BIOL380 Lecture Notes III  (Material covered between the second test and final)

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Natural Selection
Chapters 12 & 13, but jumps a little bit.

There are some things that require thinking, even philosophical a little. Concept of having a purpose, that behaviors are directed (teleology). Example about birds migrating during winter. Also, how we explain non – adaptive traits, how we test adaptation. Pages 360-362 talk about what not to expect from natural selection and adaptation. P. 361 – harmony and balance in nature. A lot of people tend to think that there is a balance in the world; environmentalists, using biology information, are trying to do something – the harmony between the species, etc. It doesn’t mean that the ecosystem is not a complicated system, and that a system will not collapse if you remove something. Notion about evolution not foreseeing the future. This is all to increase our level of sophistication – watching TV, evaluating people’s claims – there is a practical reason in understanding it.

There are several ways to define natural selection. The way Dr. Matson defines natural selection is that it is a differential survival and reproduction. Futuyma says that there are slightly different ways in defining (what is and what’s not acting). Overhead – Darwin’s origin of the species. Natural selection is the survival of the fittest – not the best way to define it. In the middle, he’s getting that variation exists. Then, he says that natural selection isn’t everything. One of the sentences ~ genetic drift. He did not call it drift, but he even allowed that there could be other things besides natural selection.

Regardless of how you take a look at it, it is not survival for the sake of survival, but for the sake of reproduction. If you just survive, but don’t reproduce, your traits are not passed on to subsequent generations.

There are three modes of natural selection. The terminology can get hairy sometimes. Fig. 13.2 – graph ~ overhead. We look at them in terms of phenotype, and what’s going to happen to genotype. Assumption that the phenotype we are looking at has a normal distribution (bell-shaped term). In real world, phenotypes do have frequency distributions, and for a number of characters with a large enough sample they approach a bell-shaped distribution.

Modes of Natural Selection  (from Futuyma, 1997)  .

1st row - phenotype frequencies of first generation before selection occurs. The shaded portions represent individuals with a relative disadvantage (lower reproductive success).  2nd row - phenotype frequencies of the second generation after the action of a corresponding mode of natural selection. x-mark is the mean of the trait before selection occurs.  3rd row - genotype frequencies for one locus before selection occurs assuming one-to-one genotype-phenotype correspondence. The shaded areas are the genotypes with a relative disadvantage.  4th row - genotype frequencies of the second generation after selection occurs.

Stabilizing selection (also known as optimizing or normalizing selection) involves the disproportionate elimination of the extreme phenotypes and favors the intermediate ones. It eliminates individuals at the tails of the curve. The curve gets narrower. The mean is still the same. At fig. B, if we assume that the phenotypes are as noted, we are eliminating both homozygotes, and favor heterozygotes. Both alleles are maintained in the population, but the extreme phenotypes are eliminated. The relationship between the alleles will determines how exactly phenotypes look. What is favored and what is not depends upon the environment. Example with SC anemia – in Africa with malaria, heterozygotes are favored, but in places with no malaria, dominant allele is favored. Malaria (bad air) is spread around the equator belt, and there stabilizing selection takes place.

Directional selection (also known as dynamic) happens when one of the extreme phenotypes is favored. Extreme selection against the right-hand side of the curve (fig. 13.2). We are selecting for one of the homozygotes  ~ what happens with malaria in non-belt places.

Disruptive selection is not as well documented or it's rare (or both). Apparently, two of the phenotypes have high selective advantages such that both of the extremes are at favor, and we have the thing that is in the middle, which is selected against. Selection against heterozygotes if we assume A&a. The effect is that of the positive assortative mating (inbreeding). If we couple these two, we can see even more extreme effects on a population. Both of these could be the mechanisms for speciation.

Evolution is not the same thing as speciation. Evolution can occur without forming a new species. But you can't have speciation without evolution. The point is that when we talk about speciation, we'll add some more mechanisms to explain it, but the foundation is right here. Microevolution and macroevolution are the same things but on a different scale. Definition - species are the ones in reproductive isolation.

