Okay, we’re going to take a break and consider the cowboy boot.  If you don’t like ’em, don’t read on.  I happen to collect them (I won’t divulge the number), because I like the way they look and consider them an indigenous American art form: one of the few items of clothing—besides jeans—that’s uniquely American.  A well-made boot is a thing of beauty, a joy to wear, and the product of a lot of labor.  While off-the-shelf boots are churned out by the thousands by firms like Justin, Lucchese, and Tony Lama, the craft survives in a resilient band of custom bootmakers (many in Texas), who either make the whole boot themselves or supervise a small workshop.  (There aren’t any online videos of the custom process, which is said to involve 370-odd steps, but you can see the making of a high quality factory boot here.)

Custom boots are not cheap: a basic calf or kangaroo boot with simple stitching from a custom maker begins at about $1200.  Fancy stitching, inlay, or tooling can take prices to the stratosphere.  Tres Outlaws, an outfit in El Paso, has made some boots selling for upwards of $25,000!

When I was in Texas I sought out a few bootmakers and boot collectors, for fellow fanatics are thin on the ground in the chilly Midwest.

And, in Austin, I found Lee Miller, Vermont expatriate and bootmaker extraordinaire.  Lee and his wife Carrlyn run a small shop in Austin, Texas Traditions, where they turn out some of the country’s prettiest boots.  Here’s Lee with his latest project:

Lee isn’t taking new customers, because he has a huge backlog.  Even if you were to order a pair today, you wouldn’t get it for three and a half years!

Here are some of Lee’s boots.  The inlay and stitching are lovely, and take a ton of skill and work, but what makes Lee’s boots stand out is their purity of line.  Even without fancy decoration on the shafts (the tube-like tops; the foot part is called the “vamp”), they’re eye-catchingly graceful.  Have a look at the boot that Lee is holding above.

Lee took over the shop from the famous Charlie Dunn, who worked as a bootmaker in Austin’s Capitol Saddlery for many years and then, after retirement, started his own shop in South Austin.  Lee moved there to apprentice with Charlie, and took over the business when Charlie passed away.  (Lee makes the boots, Carrlyn does the business side and helps design).  Here’s a lovely “pinched rose” design—the yellow rose of Texas, of course—made famous by Dunn and produced by Miller (note the initials, which most custom makers will add to your boot for a small fee):

Here’s Charlie Dunn in his later years, an elfin man with a hot temper and a fierce passion for making good boots:

Charlie was the subject of a song by Jerry Jeff Walker, probably the only bootmaker to be so immortalized.  Here’s a pair that he made for himself, incorporating a unique mirror-signature design.  Charlie had a bunion on his right foot, and you can see where it’s worn through the ostrich vamp:

Lee has saved all of Charlie’s designs.  Here’s Charlie’s famous “marijuana pattern”, used on the shafts when the counterculture took up cowboy boots in the 60s.  Apparently Charlie had no idea what marijuana looked like, and so a customer brought him a sample.

Here are the ingredients of a good cowboy boot: leather, a steel shank to support the arch, lemonwood pegs to peg the sole, and thread to stitch the tops and soles.  That’s it.  No glue, no paper, no plastic.

Here’s the “hide room,” where they keep all the different leathers on hand to make the latest batch of orders.  Some of the hides commonly used in boots are calf, kangaroo, ostrich, lizard, alligator, crocodile, shark, water buffalo, and snakeskin.  I even have a pair of camel boots (camel is a very rare hide because they don’t kill the beasts to make leather: hides are taken from camels who die of old age).

