9UNP0231SD_Mara_McDonald_WordPress

- Welcome, I'm Paul Brendle, you're coordinator for Frontiers of Life Sciences in this sixth session of our PLATO class for the fall semester. Today, we have Mara McDonald, continuing our geneticists coming to explain their research to us. Mara is the assistant administrator in the laboratory of genetics. She is administrator for the Evolution Initiative on campus. I was talking to her. There's probably 15 departments involved in the Evolution Initiative. She came to UW in 1992. 

Her visits to other campuses were to Gainesville for her BA, Berkeley for her master's, and UCLA for her PhD. So this afternoon, we will have Mara give us a genetics lesson which she entitles "Speciation of Baby Birds." 

(applause)

- Thank you. I might point out that my PhD was from the University of Florida, as much as I would have liked it from UCLA. So I got my BA at UCLA, and it was worth a goodly amount of work. Let me just, I've been asked to explain what the laboratory of genetics is. It's the most of two departments, genetics and medical genetics. So we are a laboratory, or a unit that is in the medical school as well as CALS. 

The Evolution Initiative was begun about three years ago by David Baum, Don Waller, and others. Because the UW-Madison had some of the most esteemed evolutionary biologists on campus, but no department, no center. So David and others have pulled together people interested in evolutionary biology. We do have an option, I think, for undergraduates to take an evolution certificate. We're trying to develop an option for graduate students. There is a Web site: www.evolution.wisc.edu. And we do have seminars on weekly basis, Thursday at noon, in the Genetics Biotech building in 1360. We also have an evolution reading group. We're reading "In Pursuit of the Gene," at this particular point. And there are other things going on. We will have Darwin Day, February 7. And this promises to be a really nice event. It's our fourth go of it, Darwin Day, on campus. It will be held in Microbial Sciences, starting at about 9:00. We have Sean Carroll speaking. 

And we're lining up Jim Crow as a panelist, we're hoping. Jim is our geneticist who has been in our department since 1948. He will have turned 93 at the time of Darwin Day, about a month before. The other thing that I wanted to push is that we have an all volunteer operation. Pat Becker here knows all about it, because she's sat with me in the rain. We have a Biocore Prairie Bird Banding Observatory just above Picnic Point. And we're looking for people who are interested in birds. 

We go out Saturday mornings in good weather. We put up nets. We band the birds. We take information. We release them. This is part of a national effort, an international effort, actually. There are over a million birds banded each year, 60,000 are re-captured. And all the data goes to the USGS bird banding lab. So if you have any re-captures, they can tell you where it was initially banded. So it's a wonderful resource. It's been going on for years and years. 

It gives us data on the biology of the birds, their ecology, their migration routes, and conservation. The research I'm about to talk about to you today is old and it's new. It a mixture. It's my dissertation research. I was in Haiti from 1983 to 1985. I preceded the exit of Duvalier by about four months. And I was very proud of that, that I managed to get out before they did. And it has been written up in 1990 and 1994. Sorry, I lost my train of thought. 

Anyway, the title of the talk is Speciation of Baby Birds, Studies of Hispaniolan Un-tanagers. Hispaniola is the island of the Dominican Republic and Haiti. Haiti is about a third of the island. I just worked in Haiti. And I'll tell you about the two bird species I worked with there. And I thought that the first thing that I would do is explain the un-tanager's bit of the talk. 

It turns out that when bird collectors first started collecting species in the new world, and sent them back for identification, the genus that I was working with were considered part of the tropical radiation of tanagers. They're called palm-tanagers. The genus is Phaenicophilus, meaning dark head, looking dark. They were recognized as a tanager for hundreds of years. 

In the last decade, with newer and cheaper molecular technologies used to resolve avian relationships, their relationship has become obscured. This is part of the Early Bird project coming out of the Field Museum in Chicago, and other laboratories across the US, where they are looking at sequence data instead of using other techniques to resolve some of the relationships in species. For example, Darwin's Finches are not finches anymore. 

