In my book Speciation, written with Allen Orr, we give some estimates about how long it takes to make a new species. These estimates vary, of course. In the case of speciation that involves instantaneous genome doubling, as in auto- or allopolyploidy, a new “hybrid” species can arise in as few as three generations. But under normal conditions the process usually takes hundreds of thousands to millions of years. The record we found for “normal” speciation is the production of five species of cichlid fish in lake Nabugabo, a satellite of Lake Victoria cut off by a sand bar. In that case, each of the five species has its closest relative in Lake Victoria, and the differences between these “sister species” is not large, involving mostly changes in color.
Now, however, a case of equally rapid speciation, involving even more genetic change, has been reported in a new paper in the Proceedings of the Royal Society by Jonathan Puritz et al. (reference and link below; free download). The two species are starfish, Cryptasterina pentagonia and C. hystera. They both live on the northeast coast of Australia, separated by about 375 km. In the figure below, the distribution of C. pentagonia is shown in blue and that of C. hystera in red (the latter has a more limited distribution):
Although the species are ecologically similar and look pretty much the same, there’s a profound difference in their life histories. C. pentagonia is a “broadcast spawner” that spews its gametes into the sea (eggs and sperm unite in the water column), while C. hystera is not only a brooder, keeping fertilized eggs in a body pouch until the larvae hatch, but is also “selfing”: an individual is a hermaphrodite that fertilizes its own eggs. This is a pretty profound change that involves many aspects of morphology and physiology.
Nevertheless, genetic evidence establishes these two species as each other’s closest relatives (i.e., “sister species”). The genetic analysis involved five “microsatellite” loci and two loci on the mitochondrial DNA (remember this week’s caveat about mtDNA), but they also sequenced two gene fragments from nuclear DNA, so it’s a pretty good genetic sample. What they found is this:
- The selfing species has almost no genetic variation. That’s what you’d predict since self-fertilization erodes variation, but there’s virtually zero variation in C. hystera.
- Conservative age estimates of the divergence between these two species, based on the “molecular clock” (using DNA divergence to estimate age) range between 905 and 22,628 years. The best estimate is ca. 6000 years (6159, to be precise). That is an extraordinarily fast rate of speciation given the extensive restructuring of the reproductive system involved. I almost have trouble believing it could happen so fast.
- How do we know these are true species? Under the “Biological Species Concept” (BSC), the thing that counts is that the entities be reproductively isolated; that is, they can’t exchange genes. Well, that’s true to some extent in this case. One can’t really claim that the selfing “species” is reproductively isolated from its nonselfing relative because individuals of the selfing species are just as isolated from each other as they are from members of C. pentagona (selfers don’t mate with any other individuals). But individuals of C. pentagona are reproductively isolated from the selfer, because in principle they could coexist with that species and deluge them with sperm and eggs, but that wouldn’t produce hybrids since individuals of C. hystera fertilizes only themselves. This is a mistake we made in our book when claiming that the evolution of self-fertilization from a species that “outcrosses” does not cause reproductive isolation. It does—but in only one direction.
- What were the evolutionary forces that led to the evolution of selfing from normal outcrossing? (That was the ancestral condition, as we know from phylogenetic analysis.) The authors don’t know, but one possibility is the association of self-fertilization with cold waters in marine invertebrates. The southern species, which selfs, happens to be located south of a geographic break in water temperature where the ocean becomes colder along the cost of Australia. Another reason is “reproductive assurance”: if the selfer descended from a small number of colonists, or perhaps only one, then there’s a strong selective pressure to fertilize yourself (if you don’t have another individual to mate with you don’t leave any genes unless you can self).
This is a good paper, and I hope the young age holds up with further molecular analysis (more is needed). I have only one beef, and that’s about the discussion, where the authors say this:
The timing of these evolutionary changes is critically important for testing and rejecting some alternative hypotheses for speciation in Crypasterina. In particular, our results are not consistent with the slow, gradual loss of shared alleles (and of reproductive compatibility) via genetic drift in allopatry (classic geographical speciation), or with divergent adaptation to broadly sympatric microhabitat differences such as different intertidal heights.
