POPULATIONS GENETICS AND SPECIATION CH 17 IMPACTS ISSUES

POPULATIONS GENETICS AND SPECIATION CH 17

IMPACTS, ISSUES RISE OF THE SUPER RATS

WARFARIN RATS Killed By Warfarin Survived Why? Resistance Immunity The MOST FIT

ANTIBIOTIC RESISTANCE Killed by Antibiotic Left to FOUND new population

HOW VARIATION ARISES FROM SIMILARITIES… What the rat example illustrates is a concept that turns up again and again in nature and provides proof of evolution. Many populations contain the traits necessary to survive when the environment turns on them. Which traits will be good or more common normally can’t be predicted but through variation populations can survive and evolve.

I. INDIVIDUALS DON’T EVOLVE, POPULATIONS DO Evolution is predicated on the concept that genetic variation leads to the environment choosing which version of a trait is best. What mechanism(s) allow for variation? There has to be a way for nature to allow for the creation of new alleles. Evolution starts with mutations in individuals; mutation is the mechanism for the creation of new alleles. The penetrance of this mutation is completely dependent on SEXUAL reproduction.

VARIATION IN POPULATIONS Population Interbreeding individuals of the same species in the same area. All individuals of a species have to share certain traits But individuals of a population vary in the details of these shared traits. These variations of course are because of alternative versions of the alleles that cause these shared traits.

Where does VARIATION come from? Mutations Mutation s Mutati ons Mutation s s Mutations

II. HOW TO DETECT EVOLUTION: VARIATION CAN BE CALCULATED Variation is distributed within a population. This fact is a way evolution can be studied. A distribution is an overview of the relative frequency and range of a set of values. Often, some values in a range are more common than others. A normal distribution, or bell curve, is one that tends to cluster around an average value in the center of the range. This sets the range of what’s normal and standard for a population.

NORMAL DISTRIBUTION Mean Median Mode = average = middle value = the number most repeated

THE GENE POOL The variation is founded in alleles Alleles The dominant phenotype • Different forms of the same gene • Determines genotype and phenotype Gene pool • All alleles found in one population Within the gene pool, variation is due to various alleles. Mutations are responsible for the various alleles. The Black Jaguar 6% of the South American population

VARIATION & INHERITANCE Variation is constantly changing because of natural selection but also genetic shuffling, through new combinations of alleles. You have to also consider recombination in changes in genetics…

VARIATION & ALLELES ARE TRACKED BY STUDYING ALLELE FREQUENCIES Proving evolution is partially achieved through investigating the change in allelic frequency over several generations. The change is measured against the population in genetic equilibrium. Allele frequencies • Relative abundance of alleles of a given gene in a population • Represented as percentages, much like the % composition of compounds. Natural populations are never in genetic equilibrium • Genetic equilibrium = the allele frequency stays the same. • A theoretical state which occurs when a population is not evolving

III. GENETIC EQUILIBRIUM Researchers know whether or not a population is evolving by tracking deviations from a baseline of genetic equilibrium. Five conditions required for a stable gene pool: 1. 2. 3. 4. 5. Mutations do not occur Population is infinitely large No gene flow Random mating All individuals survive and reproduce equally This doesn’t happen but the rate these change will affect the rate of evolution.

GENOTYPE FREQUENCIES VS. ALLELE FREQUENCIES The thing you need to know is that genotypic and allelic frequencies always add up to 1. Genotype Frequency (frequency of EE) + (frequency of Ee) + (frequency of ee) = 1 Allele Frequency: (frequency of E) + (frequency of e) = 1

MICROEVOLUTION Genetic equilibrium is affected by several processes that alter allelic frequency. This is how evolution and speciation happens. Tracking evolution is studied by and defined by changes in allele frequencies over time.