They're likely descended from Caribbean tanagers, much to the consternation of the folks who were working on it for 35 years. And the Hispaniola palm-tanagers are not. Their roots go so far back that they're relationships to other bird families haven't been resolved. So part of my dissertation has just been wiped out in the last year or so. 

(laughter)

 So I've taken care of the un-tanagers part of the title. And I will keep referring to them as palm-tanagers or whatevers. Now, how do the baby birds relate to speciation and evolution? That may seem a little queer. Biologists have long recognized that bird radiation has been recent, and happens rather quickly. It's one of the most speciose groups of vertebrates other than bony fishes. And it happened very quickly, or relatively quickly, geologically speaking. 

If you use the techniques that I used in the genetic analysis to look at genetic distances between species within avian groups, the average genetic distance was an order of magnitude lower than for other bird groups. And one concern was well, maybe it's because we like birds so much and study them so much that we're not really recognizing species, we're recognizing subspecies. 

But people have looked at that and have determined that the traits, the morphological traits that we use to recognize species of birds are equivalent to those for other vertebrate groups. So we are recognizing group species based on those morphological traits. They're not subspecies.

- Can you elaborate on your use of the word radiation?

- Okay, it's when you have a group of anything that just speciates all over the place. So if you look at the tanager radiation, it starts off in South America, and you just have multiple species coming up. And we see the very tip of that radiation. It's like a growing tree. Does that help?

- Yes.

- Oh, good. There's a confusion about the genetic distances among birds, in terms of relative to other vertebrates. Their order of magnitude, lower than expected, based on traditional concepts of what genes are. And I'll get into that, I'll explain that.

- What do you mean by distance?

- If you look at the measure that you're using, and calculate how far the, this isn't really DNA that we're using here. But you're inferring the differences in DNA sequence. So the farther two organisms are in their relationships, the longer they've been apart, the more you expect those DNA sequences to be different. And there's a way to measure that. With the genetic analysis I used here, it was an inference, because I wasn't actually looking at sequence data. They are using sequence data now. 

But I wasn't using it at that time. Does that help?

- Yes, the inferred DNA group.

- It's just an inference about how long they've been apart. So the longer they've been apart, the greater the likelihood that you'll have changes in the DNA sequence. One of the reasons that biologists were perplexed in terms of explaining how birds, which had radiated tremendously, had many more species than you see in mammals and some other vertebrates, how to explain that if you don't have very much genetic distance between the species. 

One of the reasons that that was confusing was that Darwin originally proposed that evolution occurred gradually, over millions of years. He did recognize gaps in the fossil record. But he attributed them to poor sampling of the fossil record, not to rapid speciation events. Stephen Gould, the lighthearted biologist suggested that Darwin wanted to contrast his theory of evolution with special creation, which was a very rapid, single event. 

In 1982, Eldridge and Gould proposed a theory called punctuated equilibrium that tried explaining the gaps in the fossil records, not as a result of poor sampling, because they had come almost a hundred years after Darwin, and there had been lots more sampling of the fossil record. And there were still these areas where there seemed to be gaps in the evolution of species groups. And they suggested that the gaps were due to very rapid speciation events. 

So rapid that there wasn't time to record them in the rocks. And their punctuated equilibrium model suggested that species undergo long periods of stasis, where very little evolution occurs. And then when they're stressed, due to climate changes, for example, they undergo very rapid evolutionary changes or they go extinct. And those periods of rapid evolutionary change occur over thousands of years. So geologically, it's very rapid. But it's not recording in the fossil record. 

Now, what I'd like to do is to kind of explain how we can look at genetic distances in bird groups and explain why they're an order of magnitude lower. And it comes to seeing how genes function. There are at least two kinds of genes that we'll be talking about today, referring to. One is the very common one, the protein coding or structural genes that make protein that run the cellular metabolism. For example, when you drink milk, milk contains lactose, which is a sugar. 

