>> Hello students. This is Plants and Animals of Southern California. Today's lecture, today's lecture, I wanted to kind of extend our understanding of the origin of diversity. So before we talked about differentiation and I'll just recap that. Here we are in the desert and then there's this little mountain range in between us and the coast, and the coast is kind of different. It has a different climate. Because it has a different climate there's different vegetation. There's also different animals out there. So if we imagine that we had a lizard that started out living on the coastal climate and then somehow or other some individuals got transported over to the desert side. Then those two populations, they would start out being very, very similar to one another but they would live in different environments, and because they lived in different environments they would each adapt to their environment. So you know maybe the lizards on the coast they have a relatively thin skin because they get rehydrated more readily, and then the new inland population it would be under strong selection to have a much thicker skin because of a lack of water even during the active period during the winter, and so it would build up keratin in its skin faster. Also the ones on the coast they would have lots of vegetation around them and they might be adapted to be kind of camouflaged in that vegetation, maybe kind of a grayish color, whereas the ones out here they would be surrounded by rocks and those rocks would be different colors than the vegetation, and so natural selection would favor individuals that matched the color of the rocks better, or hid into the rocks better, and over the generations you'd have the buildup of different colors and little flecks that made them so that they hid into the rocks and so on. Also the growing season might be much compressed on this side of the mountain compared to the other side of the mountain. So you would have a number of ways in which these two populations differentiated. That's the differentiation of populations. But the tree of life is more than just the differentiation of populations. The tree of life has branches on it and those branches on the tree of life don't merge back into each other all the time. You and a seaweed are not mating with each other and then making a new species, like that's not the way the tree of life works. So maybe this lizard that is on the desert side and the coastal side they might form a new population that is say on the coastal side but is formed by the mix of the two locally differentiated populations, and they might mate with one another and then give rise to some new variation, but that's a little bit different than you and the seaweed. So at some point as the tree of life is growing new branches, those branches come to be so incompatible with one another that they can't reticulate, they can't fuse back together. And we call that process speciation. It's kind of an unfortunate word, an unfortunate name because you might think speciation would be like the origin of species, but all of this stuff is the origin of species. Like the differentiation is also the origin of species. And there's another, a number of other aspects of the origin of diversity that we think of as, you know, kind of like the origin of species. Whereas this is picking out just one aspect of a process and so the formal definition, unfortunate though it is for speciation, is the origin of genetically based reproductive isolating barriers; genetically based reproductive isolating barriers. When two lineages have diverged so much that they can no longer inner breed very much then we say that they've undergone speciation. And that can be through lots of different reproductive isolating barriers. So if we're considering say plants then it could be that the reproductive isolating barrier that forms first is the difference between the pollen and the style tissue and they come to no longer be compatible with one another and so they can no longer regularly produce seeds. Or it might be that they do produce seeds but then the seeds that are produced are just sickly because they've co-mingled genes that are adapted to two different things and they just, you know, kind of don't work. And then if you have these plants that were adapted to different places, even if they could mate and they could form good seeds and those seeds could grow up to be good plants and those plants could produce themselves good seeds, then it could still be that the plants are so adapted to different habitats that they're ecologically isolated from one another. If a plant is adapted to the top of the mountains and another population is adapted to the coast and neither plant is adapted to intermediate elevations, then those two lineages have officially speciated whether we call them different species or not, you know, whether we name them as different species or not. So that's ecological isolating barrier which is an example of a reproductive isolating barrier. So if we then sort of follow this chain of logic, of this chain of definition, where we call something speciation when there's been the origin of a reproductive isolating barrier, then we end up calling the resulting things biological species, which is another kind of high falutin language because these biological species might not correspond to the taxonomic species, the things we actually give names to. They also might not be monophyletic groups. What if you had a widespread progenitor species and then some chromosomal change happened in some isolated population and it gave rise to a derivative species and that derivative species was just derived from a very adjacent part of the widespread species. Then the widespread species would not be a whole and complete branch of the phylogeny. The two together would be. The derived species would be but the widespread species would just still be a partial branch. In other words it would be paraphyletic in our terminology. And so having things that are reciprocally monophyletic is not exactly the same as biological speciation, which is not exactly the same as what taxonomists give names to. So it ends up that we have three different definitions of species and other people could come up with more than three, and these three definitions of species are related to each other, they all have to do with the origin of biodiversity, but they are not exactly the same. It's kind of like words in the dictionary like china, which could be a country in the Far East or it could be a kind of porcelain. Now in that process we might wonder what is causing the characters of incompatibility to have diverged enough so that they are incompatible; the characters of incompatibility. Now one thing it could be is that it could be that they're the same characters, right, like what if the character is when you are ready to breed. And on the desert side of the mountains when you're ready to breed is in March. You know that's the adapted time to breed. If you don't finish breeding then, then your babies are not going to grow up before everything dries out. Whereas on the coast side it might be that the right time to breed is during June gloom and so they diverge enough in the timing of breeding so that then they never, when they come back together they're not ready to breed with one another, you know, it's not like the right moment. So that would be when it's the same character and that's a little bit different than if what happens is they adapt to the different colored surroundings. These ones on this side of the mountain adapt to be kind of a sparkly, mica and red color and those ones on the other side of the mountain adapt to be grey, but the molecular basis for being sparkly with little flecks in it versus grey is something that's genetically correlated with the proteins that are in the sperm and the egg and allow the sperm and the egg to meet up with one another. So it could be that it's the same character, it could be that it's not quite the same character, it's two characters but they have a genetic correlation between them so that when you have adapted divergence to an ecological situation in one character, it causes a correlated response in the characters of mate recognition. Alright, well that's all I have to say about that.