This Document Contains Chapters 19 to 21 CHAPTER 19: GENES WITHIN POPULATIONS WHERE DOES IT ALL FIT IN? Chapter 19 takes a larger look at genetics in its coverage of population genetics. Students should be versed on the information in Chapters 16 and 18. Students may feel the information in Chapter 19 stands alone and is not related to the earlier genetics coverage. It should be reinforced that population genetics forms part of the explanation linking gene function to the adaptations seen in populations of organisms. The information in this chapter should be briefly reviewed before progressing with discussions on evolution and natural selection. SYNOPSIS Variation in the genetic composition of living organisms is the driving force behind evolution as a whole. Darwin and Wallace proposed that natural selection was the mechanism through which it occurs. As a population evolves it becomes better adapted to exist in its local environment. Their idea greatly contrasts with Lamarck who proposed a mechanism by which evolution occurred via inherited characteristics acquired over an organism’s lifetime. Population genetics explains the behavior of alleles within populations. Most alleles are highly polymorphic within a population and provide for greater variation than that caused by mutations alone. The Hardy-Weinberg equation was derived to explain why dominant alleles did not drive out recessive alleles and eliminate genetic variation. In large populations exhibiting random mating, the original proportions of a genotype remain constant over time. The genotypes of such populations are in equilibrium. The Hardy-Weinberg equation is a binomial expansion of the sum of the frequency of the recessive and dominant alleles. One can determine the frequency of one allele given the frequency of the other, as the sum of the two alleles must equal one. The number of heterozygote dominant individuals can also be calculated from such information. Although the Hardy-Weinberg principle predicts consistency in allele frequencies over time, actual frequencies change as a result of (1) mutation, (2) gene flow, (3) nonrandom mating, (4) genetic drift, and (5) selection. Thus the value of using the equation is being able to examine a population’s genotypes at a point in time and then follow that population to determine if the genotypes are changing. The goal of selection is to have the individuals that are best suited to an environment leave the most progeny, something that biologists refer to as fitness. In addition, fitness is a combination of mating successes, and survival. Elimination of undesirable traits is difficult because selection does not operate on rare recessive alleles, unless they are deleterious, then they could have selection pressure against them. Frequency-dependent selection can be negative or positive. When a rare form of genotype exist in a population it might have an advantage not permitted to the more common genotype, or is some cases the rare form is selected against, while the more common form is maintained in the population. Natural selection can also maintain variation in a population through the existence of successful heterozygotes. An example of this principle is sickle-cell anemia and its association with malaria in Central Africa. Individuals with the heterozygous condition are more likely to survive and reproduce than either homozygote, one which succumbs to sickle-cell anemia and the other to malaria. Disruptive selection, directional selection, and stabilizing selection act to eliminate one or both extremes or to eliminate the intermediate from an array of phenotypes. Although all five forces stated above cause genetic variation, only selection produces evolutionary change since only it depends on the nature of the environment. LEARNING OUTCOMES 19.1 Natural Populations Exhibit Genetic Variation 1. Differentiate between evolution by natural selection and the inheritance of acquired characteristics. 2. Describe methods of assessing genetic variation. 19.2 Frequencies of Alleles Can Change 1. Describe the characteristics of a population in Hardy–Weinberg equilibrium. 2. Interpret the significance of deviations from Hardy–Weinberg expectations. 19.3 Five Agents Are Responsible for Evolutionary Change 1. Describe how mutation can cause a population to deviate from Hardy-Weinberg Equilibrium. 2. Illustrate how migration can cause deviations from Hardy-Weinberg Equilibrium. 3. Discuss how nonrandom mating can lead to deviations from Hardy-Weinberg equilibrium. 4. Demonstrate how genetic drift can have a larger effect on small populations. 5. Describe how natural selection can cause deviations from Hardy-Weinberg equilibrium. 6. Explain how selection is limited by genetics. 19.4 Selection Can Act on Traits Affected by Many Genes 1. Describe the evolutionary outcome of disruptive selection. 2. Contrast the effects of directional, disruptive, and stabilizing selection. 3. Describe the evolutionary outcome of stabilizing selection. 19.5 Natural Selection Can Be Studied Experimentally 1. Recount how laboratory and field experiments with guppies demonstrated the ongoing action of natural selection. 2. Contrast laboratory and field experiments on selection on guppies. 19.6 Fitness Is a Measure of Evolutionary Success 1. List the components of evolutionary fitness. 2. List the three principle components of fitness. 19.7 Interacting Evolutionary Forces Maintain Variation 1. Demonstrate how mutation and genetic drift may act to counter natural selection. 2. Examine how gene flow can interact with natural selection to affect a population. 3. Describe the effect of frequency dependent selection. 