 on the campus here, roughly 1100 of them are involved in some sort of musical activity, and I suspect you'll probably hear all of them over here the next two days. One other bit of housekeeping announcements here before I get underway. One thing that I neglected to do was to make you aware of the opening reception of the Paul Grandland retrospective show in the Hillstrom Art Museum. This is at six o'clock. One of the continuing benefits of working at this institution has been the opportunity to walk by Paul Grandland's statues every day, and as many of you know, Paul passed away a few weeks ago, and this is a wonderful show put together to remember his work, and so I highly recommend that you stop in during a break sometime and just take a look. At this point, I think we're ready for our next speaker, and I'd like to call Dr. John Grinnell from our biology department up to the podium here to introduce Peter and Everett Rosemary Grant. John is our animal behaviorist here on our biology staff, and he's best known for his research work. He studies the roars of lions. Thanks, Tim. When Charles Darwin left the Galapagos in 1835, he took with him collections of the birds and tortoises he had found in the five weeks that he was there. He'd made similar collections at other ports of Carl in his five-year voyage around the world, but contrary to legend, he didn't attach any particular importance to his Galapagos collections at that time. It was only in looking back to a place he would never revisit that he began to realize what he had missed. Specialists in England declared his Galapagos collections to be species new to science. The birds he thought were a mix of warblers, blackbirds, and wrens were actually all a variable lot of finches. With this newfound knowledge, he reflected in his memoir that the finches were the most singular of any in the archipelago he wrote, and that in the 13 species of ground finches, a nearly perfect gradation may be traced from a beak extraordinarily thick to one so fine that it may be compared to that of a warbler. I very much suspect, he wrote, that certain members of this species are confined to certain islands. And one might really fancy, he wrote as well, that from an original paucity of birds in this archipelago one species had been taken and modified for different ends. This was his mystery of mysteries, the origin of species. You might imagine then, that years later when he finally presented his ideas on evolution by natural selection in his book, The Origin of Species, he would give the Galapagos finches an honored spot. In fact, he never once mentioned them. Why? He was baffled by this nearly perfect gradation of variation. In these finches, a beak that could fit on a warbler grades into the beak of a sparrow, which grades into the beak of a cardinal. And they were all eating the same foods, or so Darwin, and researches that followed him to the Galapagos observed. In fact, in 1935, 100 years after Darwin's visit to these islands, the ornithologist Percy Lowe declared that the beak of the beak of Darwin's finches offered no scope for natural selection. In other words, he was saying, the shape and size of these birds' beaks made no difference to their survival or reproduction. We know differently now. In the introductory biology and evolution texts that sit on my shelves, I counted nine of them the other day, the beak of the finches presented as the classic case study of evolution shaping and reshaping a biological trait in response to ecological challenges. Where Darwin too thought that evolution would be too slow to see, in his words, except in the laps of ages, we now hold up his finches as examples of evolution happening before our eyes, season to season, that we can watch. We know this now because of the phenomenal work of our next speakers, doctors Peter and Rosemary Grant, who for 30 years have watched season to season, year after year, the changing fates and shapes of Darwin's finches. Since they first went to the Galapagos in 1973, the grants have acquired a nearly god's eye view of these finches. For many years they have known each individual bird on the island of Daphne Major, what it eats, if it survives, who it mates with, and what traits they pass on to their offspring and how faithfully. They have made fundamental contributions to understanding of the role of natural selection and of culture in speciation, in how populations that share similar resources evolve to be different, in how hybridization affects the population's evolution and even in the basic idea of what a species is. They have demonstrated what you can learn if you look carefully enough for long enough. For much of the time they're conducting this groundbreaking research, they're also raising their daughters, Nicola and Talia, who essentially grew up in the Galapagos. Grabbing the children's violins and schoolwork, the family would head off for another season off the coast of Ecuador. Peter says that this was an experience that neither daughter now would trade for anything, and in fact their younger daughter Talia now lives in the Galapagos with her husband and two children. Doctors Peter and Rosemary Grant are currently both professors at Princeton University. Together they have accumulated too many honors to meet a list now, but they include the E.L. Wilson Prize of the American Society of Naturalists, the Charles Darwin Foundation Millennial Medal for Conservation in Galapagos, the Wildlife Society's Wildlife Publication Award for their book on the Large Cactus Finch, and most recently an award given by the Museum of vertebrate zoology at Berkeley for contributions to scientific natural history, an award given only three times in the last 20 years the Grinnell Medal. Please join me in welcoming Doctors Peter and Rosemary Grant. Well that was a superb introduction and I feel like saying now for the details followed by the questions that was the framework for indeed for what we will be talking about. But first things first, Rosemary and I thank the organizers very much for the opportunity to come here and address an enormous audience on just a wonderful occasion and once again I'm going to thank John for that