this lecture is the second lecture in a series of three lectures on the concept of evolution the material in this lecture is predominantly in chapter 24 of your texbook which is Campbell Biology 10th [Music] edition I have divided this lecture into two large subjects first off we're going to take some time defining what a species is second off we're going to try to talk about some of the ways you can end up with species the last lecture focused on the idea of microevolution microevolution is the change in the gene pool of a population from one generation to the next it's very small scale changes in a population the organisms in that population still are the same species however they might appear or act differently from one generation to the next showing the change over time the thing is with micro Evolution if it's allowed to continue long enough you could actually end up having populations appearing and becoming different enough from each other that they can be considered different species this is speciation speciation is the process by which one species splits into two or more species of course every time speciation occurs the diversity of Life increases what's really interesting if it's have to go on long enough for example 3.5 billion years which was when as far as we can tell the first ancestor of all living things on earth evolved we can end up going from one living ancestor or one ancestral group to the many millions of species that live on earth now this figure is a nice depiction of the idea of speciation the organism on the left could be considered species one that over time diverged into a couple of separate populations those populations became different enough that they ended up being the organisms on the right the top one being species 2 and the bottom one being species 3 now the word species actually comes from Latin which means kind or appearance so think of it as the same kind or the same appearance the thing is defining a species or exactly what individual is in one species versus a different species is actually pretty tough even though it seems like it might be intuitive for example how similar do individuals need to be to be considered the same species or how different do individuals need to be to be considered separate species and what keeps one species distinctly different from others it turns out that different kinds of organisms would need different kinds of ways to Define species therefore there are many different definitions of exactly what a species is there's not one definition fits all organisms unfortunately in this class you are going to be responsible for four different definitions of a species our first definition of a species is the biological species the biological species concept defines a species as a group of populations whose members have the potential to interbreed in nature I'd like to point out in nature meaning they come across each other and are able to interbreed uh I'm not talking about organisms that we can force gamet Fertilization in a laboratory setting or any a zoo setting uh but whose members have the potential to interbreed in nature and also produce fertile offspring this actually seems pretty intuitive if I asked you H what you thought a species was this is probably what you would come up with and this is the first definition that I would actually come up with but basically what this says is that members of a species are similar and included in the same species because they reproduce with each other and do so naturally the biological species concept would also mean that indiv individuals are separate species when they do not successfully mate with each other they are distinct from each other because they do not share the same gene pool when you have organisms that do not mate with each other you have organisms that are reproductively isolated reproductive isolation is just merely something a behavior a structure a morphological feature that prevents members of different species from successful y mating with each other this prevents gene flow between species and maintains separate species the biological species concept would therefore consider these two metal archs two different species of metal archs to be separate species the metalarc on the left is the Eastern metalark this is the metalark we have here in Georgia when we have metal ARs and the metalark on the right is the Western metalark it turns out that we have no idea if these guys can inter breed but since they do not overlap in their range in nature they do not interbreed therefore the biological species concept would consider these separate species despite the fact that they look so similar the biological species concept would also in consider all of these Strang looking organisms as being members of the same species this is because these individual idual can successfully interbreed with each other and produce fertile offspring and in fact do interbreed with each [Music] other okay so the biological species concept sounds perfect sounds like it's a very nice definition of a species however there are problems in this class you're going to be responsible to in understanding three main problems with the biological species concept I'm going to discuss these three Concepts or these three problems with the biological species concept on the next three slides feel free to refer back to this slide to visually read these Concepts I'm going to verbally discuss them on the next three slides though one problem with the biological species concept is that some organisms that are very obviously separate species do occasionally interbreed and prod produce fertile offspring for example with the reduction in habitat uh for polar bears polar bears are now ranging further and further south previously their ranges did not overlap with the grizzly bear but now that they're being first forced further south they are now overlapping with grizzly bear ranges occasionally there are successful interbreeding attempts between polar bears and grizzly bears those breeding attempts will sometimes result in something called a grower bear a groller bear is considered a hybrid a hybrid is just The Offspring of two different species so what do we do about the groller bear when it comes to the biological species [Music] concept the second difficulty with the biological species concept is that it re res it relies on our knowledge of the breeding of various organisms therefore those organisms need to be alive and around for us to observe so what do we do about organisms that only exist as fossil evidence for example this particular organism or skull is from the Neanderthal the Neanderthal is um not so much our ancestor the crom Magnum