The making of a custom boot begins with a complicated process of measuring your foot.  This can take up to an hour, and can involve all kinds of tape measures, calipers, and even inkpads (Lee has people step on one and then make a foot impression).  From those measurements a wood or (more commonly) fiberglass model of the foot—the “last” is made.  Around this is built the bottom of the boot. Here are some of Lee’s lasts with the names of celebrity customers:

Here’s a boot that Lee made for Lauren Bacall (note the “LB” initials inside the pull).  They didn’t fit at first so they were replaced:

I also visited John Tongate, retired librarian at the University of Texas and famous boot collector.  John’s specialty is tracking down vintage boot designs and having them reproduced by custom bootmakers.  Here’s John with a small part of his collection:

Boots with elaborate inlay.  Left to right:  Model Boot Co./Morado Bros, Houston, date unknown; James Morado, Houston, 1995; Bo Riddle, Nashville, 1994; James Morado, Houston, 1994.

Tooled boots (very expensive!), and a lovely purple pair with vamp stitching.  Starting with single boot on extreme left: Jack Reed, Burnet, TX, 1998; Jack Reed (Bob Dellis, tooler), Burnet, TX 1993; James Morado, Houson, 1999.

If you want to see more, there are some good books, including The Cowboy Boot Book and Art of the Boot, both by Tyler Beard and Jim Arndt.

I’m just posting this because these people, members of a Christian militia group in Michigan called Hutaree, constitute the scariest-looking group I’ve ever seen.  These are their mug shots, as they were just arrested for conspiring to murder law-enforcement officers.

Fig 1.  The militia.  Check out their website. Discussion groups include “Chaplain’s Corner” and “Evil Jew Forum”

As The New York Times reports:

The Web site, which describes the group as “preparing for the end times,” featured video clips of people running through woods in camouflage gear and firing assault rifles, along with links to gun stores and far-right media. It also features an elaborate system of military ranks for its members. The site says it coined the term Hutaree, intended to mean Christian warrior.

“Jesus wanted us to be ready to defend ourselves using the sword and stay alive using equipment,” the Web site says, adding, “The Hutaree will one day see its enemy and meet him on the battlefield if so God wills it.”

Here are the ranks in their militia:

RADOK [RD]

BORAMANDER [BM]

ZULIF [ZL]

ARKON [AK]

GOLD RIFLEMAN [GR]

SILVER RIFLEMAN [SR]

BRONZE RIFLEMAN [BR]

LUKORE [LK]

MASTER GUNNER [MG]

SENIOR GUNNER [SG]

GUNNER [GN]

PARABLES OF THE SOLDIER Ranking officers and commanders; serve your men for you lead them; humble before your team. Cause you may be a leader of flesh but in heaven leaders are of spirit.

LOW RANKING SOLDIERS AND GRUNTS Respect the officer above you and obey your commander with dignity. Each man holds his place in flesh and spirit, heaven and earth.

I won’t blame this one on religion; to do that, you’d have to assume that if there were no faith, these people would be law-abiding citizens.  I doubt it.

Over the next few days I’ll post a few “holiday snaps” from my week-long trip to Texas: beasts, boots, and BBQ.  Today we have a very rare animal I was privileged to see in central Texas, the Texas blind salamander (Eurycea rathbuni).  It’s a cave-dwelling animal, of course, and so its eyes are either absent or vestigial and, like many cave beasts, it’s lost its pigment.  Highly endangered, it’s endemic to the underground caves found in the Edwards Aquifer around San Marcos, which is itself about 40 miles south of Austin.   It’s also completely aquatic, and so breathes through external gills, which it can regenerate if damaged (a Federal wildlife guy told me that he once had a salamander whose gills were completely ablated, and it managed to breathe through its skin until the gills grew back).

They can grow up to about six inches, and eat invertebrates.  You can see a nice film of them here (note that they give the species name of Typhlomolge rathbuni; the genus name has been updated).

Here’s a picture of one I took at the San Marcos National Fish Hatchery and Technology Center, where I was kindly given a tour.  You can see the vestigial eyes, nearly completely covered with skin. Only the left eye is visible: variable and asymmetric expression of vestigial traits is common.  The eyes are much more visible in young salamanders, and then gradually disappear as the skin grows over them.

I need hardly point out that the presence of nonfunctional, vestigial eyes in an animal descended from ancestors that had functioning eyes is pretty good evidence for evolution (see chapter 3 of Why Evolution is True).

