Naturally speaking. Hello and welcome to Naturally Speaking, a podcast from the Institute of Adiversity, Animal Health and Compardive Medicine. I'm James Bragan, every year on February 12th, scientists and science enthusiasts around the world celebrate Darwin Day. This is both a celebration of the father of evolution of Eldridge's birthday and a celebration of evolution of Eldridge itself.
Now, I know what you're thinking. Darwin Day was a little while ago now, but we bring it up for a very special reason. At the end of February, Sonia Sultan visited the Institute, an alumina of Princeton and Harvard and current professor of biology at Wesley University. Professor Sultan is, well… Well, I would describe myself as an evolutionary ecologist.
I have a little bit of an unusual background, I suppose, because as an undergraduate, I studied history and philosophy of science. And in that field, you learn that ways of thinking that scientists use are things that scientists invent. And I think because of that background as a scientist, that has given me the freedom to ask questions, rather than simply to accept all the answers I was taught as a student. She was here to give her an Institute's annual Darwin Day lecture, and she has the distinction of being the first female researcher to do so.
However, before this, she took the time to chat to me about some of the most exciting and controversial new ideas in evolutionary biology. Hi, Sonia. Welcome to Naturally Speaking. If you are here to give the annual Darwin Day lecture, email Darwin is technical, that's not.
And a fairly traditional question here, nationally speaking, on Darwin Day is to ask you as an evolutionary ecologist what Darwin means to you. So I have great admiration for Darwin, because I think he was a terrific empiricist. We don't always think about the experimental work that Darwin did, but often very simple, elegant and meaningful experiments that have been overlooked in the light of his grand theory of natural selection. So I have the greatest affection in regard for Darwin as an experimental scientist, and for his humility in the way that he studied the natural world and the fact that he respected the organisms as they were, and he tried to understand them more in their terms, and had the patience to amass a lot of empirical data before he undertook to interpret it and shape it in his own way.
So to me, I think it's Darwin as an empiricist and experimental scientist that I feel the most influenced by, and the closest to. You can definitely see it in some of your publications and some of your work that you take a very experimental approach that is quite comparable. So your research in general focus is a lot on ecological development or eco-devil, which I don't think is necessarily a new field, but it's one that is definitely gaining a lot more focus. So maybe you could just explain a bit about what the field is in general and what is that you're doing in it.
Sure. I think you're right, that the field is really something very old, which is to try to understand how organisms develop in the context of their environments. And very early in the 20th century, when biologists started studying development, it was, I think, completely obvious to them, but that was the only way to study development. It's only during the mid and later 20th century that development was studied in organisms taken completely out of that natural environmental context.
So eco-devil is the study of how organisms, it's really not just development, but phenotypic expression in the context of the particular environments in which it occurs, or can occur in natural populations. And the new part, I think, about eco-devil, other than the term, is that in eco-devil, there's a focus not just on the phenotypic outcomes, but also on the mechanisms and signaling pathways in which the environment participates in those outcomes. So there's a more mechanistic focus in that. That's what integrates it really well with studies of development.
Yeah. And a lot of the stuff that you focus on seems to be epigenetic, synthetic plasticity, and so-called transgenerational effects, which, again, aren't necessarily new, but seem to be gaining a lot more traction. And I wonder if you could maybe explain a bit about what these are. Sure.
Well, plasticity, in general, simply means the way that an individual of a given genotype will express different phenotypes in different environmental conditions. So that's a very general property of all organisms. The particular ways in which that plasticity is expressed will depend on the kind of organism, for example, in many vertebrate animals, a lot of plasticity is behavioral. In plants, a lot of plasticity is through growth, through the size and shape and deployment of body parts.
So plasticity can be expressed in many different ways depending on the system. So that's a very general phenomenon. One type of plasticity, that is one way in which environments influence phenotypes, is what can be called transgenerational plasticity, which is where the environment of parent individuals affects the development of their progeny, their offspring. And to me, what's really exciting about this field is that in a Mendelian world, that wouldn't happen.
And yet, it does happen. So that's, I guess, what's really exciting is that when the environment of the parent affects the development of the offspring, it means that there is environmental information being transmitted to subsequent generations. In other words, that environmental information is part of what is inborn in the individual. So we have this very old way of thinking about internal and external, and we think of our own selves and our development as being internally determined or scripted by our genetic inheritance.
And to me, it's very interesting to know that our inborn selves also include this environmental message from our parents' environments, and in many cases, from even more distant ancestral environments. So among the influences we inherit are not just genetic ones, but also environmental ones. And a lot of this is kind of encapsulate by a lot of your experimental studies, which are all really cool. So you work on a group of plants, it bleeds the genus polygonum.
Yes, polygonum. So these include the buckwheat, the knotwheat, and some kind of plants. I was wondering if you could tell us a bit about these, actually, doing them, and why they're so good for studying these kind of questions. Yes, so polygonum is a group of extremely ordinary herbaceous plants.