Fitness

- a parameter(s) to measure selection. Fitness measures genotypes' (hence a phenotypes'/individuals') ability to obtain representation in the next generation. In real world, one of the easiest way to measure this is to look at fecundity (in sexual reproduction per female): we can count eggs, babies, or whatever. We usually look here at the relative fitness, not the absolute. We compare the number of offsprings each genotype leaves as compared to the other genotypes.

In population genetics, we assign a genotype with the highest fitness. Relative fitness in population biology is given a symbol w, and the fittest guy has a w of 1.0. They range in values from zero to one. Overhead: 3 different genotypes, in the second generation there was an increase in population; measuring fecundity
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Another measurement is ~ opposite to the fitness - selection coefficient (s)
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Measures the reduction in fitness of a particular phenotype. Like fitness, it has values ranging from zero to one, but the interpretation is 180° opposite to the fitness.

Fitness in and of itself is something very complicated. You can measure the number of offsprings, but there are other ways to measure: fertility, mating success, rate of development, age of first reproduction, or any other relevant ways.
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Even though all these things come into play, we use one - two in the real world to measure fitness.
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Mark recapture studies with the British moth
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Another table - how much time would it take to reduce q (# of generations required to effect a given reduction in allele frequency). Even with a very strong selection coefficient, it takes thousands and millions of generations to change. The point - depending on starting frequency and fitness, time can be different. 9000 generations for bacteria isn't long, but 9000000 is thousand times longer. Once the allele frequency gets low, it takes longer and longer time to eliminate an allele.

Two other tables - fitness for each genotype is different. Selection favors the heterozygous class. In the case of overdominance we get a situation when selection favors heterozygotes.

Table - long -term effects of constant selection. Favoring of one over the other, and allele frequencies change, fixation of one allele over other in long term happens. Depending upon the exact relationships and situation, stable or unstable equilibrium is achieved. Selection sometimes maintains the variability in population (stable). In unstable, variability is decreased (alleles get fixated).

Handout: 13 mechanisms that can maintain gene polymorphism (there are others): 1, 2, 3, 4, 6,10, 11, 13.

1. Overdominance: heterozygote favored.
2. Spatially heterogeneous environments: allele favored in some environments, disfafored in others.
3. Temporally varying environments: allele favored at some times, disfavored at others.
4. Epistasis: includes nonallelic interactions, modifiers, coadaptation, etc., which an allele can be favored in some genetic backgrounds, disfavored in others.
5. Balance involving life-cycle stages: allele favored at one stage of life cycle, disfavored at another (~ temporally varying environments).
6. Balance of fitness components: allele favored in viability, disfavored in fertility.
7. Density-dependent selection: allele favored at high population density, disfavore at low.
8. Frequency-dependent selection: allele favored at low frequency, disfavored at high.
9. Balance involving gametic selection: allele favored in zygotes, disfavored in gametes.
10. Balance between the sexes: allele favored in one sex, disfavored in the other.
11. Balance involving non-Mendelian segregation: allele disfavored in zygotes, but heterozygotes produce more than 50% of functional gametes bearing the allele.
12. Group selection: allele neutral or detrimental to individual, but enhances survival of subpopulation; posibly important for "altruistic traits."
13. Hitchhiking: allele neutral, but affected by selection at linked locus.

One of the consequences of natural selection can be adaptation. It's not the only consequence. Extinction is another, for example. Things don't happen for the good of species, the process is not goal oriented; they work or they don't.

In biology, adaptation has several different meanings:

• Physiological definition: adaptation is something that occurs to an individual, and it involves some sort of phenotypic adjustment to the environment. Ex: if it's cold, you put a coat on (behavioral). Another - a long example of aquarium fish adjustment. Doesn't pass to the next generation. When evolutionary biologists talk about adaptations, they don't mean adaptations that are not passed through genes (so narrow-minded!)

• Evolutionary definition: adaptation is a feature, trait, or attribute that increases fitness. As a verb, it's a process by which certain traits that increase fitness evolve (traits evolve other ways as well). Natural selection controls this process. If it's a genetic drift or a mutation only, it's hard to explain the persistence of a trait. These are random events, and natural selection is a complete opposite of random.