Here’s a close-up of the head and gills.  This individual has no visible eyes (variable expression among individuals!).   I was told that the large swellings at the base of the head contain neurons for processing olfactory information: this beast lives by smelling rather than seeing. This guy also has a bit more pigment than the one above. (I say “guy,” but I don’t know the sex.  The only way to sex these things is to hold them up against a strong light and look for either eggs or sperm ducts.)

Phylogenies show that, like all cave animals, the blind salamander descended from a sighted species that lived aboveground.  Why do cave animals lose their eyes? There are several explanations.  One is that, since they’re not useful in the dark, mutations that make them degenerate are not selected against.  The other two explanations involve positive selection.  Eyes are easily damaged and infected, and if you don’t need them, individuals with mutations reducing the eyes are less likely to risk injury/infection.

Alternatively, eyes take metabolic energy and bodily substance to build; if you don’t need them, you may have higher fitness if you divert that energy away from eyes and toward other structures or functions that enhance reproduction.  And of course all three factors could operate together.   I don’t think we know in any case the precise evolutionary forces that led loss of eyes (or pigmentation) in a cave species. The hypotheses are reasonable, though I don’t know of any experimental test (one would be to look at the genes for eye or pigment loss and see if the DNA sequence shows a signature of positive selection, though that test can be misleading).

Here are the eggs photographed in water (and slightly out of focus). You can see the tiny newts developing.

And finally, my friend Jim Bull, a UT Austin professor, built a birdhouse in his backyard. It was taken over by a screech owl, who, at twilight, would poke his head out of the hole for an hour or so. Really cute!

This is probably an eastern screech owl (Megascops asio), but I can’t tell from the photo.  Both eastern and western screech owls are sympatric in some parts of Texas.  This one, like most owls, hunts at night, and probably poked his head out each evening to scope out the surroundings.

It’s always a treat to read Greta Christina when she takes up atheism. This week she posts “An open letter to concerned believers”, addressing, in an oh-so-polite-and-unshrill way, those of the faithful who try to tell atheists how to be more politically effective. Although it’s aimed at believers, it applies equally well to concerned faitheists.

. . . It is difficult to avoid the observation that, whenever believers give advice to atheists on how to run our movement, it is always in the direction of telling us to be more quiet, to tone it down, to be less confrontational and less visible. I have yet to see a believer advise the atheist movement to speak up more loudly and more passionately; to make our arguments more compelling and more unanswerable; to get in people’s faces more about delicate and thorny issues that they don’t want to think about; to not be afraid of offending people if we think we’re right. I have received a great deal of advice from believers on how atheists should run our movement… and it is always, always, always in the direction of politely suggesting that we shut up.

You’ll have to forgive me if I question the motivation behind this advice, and take it with a grain of salt.

You’ll have to forgive me if I think your suggestions on making our movement more effective would, in fact, have the exact opposite effect. What’s more, you’ll have to forgive me for suspecting that this, however unconsciously, is the true intention behind your very kind and no doubt sincerely- meant advice.

And you’ll have to forgive me if I am less than enthusiastic about taking advice on how to run the atheist movement from the very people our movement is trying to change.

Your concern is duly noted. Thank you for sharing.

Oxford neurobiologist Colin Blakemore, a distinguished researcher and author of several popular-science books, gave the Ferrier Prize Lecture at the Royal Society on March 15 and was just interviewed by The Guardian. His topic: the evolution of the human brain. Although the lecture precis implies that Blakemore talked about several topics, the Guardian singled out one: Blakemore’s apparent assertion that a rapid increase in human brain size a few hundred thousand years ago was due to a “macromutation”—a single change in the DNA of large effect:

In a recent lecture, the Oxford neurobiologist argued that a mutation in the brain of a single human being 200,000 years ago turned intellectually able apemen into a super-intelligent species that would conquer the world. In short, Homo sapiens is a genetic accident.