The authors have made a serious mistake here by associating “allopatric speciation” (that is, the creation of new species after populations are isolated from each other by geographic barriers) with genetic drift, and “sympatric speciation” (speciation in small areas without geographic barriers) with natural selection. I have found this error pervasive in the evolutionary community: it was mentioned several times at the evolution meetings in Ottawa. The fact is that speciation of geographically isolated populations can occur by either genetic drift or natural selection, and everybody really knows this. That’s what happens, after all, when a colonist invades an island and forms new species after much modification by natural selection in a new environment. For reasons that Allen and I discuss in our book, we think that natural selection is far more important than genetic drift in cases of allopatric speciation. In sympatric speciation, selection is also likely to be involved because that form of speciation requires evolutionary forces strong enough to sunder an interbreeding population, and selection is much more likely to do that than is random genetic drift. But let’s get the record straight here. If you’re an evolutionary biologist, burn this sentence into your brain:
Just because speciation occurs among geographically isolated populations, that does not mean that the evolutionary force producing those new species was genetic drift rather than natural selection.
Got it? Now tell that to your colleagues.
I’m not sure where this mistake comes from, but it seems to be promulgated by the concentration of evolutionists’ effort on cases of speciation that occur without geographic isolation: sympatric or parapatric speciation. Because those often involve ecologically-based natural selection, somehow that’s been taken to mean that speciation that does involve geographic isolation doesn’t require ecologically-based natural selection. Serious error of logic.
______________
J. B. Puritz et al. 2012. Extraordinarily rapid life-history divergence between Cryptasterina sea star species. Proc R Soc B 2012 : rspb.2012.1343v1-rspb20121343.
Just a friendly reminder to ask your publisher to produce “Speciation” on the Kindle. I mentioned it when we met at Harvard.
s/Kindle/general ebook format/
While I do have a Kindle, I use it much less now than I did before I got a (Kindle-size) tablet, because the Tablet can display a much wider range of documents, more flexibly than the Kindle. In particular, the XXX gigabytes of PDF-format papers I’ve accumulated over the years are much more legible on the tablet.
The more general point is … don’t publish in a format that is going to be linked to particular hardware. PDF has taken nearly 2 decades to become “the default”, and a major point in that has been the release of the specification of the format for general use. When PDF first came out, it was viewed very sceptically. I remember when Compuserve made PDF the default format for publishing it’s online help files (including forum contributions), and I was severely dubious about spending several hundred pounds of my own money on a PDF-writer program for the purpose. When non-Adobe tools started to appear, for free, the acceptance of the format became much higher.
I understand the concerns of publishers about content control, and their desire to prevent re-selling. DRM is an extraordinarily difficult project, and any popular scheme will be broken one way or another. That’s a circle that I’m not qualified to square (and it is probably impossible, if I understand the logic correctly). But format-dependence and hardware-dependence are not a way that are going to succeed. If Jerry’s publisher produced a Kindle-only version of (say) WEIT, I wouldn’t buy it, unless I knew that I’d be able to ‘rip’ it into a format that I could use on my non-Kindle tablet, print hard-copy from to read in the bath, or shove half a chapter under someone’s nose (physically, or electronically) and say “what about that then?” Or even just lend the whole copy to a friend in the pub who keeps asking me sensible but ill-informed questions. These are freedoms I have from the ink-on-paper version, and if I feel strongly enough, I can always make a scan+OCR PDF from the dead tree.
Rant over. (For the moment.)
Wait, so doesn’t this make the slowest known example of speciation, since it took the entire history of the earth in order for it to take place?
(j/k)
lol. sub
Don’t be silly. Everything was created just as they are now. With the possible exception of my breasts,tummy and bum.
