So that our environment is influencing how genes are expressed and what's being selected for. Most of us actually, you know, associate this guy, Charles Darwin, with this whole theory. And certainly he made a huge contribution to that. And this was an idea he had. However, this guy, his name is...
Alfred Lewis. He was also a naturalist, like Darwin, and he was working in Indonesia. And he actually also had the same, independently came up with the exact same idea about how the environment was influencing what traits were selected for in these populations.
He was studying monkeys in Indonesia. And he actually wrote Darwin. And to talk to him about it.
And when Wallace wrote Darwin, Darwin had been kicking this idea around for quite a while. He realized that he was going to lose his claim to this idea. And so what he did was publish a paper on natural selection and this idea that they both had. It had both of their names on it. But Darwin did not consult with Wallace at all before he wrote that paper.
He just wrote it. really without without wallace's knowledge and then darwin went on to write his very famous book called on the origin of species which was you know a book long treatise on this theory of natural selection and evolution and once he wrote that in 1859 Essentially, everybody associated evolution and natural selection with Darwin and Wallace was kind of forgotten, even though he was really a fantastic naturalist. So unfortunately, this is kind of a lot of a lot of science works this way. We talked about that with the discovery of DNA.
Some people are not terribly ethical. And unfortunately, that's true even today. So, you know.
Natural selection, when Darwin and Wallace were working, it was all based on observation. And they were looking at variation in populations. And if you were looking at natural selection or evolution, you have to be looking at something that can be inherited by the next generation.
Because we want something that is persisting in the population. So this fact that it's heritable is really important. And one of the things they noticed, both Darwin and Wallace, when they were looking at populations, was that most of the time if you had, let's say, a population of monkeys living in an area, you would have only one population of monkeys. The other populations will live in other places. And that's because if you have two species that are going head-to-head in the same place for resources, somebody's going to get killed off.
It's going to lead to extinction. The same is true with plants. Plants compete for the same resources. And so you see the same type of spatial division in plant populations as well. Okay?
Any individual in a population that is better able to get more resources, food, water, shelter, whatever, is more likely to reproduce, right? And so their genes... are what are going to be passed to the next generation. So this is how you have this selection of genotypes going through populations.
Okay, so this, you know, this idea of kind of this per the individual in the population that could get more resources or was better adapted, that led to this idea of fitness. Okay, so fitness is this measure of how an individual genotype is represented in the next generation. Okay, so any organism, plant, animal, bacteria, virus, if it's more fit, it's going to reproduce more. And so those genes are going to get propagated more prevalently in the next generation.
Those that are not as fit, you're going to have less progeny. Right, so there are going to be less of them in the next generation. And if that continues with more of the more fit and less and less of the less fit, eventually the less fit genotype is going to disappear. Okay, so that's how things are selected for over time. And natural selection, because of the way it works with this fitness, it typically is going to increase the overall fitness of the population.
So that's the whole point. All this means we're not going to spend a lot of time on this. At the beginning, people, as we talked about this when we talked about genetics, you know, Mendel was a monk.
He worked in a monastery, and most people didn't know about his work. It was only much later, after Darwin published on the origin of the species, that people became, you know, in the late 19th century, that people really became aware of Darwin's work. I mean, excuse me, of Mendel's work.
And so it was only after that time that they began to kind of mesh these two concepts. This concept of genetics that Mendel had with the concept of natural selection and evolution that Darwin and Wallace had. And so people call that the modern synthesis. Because now we look at it from not just the frame of... observing things in the environment.
We also look at it from the gene side, from the genetic side as well. That's all that means. Okay, so there are a couple of types of natural selection.
You can have positive selection, pretty easy. This is a favorable allele. You could also have negative selection, so something that causes disease, causes... you know some kind of instability in the population that could be a negative selection for a harmful allele and then you can also have kind of an intermediate between positive and negative as far as selection and those are called balancing it's called balancing selection so and this is between multiple alleles so some have a Positive effects, some have a negative effect.
What this does within organisms is it kind of keeps everything in balance. Okay, and so this is kind of important in regulating the genome overall within a population. Okay, so you don't want too much of it, too much would be bad, too little would be, you know.
