VOICEOVER
Welcome to Up Close, the research talk show from the University of Melbourne, Australia.
SHANE HUNTINGTON
That’s the flight call of the White-tailed Hawk, a bird of prey from the Americas and one of a number of birds relevant to today’s episode on animal speciation. I'm Shane Huntington. Thanks for joining us. The development of genetic sequencing technology has led to significant leaps in our understanding of the biosphere. As we move towards a future of climatic uncertainty where species are increasingly susceptible to extinction it is important to understand how and when new species will arise. Just as biodiversity of an ecosystem can be crucial for adapting to changing conditions the diversity within a species is also important for its long term survival, either as a single species or perhaps as multiple new species. In some cases genetic studies are only now confirming long held hypotheses about the process of speciation; that is how species develop and evolve over time. Today on Up Close we are joined by an evolutionary biologist, Doctor Devi Stuart-Fox who has recently confirmed a hypothesis first presented in the 1950s. We will be talking about the motivation for this work and what it means in terms of our understanding of how species change. Doctor Devi Stuart-Fox is from the Department of Zoology here at the University of Melbourne. Welcome to Up Close Devi.
DEVI STUART-FOX
Thanks Shane.
SHANE HUNTINGTON
Now how do we know if two species are actually related?
DEVI STUART-FOX
Well, we can use genetic sequencing to look at how genetically related they are or we could look at how similar they are in terms of their morphology and so taxonomists have traditionally described species and looked at the similarities and differences in all sorts of traits. Things like skull morphology, dentition, even sperm morphology and we use that to estimate how closely related they are.
SHANE HUNTINGTON
Now when you talk about morphology, this refers to outward appearance or make up?
DEVI STUART-FOX
Yes, just the appearance, measurements and even similarities in development can tell us about how closely related species are.
SHANE HUNTINGTON
Pre genetic information, could we really be sure about that species relationship or are there examples where it seemed as though they were related but we were just simply wrong?
DEVI STUART-FOX
Absolutely, an example is legless lizards and snakes. They look very similar but they are not closely related at all. There are many, many, many examples in the natural world of animals that appear similar because they have similar adaptations to similar environments but in fact they are entirely unrelated.
SHANE HUNTINGTON
Now your work partly deals with colour polymorphism. Can you explain what is meant by this term?
DEVI STUART-FOX
Yes, it has a very specific meaning. It means that there are discreet colour forms, so very different colour forms like red and grey or blue and orange, very discreet colour forms that coexist in a single interbreeding population. So you can find them together and often you have different morphs forming pairs. So you might have a bird for example with a black plumage patch pairing up with a bird with a red plumage patch.
SHANE HUNTINGTON
Is there a reason for this to occur or is it a random occurrence you will find in a given species?
DEVI STUART-FOX
We don’t really know why polymorphism arises in the first place. It seems to have many functions. So some of these colour morphs might have different reproductive tactics. Some might be territorial for example whereas others might be sneakers or they might have different habitat preferences or they might have different prey capture strategies. There are all sorts of reasons or functions of colour polymorphism but we don’t know why it arises in the first place.
SHANE HUNTINGTON
Devi, when you look at a particular species that has a range of these phenomenon like colour polymorphism, are there are other scenarios other than colour that you see that give rise to the same sort of effects of a species having outward appearances that are not just colour but quite different from one individual to another or within the same species?
DEVI STUART-FOX
Absolutely, colour is the most obvious difference. It’s the one that’s obvious to us but usually the different colour forms differ in a whole lot of other ways. So they might have different habitat preferences. They might differ in their physiology. They might differ in their mating strategies, in all sorts of aspects of their behaviour, appearance and physiology and ecology.
SHANE HUNTINGTON
So we classify mating strategy as one of these polymorphisms. Can you say something more about that?
DEVI STUART-FOX
Yeah certainly, a lot of colour polymorphic species, the different morphs have different mating strategies and what I mean by that is that they have different ways of trying to attract mates or gain matings. So for example one particular morph might be highly territorial and have access to all the females within his territory whereas another morph might guard females, might ensure that no other male gets access to a particular female but might have access to fewer females. Another strategy might try and sneak matings from those other two males and in fact we have real examples of colour polymorphic species where males have three different morphs in these three different mating strategies.
SHANE HUNTINGTON
Now do we see this sort of thing in humans?
DEVI STUART-FOX
Well, humans have some polymorphisms like for example eye colour, brown or blue eye colour so discreet differences but a lot of the variation in humans tends to be continuous. So for example height or skin colour, we have got the whole spectrum of different skin colours and heights but polymorphism is specifically about discreet categories or discreet variation.