THE HARDY-WEINBERG FORMULA Determining Genetic Equilibrium… the BASELINE The Hardy-Weinberg formula can be used to determine if a population Hom is in genetic equilibrium oz dom ygous inan t oz rece ygous ssiv e p 2 (AA) + 2 pq (Aa) +q 2 (aa) = 1. 0 te o g zy o r e frequency of t the dominant He The allele (A) plus the recessive allele (a) equals 1. 0 p + q = 1. 0

THE HARDY-WEINBERG PRINCIPLE The Hardy-Weinberg principle describes a population that is not evolving. If a population does not meet the criteria of the Hardy-Weinberg principle, it can be concluded that the population is evolving. You will learn more about the Hardy. Weinberg formula soon…

A POPULATION IN EQUILIBRIUM

Finding out whether a population is evolving. The frequencies of wing-color alleles among all of the individuals in this hypothetical population of morpho butterflies are not changing; thus, the population is not evolving. Fig. 18 -3 a, p. 280

490 AA butterflies dark-blue wings 420 Aa butterflies medium-blue wings 90 aa butterflies white wings Starting Population Next Generation Fig. 18 -3 b, p. 280

IV. MICROEVOLUTION FORCES OF GENETIC CHANGE Just as the Hardy-Weinberg principle allows us to see a population that’s not evolving, so we can measure changes, these forces act against equilibrium: 1. Gene Flow 2. Genetic Drift 3. Mutation 4. Non-random Mating 5. Natural Selection

1. GENE FLOW Gene flow Physical movement of alleles caused by individuals moving into and away from populations Immigration, etc. Tends to counter the evolutionary effects of mutation, natural selection, and genetic drift on a population Example: Movement of acorns by blue jays

GENE FLOW BETWEEN OAK POPULATIONS

2. GENETIC DRIFT— THE CHANCE CHANGES Genetic drift The random drifting of allele frequencies Very much dependent on population size Like a Pendulum… Leads to… Fixation has occurred when all individuals in a population are homozygous for one allele

GENETIC DRIFT AND POPULATION SIZE

GENETIC DRIFT AND POPULATION SIZE

GENETIC DRIFT & BOTTLENECKS Bottleneck A drastic reduction in population size brought about by severe pressure After a bottleneck, genetic drift is pronounced when a few individuals rebuild a population, fumbling to figure out beneficial traits. Example: Northern elephant seals Example: The Great Dinosaur Extinction Catastrophic Event Original Population A A B B A A A C C New Population Dynamics A A B B A C

GENETIC DRIFT & THE FOUNDER EFFECT Founder effect Genetic drift is pronounced when a few individuals start a new population (Often in conjunction with bottlenecks) Inbreeding Breeding or mating between close relatives who share a large number of alleles Example: Old Order Amish in Lancaster County, Pennsylvania (Ellis-van Creveld syndrome)

3. MUTATION REVISITED Mutations are the source of new alleles that give rise to differences in details of shared traits Lethal mutations usually result in death Decrease fitness but these rarely survive the gene pool. Neutral mutations have no effect on survival or reproduction Often considered “silent” mutations. In humans, the average person undergoes 50 -100 mutations in their lifetime. Less than 3% have any consequence. Remember, ~95% of our genome is “junk” DNA Beneficial mutations convey an advantage. Rare but does occur… has to.

4. NON-RANDOM MATING = SEXUAL SELECTION

SEXUAL SELECTION With sexual selection, some version of a trait gives an individual an advantage over others in attracting mates Distinct male and female phenotypes (sexual dimorphism) is one outcome of sexual selection

MATING DANCE OF BIRD OF PARADISE http: //youtu. be/n. S 1 t. Enfkk 6 M

SEXUAL SELECTION sexual dimorphism

THE LION’S MANE… Females are attracted to males with larger, dark manes Correlation with higher testosterone levels better nutrition & health more muscle & aggression better sperm count / fertility more successful young But imposes a cost to male It’s HOT! Is it worth it? ?

