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  • Hi. It's Mr. Andersen. And welcome to the Unit 2 review. In this podcast I'm going to

  • talk about speciation. We're going to talk about speciation, extinction, mechanisms of

  • speciation. But before we get started we should define what speciation is. Speciation is essentially

  • a biological process by which new species arrive. And so all life on our planet started

  • with what we call the last universal common ancestor. All other species that we have on

  • our planet then arose through speciation. So the formation of new species. And so let's

  • start by talking about what phylogenetics are. Phylogenetics are basically the evolutionary

  • history of species and organisms on our planet. So this right here would be an example of

  • a, let me get a different color, a phylogenetic tree. And so basically time is going to go

  • in this direction on a phylogenetic tree. And so it's going to start with an ancestor

  • of all the different organisms on this tree. This one happens to be about whales. But every

  • time we see a branch point like that or if we have branch point up here, then we eventually

  • have two new species. So this would be a speciation event. Each of these junctions then on a phylogenetic

  • tree is simply going to be a common ancestor. And so what is this point here actually mean?

  • It simply means there was a common ancestor between the southern minke and northern minke

  • whale at sometime in the history. Now I don't want you to memorize a lot of phylogenetic

  • trees, except this one over here. This is the phylogenetic tree of all life on our planet.

  • And so basically we have the three domains of life. And those are bacteria, archaea and

  • then eukaryotes. And so if we were to look at this tree what we find is that there's

  • a really early branch point. In other words a branch point between the bacteria on one

  • side. And then the archaea and eukarya on the other side. What does that mean? Well

  • you're more related to an archaea then to a bacteria. And so we had a branch point here.

  • And then we had another branch point, this one broke down into the archaea and then into

  • the eukarya over here. And so basically this is the phylogenetic tree of all life on our

  • planet. We've never found life on our planet that doesn't fit into one of these three domains.

  • And so basically looking at this tree we can say this point right here is the point at

  • which that last universal common ancestor existed. Now could have there have been earlier

  • life before this branch point? For sure. It just didn't leave any kind of a fossil record

  • or it didn't leave any ancestors. And so that last universal common ancestor will come back

  • to later in the podcast. So let's talk about speciation, specifically in relation to extinction.

  • And so speciation again we say is the formation of new species. Extinction is going to be

  • the opposite of that. In other words when species when species leave. In other words

  • if we're looking at time in this direction, so this is a specific type of a saurapod,

  • a type of dinosaur. Basically this would be ancient past and this is time moving in this

  • direction. So every time we see a branch point like that, that's a speciation event. Every

  • time it comes to an end, so right here it comes to an end, that would be extinction.

  • And so all of the organisms we have on our planet today either form through speciation

  • or will disappear through extinction. Two big things that I want to talk about in relation

  • to speciation and extinction are number one, mass extinctions. Mass extinctions are going

  • to be extinctions where it's not just one species getting wiped out but a number of

  • species getting wiped out at the same time. So the extinction of the dinosaur is an example

  • of a mass extinction. And we're pretty sure that that was caused by an asteroid impact

  • just off the Yucatan peninsula, in the Gulf of Mexico. And so we had this massive extinction

  • of a number of species at that time. Now was it the asteroid impact or climatic changes

  • after that? We'll probably figure that out. But that's a mass extinction. We've had like

  • five mass extinctions. And you're lucky enough to be right in the middle of probably the

  • biggest mass extinction of all. Humans are making climate changes that species simply

  • can't adapt quickly enough to. Okay. So I said there are two things I wanted to talk

  • about. One is mass extinctions. The second is something called adaptive radiation. So

  • adaptive radiation is when we have just one species that branches into a number of species

  • very very quickly. And so example. Let me give you a couple of examples. When Pangaea

  • formed and all the continents came together we had a giant desert in the middle of the

  • super continent. And it was bad for life. So we had a mass extinction. As the continents

  • started to break apart then we had all of these little niches between the continents.

  • And so we had adaptive radiation of dinosaurs. The dinosaurs did really well and filled all

  • of those niches. Okay. That was followed by a mass extinction of this asteroid impact.

  • Which in turn was followed by adaptive radiation of mammals filling those niches that were

  • once filled by dinosaurs. And so adaptive radiations can be large scale. For example

  • the exploitation of mammals of these new niches that were vacated by dinosaurs. Or it could

  • be even at the local level. So those first finches that landed on the Galapagos Islands

  • adaptively radiated to fill all of those niches on the islands. Next thing is the artificial

  • selection lab. We haven't done this yet. But in the artificial selection lab what we'll

  • do is we'll use these Wisconsin fast plants. And we're basically going to choose traits

  • that we want in the offspring. And then we're going to set those crosses up. And so we'll

  • use a bee stick where you take a bee and you put it on a stick. It's a dead bee, but you

  • can transfer pollen from one plant to another. You then get seeds and you can choose the

  • characteristics that you want. So is this artificial selection? Yeah. Because we're

  • making the choices. Not natural selection. Now all of these creatures were made, at least

  • their characteristics were made through artificial selection as well. So dogs are wolves if you

  • look at the DNA of dogs and wolves its essentially the same thing. But humans have selected for

  • traits that they wanted over time. And through that we've been able to create species. If

  • you were to show somebody, they didn't know about dogs, a chihuahua and a great dane,

  • and say these are of the same species, they would say you're nuts. And that's because

  • we've changed them so much. Bent them a little bit to our will. What are some mechanisms

  • by which speciation can occur? Well if we're talking geographically, let me give you an

  • example of that. And so let me try and draw the United States. This is really bad. There

  • we go. So there's a species of meadowlark that lived right across here in North America.