introduction for allowing us jointly the committee and John, allowing us to come here and talk about Darwin's Finches for four hours. I think you said four, didn't you John? Well the theme of this conference, the story of life, is a very broad one. The story of Darwin's Finch life is a much narrower theme and it's the story of the origin of species and their multiplication. It's told in the language that was invented by Darwin, by Wallace and by Mendel. And it's a story that took place, takes place over approximately three million years. It's a story that could be told with other organisms from bats to bees, from fruit flies to fungi, even humans as we'll be hearing tomorrow. But the Darwin's Finch telling has the advantage that some parts of the story are exceptionally clear. Even though there are no fossils that we can work with, the islands are still in their original state, a vegetation on some of the islands is pristine and no species of the finches has become extinct as a result of human activity. Furthermore, there are traces of the Darwin's Finch history in their molecules. And with regard to the environment we can reconstruct what has happened in the past from a knowledge of geology, from a knowledge of plant communities, and from a knowledge of the other species of animals that inhabit the Galapagos with them, and finally from a knowledge of climate and climate change. So putting all these things together is the scientific equivalent of the oral tradition of storytelling. So the story is going to be told in two parts. I shall start and then Rosemary will follow. Each story has a beginning even if a story doesn't have necessarily an end and this one doesn't. I'm going to introduce the beginning, run through the stages of the radiation, the early, the middle, the late stages of the radiation before addressing the issue of how species multiply. Then I will be talking about evolution actually occurring under observation when the environment changes. This will be echoing some of the things you heard this morning from Niles Eldridge but whereas his accent, his way of talking is a New York accent, mine is strictly New Jersey. I'm going to ask you to guess where Rosemary comes from when she takes over in that same section on evolution when the environment changes and then she will discuss with you how barriers to interbreeding between species arise and how they're maintained. And then finally she will discuss this enigmatic phenomenon of hybridization between species. You might call this, you might think of this as a failure on the part of the barriers but whether it's a failure or otherwise it's very revealing about how normally those barriers operate. So the story begins as I said before between two and three million years ago with the arrival on the Galapagos islands of some finches. The date of two to three million years ago is established on the basis of a comparison of the mitochondrial DNA between Darwin's finches and what we can recognize as possible ancestral species or relatives of ancestral species on the mainland. And here is such one, a bird in the genus Tiaris. It's a tannager, a seed-eating tannager. The identity of where they came from is simply geographical proximity. They came from let us say Ecuador but we don't know, where somewhere on the mainland over to the Galapagos islands a distance of 900 kilometers. And while I have this picture up on the screen I will just make a note of where the Galapagos island is because that will come into the story in a few moments. So the Galapagos are a very remote place for birds to arrive at 900 kilometers from the mainland and moving imperceptibly east-south-east towards the continent never having been connected to the continent before. So colonization is an improbable event. Well improbable events probably arise in improbable circumstances. What might those circumstances have been to allow finches to travel such a large distance and hit this target of land? Well any answer to that question must be speculative even if rooted in modern information. The modern information that we have tells us something about dispersal of finches in the Galapagos archipelago now. And we know that dispersal is greatest under two conditions. One is following an El Nino year of abundance of rain, a high degree of productivity in the plant communities, finches breed, build up in numbers and then they overdo it. There are too many finches for the amount of food and they fly within the large islands and from one island to another on some occasions. That's one set of circumstances. The other one is when there are volcanic eruptions of an island burning the forests and causing finches to flee for their lives. So our speculative answer to the question of how they got there in the first place runs something like this. Volcanic activity in the pacific slope of the Andes between two and three million years ago caused a forest fires to burn through the spewing forth the molten lava. And destruction of the forest eventually was followed by its regeneration. Probably a very thick growth of the forest. Birds would have increased in numbers in this regenerated growth and then probably there would have been yet further volcanic activity more burning of the forest and now there are hundreds if not thousands if not millions of birds milling around in the coastal region trying to escape the flames, the smoke and being burnt. And some of them would have gone out to sea and kept going ahead of a cloud of smoke and maybe very hot fragments of spewed forth material and arrived at the Galapagos. Not just finches maybe but finches were certainly amongst them as we know with hindsight. So that's how the Galapagos we think were colonized in the first place and when the finches arrived there they encountered an environment this is a very important point for what I have to say from now on. The finches encountered an environment that was not the same as today's. So the bottom right hand panel shows you the distribution of islands in the archipelago nowadays and the top left hand panel shows what it was like three million years ago. Only five islands if we've reconstructed this correctly and between that time from three