I can already see the headline: “Godless scientist proven wrong: Problems with speciation ‘theory’ refute evilution!”
I was trying to figure out what the ancestral species was like, and came across this paper.
http://www.biolbull.org/content/205/3/285.full
I’ve always found interpreting phylogenetic trees to be a little tricky, but I think the ancestor to these two sea stars also spawned. Could you please let me know if I am interpreting it correctly?
Nevermind! I figured it out. =)
Thanks for the interesting commentary and instruction, Jerry. Learning a bit more every day is a great thing.
Very interesting case. Thanks very much for the abstract and illuminating comments.
I could not download the original paper. The link you posted brings to a cross-reference page, and the paper is not free for downloading in the Royal Society website. Unfortunately I have no access.
Best wishes,
TONI
Same here sadly 🙁
Once in a while I have seen things like “mere geographical separation,” which seems to imply that in that case, the fact of separation was the only relevant ecological change.
When you lose the “mere” this implication should be lost with it.
“Just because speciation occurred among geographically isolated populations, this doesn’t mean that the evolutionary force behind those new species was genetic drift rather than natural selection.”
I read this article, rehearsed the sentence in bold 10 times to “burn” it into my brain, waited five minutes, and then wrote it out above. Not perfect, but good enough. Now I’m going to tell all my colleagues.
Thanks for such a fascinating article.
“Speciation” on the Kindle absolutely. I’m going to make a churlish comment on the price (60USD). I suspect this book is not aimed at a popular science audience, but there are a lot of us out here with science degrees who are nonetheless in non- scientific or academic environments who would read and understand this book, but balk at a personal investment this high.
Steve Bowen
(i appear to have a gravatar account here for some reason, will sort that out as I have tried to lose my ‘alter ego’ elsewhere, and I know you don’t like those any more than I do)
I think $60 is quite reasonable given that similar academic books are often far more expensive. Or perhaps I’m just remembering the time that the Australian dollar sucked against the US dollar.
Please see my reply to post #1 for why NOT to release a Kindle-only version of this (or any) text.
“Kindle-readable” is perfectly fine by me ; I have a Kindle. But because most of my technical documentation displays better on my [non-Apple, non-Samsung] tablet than it does on the Kindle, I generally carry both, and when weight becomes an issue (for example, helicopter flights replacing fixed-wings and boats), the Kindle gets left behind.
Edit : OK – I’ll accept that user manuals for a Kindle can be safely released on Kindle-only formats. But NOT service/ repair manuals – which you may have to access from another device to repair your Kindle.
§
Ah, a compact “sub”. Like those ones that wrecked the Tirpitz?
Ha!
Jerry, is there any clear idea as to how much genetic change is necessary to turn a species hermaphroditic? Conversion of a sexual species to non-sexual reproduction seems to be a not-uncommon occurrence in a wide variety of non-mammalian organisms with very different evolutionary histories (such as lizards, and perhaps even sharks). These examples suggest to me that the mechanisms of sexual reproduction are relatively easily converted over to hermaphrodism (or at least parthenogenesis).
Much seems conflated here.
Hermaphroditism (w/ outcrossing), obligate selfing hermaphroditism, and parthenogenesis are three very different reproductive strategies that may evolve (from the ancestral dioecy) for very different reasons.
And none of them sound like much fun.
It can be fun for spectators though…
http://en.wikipedia.org/wiki/Penis_fencing
The world is full of different fruit to the one (or some) that you seem to prefer. Don’t knock it until you’ve tried it.
It’s not my cup, but those two girls with their one cup seemed to enjoy it. Or someone enjoyed it enough to pay them enough to pretend to enjoy it.
(If you don’t recognise the reference, I strongly advise you to not research it deeply, and certainly not on a monitored internet link. Take a puke bucket.)
Wow, if that holds up, that is seriously fast.
One thing that does not come across clearly is that microsats are usually also nuclear data.