SHANE HUNTINGTON
Now as mentioned in the introduction, one of the aims of your work was to test a longstanding hypothesis that’s been around for over 50 years but not confirmed. Can you give us an idea of what that hypothesis was and how it came about?
DEVI STUART-FOX
Evolutionary biologists have been interested in polymorphism for a long time because it’s been a little bit of a puzzle as to why these morphs can coexist because if one morph has an advantage then the other morph should eventually become extinct in that population. So polymorphic species have been heavily studied and because it’s easy to classify these morphs and we are interested in variation between species and colour polymorphic species is an example of obvious variation.So early evolutionary biologists studied polymorphic systems and wondered whether having different morphs allowed these species to occupy a broader range of environments or perhaps ultimately become different species. And so they hypothesised that colour polymorphic species should speciate more rapidly than non polymorphic ones because to put it in context a little bit they were also studying polymorphic systems where they saw evidence that they might be in the process of speciating.
SHANE HUNTINGTON
Speciating means becoming more than one species?
DEVI STUART-FOX
Differentiating and becoming more than one species. So for example they were wondering whether different morphs of these butterflies, in some populations you would only get one morph, other populations you would get the morphs coexisting and they were wondering whether in populations with only one morph would it become a different species?So they proposed this hypothesis but they had no real way of determining whether it was a general evolutionary pattern, whether these polymorphic species were actually speciating more rapidly.
SHANE HUNTINGTON
You work with a number of animals as an animal behaviour expert. I can imagine you work with a whole range. Why did you choose birds in particular for this study?
DEVI STUART-FOX
Birds are probably the best known animal group, birds and mammals. They have been heavily studied by biologists, by natural historians. So we know a lot about their appearance, their natural history, their biology, their taxonomy, defining what a species is. That’s very important. We also have the genetic data and that was crucial for us. So we knew which species were colour polymorphic and for those species as well as many other species we had genetic data that was publicly available and that was crucial for our study.
SHANE HUNTINGTON
Now I can imagine the dream here would be to look at this in a dynamic scenario where you are actually watching the evolution occur and the speciation occur. Is it possible to do this sort of thing in a species that shall we say replicates far faster like in the insect world or something like that?
DEVI STUART-FOX
Yes, there are lots of examples of experimental evolution particularly on bacteria and invertebrates like nematodes and fruit flies and things like that where you can manipulate particular aspects such as their appearance and create an evolutionary scenario and look at whether they ultimately diverge and speciate. We can catch evolution in the act and we have been able to for many years but, I guess, in our study we were more interested in identifying a general pattern across the vertebrate species.
SHANE HUNTINGTON
In your study you looked at thousands of birds actually, one of which we heard at the start of the show. Can you give us an example of some of these colour polymorphic bird species?
DEVI STUART-FOX
There are lots of examples. Amongst the birds of prey there are a number of examples of polymorphic owls where they have red morphs or grey morphs. An example is the Eastern Screech Owl which is common in North America and yes, there is a grey morph and a red morph. That’s quite common amongst several groups of birds of prey.There are also examples of white morphs and grey morphs and quite a famous example actually occurs in Australia where the Grey Goshawk has a grey morph and a white morph and the white morph is the world’s only all white bird of prey. Those two morphs co-occur in part of the range but in some parts of the range you only find one morph.For more colourful species often in the songbirds, a really nice example is the Gordian Finch, again an Australian example where the males have either black heads, are red heads or really yellow heads.
SHANE HUNTINGTON
This is Up Close coming to you from the University of Melbourne, Australia. I'm Shane Huntington and in this episode we are talking about bird colour and speciation with evolutionary biologist Doctor Devi Stuart-Fox. How many particular species did you actually look at Devi to do this study?
DEVI STUART-FOX
We looked at five families and the size of those families varied from about 70 species to 250 species. So we looked at five families in detail and then we looked at general age of colour polymorphic and non polymorphic species across the songbirds and that was more than 4000 species, the passerines, so all up, about 5000 species of birds.
SHANE HUNTINGTON
Devi, when you speak about family and species all these sit within a hierarchy. Can you explain how that works?
DEVI STUART-FOX
Yes, so several related species form a genus and then there are multi genera within a family and there are several orders above that in the hierarchy until we have kingdoms of course, the animal kingdom and the plant kingdom, fungus, bacteria.
SHANE HUNTINGTON
There are many of them. Now when you embark upon a study like this you have to get the information from somewhere and in some cases I suspect people actually examine the genetic information firsthand. In others they are examining the data. How about yourself? Did you have to get the genetic data firsthand or did you acquire it another way?