  • So it lived in these mid kind of latitudes. During the last ice age we had a, let's get

  • a different color, so we had the ice sheet move down right down like this and fill up

  • that center part of North America. So now what we had was meadowlarks that were over

  • here. We had meadowlarks that were over here. And those were isolated geographically. Now

  • there are two types of geographic isolation. One is allopatric. At least our book talks

  • about. Allopatric is when those different populations are separated geographically in

  • different lands. Sympatric I'll get to in just a second. Okay. So we had our meadowlarks

  • that were separated by this ice sheet. Now the ice you know eventually melted and retreated.

  • And after it had done that then we had these two populations, the western and the eastern

  • meadowlark. Now during this period of time they developed different songs. So they had

  • different behavior. And so even though in this margin we'll probably have eastern and

  • western meadowlarks in the same area at the same time, since the males impress females

  • with their songs, they can't communicate anymore. And so this would be how species are formed.

  • I'd said that sympatric speciation is different. Allopatric speciation is when you're in different

  • lands. Sympatric speciation is when you're in the same land. And so that's when we have

  • a population. And then we get a new population within that population. That generally occurs

  • in plants. And it generally occurs using polyploidy where we have a mistake. Where an increase

  • in the number of chromosomes creates a brand new species. And so that would be a genetic

  • polymorphism. So when we have a change in the chromosome number and it creates something

  • brand new. It happens a lot in plants. Rarely in animals. Now the two things I haven't mentioned

  • are peripatric and parapatric. And I say those exactly the same way. That's when organisms

  • move into a niche, nearby niche that maybe isolated or it maybe even attached. But now

  • they start adapting to their local environment. And so the forest elephants of Africa moved

  • into the forest. Moved into the niche. And so they're getting a different appearance

  • and eventually will create a brand new species. Okay. So those are geographic. Four types

  • of geographic isolation. Behavior isolation, I kind of mentioned is when you're behavior

  • keeps species from breeding. Temporal isolation is, I always remember the T stands for time.

  • That's when they mate is going to create new species. In other words if this frog breeds

  • in the spring and this one in the fall, even though the could form hybrids, they're not

  • going to. And then mechanical isolation could be mechanical isolation of the anatomy. For

  • example these snails. Some of them are turned clockwise and some are counter-clockwise.

  • So their sex parts can't quite get together. But mechanical isolation could be isolation

  • of, you know, even the egg and the sperm can't get together. And so that would be another

  • thing that can create brand new species. Okay. If we talk about natural selection within

  • species, now we're starting to talk about changes in a bell shaped curve. And so in

  • anything, pretty much every trait that we have, unless it's caused by one or even a

  • couple of genes, it's going to give you a phenotype that is a bell shape curve. So this

  • could be skin color in humans. It could be height in humans. It could be length of thumb

  • in humans. But we're essentially made up of a bunch of these bell shaped curves. And so

  • if you ever have selection on one side of that, you can push a bell shaped curve in

  • one direction or the other. We can squeeze a bell shaped curve. We can make it tighter

  • on the sides. And basically there's three things that we can do to a bell shaped curve.

  • First one of these is called directional selection. That's where we're actually moving it in one

  • direction. The quintessential example of this is the Galapagos finches that the Grants were

  • studying on Daphne Major. So basically they measured all of the beaks of the birds on

  • Daphne Major. They collected all of the birds that they could possible catch. They found

  • 751 birds. And this is the average beak depth. Okay. Now they had a massive drought. So they

  • had a bird apocalypse. And so they came back in 1978. There were 90 birds that survived.

  • So almost all of them had died. But the bell shaped curve you can see had switched over

  • here to the bigger side. And the reason why is the beaks were now able to open seeds that

  • they couldn't open before. What happened to the birds that weren't able to open up those

  • seeds? They died. So they died and that's why we see the bell shaped curve moving in

  • this direction. And so remember in natural selection it's not like organisms are changing

  • the way they are. They can't do that. They're either dying or surviving based on the characteristics

  • they have. And so the population can change. Or the population can evolve over time. Disruptive

  • selection is when we have, oops, is when we have either pressure pushing them apart. Or

  • it could be drawing them to the sides. So we have a pressure here that is removing individuals

  • that are in the middle. And so an example of that could also be found in the Galapagos

  • finches. And so why do we have so many different types of beaks in the Galapagos finches? Well

  • each of those birds are modified so they can feed on a specific seed. And so once those

  • first finches got to the Galapagos, they landed and flew to different islands. And they were

  • able to adapt to that specific climate. And then finally we can have stabilizing selection.