Any chance any of this (or upcoming speciation) will be related to radiation from Japan’s nuclear situation? (Apologies if you mentioned it inside the article.)
this happened 6000 years ago.
As for the future, who can tell?
From first principles … given that the water-borne radiation plume only recently reached the US west coast, and to get to the Australian east coast it would also have to cross one (two? I don’t have a current map to hand) westward-flowing equatorial current … I think it is extremely unlikely.
Or are you referring to the radiation from the Hiroshima and Nagasaki bombs – they’ve had 66 years longer to approach the appropriate areas.
Don’t forget the radiation from the US, French and British tests carried out in the south Facific in the 1950s (and inland in Australia from the British) : that’s at least starting on the correct side of the equatorial currents.
Could such a speciation happen in a few tens of generations ? … I think I’ll pass that question back to the genetics experts.
Is there also “crismas speciations” or “forsofjooly speciations” ?
😉
Sorry, keeping quiet now.
Do you really mean to suggest that all allopatric speciation requires natural selection?
Doesn’t Jerry address that just afterwards?
TL;DR: No.
/@
I have questions that haunts me oft and tarries long that I find it hard to find an answer to on google.
I’m a bit of a dilettante, with lots of interests, and no specialities, and I’m interested in both biology and volcanoes.
I understand that in lots of old, cold, lava tubes animals occur that are blind.
Both above and below water level.
Is there a way for the larvae of blind creatures to find their way to other systems?
Does blindness evolve separately in the different localities?
What sort of time scale is involved, if so? In terms of generations.
Is it that when there is no light genes develop bodies differently than they do when there is light?
Some sort of combination of these?
Something else altogether?
Something I’ve been interested in for a while, but no answers.
Any suggestions?
David B
As a troglophile hominid (a hominid which finds the cave habitat quite comfortable, but can live in surface conditions too ; I’ve never had the opportunity to attempt to breed underground, but I’m trying to persuade the wife of the joys of skin-tight neoprene and cold mud) …
Where was I? Oh yes, blind cave organisms … There were some interesting papers a few (5?) years ago about the genetics of cave fish in IIRC (I’m searching for the papers locally, I think I downloaded them when I had institutional access) Texas/ Mexico, where several closely related species in separate but nearby cave systems had differing degrees of sight-loss, from loss of skin pigments to loss of whole eyes.
My search has returned. This is a local search – if you’ve access to a good library, you can probably get more, but at least some of the papers I’m going to list are publicly available.
You refer to “lava tube caves” : I’m mostly a limestone caver – I’d be surprised if no work was being done on the biology of lava caves, but I suspect that it’s heavily outweighed by the karst (limestone and/ or gypsum) cave work.
Is there a way for the larvae of blind creatures to find their way to other systems?
A caver’s definition of “cave” is `underground hole big enough for a human to get into` ; larvae are (generally?) smaller than humans ; larvae can often get from one cave system to another, where humans can’t. On the other hand, there are plenty of examples of “perched water tables”, where one cave system with a water table (a water level mapped between several air-linked caves) is underlain by a separate cave system with it’s own water level at a lower level than that of the upper cave system. If the water can’t get through the pores (and/ or clay bands, sealed faults, mineral veins …) then it is unlikely that larvae could. OTOH, the larvae could be transported between surface “windows” of the two systems on terrestrial animal legs etc. So, the TLDR version is “yes and no”.
Does blindness evolve separately in the different localities?
Yes. It can evolve separately in (say) crustaceans and vertebrates in the same system too.
What sort of time scale is involved, if so? In terms of generations.
Good question … less than the lifetime of the cave system – but that is hundreds of thousands to millions of years.
Is it that when there is no light genes develop bodies differently than they do when there is light?
That question does not permit of a simple answer.
Any suggestions?
Reading list ; some may be available open access ; some you may be able to obtain from the authors, or their web pages.