is actually the ancestor of humans of modern-day humans but neanderthals and chrom Magnums actually existed in the same place at the same time in Europe about 67 million years ago well how do we decide that the Neanderthal is a specific different species from a chrom magnum we really don't know if these organisms are interbreeding there's a lot of research that has been done to try to figure out the degree of inter breeding between these organisms but frankly we actually can't go observe these organisms so the biological species concept is problematic for organisms that are extinct finally the biological species concept only relies on organisms that are sexually reproducing there are a number of organisms that reproduce asexually therefore there would not be any mate selection between individuals for example this amoeba this amoeba when it gets ready to reproduce basically gets bigger and bigger makes a second copy of its nucleus and splits in half bam it has reproduced how do we know that this sort of grayish bluish amoeba is a separate species from say a hot pink amoeba we just don't know because of the drawbacks that we have about the biological species concept there are many situations in which we have to have additional species Concepts or definitions of a species the second species concept that you are responsible for is called the morphological species concept in the morphological species concept we classify organisms as species or not species uh based on observable physical traits what they look like this can be applied to asexual organisms well that gray bluish amoeba is clearly a separate species from the hot pink amoeba because they look very different we can also apply this to things like fossils that chrom Magnum is clearly a separate species from the Neanderthal based on the shape of the brain case however one problem is that there's subjectivity in deciding a which traits to use and B where to put the cut offs what do if we know that the gray blue one amoeba is a separate species from the hot pink amoeba what about a lavender amoeba would that be a gray blue species or a hot pink species who decides what how different organisms have to be to be separate species and how similar they have to be to be the same species I'd like to point out the morphological species concept is the concept that's actually used by many field biologists and it is relied on quite a bit in field sides uh for example there are many species of oak trees in North America unfortunately in a pinch oak trees actually can interbreed with each other quite a bit so the way we delineate between different species of oak trees is by what their leaves look [Music] like according to the morphological species concept the Eastern metalarc on the left would actually be the same species as the Western metalarc on the right even even though they don't inter breed moreover the morphological species concept would also consider the Eastern spotted skunk which is on the top to be the same species as the Western spotted skunk which is on the [Music] bottom so the morphological species concept although having some strengths also has some drawbacks the next species concept you're responsible for is the ecological species concept this concept defines a species by its ecological role its Niche basically it focuses on the unique adaptations that a individual has to particular roles in a biological community for example two species may be similar in appearance so they would be considered the same and morphological species concept however you could distinguish them from each other by things like what they eat what are its needs where do these organisms live so this might be able to further separate species versus the morphological species concept the last species concept you're responsible for is one that's most recent this is the philogenetic species concept this species concept defines a species as the smallest group of individuals that shares a common ancestor and thus forms one branch of the Tree of Life this concept actually relies quite a bit on biochemical analysis so that is why it is a more recent species concept uh because we've only recently as in the last 102 years been able to genetically uh decode these organisms biologist trace the philogenetic history of a species to ascertain how long ago they had a Comm ancestor by comparing not just the morphology of the organism but also its DNA and maybe its amino acid sequences we do have a slight problem with this still though in that defining the amount of difference required between two organisms to be considered different species or how similar two organisms have to be to be considered the same species is still difficult who decides where the cut off is now with these four species Concepts do keep in mind that the appropriate definition of a species very much depends on a what organism you're looking at and B why you need to know the difference between different species and so these species may be appropriate to use or species Concepts may be appropriate to use in one situation and may be inappropriate to use in a different situation when I mentioned mentioned the biological species concept I briefly talked about the fact that the biological species concept relies on reproductive isolation organisms that have reproductively isolated from each other have what are called reproductive barriers a barrier to reproducing what reproductive barriers do is they serve to isolate the gene Poes of species and they prevent interbreeding scientists went out and checked out all the different kinds of reproductive barriers that occur in nature and they discovered that reproductive barriers come in two broad categories and these categories depend on whether the barrier comes into play before a zygote forms or after a zygote forms I'd briefly like to Define what a zygote is a zygote is merely a fertilized egg the moment that the nucleus of the sperm fuses with the nucleus of an egg you will end up with a single celled organism with a fused nucleus that little organism is considered a zygote when it's still single celled but it has a sperm and egg nucleus recently fused so these reproductive barriers sometimes kick in in a prezygotic method prezygotic barriers are barriers that kick in before successful fertilization has occurred so before a zygo forms postotic barriers are the other category of barriers these are barriers that kick in after fertilization has been successfully completed and a zygote has formed so let's think about these kinds of reproductive barriers through this diagram first off let's pretend there are no barriers if there are no barriers to reproducing we have two organism depicted as a red