I study several annual species in this group. They can be quite pretty as well though. Yes, as weeds go, they're not bad, but there's honestly nothing particularly riveting or exceptional about them. And in fact, the whole point is that they are quite ordinary.
They have a lot of experimental advantages. And the reason I chose this group in the first place is because I started with particular species when I was doing my PhD. And I wanted to do a certain kind of experiment. And I wanted to do an experiment where I could clone genotypes so that I knew I would have genetically identical individuals and put those individuals in different controlled environments so that I would have a very clean way of testing the effect of the environment in an invariant genotype.
So I needed to have something I could clone. So I chose this one species because it's very unusual, because it can be cloned through cuttings, very simple, but it also has an annual lifecycle, which means I could collect data on total lifetime reproduction or fitness very easily. And that combination of those two features was what I really wanted. So that's what led me to the species in the first place, completely strategic decision.
I didn't fall in love with it. It wasn't beautiful. None of those reasons for choosing the system. Since then, I've stayed with it, in part because I know how to grow them.
And I know a lot about them. And I can find them nearby. These are very common plants in the region where I live, which is the northeastern part of North America. So they're just very convenient organisms to work with.
And they're very ordinary, I think, makes them more appealing to me. There's never any such thing as a model system, how can any species be a model for any other species, but as plants go, these plants have many features which are similar to many, many other plants. So I've confidence that what I learned about them may be meaningful for other species. That in itself is quite nice because you do see a lot of studies on fairly unique, slightly different kinds of species.
Like, so go back to the obvious ones where a really interesting system, but they're quite an unusual system as far as fish go. So it's quite nice because you can make lots of extrapolations. I remember reading some of your papers and saying some really interesting, phenotypic differences in plants. So maybe you could tell us about one of your experiments and how it's fitting in with your inheritance of non-genetic traits, which I think is a big thing that you study.
Sure. One of the things I've been very interested in studying is how plants respond plastically to resource limitation. One example would be growing plants of individual genotypes and growing them in different moisture conditions to see how they change their body proportions and the characteristics of their roots. And what happens when you grow one of these annual plants, for example, in dry soil rather than moist soil, is that it allocates more of its biomass to root tissue and the roots that it produces are thinner so that it gets a longer root with a greater surface area per gram of root tissue that it has to work with.
That's important because when organisms are limited or resource limited, they have less tissue in total to work with. So the plants respond developmentally basically by a series of plastic changes that maximize their access to water because they maximize the surface area per gram of tissue through this combination of elocational and waffle-level changes. We've done other experiments with soil moisture where we've moved the location of the moisture in the soil and tracked root deployment in space over time and actually watched the root systems follow the moisture. So roots are foraging organs.
Plants are very active, organisms of course, and they stay in one place but they move their parts around quite a bit. So those experiments have been very interesting to understand the kind of developmental decisions that are made differently in different environments and the dynamic aspect of those decisions as environments change in time. So we've learned a fair amount through a number of these experiments about the relation between development and soil moisture. More recently we've asked questions about whether drought-stressed parent plants alter the development of their progeny.
And what we found there has been quite interesting because it turns out that when a parent plant is grown in dry soil it makes seeds that develop a drought-adapted phenotype when they are in dry soil and it develops that, so seeds offspring of parents that have been stressed by drought develop faster into deep-rooted long-rooted seedlings. And that we've done tests that show that that parental effect on seedling development actually results in higher survival in dry soil. So that experiment was very exciting to me because the conventional idea is that fitness differences are scripted in the genotype and the fitness differences on which natural selection acts result from the presence or absence of genetic alleles. And instead we found that this fitness difference came from the environmental experience of the parent.
We actually did a comparative experiment and we found that a species that occurs in both wet and dry and also variable habitats has this adaptive transgenerational effect of drought but a very closely related species that is found only in wet habitats does not have this effect. And in the second species if the parent is drought-stressed it simply makes smaller seeds that grow into smaller and more pathetic seedlings. So that provides an insight to the way that individual plasticity, including transgenerational plasticity, may contribute to the ecological breadth of organisms. And in fact one avenue of research in my lab is to try to understand the relationship between plasticity and ecological distribution and also invasiveness because of course invasive species tend to be the ones that are very tolerant of diverse conditions.
So some of what you're talking about there is essentially the inheritance of environmental information independent of genetic changes. Yes. I'm saying yes. I'm saying yes in that tone of voice for the following reason.
Yes these are environmental effects that are unrelated to genetic differences. On the other hand the way that these environmental effects are transmitted and their particular developmental impact on the next generation are influenced by the genotype. In other words the effect of parental drought in this case on sealing development is slightly different from one genotype to another. That is a good correction to make it.