“SEXY” = SUBCONSCIOUS FITNESS MARKERS The Golden Ratio Symmetry This contributes to non-random mating: Humans have preferences, just like all other sexual organisms.

BALANCED POLYMORPHISM Balanced polymorphism A state in which natural selection maintains two or more alleles at relatively high frequencies Occurs when environmental conditions favor heterozygotes Example: Sexes Example: Sickle cell anemia and malaria Hb A /Hb S heterozygotes survive malaria more often than people who make only normal hemoglobin

5. NATURAL SELECTION REVISITED Natural selection The variable survival and reproduction among individuals of a population that vary in details of their shared traits. This is a driving force of evolution. Occurs in recognizable patterns depending on the organisms and their environment.

NATURAL SELECTION Natural Selection Acts in 3 Major Ways: All Populations Have Variation Sometimes hard to detect, not so in humans Individuals Tend To Produce Too Many Offspring Individuals in a population will always have a hard time surviving All Populations Depend on the Reproduction of Individuals Fitness = the reproductive success of grandchildren.

V. Three Patterns of Natural Selection Natural selection Takes 3 forms: Directional Stabilizing Disruptive We’ll take a quick peak at all three types. population before selection directional selection stabilizing selection disruptive selection Fig. 18 -4, p. 281

DIRECTIONAL SELECTION Directional selection Changing environmental conditions, the selective PRESSURE put on by the environment, can shift allele frequencies in one consistent direction Forms of traits at one end of a range of trait variation become more common in the population. The other becomes less or drops out completely.

Directional selection. These bell-shaped curves signify a range of continuous variation in a butterfly wing-color trait. Red arrows indicate which forms are being selected against; green, forms that are being favored. Fig. 18 -5 a, p. 282

Fig. 18 -5 b, p. 282

Becomes this with directional selection Casualties of Natural Selection Now extinct… Once the norm… Fig. 18 -5 c, p. 282

PREDATION AND PEPPERED MOTHS Light color is adaptive in areas of low pollution; Dark color is adaptive in areas of high pollution

Natural selection of two forms of the same trait, body surface coloration, in two settings. (a) Light moths (Biston betularia) on a nonsooty tree trunk are hidden from predators. Dark ones stand out. (b) The dark color is more adaptive in places where soot darkens tree trunks. Fig. 18 -6 a (1), p. 283

Fig. 18 -6 a (2), p. 283

Fig. 18 -6 b (1), p. 283

Fig. 18 -6 b (2), p. 283

PREDATION AND ROCK-POCKET MICE In rock-pocket mice, two alleles of a single gene control coat color. Night-flying owls are the selective pressure that directionally shifts the allele frequency.

DIRECTIONAL SELECTION IN ROCK-POCKET MICE

Fig. 18 -7 a, p. 283

Visible evidence of directional selection in populations of rock pocket mice. (a) Rock pocket mice that have dark fur are more common in these areas of dark basalt rock. (b, c) The two color types of rock pocket mice, each posed on the dark and light rocks of the area. Fig. 18 -7 b, p. 283

ANTIBIOTIC RESISTANT BACTERIA A typical two-week course of antibiotics can exert selection pressure on over a thousand generations of bacteria. If ANY remain, they do so because they may have a mutated gene that causes a resistance to these antibiotics. Antibiotic resistant strains are now found everywhere, in hospitals and schools. The rate of these superbugs are exacerbated by people not completing their prescriptions.