We need to be able to treat an adaptation from the perspective of science: it is a hypothesis that has to be tested. Not all adaptations are necessarily complex. If an adaptation is complex, it doesn't mean that all of its parts are in and themselves beneficial. Hemoglobin: if we look at the aminoacids of this protein, we see that having a certain aminoacid replacement has no effect on the function of this protein, and it's not called an adaptation.

Studying an adaptation.

1. Collect the data. Determine the kind of genetic variance of a genetically controlled character. In a laboratory or in a wild population, we are looking for polymorphism (different forms of a trait).
2. Propose a hypothesis. Look at this particular adaptation and proceed with an idea that a particular structure has a function. We look for this correspondence of structure and function: propose a formal hypothesis about the function. Take your biology hat off and put the engineer hat on.
3. Test the hypothesis. Put a bird in a wind tunnel and measure the air resistance, for example. Or, use comparative biology to correlate structures with ecological conditions Overhead with cactuses and euphorbs. The question becomes why do these two organisms of different species look so similar. This is an example of a convergent evolution: they evolved adaptations which enable them to survive dry environment: waxy cubicle covering stem, modified into spikes leaves, stem photosynthesis.

Overhead with eyes: octopus eye is convergent evolutionary with a vertebrate eye. An eye is structure to convert light energy into an electrical nerve impulse. Images may or may not be formed. In mollusks, we see a whole array of "eyes" which consist of pigment cells which are excited by photons. One animal has very little of the eye, but at least it can detect the light. As the number of pigment cells increases, as the complexity of the structure increases (aperture, more surface area, cellular fluid, cornea, lens), we can see how this complex structure could evolve from a simpler structure, and all the individual steps are adaptations.

Preadaptation (p. 354 - 355)

Gets a little complicated, but we need to look at it.

Preadaptation is a possession of the necessary properties to permit a shift into a new niche or habitat. A structure is preadapted if it can assume a new function before it becomes modified. The way it exists now, it can serve two functions.

Overhead with the fish tree. The characters which unite all of the fish except agnatha is the possession of jaws and the possession of paired appendages. We get chondrichties on one side, and a lot of bony fish on the other side. They all have fins: pectoral, pelvic… They are stabilizers for fish, and it's easy to show that the primary function of fins is to enable fish to swim. There are two distinct groups though: rayfin fishes lineage, and sarcopterygians (the lobe-finned fish). There is one branch in lobe-finned fish - amphibians, reptiles, birds, mammals. They evolved from a certain kind of lobe-finned fish. These animals (you and Dr. Matson) have four limbs. Q: where do they come from? We think that they are modified fins of sarcopterygians. Skeletal structures were preadapted to function as limbs. In other words, we see that fish have nice fins, but it's just so happened that their structure (and sarcopterygian fins are much more substantial) allowed animals to support themselves on the bottom of ocean, then on the ground. They have such a structure that their appendages didn't even have to be modified. There are animals which walk across land on fins.

The point: 1) Limbs came from preexisted structure; evolution doesn't make things de novo. The tetrapode limbs didn't appear anew. 2) There is no foresight: fins evolved as adaptation for swimming in water. Fish didn't think in Devonian that it would be nice walking one day, and it has just happened that they fit for walking/crawling.

Another example (from textbook) is the indigenous parrot, the kea (New Zeland) - feeds on sheep's fat using a strong beak. This beak was in kea's ancestors a preadaptation when they were feeding on fruits and seeds.

If natural selection works, how do we explain the fact that there are some characters which are neutral, or even can be maladaptive?

• Remember: we were assuming that a particular trait is genetically controlled. So it could be that a trait we are looking at is controlled by environment. These traits are not subjected to selection.
• Consider "laws of nature" (physics) Ex: flying fish which jumps out of water and "flies" (glides) through the air. Q: what is the adaptive value of having this fish return to wate? A: gravity (that's lame). It's not an adaptation.
• Genetic drift - fixation of a trait attributed to a chance. Overhead (fig. 12.19): example of cryptic coloration (camouflage), because it's hard for a predator to see them. But how they are cryptic (solid lines or broken) doesn't matter as long as they can hide. Different patterns are the result of genetic drift
• Genetic or developmental constraints on a character. It can be genetically linked. Ex: allometry - a growth of a feature during ontogeny at a rate different from that of another feature with which it is being compared. A character may not be an adaptation simply because it grows at a faster or slower rate then another (overhead with head sizes of people in different ages). Another overhead: short forelimbs of dinosaurs. It can simply be a function of allometric growth. When you get that big, their proportional size is smaller.