million years ago to the present time the number of islands increased as a result of volcanic outpourings from a hot spot. I'm going to indicate it here. It's under the modern island of Fernandina. So picture it this way the plate upon which these islands is moving east south eastwards every now and again that plate is punctured by volcanic molten lava outpourings and new islands are formed. So you can consider this island of San Cristobal as your marker. Two million years ago it was over here one million years ago it was over here well away from its point of origin and there it is today. Nowadays there are many more islands than there were three million years ago. Not only that the climate wasn't the same. Here is a summary of global temperature change over the last four to five million years. Now the way to read this without looking at all of the details is interglacial refers to relatively warm conditions and glacial refers to relatively cool conditions and four million years ago the temperature was something like this on average globally as deduced from a variety of sources and gradually declined with increases in the fluctuation taking place particularly over the last one million years ago. Our point of interest is two to three million years ago somewhere in this vicinity here where locally presumably as well as globally the temperatures were higher than they are now. And finally according to some theoreticians the El Nino phenomenon you're probably all familiar with that because it's newsworthy every roughly four years. The El Nino phenomenon up to the time that glaciation began somewhere around about two and three-quarter million years ago was a permanent feature of this part of the Pacific Ocean. So with all this information put together we suspect that the environment that the Finches encountered when they first reached the Galapagos was more like what Cocos Island now has that is a rainforest right from the coast all the way up to the peak. Nowadays the Galapagos has the same temperatures as Cocos Island but it has much less rainfall except at high elevations in the most extreme El Nino years. So the Finches arrived at an environment somewhat like that and they looked somewhat like this a generalized seed eating form almost certainly and the first steps in the radiation this is now right at the beginning the first evolutionary changes took a burn that looked somewhat like that into a direction we believe given the nature of the habitat on Cocos Island took the ancestral finch in a direction of exploiting flowers for nectar and for pollen and small arthropods in other words a beak that is much smaller and finer than this general purpose seed crunching beak to something like this this is on the basis of molecular data the derivative of the oldest species on the island we call it the warbler finch now it has a very different appearance from what you saw beforehand and then this species or its ancestor strictly speaking split into two lineages this is the derivative the modern form of one of those lineages and this is the modern form of the other one I'm going to give a few names the first one was is called Olivacea this one is Fusca I might use switch from English to the scientific names without intending to these two lineages anyway were the product of the first split the radiation began with that first division nowadays the Olivacea group live on high islands at high altitude and this one lives on other islands generally at low altitude now because they're so similar because they're so different from all of the mainland relatives and because they're also so different from any of the subsequently formed species we believe that the initial steps in the radiation were taken by birds adapting very strongly to this highly unusual niche of nectar eating and pollen eating either on the Galapagos which is our best guess or possibly on the mainland and it was the mainland forms that got over to the island and then split into these two regardless of where that initial divergence took place it's secondary to an importance to what I have to say nowadays the Olivacea group live in forest at high elevations on those tall islands in the center in the west of the archipelago and Fusca lives in the low habitat generally around the coast and somewhat inland from their cactus and various spiny bushes that you can see in the foreground so that was the beginning now remarkably all of the subsequent evolutionary radiation of the finches took place from one of those lineages not from both here's a reconstruction of evolutionary history of the group as a whole based upon an analysis of microsatellite DNA if I showed you a picture of the phylogeny based upon mitochondrial DNA currently more frequently used molecule for examining phylogenetic relationships you would see almost the identical pattern namely Olivacea right down at the bottom here the first split separated Olivacea from Fusca and the remarkable thing as I said a moment ago is that it was the Fusca lineage that gave rise to everything else including the Cockos Finch so let's have a look at some of these products in the early to mid stages of the radiation one of the species produced differs remarkably from the Warbler Finch this is the vegetarian Finch no prizes for guessing what it feeds on and then this by contrast is the single species occurring on Cockos now it has a beak morphology very similar to the Warbler Finch in the later stages of the radiation ground finches were formed a group of ground finches referred to in John's introduction I'm illustrating this group of six species with the largest of them all the large ground finch nicknamed by people who work in this area a flying beak and then there's another group of species that are called the tree finch group because they live most of the time up in the tree trees and the most famous one of this group is the Woodpecker Finch so called for its excavation of cryptic prey but it does so with the unique habit of fashioning a tool out of twigs or cactus spines and probing into the crevices to tease out the bee or beetle larvae so the question is then how is it that 14 species of finches were derived from the ancestral stock if