4. Define oscillating selection, and explain how it influences the amount of genetic variation in a population. Explain how heterozygous advantage can affect allele frequencies in a population. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 19 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students believe that all genes program for visible traits • Students are unfamiliar with the exact nature of regulatory genes in determining traits • Students believe that only the observable phenotype is subject to selection • Students do not fully understand the role of and biological basis for genetic drift • Students believe that acquired traits are inherited • Student believe evolution is driven to make “better” organisms • Students do not take into account mutation in determining population genetics • Students do not take into account migration in determining population genetics • Students believe selection only kills off weaker individuals • Students believe “fitness” is an absolute set of characteristics • Students often believe that for every gene, there can only be one or two alleles • Students do not understand how assortative and disassortative mating can change the relative frequencies of homozygotes and heterozygotes. INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE It will be necessary to review manipulation of fractions and other basic algebraic skills so that students can work with and understand the mathematics associated with the Hardy-Weinberg equation. Prepare many practice problems if you intend to test heavily on that material. This isn’t as necessary if your intent is to understand the basic concepts of Hardy-Weinberg without relying too heavily on the mathematics. Use perfect squares (4, 16, 36, 49,…) and the examples will come out really nice. Students will catch on to the concept faster. Discuss the rationale behind nonrandom mating. Certain physical traits are more “appealing” (i.e., long tails in many tropical species of birds) as are certain behaviors. Red bellies in the male stickleback fish are another example. One could extrapolate on this idea in terms of human appearance, body style, and dress and how it has varied over time and with society and social status. Genetic drift is perhaps the most difficult factor affecting equilibrium to understand. Discuss the rapid radiation of life forms in newly opened territories and that it occurred after mass extinctions as evidenced by the fossil record. Pass some of those fossil types around or provide images for students to see. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 19. Application • Have students calculate allelic frequencies using the Hardy-Weinberg equation. • Have students provide examples that refute Lamarck’s view of population genetics. • Ask students to explain why certain alleles are uncommon in a population of organisms. Analysis • Have students explain how meiosis is related to gene distribution in a population of organisms. • Ask students to assess the role of genetic drift in explaining allelic variations in human populations from different regions of the world. • Ask students to hypothesize about the environmental conditions necessary for the population dynamics of an organism to obey the Hardy-Weinberg equation. Synthesis • Ask students how changes in mating preferences of a certain group of animals can affect the population genetics of the organism. • Ask students to explain what must be done in agriculture to insure little or no genetic drift in the population of crops or livestock. • Ask students describe how the population dynamics of an organism would be affected if its inheritance followed Lamarck’s principles. Evaluation • Ask students to evaluate the effects on the human population of increased mutation rates due to increased exposure to radioactivity associated with building materials using in homes and other structures. • Ask students to evaluate the accuracy and credibility of the population genetics principles used by supporters of an ideology called human eugenics. • Ask student to evaluate the pros and cons of monoculture on the population dynamics of crop plants. VISUAL RESOURCES Bring a copy of “Just So Stories” by Rudyard Kipling to demonstrate the idea of acquired characteristics. Show a close up of an actual red blood cell in its normal shape and one that is in the sickle shape. This really causes the students to appreciate the difference. Photographs or actual samples of gels showing various polymorphisms are helpful to explain the concept. Photos or drawings of various morphological polymorphisms are additionally valuable. IN-CLASS CONCEPTUAL DEMONSTRATIONS A. Virtual Hardy-Weinberg Demonstration Introduction Animated models are effective tools for visualizing mathematical concepts such as the Hardy-Weinberg equation. This demonstration provides a simple to following lecture supplement for depicting population dynamics. Materials • Computer with live access to Internet • LCD projector attached to computer • Web browser with bookmark for Oklahoma State University Hardy-Weinberg Page at http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/life4e_15-6-OSU.swf o Set animation so manual play by pressing the right mouse control and turning off the “Loop” and “Play” functions of the Flash animation. Procedure & Inquiry 1. Review the principles of the Hardy-Weinberg equation. 2. Tell students they will be viewing an animation showing how different variables affect the distribution of genes in a population 3. Start animation by pressing the right mouse control and setting animation to “Rewind” and then “Play”. 