  • An example of stabilizing selection is when we squeeze the bell shaped curve together.

  • An example I always give is babies. If a baby weighs one pound it would never be able to

  • survive. If it weighed 21 pounds it would not survive and it would take mom with it.

  • And so basically babies weigh about 7 pounds. Because there's pressure on either side. Eliminating

  • babies at the extreme. A specific type of natural selection that puzzled scientists

  • for a long time is in the amazing shows of like the peacock or the songs of birds or

  • the colors or the butterfly or the huge antlers in an elk. Basically what's going on here

  • is sexual selection. So it's not nature making a choice as to who survives. It's females

  • making a choice as to males. So essentially she's checking out this peacock. She's looking

  • at his feathers. And she's making a judgement call. If he isn't able to produce feathers,

  • isn't able to produce the correct number of eye spots, he probably can't produce fertile

  • offspring as well. And so whenever females make a choice that's when we get this weird

  • dimorphism, this change between males and females. Kind of finishing up in the beginning.

  • So basically how did life on our planet, before all of this speciation take place, how did

  • it form? Well a lot of scientists are thinking that it is through abiogenesis. In other words

  • it came from non-living material. Now we know that life just doesn't spring from nothing.

  • Especially today when oxygen is present and it's going to break down chemicals quickly.

  • But the famous Miller-Urey experiment, what they did is they basically created the early

  • earth's atmosphere. They got rid of oxygen. Included water, methane, ammonia. And they

  • added a shock to kind of simulate lightning. And what they were able to do is produce the

  • building blocks of life. Amino acids, nucleotides. And so they were able to make the genes that

  • would be found in this last universal common ancestor. Today we see an area where that

  • might be in the stromatolites that we find in this area kind of in this tide pool kind

  • of an area. It's similar to some of the first fossils that we found on our planet. But maybe

  • life was delivered here in a meteorite from Mars or from a different planet. We don't

  • know. And we'll probably never know what that first ancestor looked like, that first cell.

  • But we have a not of theories that kind of point us in the right direction. So I want

  • to finish with kind of a walk through time as far as life goes. I don't expect you to

  • memorize all the different periods of time. But I do want you to know the progression.

  • And so if we look back the earth formed about 4.6 billion years ago. For most of that first

  • part it was just a ball of magma. And so it was just a molten ball of magma. So life couldn't

  • have existed on it at all anyway. But basically around 4 billion years the first life on our

  • planet formed. And that was prokaryotic life. And so that was, let me get a different color,

  • so basically the first life on our planet was that. It had genetic material on the inside.

  • Probably similar to a bacteria. But it was a simple cell. So this is the first life we

  • have on our planet. If we play the clock forward, photosynthesis start here. We start to get

  • an appreciable oxygen in the atmosphere which actually adds pressure to species that aren't

  • designed to work well with oxygen. And so our next big thing that happens, so here is

  • prokaryotic life. Next thing we have is eukaryotic life. So eukaryotes show you know like 2 billion

  • years ago. Now eukaryotic cells are going to be different than prokaryotic in two ways.

  • Number one they have a nucleus. And they've got the genetic material inside there. But

  • they also have all of the other parts of a cell. So they have like golgi apparatus. They

  • have endoplasmic reticulum. They have mitochondria. They have lysosomes. And so they have all

  • these organelles that are separated by membranes. Now how did we go from prokaryotic cells to

  • eukaryotic cells? Well two ways. Number the membrane started to fold in on itself. And

  • so we got what's called an endomembrane system. That's how you get an golgi apparatus. That's

  • how you get lysosomes. But we also had mitochondria. So mitochondria were probably bacteria that

  • moved into cells. Chloroplasts the same way. So now we had eukaryotic cells. If we play

  • the clock forward, we eventually get to multicellular life. And then it's awhile before we get to

  • animals, plants, mammals. And then humans show way up in the end. So multicellularity

  • comes when we have cells working together for a common purpose. Why is it that we don't

  • see animals and plants moving onto land until much later? It's because the atmosphere was

  • not really formed yet. Until we had an ozone, until we had a defensive atmosphere, life

  • had to exist in the oceans where it was protected from that. And so you stand at kind of a unique

  • time. It's not been long that humans have been around. But we have had some huge impacts

  • on our climate that are probably going to impact species and lead to that maybe sixth

  • mass extinction. And so that's speciation in a condensed form. And I hope that's helpful.

Hi. It's Mr. Andersen. And welcome to the Unit 2 review. In this podcast I'm going to

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B1 speciation extinction selection ancestor planet isolation

Unit 2 Review - Speciation

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    Morris Du posted on 2015/10/22
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