—————————-
TITLE.- EYED CAVE FISH IN A KARST WINDOW
Authors.-
Luis Espinasa *
Richard Borowsky +
New York University. Department of Biology. 1009 Main Building. Washington Square, NY 10003. USA Telephone (212) [redacted]
—————————-
Central Role for the Lens in Cave Fish Eye Degeneration
Yoshiyuki Yamamoto and William R.Jeffery*
Abstract: Astyanax mexicanus is a teleost with eyed surface-dwelling and eyeless cave-dwelling forms. Eye formation is initiated in cave fish embryos, but the eye subsequently arrests and degenerates. The surface fish lens stimulates growth and development after transplantation into the cave fish optic cup, restoring optic tissues lost during cave fish evolution. Conversely, eye growth and development are retarded following transplantation of a surface fish lens into a cave fish optic cup or lens extirpation. These results show that evolutionary changes in an inductive signal from the lens are involved in cave fish eye degeneration.
http://www.sciencemag.org SCIENCE VOL 289 28 JULY 2000 page631
—————————-
Hedgehog signalling controls eye
degeneration in blind cavefish
Yoshiyuki Yamamoto1*, David W. Stock2 & William R. Jeffery1
Abstract: Hedgehog (Hh) proteins are responsible for critical signalling events during development1 but their evolutionary roles remain to be determined. Here we show that hh gene expression at the embryonic midline controls eye degeneration in blind cavefish. We use the teleost Astyanax mexicanus, a single species with an eyed surface-dwelling form (surface fish) and many blind cave forms (cavefish)2, to study the evolution of eye degeneration. Small eye primordia are formed during cavefish embryogenesis, which later arrest in development, degenerate and sink into the orbits. Eye degeneration is caused by apoptosis of the embryonic lens, and transplanting a surface fish embryonic lens into a cavefish optic cup can restore a complete eye3–5. Here we show that sonic hedgehog (shh) and tiggywinkle hedgehog (twhh) gene expression is expanded along the anterior embryonic midline in several different cavefish populations. The expansion of hh signalling results in hyperactivation of downstream genes, lens apoptosis and arrested eye growth and development. These features can be mimicked in surface fish by twhh and/or shh overexpression, supporting the role of hh signalling in the evolution of cavefish eye regression.
NATURE | VOL 431 | 14 OCTOBER 2004 | page 844
—————————-
Reduced opsin gene expression in a cave-dwelling fish
Michael Tobler1,2,*, Seth W. Coleman1,3,Brian D. Perkins1 and Gil G. Rosenthal1,4
Abstract:Regressive evolution of structures associated with vision in cave-dwelling organisms is the focus of intense research. Most work has focused on differences between extreme visual phenotypes: sighted, surface animals and their completely blind, cave-dwelling counterparts. We suggest that troglodytic systems, comprising multiple populations that vary along a gradient of visual function, may prove critical in understanding the mechanisms underlying initial regression in visual pathways. Gene expression assays of natural and laboratory-reared populations of the Atlantic molly (Poecilia mexicana) revealed reduced opsin expression in cave-dwelling populations compared with surface-dwelling conspecifics. Our results suggest that the reduction in opsin expression in cave-dwelling populations is not phenotypically plastic but reflects a hardwired system not rescued by exposure to light during retinal ontogeny. Changes in opsin gene expression may consequently represent a first evolutionary step in the regression of eyes in cave organisms.
Biol. Lett. (2010) v6, p98–101
doi:10.1098/rsbl.2009.0549
—————————-
OK, there’s a reading list for you. They’re not easy reads, and I’m not confident in my “squishy sciences” to help you interpret them. But you should get something from them, if only a longer reading list.
I have these as local PDFs. In the normal spirit of “fair use”, I can mail you copies if desired, but not through this blog.
Jerry, I helped write that paragraph. I don’t think we made a serious mistake mistake or an error of logic.