And it's broken down for you to digest. It's broken down by an enzyme called lactase. That enzyme is produced by the lactase producing, or protein coding gene lactase. There are other genes that are called regulatory genes that will turn off or on the coding genes. It's not efficient to keep the gene coding for lactase on all the time. Metabolically and energetically, it's inefficient. You're just wasting good materials for making proteins. 

So lactase is actually induced by the presence of lactose. And it's turned off when there isn't enough lactose in the system. So you have these regulatory genes that control when certain coding genes are turned on and off. They're particularly important in development. How many of you are familiar with Sean Carroll's work? 

(laughs)

 He's perhaps our, one of the better noted development in evolution biologists at UW. And he is working with PBS on a documentary for Darwin's bicentennial, which comes up in 2009. But in development, development is a very sensitive time for organisms. And some genes in development are turned on at different points in development. And they code for different proteins that will code for some sort of trait in the organism, or will induce another gene to turn on or off. 

One example of this is some genes are expressed at different ages. One example is hemoglobin. In the uterine environment, fetuses are exposed to very low concentrations of oxygen. So they have a special fetal hemoglobin that will latch on to oxygen. Once the baby is born, there's no need for that particular kind of hemoglobin. And gradually, over the next several months, the hemoglobin is changed to the adult form. Now, what occurs is that there are two loci, or two genes. 

One that codes for the fetal hemoglobin and one that codes for the adult. The fetal hemoglobin gene is turned on early in development and then turned off. And then the adult hemoglobin takes over and is expressed for the rest of the individual's life. Is that clear?

- What do you propose initiates that turning off and turning on of those two?

- Well, you have various signals coming in. Once the baby is born, it's exposed to a different oxygen tension that probably affects the turning on or off of the adult hemoglobin. I don't know the details of that, actually. So I'm not going to give you any more details. Now what Gould did was that he proposed that rapid evolutionary changes that we saw as part of the fossil record could be achieved by regulatory genes, which turn on genes that code for development. 

Small changes early in development can have major effect on the adult form of phenotype. You change something early in development, you can have a really major effect. You change something later in development, and it may be a miniscule effect. So regulatory genes are something that hadn't been considered until about the mid-'70s, in Berkeley, actually. It was out of Allan Wilson's lab. 

How many of you know about the relationship of chimps, the DNA relationship of chimps and humans, in terms of the percentage of genes that they share? This comes out of the Wilson lab. They share 95% to 98% of the same genes. But the reason we appear to be different is not due to the fact that we share the same structural genes, which is what was being measured. But that we have different regulatory genes. 

So we may share the coding genes, but those coding genes may be turned on or off at different times. So you get different forms as a result. Does that make sense? Now, Gould, in the late '70s, developed a more specific model that addresses evolutionary change. The model was heterochrony. Someone in one of my audience defined it as several old crones, but it is defined in biology as variation in developmental timing events, some of which involve regulatory genes. 

And we'll talk about the two modes of heterochrony. Paramorphosis is what we all think about when we think of evolution. It's the addition of a new feature at the end stage. So for example, you may have a bird that's sort of a dull brown. And a derived species from it may be a lovely red. That red color is the addition of a new feature. It changes the whole ecology and behavior of the bird because it will affect aggression. It will affect mating behavior. And it will affect being preyed upon. 

So the derived species, the derived feature is something that we all think about as being evolutionary, that you get a new species because you get a new feature. There's another mode that probably explains where we can have very rapid evolutionary change. And that's paedo-morphosis. That's the retention of juvenile, of ancestral or juvenile traits in the descendant species. And those are likely due to regulatory events. 

This where you probably should turn off the camera! Examples of paedo-morphosis are, a good example are humans. Some of us resemble infant apes more than the adults, and are said to be paedo-morphic to them. We've retained the juvenile features of our ape ancestors. Baby apes, you know, have less hair and don't have the big brow ridges, and have a small muzzle. Juvenile features in most animals have probably evolved to make them cuter. 

I mean, most of us, when we see a baby of something, other than the baby alligator, think of babies as being cuter. And they may have evolved to decrease aggression of adults toward the infant. In contrast, for those of you who don't know Sean Carroll, this is him. 