the archipelago had had all of the contemporaneous ecological niches in place at the time the ancestral species arrived then one could think of the process of radiation akin to the filling of boxes with balls one ball per box indeed this is how the radiation was thought of by our predecessor David Lack some 50 or 60 years ago the process of radiation therefore was just a matter of filling in exploitative machines finches finch species into the various ecological niches that were already there but we know that fundamentally the island environments were not the same when the finches first arrived as they are now and therefore one has to think of a change taking place both in the environments and the finches as the finch evolutionary radiation unfolded for one thing as you know already there were only five islands there at the outset and more islands were produced subsequently more islands means more opportunities for evolutionary diversification not only that the climate changed and that means that the conditions for different species of plants to live there changed as a result of that then insects also were able new insects were able to establish and so on so rather than all of the contemporaneous niches being present at the outset the number of niches increased as the number of islands increased and the finches evolved to take advantage of a changing environment again echoes of what Niles Eldridge spoke to us about this morning a facilitating factor and probably a very important facilitating factor was the absence of closely related species so now moving to the last stages of the radiation with these climatic changes taking place rapidly from cool to hot the vegetation moved up and down altitudinally the large islands shown in this not very good cartoon with the contrast between a tree finch zone up in a higher altitude and a ground finch zone down at the bottom that those changes may have resulted in the complete disappearance of one of the habitats and the complete disappearance of the species that occupied it at least on some islands for some short period of time here for example is a moist upland habitat photograph the Scalasia forest the Scalasia is a relative of the daisy in the daisy family and it's undergone an evolutionary radiation itself this species may have gone extinct locally on some of the islands during those climatic vicissitudes now I change from circumstances to causes and ask in more detail how this multiplication or radiation process occurred and that question can be reduced to the simpler one of how do we explain how two species evolved from a single species I'm showing the standard allopathic model of speciation as an answer or at least a framework for answering that question diagrammatically here with the arrival from the continent of the ancestral species to at San Cristobal in the southeast of the archipelago the choice of islands for this by the way is entirely arbitrary followed by colonization of other islands with adaptive change taking place at each stage of this cycle of events and leading ultimately using the word ultimate in the scientific sense leading ultimately to coexistence on San Cristobal of two species derived from one in this case it's the ancestral species plus a derived form I could have done just as well by having it on coexistence being illustrated on Santa Cruz so the crucial thing about the conditions for coexistence two crucial conditions are first of all that the two forms do not compete for resources so intensely that one disappears and the second one is that they don't interbreed or they do exceedingly rarely so there has to be an ecological separation and a reproductive separation of these two products of evolutionary diversification and I'm going to illustrate how the ecological difference arises through adaptive change at these various allopathic steps in the model and I'm going to do so with a species I haven't mentioned so far the sharp beet groundfinch which occurs on six islands and we're going to see different representatives of this species on different islands the original habitat at medium to high elevations is this forest of santhoxalum there's only one species of tree shown here it's a single band of vegetation and we think it is old now three of the populations live on islands solely in this band and three others live on lower islands in arid habitat possibly having colonized the islands when santhoxalum was present and then when the santhoxalum disappeared as a result of those climatic fluctuations that I talked about then they underwent an adaptive change to the local and now new circumstances so the upland ones have a sharp beak yes but it's a fairly blunt one they feed on mollusks they feed on arthropods and when the dry season hits and the food supply declines they turn their attention to fruits and sometimes seeds that's the highland type on one of the low islands hennavesa in the northeast of the archipelago they probe into flowers to get nectar and pollen for which they have an appropriate beak size on the island of wolf in the northwest of the archipelago apparently uniquely on this island they do some unusual things they show a great interest in the eggs of seabirds that interest is an ecological opportunity responded to but it's also driven by the necessity of food scarcity in the dry season they are versatile as a result of that combination of opportunity and necessity here they are apparently queuing up to look at an egg but what they're trying to do is to break it open and they resort to interesting behaviors to do that eventually this egg will be kicked either against a rock or over a ledge smash at the bottom all of the finches flock towards it and then consume the contents rich in moisture but rich in protein even more bizarre than that they feed on blood they do this by hopping onto the backs of seabirds appropriately named boobies and poking poking at the base of developing wing feathers and drawing blood and drinking it almost certainly this is a habit derived from an earlier stage of feeding on hippobosid flies which feed mosquito like on the blood of the boobies and run around inside the feathers of the birds so what the finches essentially