So this is the, balancing is the intermediate frequency. An example of a balancing selection that we've talked about is sickle cell anemia. Okay, so we know that, you know, the sickle allele is actually not that great, right? You get this, you get this, and it doesn't carry oxygen well. I mean really doesn't carry OT very well.
Okay, but what in balancing selection, what you're choosing for is that heterozygote. So it's going to have the normal copy and then it's also going to have the bad, the sickle copy. Okay, so this is what you get in balancing selection. You get more heterozygotes. Okay, because the homozygous that have both of the sickle cell alleles, they're going to die very early.
You know, in the past, they would have died before reaching reproductive age. So, you know, that's not going to be a problem. But what is the reason we're selecting for this heterozygous is because having that sickle cell allele actually gives you some resistance to malaria, which, as we've talked about, has killed more than...
across the history of humanity has killed more people than any all the diseases put together wars put together so it's been a serious pathogen for a very long time so in places where malaria is really rampant you're still selecting for this okay even though it has kind of a bad effect right so people that are heterozygous they're not they don't have a severe sickness but it does affect them Right, they're not, you know, they're not going to be like super long distance runners. It's going to have that effect that they are not going to be able to carry as much oxygen in their blood as somebody that has two good alleles. But they're going to have increased resistance to malaria.
So again, that heterozygosity is going to propagate in the population because they're going to be able to reproduce. Okay, does that make sense? This is how balancing selection works.
There are a couple of different patterns of natural selection. Okay, so there are three of them stabilizing, directional, and disruptive. Okay, and they're pretty straightforward.
So stabilizing selection, if you look at it on the graph, it selects against the extremes. Okay, so we're selecting against the extremes and we're kind of moving everybody Towards the middle, towards the average. Okay?
So this would be, a good example of this is actually the birth weight of babies. If a baby is born and they're too small, they don't have a very high birth weight, you know, premature babies, very low birth weight. So on this side of the graph, they have a low chance of survival.
Their chance of survival is not that good. Especially in the past before we had a lot of modern medicine. The same thing is true if you're at the other side of the curve. If a baby is too large, that is actually a problem as well.
You're going to have problems in the delivery. So that's going to cause, you know, you're going to have damage to the mother. You could have hemorrhaging. The baby could be, because the labor would be longer, could be left without oxygen.
For a long period of time, that would cause problems for the baby. So both of the extremes are not good. And so in human populations, you can see this. We have weight typically is right around three kilograms, six or seven pounds, which is just right. That's not to say we don't have babies that are born a little bit higher, a little lower.
But overall, if you look across human population, this is what you see. Okay, so this is an example of stabilizing selection within our own population. So you get the intermediate character, whatever that trait is. Directional selection is when you have a population and they're at some...
at some level in some environment and then for whatever reason it shifts completely shifts the curve completely shifts if you're looking at whatever character trait you're looking at so a lot of times this happens because of environmental stress so this would not be like a catastrophic thing but in this case what they're showing you here is a change in beak size in some finches. And the reason for this is because there was a serious drought. This was in the Galapagos.
And before the drought, the birds had these very small, kind of small beaks because they were eating things that were smaller, small seed. Actually, they weren't small seeds. excuse me that they were eating however during the drought those small seed plants tended to die off and the seeds that the plants that made it that they would feed off of had larger seeds and so birds that had a larger beak were able to get more food and so they were able to reproduce more and so what you saw was a shift in this whole population this whole species to a larger bill saw The two year span, the drought started in 1976 and ended in 1978. In the span of two years, you can already see this change taking place.
One of the things about this is because these islands... in a minute in from chapter 21. Island species tend to have smaller pop Okay, so you can see the change a lot faster in the smaller population just because there's not that many of them. Whereas in a much larger population, it would take longer to see that. Okay, so this is what directional selection is. Something in the environment, it could be a predator.
Because you could think about maybe there was something with the coat color that made the animal very obvious to the predator and so The predator was eating all those guys, but the ones that had a coat color that kind of faded into the background, they were able to survive. They've reproduced more. Now you've selected for a new coat color. You see that a lot, too. So you have all these interactions within the ecosystem that are kind of influencing what's happening at the gene level, at the genotype level.