(laughs)

 All of us resemble adult apes, which are hairier. And this is why I wanted you to turn the camera off! Apes have a large brow ridge and muzzle, among other attributes. And many of the features that are evolved in the adult are used in aggression or for sexual attraction. 

Okay, you can turn it back on! Now this is a general, whatever, it's a general process that other species, including dogs, have evolved by retaining various stages of paedo-morphic behaviors that are retained with the same level of morphology for those behaviors of their wolf ancestors. And the Coppingers have been really big on studying dog behaviors and morphology. And they have documented that dogs are paedo-morphic to wolf ancestors. 

Pat probably recognizes a couple of the pictures in here! Whereas the wolf has the pointy ears and pointy muzzle, dogs have retained some of the cuter characteristics of wolf puppies. They have rounder features. This little guy, the middle guy that looks fat and cute, has pudgy paws, has rounded ears, and looks like a cute, little puppy, adult. 

And what the Coppingers and their colleagues have found is that those breeds that look more wolf-like, also exhibit hunting behaviors, the whole sequence of hunting behaviors that are more wolf-like, or are more complete. Those puppies, like Labrador retrievers or golden retrievers that look like little grown puppies, exhibit less or fewer of the hunting behaviors that wolves, in the hunting sequence, that wolves have. 

So what you have is you have changes in the behavior that, in the morphology, for example, you retain morphology, you retain the behavior with it. So the synopsis of what I've said, and I haven't gotten to the birds yet, have I. This is a flight of fancy, actually. The retention of juvenile features in the adult of the descendant species is a faster means of evolving new species. This process probably is dependent on developmental changes moderated by regulatory genes, not protein coding genes. 

And it doesn't require long periods of selection to achieve and adaptive phenotype. The reason is that those features have already been exposed to selection in the ancestral species. So you don't require new features, and you don't require a whole lot of selection to cull out the bad stuff. Okay, now I'm going to talk about birds. There are two species of palm-tanagers, or whatever we're going to call them, endemic to the island of Hispaniola in the Caribbean. 

One species occurs over most of the island. And the other species basically occurs in the southern peninsula of Haiti, and off of Port-au-Prince. Okay, I need to go back. And shoot, this is critical. There, okay. The species that occurs over most of the island in Hispaniola is called the black crowned palm-tanager. The adult has a black crown. It's also characterized by white eye spots. In Creole, they're called four-eyes. 

And what's really interesting is there were some ground warblers that kind of looked like these guys that were considered petite-warblers by the Haitian. Everyone was saying, no, those are warblers and tanagers. It turns out that the brown warblers and these un-tanagers are closely related. So education isn't everything. The black crowned palm-tanagers are also aged on morphic. The juveniles have grayish crowns. And depending on old they are, the crowns darken with age. 

And they also have a fairly clear chest. It has some gray in it, but there's no marked gray feature. The other species is the gray crowned palm-tanager, so I have to take an aside on this. This is perhaps the first and only picture of a gray crown palm-tanager. It was taken in 1984, by taken by John -- when we were in Miragoane. I looked all over the web for another picture and it's John's. 

I just talked to him today after 20 years or so, and asked him to put it out on the web, because people need to know what the gray crowns look like. But anyway, gray crowned palm-tanager have retained the gray crown of the juvenile black crown. But they've also evolved a unique feature. And that's the gray front against the white. So gray crowns have also been confused with juvenile black crowned palm-tanagers. 

And that was the problem, in terms of knowing what their actual distribution was, and whether they were actually just geographic variants of black crowned palm-tanagers. It turns out that not only are black crowned palm-tanagers aged morphologically, but they're also aged on morphic behaviorally. Juvenile black crowns feed mostly on stationary foods like berries or insects that sit on branches. And adults are more active. It turns out that gray crowned palm-tanagers have retained this behavior. 