DEVI STUART-FOX
Well, we certainly couldn’t generate the genetic data for more than 5000 species firsthand, that would take a very, very long time but every time people do generate genetic data they submit that data to a public database called GenBank and that’s then freely available for people to use in subsequent studies.And so we used that data that was already available to reconstruct the evolutionary relationships. It’s basically like a family tree, constructing the relationships between the species that we were interested in.
SHANE HUNTINGTON
These species we are talking about have not been fully sequenced. We now have the genome as it were, so what part of the genetic information do you use to put this picture together?
DEVI STUART-FOX
No, we only have usually very small pieces of information relative to the genome of course which is enormous but most people sequence a common set of genes which allows us to look at the relationships based on that common set of genes and those genes are often genes of the mitochondrion, so not the nucleus of the cell. The mitochondrion, I guess, is the energy powerhouse of a cell. It has a small genome, the mitochondrion and then there are a few genes within the nucleus too that people have started to sequence. So we used about a dozen different genes all up for birds.
SHANE HUNTINGTON
Now, you get this genetic information. You are looking at producing this family tree. How do you go about determining at that point when a species is separate or is to be considered separate to another species you have already identified?
DEVI STUART-FOX
Well, it’s the taxonomy that defines whether it is separate. So we have already got our definition of separate species based on the taxonomy and then we get genetic sequences for those species and construct the relationships between those species. So it’s not us who have determined what constitutes a separate species. It’s generations of taxonomists.
SHANE HUNTINGTON
When you are out there in nature and you have all these species there must be some driver to cause a species to end up branching off into multiple species. What sorts of things are causing this occurrence?
DEVI STUART-FOX
The drivers of species differentiating are often geographic. So when populations are separated by a geographic barrier such as a river or a mountain range they evolve independently in those two different populations. And those geographic drivers might be combined with genetic factors or different selective regimes, and what I mean by that is different environments place different pressures on those two populations. So those populations might then evolve different adaptations to those two different environments.
SHANE HUNTINGTON
Devi, do we find that the opposite occurs in nature as well where you have a scenario where a species is broken up into multiple species and then through environmental conditions is brought back together?
DEVI STUART-FOX
Well, if the species is broken up into multiple populations those populations might not have evolved reproductive barriers so that if they do come together in the future they could still reproduce, but usually when we talk about separate species we talk about populations that have evolved reproductive barriers. So if they have become separate species then usually there are barriers to them reproducing if they come together again. The hybrids might be less fit, for example.
SHANE HUNTINGTON
I'm Shane Huntington and my guest today is evolutionary biologist Doctor Devi Stuart-Fox. We are talking about bird colour and speciation here on Up Close coming to you from the University of Melbourne, Australia.Devi, your study has shown that colour polymorphic species have accelerated speciation. Can you explain what this means?
DEVI STUART-FOX
What it means is that they speciate more rapidly. So they are more likely to become separate species within a shorter space of time than species with only a single colour form. So we just compare the relative rates that they might become separate species because when we have an evolutionary tree or a tree of relationships we can see where species split. It’s a branching tree so we can see where they split. And where they split we say that’s speciation.
SHANE HUNTINGTON
I'm always curious when you look at this genetic data and you look back into the past, how do you determine at what point in the past from the genetic data we have today that these events occurred?
DEVI STUART-FOX
Well, we can determine the point at which they split from the amount of difference in the genetic sequence. So the more different the sequences are the longer ago they split. So the genetic sequences give us an idea of the relative age of species and that was essential for our study.
SHANE HUNTINGTON
How do you go about calibrating that timeframe? So you see a certain amount of difference between them, but over what timeframe is assumed that is required for that to occur?
DEVI STUART-FOX
Well, we didn’t actually try and put absolute dates on it because we were interested in relative rates. So the rates of speciation for polymorphic and non polymorphic species but people often are interested in absolute dates and they date their evolutionary trees that are based on genetic data using the fossil record. So for example they know that these species must have split at least say three million years ago based on a fossil specimen and used that to calibrate their tree.
SHANE HUNTINGTON
Now when we talk about these polymorphic species and them being ones that have accelerated speciation, does this mean that they are less stable and more at risk?
DEVI STUART-FOX
It’s been hypothesised that they might be more at risk but my view is that we really don’t know and it would vary amongst species. Some colour polymorphic species we know are at risk. For example the Gordian Finch that I talked about earlier that occurs in northern Australia. It is an endangered species but there are certainly many examples of very common colour polymorphic species and it’s not entirely clear why they would necessarily be at more risk, just because of the fact that they are colour polymorphic.