SELECTION AGAINST OR IN FAVOR OF EXTREME PHENOTYPES Stabilizing selection Natural selection that favors an intermediate phenotype and eliminates extreme forms Disruptive selection Natural selection that favors extreme forms of a trait and eliminates the intermediate forms

Time 1 Number of individuals in population Stabilizing Selection Range of values for the trait Time 2 Time 3 Stepped Art Fig. 18 -8, p. 284

STABILIZING SELECTION: BODY WEIGHT OF SOCIABLE WEAVERS

What is the optimal weight of a sociable weaver bird? Fig. 18 -9 a, p. 284

Stabilizing selection in sociable weavers. Graph shows the number of birds (out of 977) that survived a breeding season. Figure It Out: What is the optimal weight of a sociable weaver bird? Answer: About 29 grams Fig. 18 -9 b, p. 284

DISRUPTIVE SELECTION

Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms. Fig. 18 -10 a, p. 285

Fig. 18 -10 b, p. 285

Fig. 18 -10 c, p. 285

DISRUPTIVE SELECTION: BILL SIZE IN AFRICAN FINCHES In African seedcracker populations, birds with bills that are about 12 or 15 millimeters wide are favored. The difference is a result of competition for scarce food during dry seasons. But the middle phenotypes are not good at eating the food.

lower bill 12 mm wide = the “splitter” Fig. 18 -11 a, p. 285

lower bill 15 mm wide = the “crusher” Fig. 18 -11 b, p. 285

MAINTAINING VARIATION Natural selection theory helps explain diverse aspects of nature, including differences between males and females, and the relationship between sickle-cell anaemia and malaria.

SICKLE CELL ANEMIA AND MALARIA

Distribution of malaria cases reported in Africa, Asia, and the Middle East in the 1920 s, Fig. 18 -13 a, p. 287

Distribution (by percentage) of people that carry the sickle-cell allele. Fig. 18 -13 b, p. 287

Notice the close correlation between the maps. Individuals with SS (normal RBCs) get malaria and can die. Individuals with ss (sickle cell anemia) usually die early on. The hybrid (Ss) can survive with malaria and suffer little side affects associated with sickle cell anemia. Fig. 18 -13 b, p. 287

The data would indicate that sickle cell anemia and malaria respond to each other. Both alleles have success so natural selection favors a mix of both over one or the other. Malaria and sickle-cell anemia. (c) Physician searching for mosquito larvae in Southeast Asia. Fig. 18 -13 c, p. 287

NATURAL SELECTION REVISITED Natural Selection supports the best traits But Natural Selection can be limited because: Indirect Force: Natural selection doesn’t act on genes. Natural selection acts on unsuccessful physical traits… Not the genes that make them. Since traits (phenotypes) are determined by genes (genotypes), sometimes these unsuccessful phenotypes can pop up if they are recessive. Role of Mutation; Usually recessive alleles Recessive alleles can be hidden from targeting by natural selection.

CONCEPT CHECK What is microevolution? How populations change due to changes in allele frequencies. Which type deals with allele frequencies that result from a population of rats that stow away on a barge that lands on an island? Founder affect… genetic drift. Some years black moths are favored, in other years white moths are favored. This form of natural selection is what? Directional stabilization.

VI. SPECIATION Once Genetic Drift Ends…

SO WE’VE DISCUSSED THE MECHANISMS THAT CAUSE ALLELE CHANGES Now… Once gene flow ends, reproductive isolation occurs. Once reproductive isolation occurs, speciation soon follows

REPRODUCTIVE ISOLATION Speciation Evolutionary process by which new species form Reproductive isolating mechanisms are always part of the process Reproductive isolation The end of gene exchange between populations Beginning of speciation

FOUR BUTTERFLIES, TWO SPECIES

REPRODUCTIVE ISOLATING MECHANISMS Reproductive isolating mechanisms prevent interbreeding among groups. Heritable aspects of body form, function, or behavior that arise as populations diverge… they start to change because of the different selection pressures of the different ecosystem and the traits available the founding population. What are the isolating mechanisms? 1. 2. 3. 4. 5. 6. Mechanical Behavioral Hybridization Allopatric Sympatric/ Polyploidy (genetic) Parapatric

1. MECHANICAL ISOLATION

2. BEHAVIORAL ISOLATION

3. HYBRIDIZATION Reduced hybrid viability (ligers, tigons) Extra or missing genes Reduced hybrid fertility (mules) Robust but sterile offspring Hybrid breakdown Lower fitness with successive generations