One time I was out looking for these birds. And I came across a juvenile that was sitting on a bush. There was a gnat flock going around its head. And it was following the gnats. Usually, an adult will see a gnat swarm and go after the gnats and eat them. This little guy was watching them, trying to figure out when to go after them, and he actually fell off the bush. 

(laughter)

 The other time, I was watching a juvenile go along, foraging on the ground. It came across a snail shell. It started hitting the snail shell against a rock, trying to break it open. It spent a lot of time. I was there for about 20 minutes. I was recording this on tape. And I was laughing through the whole thing, because I could tell there was nothing in that shell. 

It got so intent on hitting the shell, that it actually lost its balance, tumbled a couple times, came back, picked up the shell and realized that it was empty and walked away. Well, it wasted a huge amount of energy and time, in terms of finding food. So the juvenile black crowns are not terribly efficient. It takes them a while. What I found, in eight foraging variables that adult black crowns were significantly different from juveniles in five of those variables. 

That's in terms of activity, in terms of average speed, in terms of the amount of time that they spent stopped during their foraging, in terms of the proportion of time spent stopped, and in terms of food catching attempt per perch change. So sometimes, if you watch chickadees going along a branch, especially in the wintertime, they'll hop, hop, go after something, hop, hop, go after something, and hop, hop, go after something, depending on resource dispersion. 

With the juvenile black crowns, they would, hop, hop, hop, hop, hop, hop, hop, hop, go after something, maybe and not get it. Whereas, the adults were much more efficient at that. It turns out that adult black crowns also differ significantly from gray crowned palm-tanagers in four of those variables. In none of the eight variables I measured, did juvenile black crowns and gray crowned palm-tanagers differ. 

So what we see is that gray crowned palm-tanagers have not only retained the morphology of juvenile black crowns, but they're also retaining the foraging behavior. Now, I mentioned earlier that juvenile traits have evolved to deflect aggression from adults. And juvenile behaviors that are associated with juvenile morphologies, and this was noted in humans, children would not respond behaviorally to something until they had reached a certain morphology in their growth. 

And the Coppingers have shown this for dogs. That juvenile traits deflect aggression has been shown by researchers in red winged blackbirds. They took stuffed blackbirds, one with adult plumage and one in juvenile plumage, and showed it to an adult male. And the adult male would always try to attack the adult plumage blackbird, but not the juvenile plumage blackbird.

- Why would that be?

- Why? Because juveniles often don't serve as a threat to the adult. It's the adult blackbird that's trying to take mates, food or territory from the other adult. Whereas, juveniles are usually running around falling off trees, and things like that. So there's a process. There's an observation, I know, in a lot of birds, especially long-lived ones, juveniles will retain their juvenile morphology even through their first year or so of breeding. 

And that is thought to occur because they don't have to worry about having the aggressive male coming and bothering them while they're trying to learn how to breed and raise young. So the prediction from their retention of juvenile traits is that paedo-morphic species would be more social and found together. So what I did was I looked at my data for gray crowned palm-tanagers and black crowned palm-tanagers, in the non-breeding season. 

In the breeding season, they're going to be running around with mates. And they're going to be running around in family groups. So I basically just looked at the non-breeding season. And I asked, is there a higher probability that gray crowns will be found in groups of more than two than black crowned palm-tanagers. And the probability was significant. When I looked at gray crowned palm-tanagers, they were often in flocks of three or more individuals. 

Whereas I never saw black crowns, other than in family groups during the breeding season, in more than two individuals. So the flocking behavior, the social organization has changed in gray crowned palm-tanagers. Gould's heterochrony model also makes predictions about body sizes of the derived species, in this case, the gray crowned palm-tanagers. And these predictions are based on the first phase of reproduction in a given environment. 

If you're in an environment where there are lost of resources, birds can breed when they're sexually mature, even though they may not be morphologically mature. It turns out that in harriers, when there are lots of voles out there for harriers to eat, juvenile males in their juvenile plumage will breed. When there aren't a lot of voles out there, because you have vole cycles, juvenile males will not breed. 

