Hershey and Chase used bacteriophages radioactively labeled with phosphorus and sulfur to demonstrate that DNA was the genetic material. Their experiments showed that radioactive labeled phosphorus entered the bacteria, while the radioactive labeled sulfur did not.

Selection pressure can work quite rapidly to alter structual and functional characteristics of vertebrates. Galapagos Islands finches are an example of evolution in our time. And natural hybridiziation, according to Arnold in the reference given above results in speciation as well. Depending on the situation and organsim involved ... anywhere from 5 to 50K years would be about right for this.

The fact that it may happen in days, weeks or months where bacteria are concerned is probably responsible for the labeling of "new" (variants) organisms as serotypes or serovars rather than species. Salmonella is a case in point. There are more than 600 variants or serotypes of ths single genus.

 

[MRC_Hans]

I'm always wondering at these people who, while having only casual scientific insight, say something like: "I don't understand exactly how speciation (or big bang, or whatever) occurs, so I don't really believe it is true".

Now, on speciation: This planet is crawling with millions of different species of plants, animals, fungii, bacteria, vira and some that defy classification, so obviously, regardless of whether we fully understand the mechanism or not, speciation does indeed occur.

The question, IMHO, is very basic: Do we believe that

a) God does these things by magic whenever he so wishes.

b) Things happen according to knowable physical laws.

Note that b in no way precludes the existence of God, only that God (at least normally) allows things to happen according to physical laws.

If we choose a, then everything can happen, and we might very well ask why we never see any of that magic in action, and why things happen exactly according to physical laws whenever we are able to test it.

If we choose b, then obviously speciation occurs.

Hans

 

[Dancing David]

Butterflies may be a good place to investigate, there are many varieties of black swallow tails, they are regional, then there is the red spotted purple, it is a single species but shows great color variation in the northern and southern varieties.Sorry I forget the scientific name I think the black swallow tail is Polyxenes)

Peace