4. ALLOPATRIC SPECIATION Geographic Isolation = “Allopatric speciation” A physical barrier arises and ends gene flow between populations Genetic divergence results in speciation Example: llamas, vicunas, and camels

ALLOPATRIC SPECIATION

THE INVITING ARCHIPELAGOS Winds or ocean currents carry a few individuals of mainland species to remote, isolated islands chains (archipelagos) such as Hawaii Habitats and selection pressures that differ within and between the islands foster divergences that result in allopatric speciation

ALLOPATRIC SPECIATION ON AN ISOLATED ARCHIPELAGO

A A few individuals of a mainland species reach isolated island 1. In the new habitat, populations of their descendants diverge, and speciation occurs. B Later, a few individuals of a new species colonize nearby island 2. Speciation follows genetic divergence in the new habitat. C Genetically different descendants of the ancestral species may colonize islands 3 and 4 or even invade island 1. Genetic divergence and speciation may follow. Fig. 18 -21 a, p. 293

OTHER SPECIATION MODELS Populations sometimes speciate even without a physical barrier that blocks gene flow. Sympatric speciation Parapatric speciation

5. SYMPATRIC SPECIATION In sympatric speciation, new species form within a home range of an existing species, in the absence of a physical barrier Polyploidy An example when there is a change in chromosome number that can cause instant speciation. On Lord Howe Island, species of palms are reproductively isolated because of polyploidy

SYMPATRIC SPECIATION IN PALMS

6. PARAPATRIC SPECIATION In parapatric speciation, populations in contact along a common border evolve into distinct species Hybrids in the contact zone are less fit than individuals on either side

PARAPATRIC SPECIATION

T. barretti hybrid zone T. anophthalmus Fig. 18 -24 c, p. 295

DIFFERENT SPECIATION MODELS

KEY CONCEPTS HOW SPECIES ARISE We have looked at microevolution, small allele frequency changes. Microevolutionary events that occur independently lead to genetic divergences, which are reinforced as reproductive isolation mechanisms evolve Now let’s look at macro, large-scale changes. Macroevolution refers to the appearance of new species over time New species evolve mainly because of DIVERGENCE. These show relationships influence the creation of new species. Speciation, the formation of new species due to evolution, links the two.

VII. MACROEVOLUTION Macroevolution Large-scale patterns of evolutionary change Includes patterns of change such as one species giving rise to multiple species, the origin of major groups, and major extinction events Coevolution Stasis Exaptation Adaptive radiation Key innovation Extinctions

MACROEVOLUTION…THE PATTERNS OF EVOLUTION Patterns of Macroevolution: that affect species. Co-evolution: Organisms are part of one other’s environment, so they can affect one another’s evolution. Species that live in close contact often have clear adaptations to one another’s existence. Adaptive Radiation: Over time, species may split into two or more lines of descendants, or lineages. As this splitting repeats, one species can give rise to many new species. The process tends to speed up when a new species enters an environment that contains few other species (meaning less competition). Helps explain finches. Extinction: If all members of a lineage die off or simply fail to reproduce, the lineage is said to be extinct. The fossil record shows that many lineages have arisen and radiated, but only a few of their descendants survived and evolved into the species present today. Scientist estimate that 99% of all species that have lived, went extinct.

COEVOLUTION Two species in close ecological contact as agents of selection on each other (coevolution) Predator and prey Host and parasite Pollinator and flower Over time, the two species may come to depend on each other.

Coevolution Hawk moth & Orchid Coevolved species. The orchid Angraecum sesquipedale, discovered in Madagascar in 1852, stores its nectar at the base of a floral tube 30 centimeters (12 inches) long. Charles Darwin predicted that someone would eventually discover an insect in Madagascar with a proboscis long enough to reach the nectar and pollinate the flower. Decades later, the hawkmoth Xanthopan morgani praedicta was discovered in Madagascar. Its proboscis is 30– 35 cm long. proboscis nectar tube 1018 -25, cmp. 296 Fig.