And then disruptive selection. This is where you're actually selecting for the extremes. Okay, so now we're selecting for extreme. So what they're showing you here are differences in a certain insect, insect feeding habits. So the insect started out and it would eat apples, okay?
And that was because apples were flowering. and fruiting at the same time that insect larvae were growing. And so it was a natural fit. That would be their food. However, because of climate change, you know, things changing over time, the time for apple fruiting got out of sync with the larvae.
And so the insect now, there's no apple. So what is left? Well, first. Hawthorns have kind of an apple-like fruit, actually, and they were actually fruiting at the same time.
And so this whole population moved to feeding on hawthorns. So we selected for an extreme within that environment, and that shifted the population. Okay, so disruptive selection is, you know, usually you have, what's happening is you have the species in the same place when this is happening, and then something gets off in that particular environment. Does that make sense?
Yes, no, maybe? We are doing, we do this, humans do this, something called artificial selection. We select for things we want in plants and animals all the time.
We've been doing this for thousands of years. And there's actually an experiment that's been going on since 1890 at the University of Illinois. And what they have done is they're looking at corn.
They grow corn plants, and they select for high corn oil. Concentration reduction. So that was one of the things they did. They also had another part of the experiment where they looked for low reduction. So this is the high up here.
So since they started this experiment in 1890. They've just continually selected for only the ones that have the highest oil concentration, replant those, go in generation to generation. This thing now makes 20 times more corn oil than the one they started with. The low, these are the low-gum.
They actually stopped this experiment. Had to. Because the same thing was happening.
They would select for the low oil, replant those. That Reduced the fitness of those plants so much after 80 generations that the plants, they were not viable anymore. So they ended up stopping that part of the experiment because essentially they were selecting for something that was detrimental to the plants.
And so this experiment is still going on at Illinois and who knows, you know, in another hundred years, who knows how much oil these corn plants will produce. But you know we've been doing plant breeding forever. We have domesticated plants, we've domesticated animals. So all of the dog breeds that we have today, those were all selectively bred by human beings for specific purposes.
And so they're you know they're breeding for you know Datsuns right here. Now they have kind of long kind of angular heads and they're small bodies. they're actually made to go into little holes in the ground and get things out. They were bred for that.
Now we kind of look at dogs as pets. We don't use them quite for the same jobs anymore, but humans have bred these dogs. We domesticated dogs from wolves.
That was one of the first genetic experiments back in prehistoric times. People didn't even know they were doing it. Okay, so, you know, through breeding, we are influencing genotypes in plants and animals. So the last thing that Darwin and Wallace both noticed was, if you're looking at sex, so in these populations, you're looking at populations that are reproducing sexually, right? So if we're looking at evolution, we're looking at sexually reproducing populations.
They noticed that traits were linked to, of course, reproductive success, and there was some selection that went on as far as who reproduced and who didn't. Okay? And so there are two types.
Okay, the first is what we call intrasexual selection, and this is typically between males. General. So this is where males compete for females to reproduce with.
So here we see some moose who are fighting. This is a normal part of their courtship. You know, one wins, one loses. The loser doesn't get a mate. So the loser doesn't get to reproduce that year.
You know, maybe they have better luck next year. So you In this way, the strongest are going to be able to mate and reproduce more often than those that do not. Okay, so this is intrasexual, right?
So, you know, this is what you're focused on. one sex is involved in the selection. Okay, so the females are kind of outside of this. The other type is intersexual.
Okay, bird rate examples of this. So this is between males and females. And so a lot of times you'll see brilliant plumage in different birds.
So peacocks are a great example. Males have these ones we consider peacocks. The peahen, it's very drab. You know, she's just kind of brown.
But it's the, you know, it's that bright plumage that attracts a mate. Okay. So this is actually a bird of paradise.
It's a very beautiful plumage. You can see that. And the females in Bird of Paradise, they choose their mate based on those elaborate tail feathers.
So the males that have the better tail feathers are the ones they preferentially choose to mate with. So this is an example of intersexual selection. It's an interaction between males and females.