Yeah definitely important. So I know that some of these concepts have been developed into something called the extended evolutionary synthesis which I'm not sure if that's something that you're a big supporter of. It kind of feels as though your work at least is along the same sort of vein. So I wonder if you could explain a bit about what the extension to our evolutionary concepts are and how this contributes or conflicts with previous understanding of evolutionary biology.
Yeah that's a big question. It is. How many days do we have? Is what stimulated not a lot of debate in my lab recently as we're trying to really understand the real difference in the extended evolutionary synthesis and what we should be taking the key message from it?
Yeah I'm glad you're glad you're glad I was discussing and arguing about that question. I think it's extremely important. So just to be clear there was a book called the extended evolutionary synthesis. I was not an author or involved in that book anyway.
In fact there were no women scientists involved in that book anyway at YI and I've always felt that that was very wrong. The two people who I think would have been the most natural and important choices to be originators of an extended evolutionary synthesis at the time that book came out would have been Mary Jane West Eberhard who initiated the idea of phenotype first or plasticity first evolution and Ava Jablanca who has been the pioneer for studying epigenetic inheritance and neither of them was included. Since years later there's been a very large and very exciting international research consortium which is called the extended evolutionary synthesis project which has private funding and I am a satellite researcher on that project but I'm not one of the labs funded by that project. So the answer is I'm very interested in the whole EES movement which if you want to call it that as sort of intellectual movement.
I'm not an intrinsic player in these particular scientific activities but yes what I've worked on my whole career before that phrase was invented is something very central to the EES which is to try to understand how development and how environmental inputs participate in the process of evolution. And there's certainly a great deal of debate about as you say whether our model for evolutionary change must be modified in light of these ideas. I would say the following. We know a lot more now about how genes work than Sir Ronald Fisher and people who invented the so-called neo-darrinian synthesis in the 1930s and 1940s did a beautiful job creating a mathematical framework for understanding selective change based on what was known at the time.
What we know now about development, about epigenetic mechanisms of inheritance, about phenotypic flexibility or plasticity, they didn't know those things so I don't criticize them for the models they created. However, we do know these things now and I don't understand the idea of closing our eyes to that knowledge and remaining faithful to conceptual models that cannot incorporate these additional mechanisms. So I've been very surprised by the sense of conflict or resistance to new models because it seems to me that as scientists we want to take in all the new information and move forward. So the first thing that I want to talk about is the fact that the evolutionary change in the world is not a real opportunity and I understand this.
If you reach a point where what you're studying simply cannot be explained or encompassed by a framework of allelic substitution then you're sort of in the standard evolutionary practice or outside of it. That's a very uncomfortable place for people to reach. So my hope is that the evolutionary framework we've all been trained in can expand to include life. This is the great irony.
The problem is not what's called neo-darwinism. The problem is neo-mentalism. The problem is a fidelity to a Mendelian model that was always kind of a boutique subset of transmission genetics but it's just completely obsolete. And one question I have is when people like me will stop teaching Mendelism as our model for genetics.
Those are very unusual systems. You know the big A and the little A, the gene for tall and the gene for short. That's really not how genes work. That's the vast majority of genes.
So I think Darwin would be all over this. I think Darwin would be fascinated by epigenetic mechanisms and by the complexity of inheritance. In fact, Darwin understood in his day the great problem for his theory was that no one knew how inheritance works. You've always had a very distinguished career.
So you've attended Princeton and Harvard. You're now working at Wesleyan. You have an incredibly long publication record and invite to speak out of record. So I wonder what would you say is your biggest accomplishment or the thing you're most proud of and what you wish that you'd known before entering this field.
So for an elder career researcher who's looking at your career and wanting to pursue something similar like what advice would you give them? That's a good question. Well, I have to say from my perch of many years, the thing I'm as proud of I guess is having pursued an idea that everyone told me was proud. So as a graduate student I was warned, don't study this stuff.
A, it's too hard. B, nobody cares about it. So I guess I'm, I don't know if proud is the word I'm relieved that I had the stubbornness to say, well, no, I mean this seems important to me and to just stay with it. And I didn't, I did not know if I'd be able to have a career studying plasticity when everyone else I knew was studying genetic differences as such, sort of a real differences.
So it was a bit of a risk. And I'm glad now that I took the risk because it has been an exceptionally interesting bunch of work to be involved in. And it was wonderful and great fun to now be able to meet people and find so many people who are interested in this work and how it might relate to their own ideas. So I don't know.
The advice is, you know, to take your own work seriously and to disregard other people if you must and to, to do your work carefully and seriously, but then to respect it. Sounds like very good advice. Well, thank you very much for talking to us. I am sure that your topic is going to go brilliantly and I am more than sure that it's going to spark an awful lot of discussion afterwards.
I hope so. I hope so. You're actually the first female, I want to speak here that many of us have ever witnessed. So we're all quite excited about that.
Definitely, definitely. So yeah, thank you very much for joining us. Thank you, James. Thanks for listening to The Battery Speaking Podcast.
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