SHANE HUNTINGTON
I suppose in that case you have a real difficulty of factoring out the different environmental conditions that all these species are interacting with.
DEVI STUART-FOX
I guess the reason that it has been proposed that they might be more at risk is that some of the colour forms are often quite rare and if that rare colour form were to disappear for any reason it could destabilise the whole system, so to speak. So a couple of people have proposed that there might be a link between colour polymorphism and extinction risk or rarity.
SHANE HUNTINGTON
Do members of a colour polymorphic species have any advantages?
DEVI STUART-FOX
They may well have advantages in terms of the species being able to occupy a broader range of environments. So for example if different colour morphs specialise in different habitats the species as a whole could occur over a broader area and across a broader range of environments. We know that that happens in the birds of prey. We have evidence that that’s the case and we think that that’s why they may be more likely to speciate because as I said, there is often a geographic component to speciation. So occupying a broader range of environments or a larger total range might make you more likely to ultimately split up, if you like, in terms of separate species.
SHANE HUNTINGTON
If we go from a scenario where you have a reasonably stable polymorphic species to a very stable monomorphic species where that split has occurred, over time when we talk about things like some of the bird of prey and so forth, these are highly evolved animals, why would we see polymorphism at all? Why hasn’t it all gone down the path of becoming the mono forms of those particular species by this stage?
DEVI STUART-FOX
Well, one of the processes that tends to maintain polymorphism is when there is an advantage for a rare morph. That’s called frequency dependent selection. So an example might be where females prefer males that appear novel. There have been experiments, some very cute little experiments done where if you stick a little paper hat or a little colourful band on a finch ,the females love it. They go for it because it’s new and they’ve actually shown that in lots of species that females prefer novel males.So a new morph or a rare morph might have an advantage in terms of female choice. Another reason that a rare morph might have an advantage is because it might not be recognised as a predator by prey or it might not be recognised as prey by predators since the predators wouldn’t have encountered it before. So where rare morphs have an advantage it tends to maintain the polymorphism. When those morphs become too common they are then disadvantaged. So I guess it’s cycles. The frequency of the morph cycles over time and the end result is that the polymorphism is maintained.
SHANE HUNTINGTON
I suppose in the case with birds where colour has such an important role in mating, this effect comes out more predominantly. Are there other species where colour is not as important in the mating cycle but more in the predatory prey cycle where you still see these sorts of changes?
DEVI STUART-FOX
Absolutely, obviously colour is very important for camouflage. So there are a lot of examples where the colour polymorphism appears to be maintained by selection for rare morphs that aren’t recognised as prey. There're famous examples of shell banding patterns in snails that seem to be related to environment and in many invertebrates different colour morphs appear to have advantages in terms of camouflage.
SHANE HUNTINGTON
When we talk about birds like the ones you indicated earlier, some of the birds of prey, over what timeframe are we looking at to see these kinds of speciation changes?
DEVI STUART-FOX
Well, it varies enormously but it can be from thousands of generations to tens of thousands of generations. We were looking for overall patterns, so essentially the average age or rate of speciation for polymorphic species versus monomorphic species but within those groups of course there are a lot of variation amongst species.
SHANE HUNTINGTON
Why is it so important that we have a good understanding of this speciation? How will it help us in our protection of the environment in the future?
DEVI STUART-FOX
Well, I guess, as evolutionary biologists we want to know why and how things speciate in its own right that’s part of our understanding of the natural world and the diversity we see and how it got to be here. But we are also interested in conserving the processes that generate the biodiversity and those processes are never static. So, I guess, if you take an evolutionary perspective it’s very important for conservation to think about how we might conserve processes rather than just what we see here and now.
SHANE HUNTINGTON
Doctor Devi Stuart-Fox, evolutionary biologist in the Department of Zoology here at the University of Melbourne, thank you for being our guest on Up Close today and talking about bird colour and speciation.
DEVI STUART-FOX
Thanks very much Shane.
SHANE HUNTINGTON
Relevant links, a full transcript and more info on this episode can be found at our website at upclose.unimelb.edu.au. Up Close is a production of the University of Melbourne, Australia. This episode was recorded on 24 May 2012. Our producers for this episode were Kelvin Param and Eric van Bemmel, audio engineering by Gavin Nebauer, background research by Dyani Lewis, bird call recording by Arthur Bispo. Up Close is created by Eric van Bemmel and Kelvin Param. I'm Shane Huntington, until next time, goodbye.
VOICEOVER
You’ve been listening to Up Close. We are also on Twitter and Facebook. For more info visit upclose.unimelb.edu.au. Copyright 2012, the University of Melbourne.
© The University of Melbourne, 2012. All Rights Reserved.