Not everything is optimally adapted. Overhead of water oozer (dipper). It runs under water and picks up insects which are on the rocks under water. It doesn't look like an aquatic animal. But it still works fine, and that's all that counts. As long as it works, as long as it increases survival and reproduction, it's an adaptation.

Now, we will use everything we've gone before, and build on it to explain where the 1.5 million of species come from.

Species & Speciation

There can be two major patterns of what happens within an evolutionary lineage. Overhead with 2 + 3 birds: two patterns of lineage change (~ fig. 15.4 p. 451). Anagenesis (B) - we have a type of change within a single evolutionary lineage. At a certain point something happens that makes one specie to evolve in another specie in a linear pattern. Cladogenesis (mostly responsible for formation of new species; A on fig. 15.4) refers to branching patterns in evolution: at some point in time something happens to the population of ancestral specie that branches of a new species. We end up with two, and they are different (different morphological features). Cladogenesis is by far the most important mechanism by which speciation occurs.

What are the processes happening at the cladogenic event (branch)? - we can understand how speciation occurs. The process by which the new species are formed (chapter 15).

Linnaeus - he gave us a classification scheme and binomial nomenclature. Within the classification scheme, there are categories, and species is the lowest class. 2 names: Genus and species. Here, species is a unit of classification. He was not thinking in terms of evolution; accepted scala nature, that god created them. He had a typological species concept (Aristotelian - Platonic idealistic way of looking at world). Linnaeus was looking at morphological similarities/differences to define what a specie is. Species are essentially different kinds of things. But people started to find out that there were problems. Overhead (fig. 15.5): four ducks, can't decide how many species we have. Depending on how one defines, thinks that one, two, or four species (wonder why nobody came up with a number 3).

Hybrid - mating between two different species. Horse + donkey = mule, but mule is not always sterile (usually it is, though). From an evolutionary perspective, hybrid is a waste of energy mixing the genes together.

From a purely typological perspective to classify the ducks as four different species would be a mistake from a perspective of the ability to exchange genes.

So, how do we decide what a specie is? Ernst Mayr said that we need to define from a biological perspective. In 1940s, he came up with a Biological Species Concept. He thought it as an "improvement" because it incorporated biology (and reproduction) of living things. He says that under the biological species concept,

We've got a reproductive isolation, and hybridization doesn't exist. Not really. Mayr means that  hybridization is rare (some people say that there's absolutely no hybridization).

Using the biological species concept, lets take a look at speciation.

Overhead (~ table 15.2 p. 457): Classification of isolating mechanisms. Simplistically, we brake down into prezygotic and postzygotic isolating mechanisms. The point: we have the mechanisms that isolate before the zygote is formed, or after, when the egg gets fertilized, but the development is not successful in either case.

Prezygotic barriers:
     A. Potential mates do not meet (temporal/habitat isolation)
     B. Potential mates meet but don't mate (ethological/behavioral/sexual isolation)
     C. Copulation occurs but no transfer of male gametes takes place (mechanical isolation)
     D. Gamete transfer occurs, but egg is not fertilized (gametic incompatibility)

Postzygotic barriers:
     A. Zygote dies
     B. F1 hybrid has reduced viability
     C. F1 hybrid viable, but has reduced fertility
     D. Reduced viability or fertility in F2 or backcross generations

How do these mechanisms evolve? But before, some terminology (in somewhat different ways): Terms for how organisms are distributed in space (overhead)

• sympatric distribution - completely/partly overlapping (geographically) populations

• parapatric distribution - geographically adjacent populations (neighbors)

• allopatric distribution - populations are not connected at all

Modes of Speciation

• allopatric speciation - (a -on the handout) - populations are geographically isolated. Based on observation that relatives are often found in geographically different areas. Like Drosophilla in capoocas.