In that first sentence you quoted, we contrasted our data and patterns to two possible speciation processes: drift in allopatry; and selection in sympatry. We didn’t say those are the only two alternatives, and we didn’t say that allopatric speciation only happens by drift.
Of the four possible combinations of allopatry/sympatry and drift/selection we put those two combinations together in the same sentence because both were plausible for Cryptasterina before we did the study, and both were ruled out by the data, so we rejected them in the same sentence.
I agree with you (probably so would my coauthors) that this new species probably arose in the way you suggested as a colonist invading an island and adapting to a new environment. In fact, the new species Cryptasterina hystera does live on islands. That’s why we wrote in the next sentence of the same paragraph:
“Instead, the geographically localized evolution of [the derived life history in the new species was probably] an adaptive response to some environmental variable.”
So we meant to agree with you, but I guess we didn’t make our agreement clear enough. Maybe instead of “geographically localized evolution” we should have recycled the phrase “evolution in allopatry”. Maybe that would have avoided the appearance of a bloggable error?
I have to admit to at least one embarrassing error: we misspelled the genus name in the first sentence of that paragraph (Crypasterina, jeez…).
Mike
lesson learned: Read your proofs!
I know, but read ’em again!
Get someone knowlegable, but not connected, to read your proofs. If you’re too close to a piece of work, you can easily simm the obvious.
+
Michael,
Fair enough, but my point was that you characterized “classic allopatric speciation” as “the slow, gradual loss of shared alleles (and of reproductive compatibility) via genetic drift in allopatry”. Now surely you know that is not classic allopatric speciation, or at least any form that I recognize. It can be rapid if selection is strong, and “classic” allopatric speciation often (nay, nearly always) involves divergence by natural selection. Can you admit that your characterization of classic allopatric speciation was just wrong? I am not trying to hector you here, but a whole generation of young evolutionists are being brought up thinking that this, indeed, is what allopatric speciation is.
This is just a quibble of course (though one important to me); the rest of the paper is excellent–and surprising.
cheers,
jac
Hi, Jerry.
Yes, I’ll own that one: we were wrong to say “classic”, should have said “one form of”. Thanks again for posting about our paper, there’s more to come.
Mike
I just wanted to support what Mike was saying here. I think part of the problem, as well, is that this is largely a group of population geneticsists and phylogeographers writing about speciation. Typically, we only work with neutral loci, so, I think that, in our heads, we read that sentence as, that allopatric speciation is “the slow gradual loss of shared alleles in neutral loci (and of reproductive compatibility) via genetic drift in allopatry.”
I think that makes the sentence a little less egregious. However, I think we all see how that sentence is unclear, and how it could be interpreted as an incorrect characterization of “classic” allopatric speciation. Like Mike said, we really do agree with you.
Thank you for posting about our work!
Jon
But what does our most distinguished super-evolutionist Duane Gish maintain about all of this? After all,he wants us to remember how fast subspeciation worked making for races after the Tower of Babel! In just hundred of years!
Why, we need to honor him before he dies! Would an effigy do?
Note that Augustine and Aquinas revel in pyre-work,Luther in Judeophobia and peasant-loving and Calvin in loving Bruno so much that he had him murdered!
What is the context for bring my enemies before me and slay them that Yeshua utters in a parable-he that cult leader that wanted his sheep to commit logicide-faith,love him more than others, coming with a sword, not to bring peace and enjoying the prospect of others roasting when they don’t even hate or love him! Yes, that false dilemma can get you roasted!
Love is murdering others so that their apostasy won’t get others to go to Hell!
Why, who is that says that their mothers should have aborted the vermin! Yeshua also?
We gnus to to the Christ-addicts’ jugulars and with this to the theists’ jugulars we owe putative God nothing and have no obligation to worship that narcissist and megalomaniac! That square circle would have had to face the one-way street that Fr. Meslier’s the problem of Heaven poses!
How do they get that far inland?