4. Stop the animation by pressing the right mouse control and setting animation so “Play” is off. 5. Run the animation series and have students explain the results of each factor that affects the outcomes of gene distribution in a population. 6. Have the class answer questions related to the limitations of the Hardy-Weinberg equation. B. Chapter Relationship Concept Map Introduction This fun and fast way to build a concept map engages students in developing a scheme for reviewing all the facts and concepts associated with DNA replication. It helps student select relevant information needed to understand DNA replication. In addition, it helps them incorporate concepts learned in other sections of the book that contribute to an understanding of DNA replication. The simple click and drag animated concept mapping tool should be practiced before using in class. Materials • Computer with live access to Internet • LCD projector attached to computer • Web browser with bookmark to Michigan State University C-Tool: http://ctools.msu.edu/ctools/index.html • Chapter outline of book for Chapters 1 through 19 projected on overhead Procedure & Inquiry 1. Tell students that you would like to do a quick assessment of how population genetics is related to the information covered in the prior chapters.. 2. Then go to the Michigan State University C-Tool and add the concept map term “Population Genetics”. 3. Use the “Add” and “Concept Word” feature to place a term on the map background related to a concept in one of the prior chapters. 4. Solicit a few more terms or concepts from prior chapters and then ask the class how the concepts are connected to population genetics. Use the “Add” and “Linking Line” feature to build a connecting line. 5. Then ask the students to justify the concept linking lines. Use the “Add” and “Linking Word” feature to place student comments on the map. 6. Continue the activity until you feel the students made a comprehensive map. LABORATORY IDEAS This virtual laboratory session provided by the University of Connecticut permits students to control the variables associated with the population genetics concept genetic drift. It engages students in an inquiry activity that provides graphical displays of their hypotheses. a. Students should be provided with the following materials to perform open-ended experiments on plant development. a. Computer with Internet access b. Web browser linked to http://darwin.eeb.uconn.edu/simulations/drift.html. b. Tell the students that they will be asked to predict population dynamics of two alleles by adjusting the frequency of p. c. Have them to interpret the graphs and evaluate the change of p for different sized populations. d. Ask the students to explain the graphical results obtained for a particular population and to compare the frequency of p for different population sizes. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. 1. Have students design population dynamics flash cards for use in high school biology classes. 2. Have students tutor high school students covering population genetics in a biology class. 3. Have students do a short PowerPoint presentation on the Hardy-Weinberg equation for high school teachers. 4. Have students collect an up to date list of references on population genetics for the college library or a biology department website. ETYMOLOGY OF KEY TERMS -gen that which produces (from the Greek genes- born or produced) hetero- different (from the Greek heteros- the other of two) inter- between; among (from the Latin inter- between) intra- within; internal (from the Latin intra- within) mono- one; single; alone (from the Greek monos- alone) morph- form (from the Greek morphe- the shape of a thing) poly- many (from the Greek polys- many) CHAPTER 20: THE EVIDENCE FOR EVOLUTION WHERE DOES IT ALL FIT IN? Chapter 20 builds on the population genetics information covered in Chapter 19 to provide a rationale for evolution. Students need to recall gene expression, heredity, and gene distribution to fully understand the information in this chapter. A complete knowledge of Chapter 20 is essential for understanding the principles of organic evolution covered in Chapter 21. In addition, any coverage of organismic diversity and adaptations relies on the concepts expounded in this chapter. SYNOPSIS There is solid scientific evidence and it exists in multiple lines of evidence other than just the fossil record. Many students upon hearing the term “evolution” even though they may be biology majors feel that this means that humans evolved from apes. Unfortunately, this is only a very small part of the theory, but because it challenges various religious beliefs, evolution is frequently rejected as heresy. His studies of fossils, geological strata, knowledge of artificial selection, plus the five year voyage on the Beagle helped Darwin to formulate his theory of evolution by natural selection. As a result of more accurate radioactive dating methods the fossil record today is much more complete and the strata that contain those fossils can be aged more accurately. The fossil record for horses is quite complete and clearly shows how they evolved over a long period of time. The primary physical changes from Hyracotherium to Equus involved increase in body size, toe reduction, and changes in dentition. In many ways this evolution parallels that of humans, most notably in the present lack of species diversity. The initial examination of the Galápagos finches aided Darwin in his development of the theory of evolution by natural selection. Peter and Rosemary Grant’s conducted a reexamination of several of the species in 1973 and reaffirmed