I'm just going to say a little bit about this. So there is a concept called genetic drift, okay, and it is sort of a random change in allele frequencies from generation to generation. And there are...
Two ways that you see this, you have bottleneck events and you have something called the founder effect. bottleneck effect is we talked about that last time actually so like at the end of the last ice age most humans died only there was only a small population of humans that survived to go on and reproduce okay that was a really catastrophic event and now you've shrunk your population down to a few members so you have actually caused a bottleneck in that genetic variety That's the bottleneck effect. So only those individuals that survived get to go on to reproduce.
And the difference in alleles that we had before, we don't have. The founder effect is something you can see really on any island. The founder effect is when you have a small population of individuals that move to an island. So they're separated in space from the...
the ones on the mainland. As they reproduce on the island, their genetic makeup is going to diverge from those on the mainland until eventually what's going to happen is they'll become so different that they cannot reproduce together. So now you'll have a new species that's born. Okay.
And so the, all of this, the reason you get this. Neck effects as far as genetics and founder effect is because of this genetic drift, okay, between the former population and the new population. I think that's pretty much it.
The only thing I also wanted to mention is can. Okay, so this is where individuals are preferentially choosing mates according to genotype. Okay, so that, so essentially you have...
You know, extreme cases where individuals of one genotype are only going to mate with people of the same genotype. In human populations, we see this in inbreeding. So in small communities where maybe the Ashkenazi Jewish community is an example of this, they only marry within their own community. So this is non-random mating. And that affects their genetic diversity.
The same thing is true that if you think about, some of you may have taken history, if you look at the European royal families, there used to be very close relatives who were marrying and having families. A great example of this is the Habsburgs in Spain. They have this...
they had actually a genetic defect of their skull that caused them to have these really long chins. If you look at the art from that period, you can see it. It's called the Habsburg chin. That is a genetic defect that's because of inbreeding between close relatives. And it only disappeared after the family started to, you know, choose mates that were not close relatives.
Okay, so inbreeding is a cause of this non-random mating. And the other thing you often see when you have populations that are, you know, not choosing mates at random, so you're not having new genotypes brought in, you will see some very rare birth defects and diseases that just pop up because you have better chance for those recessive alleles to show up because you're not actually bringing, you know, new people in. So there's very little variety in that, in the genotype for those individuals. Okay.
And the only thing I have to say about this is, this is the last part of the chapter, is that, you know, we used to just do evolution, look at evolution and natural selection by observation. Now what we're looking at, we're looking at observation, we're looking at the ecosystem level all the way to the molecular level. So we use, you know, modern genomic techniques, DNA sequencing.
We can actually track the evolution of genes, okay, and that's led to something that's called a molecular clock. So if you look at certain genes, you can see how much they've changed over evolutionary time between individuals. So hemoglobin, you can see, has changed quite a bit since our last common ancestor with... plants, animals, and bacteria, you know, millions of years ago.
One of the things that hasn't really changed as a vet, so this has a fast, what's considered a fast molecular clock. It's changed quite a bit. Pistons have a slow clock, right?
So you can see from our... The, this is the last, this is the last, so zero is the last common ancestor between vertebrates and insects. So 600 million years ago.
Histones have not changed much, right? They're just kind of sitting there. Very, very slow.
They're extremely conserved. Okay, so you can look at different genes and use this information, the differences between these genes, use this information to tell you how far apart. members of different populations are genetically.
And so this is the modern way we use to differentiate between species and subspecies. Okay, so that's what the molecular clock is. Any questions about everybody's tired Instructors are tired too.
So the last chapter is actually pretty straightforward. It's on how species develop, which is a direct, you know, directly coming out of what we just talked about. The most important concept in this chapter is the concept of ...logical species concept, and your book just abbreviates it as BSC.
And this is essentially one of the basic definitions we have for what defines a species is a species is a group of individuals that can... can reproduce together. If the other population can't reproduce with population A can't reproduce with population B, then population B and population A are different species.
It's the most common definition for this biological species concept. So it all revolves around reproductive. isolation. So when people kind of started doing this information, they kind of looked at, we look at specific traits. So what this is showing you is just basically looking at antenna and wing length in different butterflies.