1. Vicariant/geographic speciation (p. 483) - occurs with a physical isolation of two relatively large populations. Based on assumptions that once they are separated, local adaptations will occur that will make them reproductively isolated. Associated with a some sort of vicariant event which forms a geographic barrier which also forms a barrier to gene flow. They are no longer exchange genes with one another and diverge, Later, we recognize them as different species. Examples of vicarian events: rivers, plate tectonics, earthquakes, erogeny (formation of mountains), volcano lava, glaciations; even a road can separate one population from another. Evolutionary mechanisms: genetic drift (but not as likely as in (b)), natural selection and adaptation. Whether they will become different species is directly proportional to the selective pressure, and inversely proportional to the gene flow.

1. Peripheral isolates model (~peripatric speciation, p. 493)- supposes that new species arrive in marginal habitats that are on the ages, or boundaries, or periphery of a larger population. Primarily concerned with what is going to happen with a small population compared to a large population. Overhead - one big circle, then a small circle becomes adjacent to a large one, then the small circle changes color. Looks like parapatric at that point. Q: What can differentiate them? A: Natural selection and adaptation (but don't have to be), genetic drift (founder effect, inbreeding). Some people would hypothesise that genetic drift would be dictating the mechanism of speciation.

Most biologists think that allopatric is the primary (but not sole) mechanism for speciation.

Overhead/handout: 2 models: phyletic gradualism and punctuated equilibria. 2Q: 1) how speciation occurs, and 2) how fast it occurs.

Phyletic gradualism (y). On one of the handouts, notions that evolution occurs usually slowly and gradually. The notion here is that over a large amount of time the number of small changes accumulate, and populations diverge from one another. The lines represent populations at different points in time. We see that there is a distribution around a mean of the frequency of some character. Over time, some structures fluctuate (graphs have diferent shapes). But not much exciting is happening untill the middle of the graph. Something happens that the large population splits into two. This is a claidogenic event - a speciation event. In some time in the future these two lineages are considered as two different species if they are reproductively isolated. Point: this type of evolution occurs slowly and gradually over time.

We know from Mendelian genetics that most mutations are harmful, and it makes a perfectly good sence that these kind of differences in the distributions require a lot of time.

But paleontologists, looking at fossil records see that species tend to persist over a fairly long period of time, and then - BANG! - rapidly, over a short period of time, speciation occurred. The gradual progressions were punctuated in those times.

Punctuated equilibrium (µ)- we see one species, and then something goes on that a population diverges to the right, while the parent population continues to fluctuated around its mean. If that's true, Q: under what circumstances that occurs? Hypothesize that these changes occur via allopatric speciation, and a peripheral isolates model is the explanation for it (genetic drift). This model was proposed to ~ counterbalance the phyletic gradualism model (standard stuff).

It split people in two camps. But the reality is that both of these things are possible and they are not mutually exclusive. Biases: people that support punctuated equilibrium are at least historically paleontologists. The phyletic gradualists are neoontologists (people who study modern organisms living today). Neoontology can do experiments with living organisms. So, these two groups of scientists work on different time scales. A centimeter of separation in a fossil may represent 10s of 1000s of years, separating many generations. If punctuated equilibrium represent a change which occurred over time, how many generations it represents? Bottom line, some discrepancy between the two is in fact that the neoontologists and paleontologists work on different time scales.

• parapatric speciation - geographically adjacent populations (neighbors). One large population splits into two of equal size, but at least for a time they are contiguous: they are adjacent but not overlapping. Through the process of genetic drift or natural selection or other they will diverge (b on handout). It's probably not too common. Certain situations when it might have occurred can be found (chromosomal aberration which does not allow to exchange genes (for example). People argue whether it happens and how often, but at least it's possible.

• sympatric speciation - completely/partly overlapping (geographically) populations (c on the diagram). Speciation occurs totally within the ancestoral geographical range. The new specie becomes reproductively isolated but still residing in the same geographical area. While there are not a whole lot examples for this speciations, there are at least few situations when this model works.