Once individuals breed, it often leads to arrested development in body size, because it's energetically difficult to both breed and grow. So once you've reached the breeding age and size, you usually arrest the development of the growing of the individual. It turns out that gray crowned palm-tanagers are significantly smaller than black crowned palm-tanagers in several body size measures, including bill length, toe length, wing cord, brain case length, and proximal bill and depth measures. 

So the derived species of gray crowned palm-tanagers are smaller, as predicted by the heterochrony model. What was really surprising, and I used genetic procedures that are considered archaic by many of my colleagues and many of the graduate students in the department. I don't know if they consider me a colleague or not. I used what's called protein gel electrophoresis, or starch gel electrophoresis. 

You take some starch, you mix it up in certain proportions, and a buffer, you let it gel, and then you put little dabs of tissue juice at one end. The origin, you apply an electric field, and proteins will be pulled across the gel. If you have a single band for a protein, it means that you've got a homozygous individual, and I'll explain that. If you have multiple bands, you've got a heterozygous. And it changes for the protein shape and size, as well. 

What we found was that there were no significant differences between gray crowned palm-tanagers and that black crowned-tanagers, in levels of heterozygosity. But there were significant differences between juvenile black crowns and adults. And juveniles were twice as heterozygous as their parents, which makes you wonder where the mailman came in. 

(light laughter)

 How do you get variable kids if you're mostly homozygous? And we know that vertebrates have paired chromosomes. And along the chromosomes, there are genes that code for different proteins. And some genes, on each chromosome, on the corresponding gene may be exactly alike, and some may be different. And those are alleles. If they're different, they're heterozygous. So here is an attempt to explain, and I guess we needed you guys to get your parents’ permission for sex education. But at any rate…

(laughter)

 I'm going to make some assumptions about what you know. If the parents don't have variable genes, the pink represents the mother of the cross. And the blue represents the father of the cross, and we have two gene loci on each chromosome. In the mother, we have the same genes for-- We have the yellow for one locus, and on the father have yellow for the same locus. We have green for the second locus. And we have green in the father for the second locus. 

What you expect from this cross, then, is that the juvenile will have yellow for the first locus and green for the second locus. What we observed is that there were differences in the loci, that the juveniles were more heterozygous, that they varied at the same locus. At least we thought it was the same locus. And I've pondered this for 20 years. This goes against everything we know about genetics. 

What I did one day, when I wasn't doing anything else, was I noticed that six of the genes in juveniles that are heterozygous, but are homozygous in the adult, code for age dimorphic proteins, like the hemoglobin. So you're actually looking, if you have a juvenile and an adult, and if you're looking at a protein coding locus, you're actually looking at two different loci. The juvenile locus is coding for the genes required by the juvenile. And the other locus codes for the adult form. 

And there's a regulation, where the juvenile locus will get turned off once they become adults. And what we're assuming with that model, and it hasn't been tested, is that adult genes, when they replace the function of the juvenile genes, are more homozygous. Why we think juveniles might be more heterozygous, or more variable, in terms of their metabolic pathways, and that's what it comes down to, is that it's been noted that individuals under stress do better if they're heterozygous. 

So take a bunch of mice and feed them normally, everybody's the same. Measure everything that goes into the mouse and everything that comes out. And that's not a job most of us want to take, you see that there are no differences among the mice. If you make the diets less nutritious, and you measure everything that goes into the mice and everything that comes out of the mice, you find that there are differences among mice. 

When you check the mice for heterozygosity, it's the heterozygous ones that are able to digest the food more completely. And that's likely because they have two different alleles in a metabolic pathway that may take the breakdown of the food through two different metabolic pathways to digest it. So heterozygosity is seen to be beneficial in a stressful environment. And as I noted above, or earlier, juveniles are not very efficient foragers. And so, they're under food stress. 

They're not feeding themselves as well as adults. And so, it would help them if they were heterozygous. Now this is all conjecture. None of it has been tested. And I don't think that there's been any comparable work on other organisms like this. So if you guys are interested in testing this, we have a lab. Oops, drat. Okay. There. So our synopsis is that we have age dimorphic black crowned palm-tanagers. They're age dimorphic morphologically and behaviorally and genetically, which is a surprise. 