And you can see that, you know, the small guy, the small butterfly. Right, cluster's right. Here the medium right here and the large one right here. So very distinct groups.
Okay now this doesn't this information does not tell me if these are different species per se. I can't tell that. I have to have information on their do they reproduce together. Maybe they do.
They just have different coloring. But you can see that these individuals in these different populations that look very different all kind of clustered together and they're pretty far apart when you graph them. Okay so initially when people were looking at this just kind of doing observational work in the field this is one way they started to tease apart different species okay and it actually was um It actually was Russell Wallace, I guess he went by his middle name, so it was Wallace that actually came up with this biological species concept because he was working in, you know, Southeast Asia and he also looked at elephant populations.
And so, you know, these are... If you look at Indian elephants and Sri Lankan elephants, they are reproductively isolated because of space. The Sri Lankan elephants are only in Sri Lanka, which is an island, and the Indian elephants are in India.
This doesn't mean that these elephants could not reproduce together. In fact, I think they can. But because they do not... We do consider them, we consider one of them a subspecies, okay, because they are isolated in space from one another.
They're not going to reproduce together unless you just physically put them together somewhere in a zoo, right? Because they're not going to be swimming to India or to Sri Lanka, okay? The other thing to think about when you have a species, you can have... Species that can reproduce and produce offspring.
Okay, so a horse and a donkey, for instance, they can mate and you get a mule. There's nothing wrong with the mule. It's physically healthy, but it's infertile.
It cannot reproduce. Okay. So it's not enough that you can just mate.
You also have to mate and have offspring that are also fertile to be the same species. So a horse and a donkey, even though they can mate, they produce a viable offspring, it's infertile. So they're different species. And the reason they're infertile is if you look at the chromosomes, they have a different chromosome number.
So you can't split it evenly and recombine and get the same thing. So the gametes are just toast, essentially. This is just looking at kind of the rule of thumb way to distinguish species is what it's called. We're looking at things that look alike. So these are three different butterfly species, but you can see they're, this is the chromosomes right here, and you can see they're all different.
Even though they look the same, okay, so you need a lot of information. It's not just enough to kind of see them and look alike. Say they're the same species, you need more information than just, you know, looking at something. A lot of times it does work, but sometimes it doesn't work.
So this is why we use something called DNA barcoding. to look for similarities in the DNA, okay? So, you know, there are some kind of complications to this.
So this, you know, again, if you have closely related species, they can interbreed and reproduce. And so in this case, what you get, so we have these two bird populations that live in Central America. So these are the parents and this is the offspring. Right, so they're the same genus, different species.
Okay, but they can interbreed and you get this hybrid. Okay, that happens quite a bit. The hybrid cannot reproduce with a member of either of the parental species. The hybrid can only reproduce with other hybrids.
And so as this hybrid group grows, they're going to become their own species because they are reproductively isolated from the parental species. And so what this map is kind of showing you, it's showing you the range of these birds. So in some cases, the birds are very much separated. So they're reproductively isolated in space, but in some places they overlap. And so you start to get these, this is where you'll start to get those overlapping hybrid populations, right?
And when you get enough of them, they're going to start to form their own population. So this is kind of another complication of identifying species. So as ecologists have kind of gone along, they've tried to kind of modify this whole thing to fit better.
And now they have this ecological species concept. And this is all based on a niche. So this is where something lives.
Right, so this goes back to when we were talking about competition between populations in the same place. When ecologists have gone around, they've kind of noticed that there are certain species that are very successful in certain environments, in their niche. When you get outside of that niche, they're no longer competitive.
Something else is competitive. And so this ecological species concept is... Looking at identifying a species based not just on all the information you have, but also on what is the niche that this is living in. And this has actually proven to be actually a very good rule of thumb.
It identifies individual species quite well. So in this case, we have some ladybug species. So they, you know, some of them live on the underside of one plant.
Others are living on these more upright leaves of a completely different plant species. Okay, so they live on different plants. They have different niches.
They're a different species, it turns out. If you look at all the molecular data, if you look at everything else, they're different. Okay.
They have different habitats. They have actually, they actually have different nutritional needs. They have different needs for water. So it really has worked out that this is a good, this is a good measure to kind of look at species.