1. Hybridization case. It's defined as mating between two individuals that are of different species. If it occurs, and the hybrid offspring is somehow genetically distinct from the parent, and can not mate with the parent population (backcross with parents not possible). Then, it can be considered as a new specie. For this to occur, the parents have to live in the same place, the offspring lives in the same place, and it's a sympatric distribution.

AA = 14 Triticum monococcum (einkorn) exchanged genes with BB = 14 Triticum searsil? (unknown wild wheat) and the result was a hybrid offspring AB = 14 (sterile hybrid), but then a mutation (chromosomal aberration) occurred, and AB doubled the number of chromosomes to get AABB = 28 (Triticium turgidum, wild emmer), a fertile individual. Can exchange genes with other tetraploids, and new species emerge. An example of instantaneous speciation which occurred essentially over one generation. To complicate things, AABB mated with DD = 14 (Triticium tauschii, a wild relative) to gt AABBDD = 42 (Triticium aestivum, a common bread wheat). All these events had to occur within the same geographical area.
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2. Parthenogenesis (virgin birth, a type of asexual reproduction). Example: Cnemidophorus lizards

There are other examples in worms, some plants, crustaceans, amphibians, fish, and these lizards.

There is at least a little bit of data to support that …

Table: frequencies of modes of speciation (biases: small samples, all vertebrates)
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Another table for different species of birds (biased towards birds). They looked at distributions, and they think that ~45% f the speciation events are best explained by allopatric via vicariant, ~2% peripheral isolates, ~20% sympatric, and 31% indeterminate. Allopatric via vicariants is the predominant mode of speciation.

The examples show that at least theoretically the instantaneous speciation is possible, through the changes in genotype. It has been documented, that in some organisms it can be how the speciation occurred, but it's more an exception then a rule.

When we look at the 1.5 million species that existed, we see that speciation occurred rather slowly and gradually. Back to the Cambrian time, that's when the modern groups have evolved. So, 550 million years ("long" period of time), but there is some data to suggest that speciation can occur rather quickly - 5 million years. It's a relatively short period of time. And what we see (even in the Cambrian) that most of the diversity occurred over 5 million years, a short time. There are other examples of rapid speciation:

Alternative species concepts

- look at table 15.1, some of the alternative species concepts are mentioned there.

One most commonly used is biological species concept. There are also problems with it, however. See definition of species from biological species concept view.

BSC has problems, weaknesses, doesn't cover all situations. Some people came up with alternatives.

The problems:

1. What do you do with hybrids? Generally speaking hybrids are not considered as distinct species. It's based on the assumption that hybridization is relatively rare. Ernest Mayr and others, who came up with the BSC, say that it's so rare we don't have to consider it. But not with plants - there, hybridization occurs fairly often. He didn't take into consideration taxa other then birds. If we look at other vertebrates, BSC falls apart. In a recent study, ~20% of bird species could hybridize among each other. It doesn't mean that a sparrow will hybridize with an ostrich. But within ducks, ~20% of them can hybridize with one another, and ~20% of sparrows can hybridize with one another. We see that even with the birds, there's still a whole more hybridization occurs then Ernest Mayr thought.

1. What about asexual reproduction? Not all species reproduce sexually. Is every single bacteria a different specie?

Look back at the table: 11 additional species concepts  Overhead with alternative concepts, they are all in the book. Know only the ones that are listed in the book (underlined).

• Morphospecies concept - for paleontologists, because it is hard to prove if two fossils mated (unless some geological event caught them in act).

Paleospecies concept - another one for paleontologists. BSC is hard to use in these cases.

• Evolutionary species concept

• ESC: A specie is a lineage (an ancestral-descendant sequence of populations) evolving separate from others and with own unitary evolutionary roles and tendencies (Simpson, 1961)

• ESC: A specie is a single lineage of ancestor-descendant population which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate (Wiley, 1981)

• ESC: A specie is a population or group of populations that shares a common evolutionary fate through time (Templeton, 1989)

Advantage: no problem in calling these distinct groups a species regardless of their geographical distribution. Under this definition, the Florida panther would be fine, because it's a single lineage, and presumably it has it own historical fate and evolutionary tendencies. The so-called problem of hybridization disappears: it's simply not an issue. You can't say that the panther is not the panther because it has those extraneous genes. Mayr in the paper was saying that under his BSC, it was still possible to save the panther.