have done in going straight for the blood is they shorten the food chain and they have long beaks appropriate for this task so all of that tells us that birds adapt in isolated populations to different food conditions now the role of natural selection is much more secure securely inferred if we can actually demonstrate it in contemporary time and i'm now going to show you evidence for this from a study on the little island of Daphne it's been successful because the climate as you see from this figure changes enormously from El Nino conditions as indicated here to La Nino conditions when there's virtually no rain we started the study in 1973 on this little island of Daphne right in the middle of the archipelago banding birds and following their fates and we found that in 1977 a large number of birds died in fact 85 percent of the medium ground finch population died through a drought when there was no regeneration of the seed supply and this is shown in this diagram where an index of body size or beak size is shown on the vertical axis over here and the average beak depth or body size doesn't really matter which one is we take as this index of overall size stays constant across a period of time up to the drought increases in the drought and only levels off when the rains resumed in 1978 as a result not of growth there was no growth taking place here but of differential survival large birds survive better than small birds as a result of their ability to deal with large and hard seeds that became not absolutely common but relatively common in the environment as the small seeds were eaten down to a low level of abundance now Darwin's principle of evolution or his explanation for evolution required three things it required variation in a trait it required inheritance of that variation and it required natural selection given those three conditions Darwin argued evolution would take place i've shown you the evidence for natural selection what about variation and its inheritance and how do we put them all together this is the best way that i can do it although i'm not showing inheritance here what i am showing is a reflection of inheritance and i'm now going to explain in the top panel you see the distribution of beak depths let's see here on the horizontal axis it's beak depth the frequency distribution of beak depths in the population in 1976 the distribution of white bars has within it a distribution of black bars and the black bars indicate the birds who survived the drought of 77 clearly not a random selection they were above average in size and let me just point out the average of the population here before selection the average after selection the difference is a measure of natural selection inheritance as i say it's not demonstrated here inheritance is the association through genetic transfer between generations but it is reflected in the fact that the offspring of the 76th generation were the same as the parents before selection had happened well the survivors of 1976 bred in 1978 and those offspring likewise were very close to the average size of the parents that produced them now evolution is the difference the change from one generation to the next and it is measured by taking the first generation before selection and the second generation after selection and measuring the difference what i've just indicated is the two points of the evolutionary change that took place the starting point and the finishing point that difference is a measure of evolution and now i'm going to very quickly go through a series of slides to show you that when the environment changes so does the direction of natural selection and the short summary statement of this is that under the very wet conditions produced by an incredible El Nino in 1983 the environment changed from basically a large seed island to a small seed island and under these conditions small beaked birds had the selective advantage very quickly then to uh here's the visual overview the plateau so-called of our island of Daphne with no leaves on the trees at the back and very little vegetation on the ground in the foreground in the dry season in the wet season the trees are leaves and in the foreground you see low growing plants including this one tribulus which made all the difference between survival and non-survival of the finches in 1977 because this is the one that produces large and hard seeds actually groups of components of a fruit which is woody and spiny and obviously difficult to get at but the finches do get at them they tear and twist at the wood to get into the seed lockules to pull out the seeds on the inner surface of the fruits and that's the view of El Nino in 83 with grasses and herbs growing up and smothering the tribulus plant and the rain kept going it kept going for eight months vines grew everywhere smothered the captus bushes almost smothered the bushes that the birds were nesting in so it was difficult for us to find the nests and completed the job later they just simply disappeared from sight and even in the dry season afterwards you could see the aftermath of the El Nino effect with all these vines over trees and bushes and that's not all which Rosmy will tell you about now Peter was talking about the selection happening over the drought of 1977 here and when the seed bank was made up of large hard seeds so that the birds with large body size and large beaks survived 80 percent of the birds with smaller body size and small beaks died and then he covered the enormous El Nino event of 1983 which completely altered the ecological conditions of the island and caused the island to go from a large hard seed island to a small soft seed island so that when we came to the drought of 1985 the seed bank was made up of these small soft seeds and this time there was a lot of mortality the large bill of birds died and the ones that survived were the smaller birds with small bills but as you can see across the 30 years that we have studied these finches the climate has continued to oscillate backwards and forwards from extremely wet years down to droughts we have a two-year drought here another drought in 1996 and then even this year was a drought so what happened