Okay, you're going to talk more about this next semester, but you can also look at speciation using phylogenetic trees. And I'm not going to spend a lot of time talking about this. I just want to familiarize you with what this tree looks like. You're going to start at a certain place. This is the common ancestor.
And then you have kind of branch points, right? Every node is going to be a common ancestor and then you can branch. So this is actually looking at monkey, chimpanzee, gorilla, humans, right?
So chimpanzees and gorillas are, excuse me, chimpanzees and humans are the closest. We had a common ancestor, I don't know how many millions of years ago, right? So this is how you kind of read these things.
And the closer the bars are, you can see that those are the most closely related species, based on all information that we have. Okay, so you'll look at a lot of these phylogenetic trees next semester. And so this is actually, people that work in phylogeny call this the phylogenetic species concept. Okay, so something to be a separate species, it has to be reproductively isolated. Okay, and there are two different ways this can happen.
You can have reproductive isolation that happens before fertilization. That's called... something isolating that happens after fertilization that's post zygote so it's important to kind of be able to tell what these different things are and really we're just gonna we're actually gonna kind of look at them on this chart okay Lots of pre-zygotic barriers.
You can have behavioral differences, so they only mate based on specific behaviors. You don't have that behavior, there's no mating. So you can have that. You can have mechanical differences, so the reproductive organs themselves are incompatible.
Snails are actually a great example of this. Their shells have to... kind of have to have the same pattern for them to be compatible.
If it's the opposite direction that the shell is, the reproductive organs won't meet, so they cannot mate. You can have incompatibilities between the gametes themselves. They just won't hybridize. Okay, so that's gametic isolation. Temporal isolation happens a lot, especially in plants.
Plants are flowering. at different times. So when they flower, they produce the egg cells. They also produce pollen, which is the sperm cells. If they're not at the same time, you're not going to have them meet up to have a seed form.
This is a lot of temporal separation. That happens in animals as well. And then you can have what's called ecological separation.
They're they're divided in space by geographic features, mountains, rivers, whatever. Okay, so lots of those factors fall, you know, for prezygotic barriers. And then there are some postzygotic barriers.
So you can have, basically this is two ways. You can have fertilization occur, but the embryo, the zygote, does not develop. it just dies. Or you can have, as in the case of the horse and the donkey, you can have a viable offspring that's produced the mule, but it's not fertile. So it doesn't, it cannot reproduce for the next generation.
Okay. That's considered a post zygotic barrier. Okay. So this is the, what, these are the ways you get reproductive isolation. Okay, so if we look at populations that are in the process of becoming new species, so they kind of start out and then for some reason they separate a little bit, and maybe they're interbreeding, maybe they're not.
As you have generation after generation, you have mutations that get introduced, so they become more and more different. until you get two different species. Right, so they cannot interbreed, they cannot produce viable offspring. So the easiest way for this to happen is what's called allopatric separation.
So this is... Separation by geography. So like a mountain range.
In modern times this could be an interstate, this could be a highway that has now broken a population in two. Because they get killed if they cross the highway, they're allopatrically separated, okay? There are two different kind of subtypes of allopatric separation.
One is that individuals are colonizing a new area, okay? So that would kind of give you that founder effect that we talked about. So this is dispersal, right?
And then you also have this vicarious. This is where you have this mountain range or a river or something that is physically separating the two species. Or maybe there was a volcanic eruption and it created new features, you know, stuff like that.
That's vicarious, where you have this geographical barrier that splits them into two species. And then over time, because of mutation and because of... you know the separate sets of alleles that are within those populations you now will you will end up at a certain point with two separate populations um a good example of this is actually in some crawfish species that form that there used to be one population and this is so before the isthmus of panama formed Three and a half million years ago.
So actually, you know, in geological time, three and a half million years is like the blink of an eye. OK, so before you had this population, they were able to go across from the Caribbean to the Pacific. No problem. They were one species.
