Species

hi. In this video, we're going to talk about species, what they are and how they form. Now. Speciation is the process by which an ancestral species splits into two or more species, and we can see that there are really two types of evolution at play or to kind of broad categories. You can have micro evolution, which is the change in alil frequencies in a population and macro evolution, which is broad patterns and evolution well above the species level. So speciation kind of serves as a link between micro and macro evolution. As the change in Lille frequencies in a population grow, we can eventually have a speciation event, which ultimately will lead thio patterns of broad evolution over long periods of time. Now we're normally going to be talking about species according to the biological species concept, which is basically the idea that species are defined by reproductive barriers. So what does this mean? Well, you can have something called reproductive isolation, which are basically mechanisms that prevent two species from mating and producing viable offspring, and we'll get into the details of that in just a moment. However, it's also worth noting that you can also form hybrids which are offspring that result from inter species mating. However, thes offspring tend to not be viable, and we'll talk about what all that means in a moment. So here you can see a sort of nice example of speciation. You have this initial population of fruit flies, you separate them and give them different foods and let them, uh, go through several several generations of breeding. And then when you mix those two populations back together, well, most of the yellow flies that were in this had the starch available is food. They're gonna want to mate with each other. Those maltose flies, they're gonna want to stick with each other. Inmate You might have a few that will mate with each other, but you have the beginnings of speciation. These organisms are starting to diverge. Now, when we talk about reproductive isolation, there are different types of barriers that must be overcome. And we group these into pre psychotic barriers as in mechanisms that prevent zygote formation and post psychotic barriers which prevent thes I go from functioning properly. So pre psychotic barriers include gametes that won't fuse behavioral differences in court, in courtship and what's called mechanical isolation, which is basically the idea that organisms don't have the right parts to mate. Uh, think of this as a sort of round hole square peg scenario. Now, post psychotic barriers are basically when hybrids are sterile or do not survive. They die very quickly because again, these are not viable offspring. So if the offspring are sterile or, uh, do not survive and die very quickly, that means they are not viable. And over here you see a nice example of post psychotic barriers. These organisms are called Lie Gers. Yes, this is a hybrid between a lion and a tiger. It's Napoleon Dynamite's favorite animal. And guess what? Lie gers are totally sterile. You can make laggers, but you can't have laggers mate with each other and make more laggers. You can Onley form the hybrid through a mating of a lion and a tiger. Now let's turn the page and talk about some other details

Now, in addition to the biological species concept, there are other definitions of what a species is. For example, there's the morphological species concept which defines species based on morphological features as in how they look, what sort of shared features do they have. Um these can both be sort of outward appearance things and more internal physiological similarities. There's also the ecological species concept which defines species in terms of their niche, and that basically means their little carved out role in their environment. So the nice thing about the ecological species concept is it really works for a sexual species, which you may not have realized. The biological species concept doesn't work so well for because the biological species concept kind of relies on sexual reproduction instead of a sexual reproduction. Now lastly, there's the villa genetic species concept and that's the defining species based on the smallest group of individuals sharing a common ancestor on the philo genetic tree. And that tends to be a nice way of defining species, especially when you're trying to make broad stroke inferences and looking at both sexual and a sexual organisms. So how does speciation actually occur? Well, one type of speciation probably the easiest to understand is called aloe patrick speciation and this is speciation that begins with geographic isolation. Ala Patrick actually means different country in greek. So the idea is that the species resulted from one species getting split and divided by geography. So here you see that we have this initial species of tree. But over the course of a really long time and that's an important point to make a really on time. A river divides these two populations and due to the difference in their environments. As a result of this division, they will begin to diverge until eventually they become two different species. And there are many examples of this that you can look up if you're interested. Now let's turn the page and talk about a different type of speciation.

Unlike Allah Patrick speciation in Sim Patrick speciation. The population that divides into multiple species actually lives in the same geographic area. Sim Patrick means same country in Greek, and this can occur due to disruptive selection, which favors those extreme FINA types like we saw before. And once we have disruptive selection with those extreme FINA types favored, those FINA types can continue to diverge, get more and more different from each other and eventually become two different species. Now you can also have Sim Patrick speciation due to something called Polly Ploy T, which is when a biotic or my ta tick error leads to the doubling of chromosome number. Now this tends to be fatal for organisms like you and I, but for plants, it's actually not that harmful. And this has led to some major evolutionary leaps in plants. You can have what's called auto polyp Lloyd E, which is that when that mutation resulting the doubling of chromosomes comes from the same species, so you have two sets of chromosomes from one species. You can also have a low poly ploy T, which is when parents from two different species mate and produce an offspring with two sets of chromosomes from both species, So this is generally seen in plants. And we can say that here, in our example here, in our example, perhaps what's happening is a form of disruptive selection or polyp loyalty. Either way, this population of trees is in the same location. However, speciation still occurs now. Generally, when speciation happens, you tend to see something called reinforcement, which is natural selection for traits that isolate a population or essentially reinforce those barriers between species. However, sometimes you will see the formation of what's called a hybrid zone, which is a geographic region. Were interspecies. Breeding occurs and hybrids are common, and we have these all over the world for various different species. What's interesting is from hybridization. New species will sometimes arise because in hybrid zones you'll tend to see three things happen. You'll either see reinforcement like we talked about and in reinforcement, the hybrids. These guys right here, this that's what be kind of bluish purple color is supposed to represent. These hybrids are less significantly less fit than the pure bred species and the pure bred species. The pure bred species continues to diverge, so we see one offshoot going this way. One going that way. So they're going to continue to diverge, which is going to reinforce those barriers. Those differences between them. Occasionally, though, you will have a fusion, which is where those two separate species actually merge into a single one. And that's when those hybrids these guys right here. Those hybrids tend to be very fit. Lastly, you can have a sort of stability situation. So here we just have a stabilizing Oops. Stabilization. And here what's gonna happen is the hybrids will continue to be present. The two species will continue to be present, but they won't continue to diverge from each other. Everyone is going to just kind of chug along businesses usual. No reinforcement, no fusion, just a stable situation. So that's all I have for this video. Guys. I'll see you next time