Blakemore asks:

The question is: why is [our brain] so big compared to the brains of our predecessors, such as Homo erectus? Until 200,000 years ago, there had been a gradual increase in brain size among hominins, starting three million years ago. Then, abruptly, there was a remarkable increase of about 30% or so.

Blakemore suggests that this big mutation might have occurred in “mitochondrial Eve,” the woman from whom, he says, we all descend:

Genetic studies suggest every living human can be traced back to a single woman called “Mitochondrial Eve” who lived about 200,000 years ago. My suggestion is that the sudden expansion of the brain 200,000 years ago was a dramatic spontaneous mutation in the brain of Mitochondrial Eve or a relative which then spread through the species. A change in a single gene would have been enough.

Finally, Blakemore suggests that the spread of this mutation through our ancestors, and its fixation, was not due to natural selection!:

How have scientists explained this jump in brain size?

Many have argued that if there was a dramatic increase in brain size, there must have been a fantastic advantage that came with it: improvements in tool construction, more complex language and other cultural changes. In other words, they say simple natural selection explains what happened.

So what is your take on this view?

I think they’re fooling themselves. There was very little change in human behaviour at this time, as far as we can see from the fossil record – certainly not one that is explained by a sudden jump in the size of the human brain. These hand-waving arguments about tiny changes in culture explaining the emergence of such a huge change in brain structure just doesn’t hold water. It’s like arguing that a reptile suddenly developed fully formed wings and then sat around for 200,000 years before suddenly saying: Oh my God, I’ve discovered I can fly. It’s ridiculous. . .

What effect did this have?

Very little at first. The environment of early humans was so clement and rich in resources that this greedy new brain, which would have absorbed even more of the body’s energy, could be sustained without danger. Later, when times got hard, during droughts or climate changes, it helped us deal with these crises, which could otherwise have killed us off, by dreaming up novel ideas to problems.

Okay, here are just some of the problems with Blakemore’s thesis:

1.  First of all—and this has been endlessly repeated by geneticists—it’s misleading to say that “every living human can be traced back to a single woman called ‘Mitochondrial Eve’ who lived about 200,000 years ago.”  What we know is that all the DNA in one of our cell organelles, the mitochondrion, descends from a female that lived then. But the rest of our DNA, the vast majority of it, descends from other ancestors, so that each bit of our genome comes from (to use the technical jargon “coalesces back to”) a different ancestral individual.  Our genome is a mosaic of bits of DNA from different people.

Mitochondrial “Eve” was the ancestor of only our mitochondrial DNA. It’s extremely improbable (I’d say the chances are zero) of any other gene not in the mitochondrial DNA descending from this same woman. Blakemore does allow that the big-brain mutation could have occurred in a “relative” of Eve, but that’s not necessary either, except in the sense that all humans living at that time were relatives because they shared a common ancestor.

2.  There’s not the slightest bit of evidence that this large increase in brain size resulted from a single mutation in the DNA.  Yes, the increase in brain size may have been geologically sudden, but we can get things that would look instantaneous in the fossil record through a sudden bout of natural selection that fixes several or many genes over a relatively short period, say thousands of years.  A punctuated pattern of evolution does not necessarily point to the occurrence of single “macromutations.” Steve Gould sometimes made this mistake when talking about punctuated equilibrium.

Blakemore has every right to theorize about macromutations, but in a public lecture (or interview) it would be seemly if he mentioned the problems with his “macromutation” idea.

One is that a big change in brain size without a corresponding increase in skull size probably would have been maladaptive, if not fatal. It’s much more likely that brain and skull co-evolved gradually due to the accumulation of several to many mutations, which is normally how the evolution of complex traits occurs in nature. Too, the brain is plastic, but is it plastic enough to suddenly accommodate a 30% increase in volume without evolutionary changes in wiring?   Finally, the usual finding when you look at the genetic basis of “complex” adaptations in the wild (and I’m talking about things other than color, or the disappearance of traits like stickleback spines), it’s almost always due to more than one gene.