Problem: how do we measure evolutionary fate or historical tendency: look at two fish: blue gill in Lake Alatoona and blue gill in Lake Lanier: do they have historical tendencies same or different? - it's hard to measure.

• Isolation Species Concept: Species are systems of populations the gene exchange between these systems is limited or prevented by a reproductive isolating mechanisms or perhaps by a combination of several such mechanisms (as defined by Dobzhiansky 1970, in Templeton, 1989).

• Phenetic Species Concept: (~ typological concept) A specie is a set of organisms that look similar to each other and distinct from other sets (Ridley, 1993) Good for an initial understanding of species.

• Phylogenetic Species Concept: A specie is the smallest (irreducible) diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent (Cracraft - avian paleontologist, 1983).

Under this concept, the Florida panther would be protected: have morphological characters that make them different. They would be called not a subspecies, but a species (and be back in the Endangered Species List).

Problems: how do we define "smallest diagnosable cluster"? If you do the genetic DNA finger print, blue gills will be different not only in between two lakes, but within each lake.

• Recognition Species Concept: A specie is the most inclusive population of individual biparental organisms which share a common fertilization system (as defined by Paterson, 1985, in Templeton, 1989)

• Cohesion Species Concept: A specie is the most inclusive group of organisms having the potential for genetic and/or demographic exchangeability (Chislin, 1974).

• Ecological Species Concept: A specie is a lineage (or closely related set of lineages) that occupies an adaptive zone minimally different from that of any other lineage in its range and which evolves separately from all lineages outside its range (Van Valen, 1976).

• Internodal Species Concept: Individual organisms are conspecific by virtue of their common membership in a part of the geological network between two permanent splitting events or between a permanent split and an extinction event (Kornet, 1993)

Extinction

What are the processes that occur at the cladogenic events? - that's what we were trying to answer from the beginning during these eight or nine weeks. Now, we are taking an opposite look: extinction as a taxonomic equivalent to an individual's death.

In the book, chapter 17, 23, 24. Most of the stuff on extinction is in chapter 25.

Lokig at the history of our planet, we see a pattern that looks like this: (overhead/handout, looks like an upside down Christmas tree). 5-6 hundred millions years ago (Cambrian explosion) there was a whole lot of other things that are not represented today. Burgess Shale (well preserved fauna in British Columbia, p. 172). This is the top of the tree. There have been 6 major extinction events: the one when the dinosaurs went extinct is on the boarder of Cretaceous and Tertiary. Mass extinction: reduction of a large number (30-50%) of taxonomic units (animal families, for ex.). But there is a bias in the making this pattern because it is hard to say whether a couple of fossils are of one specie or of different species.

Overhead: numbers of fossils from different species over time. Some have extinction events, some don't. What happens, depends on a group. The Christmas trees for different groups are different.

Overhead: from the middle of the first Christmas tree (Permio-Triassic). We see that besides the mass extinction events there are background extinctions. They are not massive, just some species go extinct, and it varies depending on the group we are looking at. But why is it that some groups of organisms more prone to extinction?

Q: is extinction bad? - no, things go up and down: extinction event, then diversity increases. It's not bad, it just happens.

Overhead/handout on recorded extinctions. Look at the right hand side of the table (number of species)Since the 16 hundrends, anywhere from 0.1% to 2.1% are extinct. Mammals have the highest extinction rate. Look at the graph: it's almost exponential. Most of the extinctions for the bird and mammals occurred over the last 100 years. That's why some people say that there is a mass extinction occurring now. One of the reason is we (habitat distruction, polution). The concern is not the extinction itself, but the rate. Because it's so high, people are concerned. And biologists don't know how many species we can lose not to dramatically change an ecosystem.
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