sphere and a yellow sphere at the top those two organisms find each other they successfully mate the egg and sperm nuclei successfully Fus through fertilization resulting in a zygote and that zygote is actually fertile and viable and a able to make offspring of his own that would be an example where there is not a reproductive barrier however if these two organisms do have reproductive barrier there's a number of possibilities about when and how those barriers will come into effect if the barrier occurs before fertilization it's considered a prezygotic barrier you are going to be responsible for five kinds of prey zygotic barriers which I will get into in the next few slides if that reproductive barrier kicks in after fertilization has successfully happened and thus a zygote is formed then it's called a post ptic barrier there are three kinds of postotic barriers you're responsible for in this class so let's start with those prezygotic barriers the remember prezygotic barriers either prevent nating or definitely prevent fertilization between members of separate species the first kind of prago barrier is when organisms are separated from each other because they live in separate habitats by separate habitats I do not mean two separate Geographic ranges these are organisms that live in the same the same area but they actually are isolated by the portion of the area that they occupy an example of hypat isolation are these two garter snakes right here these little garter snakes are very closely related and if you are in the range where they occur you'll find them both in the same place however the gter snake on on the left is primarily aquatic when this little snake actually is looking for someone to mate with it will look for mates in its aquatic environment the little garter snake on the right however is terrestrial when this individual is looking for someone to mate with it will look in a terrestrial a dry environment instead so although these organisms still live in the same Geographic range they are not looking for mates in the same place they are isolated by their habitat the second kind of prezygotic barria is called temporal isolation this is when two species are isolated by time they breed and are ready for breeding at different times now it can be different seasons it can be different times of day it can be different years uh for example um I'm sure you've heard of morning glories morning glories are actually open and pollinating during the morning whereas something like honeysuckle is actually opened and ready for pollen in the evening um in terms of different years there is a kind of an insect that only emerges periodically there's the 3year cicada the 7year cicada 13e cic these organisms emerge from the soil and come out and are ready for breeding only in these periodic Cycles another example in terms of uh bamboo Bamboo is a lot like cicas in that bamboo will only breed in specific years in terms of seasonality there are two species of pine tree in central California that are very closely related to each other uh if you took them into a lab you could probably force them to successfully interbreed however in nature one species pollinates in febru February whereas the other species pollinates in April this is enough to keep the two species separated another example of temporal isolation are the Eastern on the top and Western spotted skunk these little skunks are very closely related potentially could successfully reproduce however they breed at different times of the year the Eastern spotted skunks m in late winter as as a matter of fact when you are driving to and from school in the early of spring semester say late February or so you will see a lot of Eastern spotted skunks that have been hit by cars on the side of the road these poor little guys were just running around looking for love and ended up getting smashed by a semi-tractor trailer now the Eastern spotted skunks are mating in late winter but the Western spotted skunk actually made in the fall and so if you were out closer to the West Coast you might see these guys uh in October or November Instead This timing actually prevents them from interbreeding with each other the Third Kind of preotic barrier you're responsible for is called behavioral is isolation in behavioral isolation individuals do not attempt to mate with each other because they just don't recognize each other as acting right so there's little or no mate recognition between females and males because they just aren't acting right these videos all de demonstrate examples of behavioral isolation feel free to take a look at these videos that are available on your e-learning website I'd like to point out that behavior life isolation has actually what resulted in all of the elaborate courtship rituals that various kinds of organisms engage in now obviously Birds we I'm sure you've all heard about how birds go through these elaborate rituals however it's not isolated to birds there are a number of mammals that go through ctrip rituals as well and there are insects that go through courtship rituals when you watch the uh peacock spiders ritual those are various species of male peacock spiders that are trying to convince a female peacock spider to mate with them now the three types of prezygotic barriers we have discussed so far habitat isolation temporal isolation and behavioral isolation are all types of barriers that prevent mating from even being attempted so mating doesn't even occur at all the next isolation mechanical isolation is a situation where mating is actually attempted but it is not successful because the male and female parts just do not fit together correctly there are many insect species that have very elaborate copulatory organs uh for example uh male fruit flies male fruit flies will try to mate with anything you could uh use a pencil and draw a little speck on a piece of paper and if there's a male fruit fly nearby he might fly down onto that little speck and try to mate with it so male fruit flies are often trying to mate with female fruit flies that are the wrong species but their parts just do not fit together correctly so mating is unsuccessful another example in plant in plant communities is flower color and shape of plants very much determines what pollinators uh visit that plant if you end up with a pollinator that doesn't fit your flower then you end up not receiving or correctly getting the type of pollen that's on that pollinator here is a third third example of mechanical isolation these two snails are actually only different from each other based on one uh based on the alals for one particular Gene what's different about them is the way that their snail