3.  Finally, perhaps the biggest problem with Blakemore’s suggestion is this: if the mutation wasn’t favored by selection, how did it get fixed? He says that the big-brain mutation was initially “neutral”—that in fact it normally would have been disfavored because a bigger brain eats up too much metabolic energy, but was tolerated because there were lots of foods and resources around.  Then, when the environment became leaner and meaner, that big mutation would show its adaptive effects. To repeat from above:

The environment of early humans was so clement and rich in resources that this greedy new brain, which would have absorbed even more of the body’s energy, could be sustained without danger. Later, when times got hard, during droughts or climate changes, it helped us deal with these crises, which could otherwise have killed us off, by dreaming up novel ideas to problems.

This scenario invokes a big brain as a preadaptation: a trait that just happened to be hanging around but then became useful when the environment changed.  Note that Blakemore is claiming more than just that the macromutation stayed around at low frequencies because it was tolerated during fat times and then later became fixed through selection when times got tough.  Rather, he’s asserting that the mutation swept to fixation without natural selection. Again:

In other words, they say simple natural selection explains what happened.

So what is your take on this view?

I think they’re fooling themselves. There was very little change in human behaviour at this time, as far as we can see from the fossil record – certainly not one that is explained by a sudden jump in the size of the human brain.

I find this scenario pretty implausible.  Implausible not just because you need other changes in the body (like a bigger cranial capacity and perhaps some new wiring) to accommodate a brain that is suddenly 30% larger, but because Blakemore gives no explanation for how a big mutation that has no effect on fitness (or even a slightly negative effect) swept through the population in the first place (i.e. gets “fixed” as we geneticists say). A mutation can be “tolerated” in a species, but that doesn’t explain why it spreads through the population until everybody has it.  It seems much more likely that changes in brain size, since they were sustained over millions of years of evolution, resulted from natural selection.

Granted, we don’t know what kind of selection. There are as many theories for the evolution of bigger human brains as there are theorists.  Suggestions have included the advantages of big brains for hunting, for living in social groups, for attracting females, for trying to suss out the intentions of your fellows, for using tools, and so on.  This is one of the questions whose answer we may never know.  All scientists must live with the idea that some answers are simply beyond our ken. (That’s why it’s easier for us to not invoke gods to explain the unknown.)

But I think that Blakemore’s own suggestion is deficient in several ways.  The Guardian can’t point them out in an interview, but that’s what websites like this one are for.

I have to say that although lots of people concoct evolutionary stories about humans, many of those folks could benefit from a little acquaintance with population and evolutionary genetics.

My hot-dog student, Daniel Matute, has published a new paper in PLoS Biology, and although I say the paper is from “our lab,” it’s entirely Daniel’s work.

The paper is about a phenomenon whose importance in speciation is contested: reinforcement. Reinforcement describes a form of natural selection that can actually increase the reproductive barriers between a pair of species that descend from a common ancestor.

As I’ve mentioned on this site, most evolutionists define “species” as “groups of populations separated from other such groups by reproductive isolating barriers (RIBS, an appropriate Chicago acronym).” Those barriers are all the genetically-based traits of organisms that prevent them from exchanging genes where they co-occur in nature.  RIBS include things like mate discrimination, a preference for living in different niches (so that members of different species don’t encounter each other), different mating seasons, or the sterility or lethality of any hybrids that are formed.

Most of us think that these barriers are simply the byproduct of evolutionary divergence that occurs when geographically isolated populations of a single species begin to evolve in different directions. I give examples of how this works in WEIT, but the discussion is too long to repeat in this short post.

In this view of life, species are simply evolutionary accidents. That is, nature doesn’t somehow favor the production of species, nor does natural selection favor the erection of reproductive barriers between groups per se.  Rather, physically isolated populations evolve in different directions due to natural selection or random genetic drift, and when that divergence has proceeded to a certain extent, reproductive barriers appear simply as a byproduct. For example, if two species adapt to two different niches, their physiologies may diverge to the point that the combination of both species’ genes in a single hybrid makes it unfit or inviable.