to the finches did they continue to be subjected to natural selection with evolutionary responses to natural selection and the answer is yes indeed they did natural selection occurred repeatedly now down this column is geospisa fortus the medium ground finch down this column is geospisa scandens the cactus finch and the x-axis shows that the 30 years that we studied the finches and you can see that in body size in both fortus and scandens natural selection occurred repeatedly and oscillated in direction as it did in beak size and as it did substantially in beak shape so what was the consequence of this did it just oscillate backwards and forwards so that the birds in average or mean body size beak size and beak shape are just exactly the same as they were when we began the study in 1973 or has there been a change over these 30 years so to answer that question oops sorry to answer that question we looked at the mean trait values across these 30 years and this framework is exactly the same with fortus down this column scandens down this column and we took our 1973 starting point which is here and we looked at the mean trait values and we took the 95 confidence limits across the years so if we look at fortus and oops and body size then if it had stayed the same the body size would have just fluctuated and backwards and forwards in between sorry this line here in between these two lines and as we see clearly it has not body size today or in 2002 is significantly smaller than it was in 1973 and exactly the same with scandens body size is significantly smaller than it was in 1973 beak size is interesting because in fortus it increased and over the selection episode that peter told you about and then it decreased and so now today it really is the same size as it was in 1973 in scandens beak size is smaller than it was in 1973 beak shape is a really remarkable one that is really changed substantially in fortus beak shape is significantly more pointed and i'm going to say right now more scandens like than it was in 1973 this is a big difference and likewise in scandens bill shape size now is significantly blunter so more fortus like than it was in 1973 in fact the two species have converged on each other in bill shape and they have gone 25 percent of the way towards each other so if you keep this in your mind this will become clear why this happened and the consequences of this later on so what you can say at this point is that the natural selection on dafne has given us four lessons it is an observable measurable and interpretable process in a natural environment it oscillates in direction it occurs when the environment changes and it has evolutionary consequences but with all this natural selection that is going on and we all know that natural selection requires genetic variation if there is going to be an evolutionary response so the question really becomes how is this genetic variation maintained the other question that this raises and i just told you that these pinches in bill shape at least are converging in towards each other is how do these species coexist and this question can be or these questions can be answered if we ask what is the reproductive barrier between these closely related species and is this barrier leaky or if it is leaky under what circumstances is it leaky there are two pinches that i'm going to talk about because they're the two most common pinches on dafne is as i have been talking about four is scandence the cactus finch and it is a finch of about 22 grams and it you can see here it has a long relatively thin beak the fortress the ground finch is a smaller bird it is 18 grams and has a much blunter bill so the two differ in morphology they also differ in song um fortress the ground finch sings a rendering of mostly mostly mostly mostly and the cactus finch has a long drawn out song which is cha cha cha cha cha cha cha if i took any of you on to dafne for five minutes you'll be able to tell the difference in song between these two birds is very distinct and very discreet however the birds are similar in ways um they build the same sort of nest um they look the same as far as plumage goes males are black females are brown and as far as we can tell they have the same sort of courtship behavior we have not been able to measure any differences in courtship behavior and so first of all we asked well um are the birds capable of discriminating between their own and their other species um on the bounds of morphology we can tell the difference can the birds tell the difference so we did some tests and this was um with laurene ratcliffe we took museum specimens so they were dead specimens stuffed and we put two female specimens one fortress one scandals on either end of this rod and we put the females in um a posture which was soliciting copulation and this absolutely makes the birds go bananas in fact it was so evocative that we had to cover these specimens with a handkerchief put them on the ends of the um on the ends of the rod and then just back up and take off the handkerchiefs and back off and the birds responded beautifully we had to do this of course in the breeding season they wouldn't have responded otherwise um they responded beautifully and they came in and they fluttered and they quartered and they even got to the point of jumping up on the back of the bird the stuffed specimen and um completing their whole process and they did um absolutely um discriminate between scandals and fortress there was no um no question about this in all the tests they did they went straight to the to their own species so they can tell they can discriminate on the basis of morphology however they can also discriminate on the basis of song and so we did a series of playback experiments where we did not have the museum mounts so we did not have um we only had one stimulus which was um the vocal stimulus and once again if you play back a Scandin's song Scandin's comes booming into the loud speaker flies constantly backwards and forwards over the top and if you play a fortress song fortress will do the same but Scandin's will completely ignore it so they only respond to their own species song and once again this was a very clear