BEE & THE ORCHID

ECOLOGICAL NICHES A niche is the entire collective habitat where a population lives. When populations inhabit different niches, divergence often follows…because there are different selection pressures. Adaptive radiation A burst of speciation that occurs when a lineage encounters a new set of niches because of a Key Innovation: A structural or functional adaptation that allows individuals to exploit their habitat in a new way Again, caused by variation and natural selection

rabbits rodents primates horses, other perissodactyls deer, other artiodactyls dolphins whales, carnivores bats shrews, other insectivores; armadillos anteaters manatees elephants, other proboscideans kangaroos, other marsupials platypus, other monotremes Eomaia scansoria Cenozoic Evolutionary tree diagram showing the adaptive radiation of mammals following the K–T extinction Mesozoic event. Branch widths indicate the range of biodiversity in each group at different times. We show only a sample of modern mammals. The entire mammalian lineage includes more than 4, 000 modern species. The photograph shows a fossil of Eomaia scansoria (Greek for ancient mother climber), complete with the imprint of its fur. About 125 million years ago, this mouse-sized insect-eater crawled on low branches. It is thought to be an offshoot of the lineage that led to mammals. Fig. 18 -26 a, p. 297

PATTERNS OF MACROEVOLUTION How do Species Evolve? There are two main schools of though… 1. Gradualism 2. Punctuated Equilibrium

MACROEVOLUTION Gradualism : In Darwin’s day, the idea of slow, gradual change was new to geology as well as biology. Darwin had argued that large scale changes, such as the formation of new species, must require many small changes to build up gradually over a long period of time. This model is called gradualism.

MACROEVOLUTION Gradualism conflicts with another more modern theory that suggests evolution can happen in bursts over a very fast period of time. Punctuated Equilibrium: Equilibrium Some biologists argue that species do not always evolve gradually. Species may remain stable for long periods until environmental changes drastically and suddenly create new pressures. Then, many new species may “suddenly” appear. This model is called punctuated equilibrium.

Which way is correct? Probably both but there is a lot of evidence that PE is the more correct. Gradualism Punctuated Equilibrium Small evolutionary changes accumulate over long periods of time. These result from mutations present in alleles present in population. Catastrophic events, like volcanoes or meteor strikes, suddenly change the environment, creating new selection pressures. The fittest survive.

VII. HOW DOES EVOLUTION STOP? Eliminated Evolution… Stasis Exaptation Extinction

STASIS AND EXAPTATION Stasis A lineage exists for millions of years with little or no change (e. g. coelacanth) Exaptation (preadaptation) Some complex traits in modern species held different adaptive value in ancestral lineages (e. g. feathers in birds and dinosaurs)

EXTINCTION Extinction The irrevocable loss of a species from Earth Mass extinctions Extinctions of many lineages, followed by adaptive radiations Five catastrophic events in which the majority of species on Earth disappeared K–T extinction, abbreviation of Cretaceous–Tertiary extinction, also called K–Pg extinction or Cretaceous–Paleogene extinction a global extinction event responsible for eliminating approximately 80 percent of all species of animals at or very close to the boundary between the Cretaceous and Paleogene periods, about 65. 5 million years ago. http: //www. britannica. com/EBchecked/topic/1314796/K-T-extinction

SO… Exhausted Yet? We’ve covered a great deal today - The Parameters of Genetic Equilibrium - The Mechanisms of Microevolution - The Methods of Genetic Change - The Major Patterns of Macroevolution Do you have to remember EVERYTHING? - Pretty much. Should you be aware of these terms for later investigations? - Yep. Review the list on the board and be prepared to use these next week.

CLOSURE Questions? Reflect on what you’ve learned… Go to the website & download the ppt to make up anything you missed. Block periods: Natural Selection Lab Friday: Bacterial lab: Last Check