But there is one form of selection that can favor the evolution of reproductive barriers, and that’s reinforcement.  Reinforcement begins with two physically isolated populations that have been apart long enough to evolve some barriers to gene flow, but barriers that are not quite complete—so that they can’t qualify as “full” species.  For example, two populations of flies might produce hybrids that are partially (but not completely) sterile, so if they meet there is still the possibility of some gene flow between them through the bridge of semi-fertile hybrids.

Now assume that these populations expand their ranges and, though previously isolated physically, now encounter each other. (This happens all the time in nature as geographic barriers like rivers, forest, and the like disappear or change their positions.)  Members of the two populations will encounter each other, and some of them will mate.  But if you mate with members of the “wrong” population, some of your offspring will be sterile or partially sterile.

There is thus an evolutionary disadvantage to mating with the wrong group, and an advantage to mating with the “right” one. Under these conditions, natural selection will favor individuals with genes that favor their mating with the right group, because those genes leave more copies than genes that don’t promote discrimination—”nondiscrimination” genes tend to wind up in sterile hybrids!

Thus, over time, a partially isolated species can become a fully isolated one through natural selection, and that’s how reinforcement works.  It’s a process that directly favors the erection of reproductive barriers, and can, we think, put the finishing touches on speciation.

The problem is that though this sounds nice, and can indeed work if you make mathematical models, it’s hard to demonstrate in nature.  To do so, you’d need to show that, in a pair of species that have some geographical overlap, the degree of mate discrimination, or of other reproductive barriers that prevent the formation of hybrids, is higher between populations in the area of overlap than it is between populations taken from areas where they don’t overlap (these tests are done in the laboratory).

There are a few promising examples of this (one was published in 1995 by my ex-student Mohamed Noor), but the frequency of reinforcement remains unclear. (When I was young, I was taught, for example, that it was always the final step in speciation. That of course can’t be true, because speciation can go to completion between groups that never contact each other in nature, for example species like the Galápagos tortoise that evolved after an ancient colonization of a remote island.)

Daniel noted that the species of Drosophila on the small African island of São Tomé, where we’ve worked for some years, have a distribution that looks promising for studying reinforcement.  One species, Drosophila yakuba (“yak”), lives not only on the island but also on the African mainland.  The other species, D. santomea (“san“) is endemic only to the island, and presumably evolved after the island was colonized by the ancestor of yak (we estimate this happened about 400,000 years ago).

The situation is propitious for studying reinforcement because, on the island, which is basically a volcanic mountain, the species have overlapping distributions: yak lives at sea level and up to about 1400 meters on the mountain, while san is found between 1100 and 1400 meters. There is thus an area of overlap between 1100 and 1400 meters, and in this area you can find a few hybrids (about 5% of the individuals).  These hybrids are at a disadvantage, evolutionarily, because half of them—all the males—are sterile.

Thus we have two species with overlapping ranges, some hybridization in the area of overlap, and the possibility of gene flow through the fertile female hybrids.  This is just the situation we need to look for reinforcement.  So, is the mating discrimination between yak and san stronger when they come from the area of overlap than from the areas where they don’t overlap? (Remember, we do these tests in the lab and so can examine any pair of strains.)

Surprisingly, the answer, which we got eight years ago (Coyne et al. 2002), was no: mating discrimination, though strong, was equally strong no matter where you took your samples from. There didn’t seem to be any reinforcement.  We don’t know why, but there are several explanations (perhaps, for example, there simply weren’t any mutations that sharpened mate discrimination.)

Daniel, however, went further, and found that there is indeed a form of reinforcement between these species, but not reinforcement of mate discrimination.  Rather, it’s reinforcement of what we call postmating, prezygotic isolation or gametic isolation: barriers to gene flow that act after mating but before fertilization. One example is females of one species not using the sperm of males from the “wrong” species if they are inseminated by them.