😉
I did see and cavail at that until I realised that this is an abstract of a larger map, and the rectangular areas are (probably) expanded “off-[our]-screen”, where I guess the marine distribution of the starfish is obvious.
My first thought on “how would I present this?” was to think of putting bars along the appropriate parts of the coast. Then I interpreted the thinner red/ blue lines … and bit my tongue. So, you’re not the only one to at least “double-take” on that.
I remember a paper that was in nature a couple of years ago about speciation (I believe it was Phylogenies reveal new interpretation of speciation and the Red Queen by Vendetti et al.) where they looked at patterns of speciation. I bring this up because not long after this paper was published, I came across a creationist claiming that this was another nail in Darwin’s coffin – that there was yet another thing that natural selection was said to do (cause species to split) which turned out not to be the case. Somehow they made the leap from “stochastic events play a role” to “doesn’t involve natural selection” and “therefore, evolution is failed science”.
Any thoughts on this? Design and Construction of “Synthetic Species” http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0039054
How many generations did this speciation take? If as per wikipedia starfish mature in 5 years then 6000 years is approx 1200 generations. Sounds plenty to me, but I don’t know how many genes are involved in this speciation change.
http://en.wikipedia.org/wiki/Mangrove_rivulus
Kryptolebias marmoratus is a usually self-fertilizing hermaphrodite. It is in the family Rivulidae, the family of New World aplocheiloid killifishes. It is a really interesting animal, with a wide distribution.
Apologies if this is stupid question – it’s been a long week and my brain is feeling fuzzy. Can you just clarify exactly what you mean by:
“Just because speciation occurs among geographically isolated populations, that does not mean that the evolutionary force producing those new species was genetic drift rather than natural selection.”
My understanding was that in truly isolated (i.e. zero gene flow) populations, speciation is occurring neutrally with respect to generating reproductive isolation. Obviously, reproductive isolation could be caused by changes in various traits that themselves are under natural selection but – and this is the bit I want to clarify – it is not selection for reproductive isolation. (If they are truly isolated, it cannot be.) Would you agree with this?
(In other words, the widespread repetition of this idea might be lazy and erroneous conflation of “genetic drift” with “neutral change” rather than explicitly meaning that natural selection did not feature at all.
A population can be evolving adaptively with respect to one trait and still be changing neutrally with respect to another. This could be pleiotropy rather than random genetic drift but I think the principle still stands – the speciation is a side-effect of the changes that have occurred (be they due to selection or drift), not the driver of those changes.)
Please school me if I am wrong! (Hopefully, I won’t re-read this in the morning and face-palm.)
PS. Apologies for all the bold. Tired eyes (and no preview option) = missed tag closure!
Yes, if two sister populations are allopatric and diverging, development of isolating mechanisms is a a matter of happenstance. That is one of the reasons it is difficult, if not impossible, to recognize allopatric speciation in process in the field. What will happen should the two populations become syntopic? Will they function as separate species or will they reintegrate into a single population? The biological species definition is least helpful in situations where populations are allopatric.
I believe this is the Argument from Monty Python. – – – – –
All things dull and ugly,
All creatures short and squat,
All things rude and nasty,
The Lord God made the lot.
Each little snake that poisons,
Each little wasp that stings,
He made their brutish venom.
He made their horrid wings.
All things sick and cancerous,
All evil great and small,
All things foul and dangerous,
The Lord God made them all.
Each nasty little hornet,
Each beastly little squid–
Who made the spikey urchin?
Who made the sharks? He did!
All things scabbed and ulcerous,
All pox both great and small,
Putrid, foul and gangrenous,
The Lord God made them all.
Amen.
http://www.lyricsdepot.com/monty-python/all-things-dull-and-ugly.html
Oops. Sorry. Posted in the wrong discussion. (I had two windows open at the same time, apparently.)
Has anyone been able to get free access to the paper? I’m interested in knowing how the ‘zero’ genetic variation was measured/determined in C Hystera? I’ve been reading a little about ISSR…