The gray crowned palm-tanagers resemble juveniles morphologically in plumage by retaining the gray crowns, behaviorally in foraging behavior. As a result of their juvenilization, they have a smaller body size and they're more social than the ancestral species. And genetically, and I won't go into the details, of this, genetically, they can be derived from a small colonizing founder population composed mostly of juveniles. 

Because if you recall, and I forgot to put this in, if you recall the average level of heterozygosity of gray crowned palm-tanagers was between adults and juveniles. In order to maintain that level of variability in an island population of birds that probably, was in the smaller part of the island, you would need to bring in variability from the juveniles. So during the Pleistocene, when none of us were around, glaciers melted, sea levels rose. We may see this ourselves. 

During the Pleistocene, Hispaniola was cut into two islands by inland seas, several times. The big arrow on the cul de sac plain is where the island was thought to be separated. And it is a fairly substantial plain. It's the lowest point in Hispaniola. It has a brackish water lake that has lots of crocodiles in it. I know because I helped a friend tag some in a rain that you couldn't see your nose in front of your face. Anyway, in a dangerous moment. 

So it has a brackish water lake that's left over from the Pleistocene. There's also another valley called the Twin Valley, or the Jacques -- Depression, that corresponds to the gray crowned palm-tanager's eastern most distribution. And some people think that that may have been flooded, too, during the Pleistocene, and separated the islands. And the model is that small founding populations from the main island flew over to the south island. 

The populations were composed mostly of heterozygous juveniles. And without competition and with abundant resources, juveniles were able to breed successfully. They could breed as soon as they were sexually mature. Because reproduction is energetically costly, growth stopped, and the juvenile traits of the ancestral population were fixed. The genetic theory, and as I said, I'm not going to go into this, supports the model of the derived population that retained gray crowns. 

And then they, in being separated from the ancestral species, they evolved a unique trait in terms of their throat and chin patterns, the gray throat and the white chin. They also retained other juvenile features of black crown antecedents, like their foraging behavior. When Hispaniola was rejoined, the populations that had differentiated, populations had differentiated to reduce gene flow. So even though we have a hybrid zone between the two species, it's a hybrid sink. 

There's very little gene flow going across it. So in conclusion, what I wanted to bring to this talk is that the heterochrony model, especially with paedo-morphosis part of it, it explains how rapid evolutionary change can occur by invoking developmental, tiny changes in the derived species. 

We've shown that gray crowned palm-tanagers who retain many of the juvenile features of its antecedent, and we were able to argue that based on levels of heterozygosity in the two species, and the age groups within black crowns, that the two species diverged during the Pleistocene, when sea levels were high and the island was divided into at least two islands, possibly three. 

Now it turns out that with the genetic data were able to estimate the divergence of the two species, which is fairly recent. Instead of the millions of years that Darwin invoked for evolutionary change, we have a divergence occurring between 50,000 and 250,000 years ago. And it's a geologically recent development. And it's concordant with what was going on in terms of sea level rises and island formation. Gould actually thought birds were not a good model for his heterochronic speciation model. 

But researchers, and our work on Hispaniola and whatevers, suggests that birds are really good candidates, and that the small genetic distances between species is likely due to the fact that in those studies measuring genetic distance, they were measuring coding loci, not regulatory loci. Rapid speciation and diversification of birds support the need for fast mechanisms of evolution. 

And I believe strongly that avian groups are likely speciated through primarily regulatory changes, and not coding protein loci. Just a minute. For those of you still awake, thank you. 

(laughter)

 And I'd like to acknowledge a number of people, and a number of groups that supported this work. One person I'd like to point out is James Bond. How many of you know that James Bond was the ornithologist who wrote "The Birds of the Caribbean"? Ian Fleming stole the name. 

(laughter)

James Bond's wife sued Ian Fleming because he had stolen the name. Ian Fleming thought it was really manly, and liked the name.