This is what Daniel found:

1.  Yak females from the area of overlap produce many fewer eggs (and progeny) when mated with san males than do yak females derived from outside the area of overlap.  Thus, the reproductive barriers between the species were higher from places where they encountered each other. The effect was very strong and highly statistically significant. (Daniel’s Figure 2 shows this clearly).  Daniel didn’t find this effect, however, when he looked at san females.

2.  But what is the evolutionary advantage of producing fewer eggs/offspring when you’re inseminated by a male of the “wrong species”? For that would have to be the selective pressure that impelled the evolution of the “fewer-egg” syndrome in yak females who encounter san males.

One possibility is that if you live in the area of overlap, and sometimes mate with the wrong species, you have an evolutionary advantage if you can “recognize” this (I’m speaking of course of physiological recognition), dump those foreign sperm that produce semisterile offspring, and thus get a chance to mate sooner with the right species. (Species in this group tend to mate multiple times over their life.)

Sure enough, Daniel showed that when yak females were mated in the lab to san males, those females from the area of overlap lost sperm much faster than did yak females from outside the area of overlap.  And he also showed that those females remated more quickly to their own males (yak) than did females who hadn’t used up their “wrong” store of sperm. In other words, there was an evolutionary advantage to dumping sperm when you’re inseminated by the wrong species, because by so doing you will, in the long run, produce more offspring with members of your own species. (We don’t know the mechanism by which females from the area of overlap get rid of the wrong sperm more quickly).

3.  So, we find a pattern suggesting reinforcement and show that this pattern comports with how selection should operate.  But can we mimic this whole process in the lab?  Surprisingly, Daniel did, and it took only a few generations.

Daniel simply forced strains of the two species (taken from areas where they do not encounter each other) to live together in glass bottles in the lab. There were seven different pairs of strains to serve as evolutionary replicates.  Each generation he removed the hybrids, mimicking complete sterility of the hybrids (of course, they’re not completely sterile in nature, but we wanted to avoid gene flow between the species, which makes it harder to tell them apart).

And, in only four generations (about two months), he observed that yak females had indeed evolved the “reinforcement” trait seen in the lab: when inseminated by san males, those females laid fewer eggs than did “control” yak females who were reared at the same density, but without the presence of the other species.  Moreover, the degree of mating discrimination also increased, something that we didn’t observe as a pattern in the wild.

CONCLUSION:  Well, the reason the study got published in PLoS Biology, I think, is because it’s not only a rare, pretty-well-documented case of reinforcement, but also because it’s the first case in which reinforcement in nature strengthened not mating discrimination, but a reproductive barrier acting after mating: gametic isolation.  Most people hadn’t realized that postmating barriers could be also strengthened by selection.  But they can be, and cases like this may be common.  The reason why they might have been missed is, of course, because detecting the presence of a gametic barrier is much harder than simply measuring increased mate discrimination.

The next step is to allow some gene flow between the captive species, and see if we can still observe the evolution of gametic (and sexual) reinforcement under more realistic conditions.  After all, in nature some fertile female hybrids are produced in the area of overlap, and presumably mate back to yak or san. That study is underway.  And we’d like to understand why the evolution of higher mating discrimination occurs so readily in the lab, but isn’t seen in nature.

And a h/t to Daniel here, a terrific student who promises to be a star.

_________

Matute D. R. (2010) Reinforcement of gametic isolation in Drosophila. PLoS Biol 8(3): e1000341. doi:10.1371/journal.pbio.1000341

Coyne J. A, Kim S. Y, Chang A. S, Lachaise D, Elwyn S (2002) Sexual isolation between two sibling species with overlapping ranges: Drosophila santomea and Drosophila yakuba. Evolution 56: 2424–2434. (Our earlier study failing to find increased sexual isolation between the species in the area of overlap).

Noor M. A (1995) Speciation driven by natural selection in Drosophila. Nature 375: 674–675. (One of the best examples of reinforcement in nature, done in my lab by Mohamed Noor fifteen years ago.)