cut experiment any of you could go on to Daphne and repeat this experiment as actually some people have done and they get you get absolutely this clear cut result now it turns out that song is very very important in this case i would say song is even more important than morphology so what do we know about song we know from work done by Bob Bowman in the early 60s when he was able to take birds away and take them back to California and do experiments on them that these birds learn their song in the in the short sensitive period early in life and this is from day 10 to about day 30 now it's an interesting period because it coincides with the last few days in the nest and the time when they're outside the nest being fed as fledglings by their parents and mainly by their father so it's at this time they learn the song we also know from repeated we are constantly taking um recordings of birds and we know that once they have learned their song and sung their song they retain that same song for life and we have literally hundreds and hundreds of recordings i have chosen four here for two reasons one to show that the songs of any of these birds do not change across years um and the other one to show that in this framework of mostly there are variations so you can actually follow um follow the the birds and their individual songs and what we find is that most of these birds sing an exact rendering of their father's song and this is which is not surprising because they learn in the short sensitive period the bird they hear most is their father singing and so it's not surprising that they learn the exact rendering of their father's song so if this is a great great grandfather the great grandfather um grandfather father son you can see that they all have basically the similar song down this pedigree and 80 to 90 percent of pedigrees are like this um on Daphne we do get some exceptions sometimes the birds sing the song of the natal neighbor as this one did and not the father and um and you get some situations as i've shown on this side of the diagram where you don't get the exact copying of the father's song exactly the same happens in scandin this is a scandin song and you can see that the son sings a song rather similar to its father um here son father son father and in this one it is different so it's about the same about 80 or 90 percent of birds do this and um about 15 percent of birds um actually copy their natal neighbors or another bird's song um this copying of song is extraordinarily um you can you can see this it's extraordinarily consistent and there's one anecdote it's often these anecdotes that really sort of show you that this is true and one of these birds the father got a cactus spying through its throat so it sang a very croaky song and this happened in the late 1970s and even um it's um well it's great i haven't found it at this time it says great great great grand children some of them are now singing this croaky song so you still have the remnants of this croaky song on the island which has been faithfully copied from the croaky father to the son and onwards so i've talked about um males now let's see about females females do not sing it's only the males that sing but nevertheless they are very seem to be very much aware of song differences between the species we have 392 fortes where both the father and the mate songs have been recorded and so of these 392 378 did what they should do which is mate with their own species but 12 of them mated with um a small ground pinch phylogenosa which there are few of these on the island and these 12 mated with the wrong species this little bird is a 14 grand bird compared to about an 18 grand bird and the remarkable thing about these 12 males that um these females mated with is that they sang a fortes song so they were mating according to song type um and not according to morphology um we do not know about these two unfortunately i wish we did we don't know the history of those but we do have 90 scandals where we have the father and the mate song um recorded and we were extremely interested because four of these scandin's females were born from a scandin's father that sang a fortes song so we were watching who they should mate with and sure enough they all mated with fortes so they all hybridized they all mated according to song type and not according to morphology so we now have the question why is it that some of these males sing the other species song well we know fortunately because we've been on the island and we've got all these birds banded and we're able to follow them um we know fortunately the answer to at least some of these and most of them um and one is that sometimes scandin's comes and takes over the nest of a fortes usually when this happens they turf out all the eggs but occasionally they will leave one egg behind that egg will hatch out um perhaps a day before scandin's clutch it will be a true fortress um both genetically we can tell this from the the blood the dna that we can take and also in morphology but it will sing it's foster father's song it will sing a scandin's song other cases are when the male dies and the young grow up in the nest singing the song that they hear most which is then nearest neighbor and if that neighbor happens to be another species then it will sing the other species song um and then other times there are two nests very close together the dominant male of a larger species sing will sing more frequently chase the other male constantly away the true father may have very little chance to sing and the birds in the nest learn this other species song so all those things we have seen and documented happening so the next question is then um how fair to these hybrids relative to their parental species now in the first part of the study from 1973 up into 1983 none of these hybrids survived to reproduce um they're produced at about one percent of the breeding population or less and the same rate has occurred throughout our whole 30 years of study so very few hybrids are produced but nevertheless between 1973 and up to 1983 none survived to reproduce this could have been as we thought because there was genetic incompatibility or it could be be