But once the isthmus formed, now they are separated. OK, so this is a vicarious event. OK, so now what you actually have.
are many different species that have formed over time on both sides. If you were to look at them, they look pretty similar. So you can tell at some point they used to be related, but they can no longer reproduce and produce with one another and produce fertile offspring. Okay, so you can see these little guys. So these are all the Different ones, you can see in this phylogenetic tree how they have differentiated from one another over three and a half million years.
Allopatric speciation, this is, again, this is allopatric speciation. It's just, again, it's the island effect. It's founder effect. You have, so this is the kingfisher.
It's a good example. Beautiful bird. It lives in Papua New Guinea and what people have seen is you have certain species on the mainland. Those are in the kind of the red and pink and then you have these very distinct populations on the islands in the blue and the purple.
They're new species. They can no longer interbreed with the mainland species anymore because they're separated by space. So this is an example of dispersal.
We're not going to worry about, you can learn about this in ecology, it's a little bit much. The other big type of speciation event that occurs is called sympatric. So this is actually where you have populations in the same place, so same, same.
Okay, so we saw those birds earlier that went from small beaks to large beaks, okay, and that's because they went from being specialized in all seeds to specialized in the large seeds. This had nothing to do with them being separated in space. They were still in the same place.
It had to do with the effects, an environmental effect, that caused the change, that brought on the change. Okay, so this is a result of disruptive selection, right? We have a natural event that is very disruptive in the population. In this case, it was a drought, okay?
So, you know, this is where you have kind of natural selection occurring in a relatively short time period. Results. that change in the beaks in what three years so and again it was in a small population okay so you're going to see changes like speciation types of changes trait changes way faster in an isolated small population than you are in like a large population over a huge geographic area you just have more individuals to deal with okay you can get speciation with or without natural selection Okay, it doesn't always, just because you have natural selection going on, doesn't always mean there's going to be a new species. Okay, so in this case, you had two species that formed in response to a very disruptive environmental catastrophe, a severe drought. Okay, but the drought went away.
Okay, so you probably still had some heterozygous in there, right? What can happen if this disruption is something like, you know, a volcanic eruption, you know, something really big that causes any mountain range or something where you really have big barriers or big changes where they're completely separated. So now you have these two populations that are separated for much longer periods of time. That is going to result in speciation. You're going to get new species because...
The heterozygous are just not going to really be there. Okay, and I think, so this is kind of just the review of speciation. So you have allopatric, right, separation by geographical space.
We have vicarious and dispersal, and then we have that peripatric speciation. We know there's sympatric speciation, but it's actually a lot harder to find sympatric speciation events than it is allopatric speciation events. So we don't really, at this point, we don't have a handle on how much speciation or species diversity has been caused by sympatric effects.
opposed to what we see from allopatric effects. We think that sympatric types of speciation happens a lot more in plants than it does in animals. Plants are unusually flexible.
They have huge genomes. Many of them are polyploid, like really polyploid. Plants can duplicate their genomes and they can tolerate that. ...this huge duplication of their genomes and it doesn't cause problems that actually makes them more fit, which is very different from what you see in mammalian populations. This is actually an example of sunflowers, helianthus or sunflowers, where you had a hybridization event between these two sunflowers, helianthus annus and petalaris.
They kind of grow in dry desert regions and they form this hybrid. Again, it's a helianthus, but it is reproductively isolated from its parents. So you get this, and this is kind of what they call instantaneous speciation. Because now we get a new species, it can only interact with itself.
So plants have some interesting... things that happen and one of the things that happens because plants form these hybrids a lot more often because what you see changing most of the time is the chromosome number. So maybe these are all diploid but this guy is triploid okay. Plants have a lot more flexibility.
If you take plant physiology, we'll talk about it. This is just kind of showing you a graph of polyploidy in plants. Plants have, they just duplicate their genomes many times.
This one is sitting somewhere up here. It has a ridiculous number of genome duplication events. It is these. Instead of being deleterious, if we had an extra chromosome, that would be a big problem.
In plants, it doesn't cause a big problem. It actually makes them better. So it's an interesting observation, differences between animals and plants.
Don't worry about that. All right. So our final exam is on Monday, 1030 in the morning, Lloyd Hall. I really enjoyed teaching all of you this semester.
It's been great having you in class. And I hope I see you in some of my upper level classes. Good luck on your final exams.