shells rotate the snail on the left has a snail shell that rotates in a clowner clockwise Direction whereas the snail on the right has a shell that rotat rotates in a clockwise correction now these snail shells if you were to see them in 3D you would notice that the snail shells sort of Bulge out towards you they're not flat well what that means is is that these two snails are unable to get their copulatory organs touching each other which is what they need for sexual uh reproduction the ctory organs on these snails are where the arrows are because their shells bulge out in a direction that uh makes it so they cannot get these two organs together then mating attempts are actually unsuccessful the last kind uh prezygotic barrier to reproducing is called gtic isolation this is a type of reproductive barrier that applies to organisms that although they reproduce sexually there's not actually any mating that is attempted for example a lot of kinds of animals and plants do not have any interaction between males and females these organisms merely release their gametes into the environment for example these two types of sea urchins have gtic isolation these organisms when they reproduce merely release their sperm into the ocean or merely release their eggs into the ocean the sperm and eggs find each other and fertilize each other and become zygotes so there's no interaction or mate choice between the adults gtic isolation is a type of isolation where the gtes are actually incompatible with each other for example these Red Sea Urchin gtes are actually unable to fuse with the purple sea urchin gtes because the gtes the eggs actually will not allow penetration by the sperm of the wrong species so zy formation of a zygo is in unsuccessful so we reviewed the prezygotic barriers to successful reproduction let's go ahead and move on to the postotic barriers to reproduction keep in mind these barriers are ones that kick in after a zygote has formed the first postzygotic barrier is called reduced hybrid viability keep in mind hybrid is basically just The Offspring of of a of members of two different species The Offspring of parents of two different species yes okay viability basically means healthiness so in this situation yes a zygote hybrid it was successfully formed but that hybrid is feeble that hybrid is not as healthy as the non-hybrid individuals so these hibrids because they're not very healthy they get out competed for food sources when there are predators these are the ones that are most likely to be picked off they just don't do as well a nice example of this is uh salamanders there are many species of closely related salamanders that all lay their eggs and deposit their sperm into the same little puddles or small ponds so these gametes are able to find each other fairly easily and hybrids of these salamanders are formed all the time however the hybrid Salam commanders just are not able to get enough food when competing with The non-hybrid Offspring and if there are any Predators the hybrid offspring are easy pickings for those Predators the second time type of um postotic barrier is reduced hybrid fertility in reduced hybrid fertility the hybrid is actually vigorous so it's healthy however it is sterile it is a genetic dead end because it is not able to produce offspring of its own I have an example of reduced hybrid fertility on the next slide but I'd like to move on to the Third Kind of postotic barrier for now the last kind of postotic barrier is called the hybrid breakdown in the hybrid breakdown the first generation of hybrids the kids so to speak are viable so they're healthy they are fertile but when those individuals try to reproduce prod their kids are either feeble or are sterile this is actually very common in plants for example the kind of cotton plants that farmers purchase um have hybrid breakdown they can plant their cotton plants their cotton plants will produce lots of cotton but if they were to collect the seeds from those cotton plants and plant again the next year those seeds would not be very successful they have to go back to the first generation of hybrids for uh their cotton seeds now keep in mind if an organism does not have a prezygotic barrier and it and it does not have a postotic barrier then it does not have a reproductive barrier this particular image shows the idea of reduced hybrid fertility a type of postotic barrier I'm sure you guys have all heard of a mule a fairly sturdy organism the mule is the result of a mating of a horse and a donkey horse hes and donkeys have different chromosome numbers therefore a mule has an extra chromosome it is has an offset number of chromosomes because of that the mule is sterile so let's review this keep in mind that if there is not a reproductive barrier between two organisms those organisms are able to find each other they're able to mate with each other successfully fertilize and make a zygote and that zygote is able to to grow up and produce offspring of its own that is where there is not a reproductive barrier if there is a reproductive barrier to successful interbreeding that barrier can either be a prezygotic barrier that kicks in before a zygote forms and we learned about five different kinds of prag Artic barriers temporal isolation habitat isolation and behavioral isolation prevent mating altogether mechanical isolation prevents successful mating if in if it's attempted and gtic isolation prevents fertilization between gamt that barrier could also be a postotic barrier in postotic barriers you can either have a hybrid offspring that is feeble and is not able to survive due to physical means or that Offspring could be sterile resulting in unsuccessful passing on of its genotype or The Offspring could be viable and fertile but it's off spring on its own are have reduced viability or fertility so here's a question for you I'd like you to keep in mind that natural selection favors the cheapest alternative going through mate selection going through mating going through fertilization and raising of Offspring is very expensive If an organism is going to engage in these things that that organism wants to ensure that its genes will be in future Generations therefore if two related species live in the same area and there is some sort of reproductive barrier between these species would natural selection favor the evolution of prezygotic barriers or postzygotic barriers to successful reproduction the answer is prezygotic reproductive barriers because prezygotic productive isolating mechanisms are much less costly than postotic barriers postotic barriers lead to provisioning and in some species care of an offspring that is an evolutionary dead end