because the hybrids being intermediate in bill size did not have the appropriate food um they were unable to eat the large hard tribular seeds we saw them try but never saw them succeed and they took about three times longer to crack open and a puncture seed than the um scandins the cactus pinch did however after 1983 when the island turned into a small seed island and the seed bank was full of small soft seeds the hybrids with their intermediate bills survived and they survived long enough um to to breed they did not breed with each other but they did back cross so then the question comes is the energetic genetic incompatibility at all and so what we did I'll just go back what we did is we took all the birds born in 1983 very few birds um actually were produced in um the following years 1987 a lot of birds were produced so we took that year as well and 1991 and we took the cohorts from those three years and we asked how well did the parental species forters and scandins survive and um in the 1983 cohort we had um 119 forters and 553 scandins 12 hybrids and so this is a graph of forters and scandins survival across um the next um years until finally um that cohort disappeared we did the same with 1987 cohort and the same with 1991 cohort so if there had been any genetic incompatibility at all um we should have seen the survival of the hybrids coming below try and do this below these lines but actually what we found was that they didn't the the hybrids survived um extraordinarily well they survived as well as and if not better than the pure species um this 1991 these were actually the first generation backcrossers they were the first generation hybrids in 1983-87 but the backcrossers in 1991 all of which survived very well they also although I haven't got a slide to show you there was also no significant difference between the number of eggs they produced between the number of nestlings and the number of fledglings they produced so there seems to have been no genetic incompatibility in the hybrids it was just that the appropriate food was not available when they were not surviving so intergression is um interesting because it follows once again the lines of song hybrids do not sing intermediate songs song being learnt um they sing the song of their father so if we take this hybrid this is a Fortis Scandens hybrid with a Fortis father that sang a Scandin song so he himself sings a Scandin song he mates with a Scandin's female produces the first backcross generation which also sings a Scandin song makes for the Scandin's and produces the second backcross generation and this happens whether this is a male or a female and the same happens in Fortis so integration increases genetic variation on which the selection can then act so this explains partly why we get this um this pattern of um selection um of there being enough genetic variation for selection to have acted over um this period of 30 years and also I want to remind you that this um hybridization is likely to have been episodic this El Nino year which completely altered the um in 1983 which completely altered the ecological conditions on the island um was a very unique event um in Coral Cause it was the most extreme event in 400 years so over that time scale it has been quite a unique event and has completely caused this ecological difference on the island so we think that possibly these periods when hybrids can survive and back cross has probably been episodic in the past so in summary um to summarize both our talks the radiation of Darwin's pinches took place over two to three million years um somewhere um the the first split started about 2.83 million years and as Peter showed you this could have occurred when the pinches first came out of the islands so we know from these our geological colleagues tell us it was a period of volcanic activity on the mainland it was also the time when as now as Eldridge said which was a last closure of the Panama Canal and we think that this um altered we certainly altered the um currents and wind patterns and may have had an effect also in bringing the pinches out to the Galapagos um over that time 14 species were produced and they were adapted to different ecological niches um 13 species are on the Galapagos one is on Cockas Island and environmental change was an important factor we thought at the beginning of the radiation and through the radiation and we have shown that environmental change is also an important factor today our detailed studies on DAPNI has shown that populations track um these environmental changes um through natural selection and evolutionary responses to natural selection we have seen that significant morphological change can occur over a very short period of time if you take 30 years as being a short period of time many of you in the audience will think 30 years is more than a lifetime but for us it is a quite a short period of time song a learnt culturally transmitted trait acts as a reproductive barrier between species and rare misimprinting on song can lead to hybridization and to integration that is genes flowing from one species to another now this i think is very important when the same novel environment drives selection and hybrid survival introgression increases genetic variation on which selection can act so the same novel environment was of course a change to um to soft seed island to soft seeds and this was appropriate for a hybrid survival and it also um drove selection on the pure species as well but when you get this situation this reinforcing process can be a really rapid route to change so in this case hybridization has um been a force um um speeding up this um change and a message we would like to leave you with is that speciation involves an interaction between ecological conditions genetics and also learning which is culturally transmitted we've talked about biodiversity and we've talked about extinction that these Niles did um this morning and another message which i hope will resonate with Niles is that neither species nor environments are static entities but dynamic and constantly changing and to conserve species and their environments we must keep them both capable of further change thank you