Darwin’s original work. It further supported the impact that the environment has on the nature of an organism. Peppered moths and industrial melanism show how natural selection favors new traits as the environment changes. Coal burning by heavy industry is attributed to causing these changes by darkening tree surfaces, which resulted in a predominance of dark colored moths. The white moths stood out against the darker background allowing the birds to selectively forage on them versus the darker colored moths. Artificial selection occurs when humans favor certain genetically based phenotypic traits in plants or animals resulting in the development of new forms. Evolution at this level has occurred in the laboratory and has been operational through centuries of agricultural development and domestication. Examining anatomical homology (forelimbs of vertebrates), developmental processes (similarities of embryo development), imperfect structures (neck vertebrae in giraffes) and vestigial structures (vermiform appendix in humans) provides further evidence for evolution. Most recently, the molecular record has provided a wealth of support to help determine evolutionary relationships among species. One would expect organisms with similar appearance to have similar expressed DNA. Non-coding regions of junk DNA are equally similar unequivocally and thus provide strong supporting evidence for evolution. Studies in biogeography reveal that convergent evolution can result in similar appearing communities that are only distantly related. Natural selection actually favors such parallel evolution. The similarity in the organisms is a result of analogous rather than homologous evolution. A classic example of convergent evolution is the comparison of placental and marsupial mammal communities between North America and Australia. Although there is little dissention in the scientific world with regard to Darwin’s theory of evolution by natural selection, there is still great controversy among the general public. Darwin’s critics raise seven arguments, all without scientific merit, as to why evolution should not be taught in schools. LEARNING OUTCOMES 20.1 The Beaks of Darwin’s Finches Provide Evidence of Natural Selection 1. Describe the different feeding adaptations in Darwin’s finches. 2. Explain how climatic variation drives evolutionary change in the medium ground finch. 3. Describe how the diversity of Darwin’s finches arose in the Galapagos Islands. 20.2 Peppered Moths and Industrial Melanism Illustrate Natural Selection in Action 1. Explain the relationship between altered environment and evolution in peppered moths. 20.3 Human-Initiated Artificial Selection Is Also a Powerful Agent of Change 1. Contrast the processes of artificial and natural selection. 20.4 Fossils Provide Direct Evidence of Evolution 1. Explain the importance of the discovery of transitional fossils. 2. Describe the patterns of evolution seen in the horse. 20.5 Anatomical Evidence for Evolution Is Extensive and Persuasive 1. Explain the evolutionary significance of homologous structures. 2. Describe how patterns of early development provide evidence of evolution. 3. Illustrate how imperfect design is evidence for natural selection. 4. Explain the evolutionary significance of vestigial structures. 20.6 Genes Carry a Molecular Record of the Evolutionary Past 1. Describe the molecular evidence that evolution has occurred. 20.7 Natural Selection Favors Convergent Evolution in Similar Environments 1. Explain the principle of convergent evolution. 2. Demonstrate how the biogeographical distribution of plant and animal species on islands provides evidence of evolutionary diversification. 20.8 Critics of Evolution Raise a Variety of Objections to Darwin’s Theory 1. Characterize the criticisms of evolutionary theory and list counterarguments that can be made. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 20 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students believe that all genes program for visible traits • Students are unfamiliar with the exact nature of regulatory gene in determining traits • Students believe that only the observable phenotype is subject to selection • Students do not fully understand the role of genetic drift in variation • Students believe that vestigial traits disappear over time because of disuse • Students believe that acquired traits are inherited • Students believe evolution is driven to make “better” organisms • Students believe that organisms adapt to change rather than being selected • Students do not take into account mutation in determining population genetics • Students believe selection only kills off weaker individuals • Students believe “fitness” is an absolute set of characteristics • Students believe that species are genetically distinct and fixed • Students are not familiar with the similarity of embryological development between different groups of organisms • Student are unaware that plants undergo embryological development INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE Stress that the environment doesn’t cause changes in characteristics of an individual; instead it causes changes in the species itself. The changing environment opens up new habitats for individuals possessing different allele combinations to thrive and be successful which increase their fitness. Species that are unable to change with the environment will eventually die out due to decreased fitness. There are advantages to possessing genes that enable flexibility – being a “jack of all trades” as opposed to being a specialist. Consider the human types that are most likely to survive catastrophes – those that can adjust to all circumstances, are inventive, creative, and generally able to make something workable out of string and sealing wax. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 20. Application • Have students describe examples of artificial selection at the grocery store. • Have students why the body size of coyotes living in urban areas is smaller than those in the wilderness. • Ask students to explain how the disappearance of alleles from a population can lead to speciation. Analysis • Have students explain why mosquitoes do not develop resistance to being killed by a chemical called DDT. • Ask students to analyze the role of genetic drift in explaining speciation. • Ask students to hypothesize about the cockroaches remained virtually unchanged for millions of years. Synthesis • Ask students to explain what conditions must be necessary for humans to speciate. • Ask students to explain if a complete reliance on computers to calculate everyday tasks would lead to populations of people with smaller brains. • Ask students to describe how a plant can speciate in one generation without undergoing changes in chromosome number. Evaluation • Ask students to debate the value of selective breeding in agricultural animals. • Ask students to evaluate the biological consequences of extinctions caused by human activity in an environment. • Ask student to assess the accuracy of using protein differences to distinguish the differences and similarities between two related species. VISUAL RESOURCES Prepare slides or transparencies showing additional evidence for evolution: fossils, homologies, vestigial structures (including hip bones in python pelvis), development and so forth. Pass around during class actual fossils for students to examine while you describe them, their age, and where they were found around the world. Have a paleontologist visit your class and present a short lecturer on the fossil record of plants and animals. Introduce students to some of the writings of Stephen J. Gould, such as “The Panda’s Thumb.” Bring several different types of onions, carrots, potatoes, tomatoes, squash or apples to class for discussion of artificial selection. IN-CLASS CONCEPTUAL DEMONSTRATIONS A. Darwin’s Voyage Introduction Misconceptions and a lack of knowledge about Darwin’s voyage on the HMS Beagle are major hindrances to developing student understanding of evolution. This activity provides a visual time-line of Darwin’s memorable journey. Materials • Computer with live access to Internet • LCD projector attached to computer • Web browser with bookmark for About Darwin Voyage Page at http://www.aboutdarwin.com/voyage/voyage01.html Procedure & Inquiry 1. Review the principles of evolution proposed by Darwin. 2. Tell students they will be viewing a history of the Beagle’s voyage. 3. Go through the history and click on the detailed note pages. 4. Have the class answer questions related to particular parts of the journey and have students hypothesize on Darwin’s observations as if they were not yet familiar with the theory of natural selection. B. Extrapolation Concept Map Introduction This fun and fast way to engage students in developing a sense of evolution is to link evolution to observations seen today. Have the students select relevant examples of natural and artificial selection in everyday life. The simple click and drag animated concept mapping tool should be practiced before using in class. Materials • Computer with live access to Internet • LCD projector attached to computer • Web browser with bookmark to Michigan State University C-Tool: http://ctools.msu.edu/ctools/index.html • Chapter outline of book for Chapters 1 through 19 projected on overhead Procedure & Inquiry 1. Tell students that you would like to do a quick survey of everyday examples of natural and artificial selection. 2. Then go to the Michigan State University C-Tool and add the concept map terms “Natural Selection” and “Artificial Selection”. Space out the terms to permit branching. 3. Ask the students to find examples of each. Also ask them to think of any overlapping examples. 4. Use the “Add” and “Concept Word” feature to place the terms on the map for “Natural Selection” or “Artificial Selection”. 5. Then ask the students to justify the concept linking lines. Use the “Add” and “Linking Word” feature to place student comments on the map. 6. Continue the activity until you feel the students made a comprehensive map. LABORATORY IDEAS This quick laboratory activity encourages students to artificially select for yeast that live at alcohol concentrations. Artificial selection with this goal is used to develop yeast that can be used in the brewing and backing industries. a. Students should be provided with the following materials to perform this open-ended experiment on producing yeast that can survive in high glucose environments. a. Sterile Petri plates containing solid Yeast Growth Media or nutrient agar supplemented with glucose at 1 g/l b. Packet of bakers or brewer yeast dissolved in 250 ml of sterile nutrient broth supplemented with glucose at 1 g/l c. 100% ethanol d. Sterile water in screw-top container e. Sterile test tubes covered with culture caps or cotton f. Clean graduated cylinders g. Droppers h. Sterile 1ml pipettes i. Microbiology laboratory references b. Discuss how yeast can be grown in liquid medium and transferred to Petri plates as a way of counting yeast concentration c. Ask students to design an experiment to see if they can select for yeast that grow at high alcohol concentrations d. Have the students set up the experiment and check the progress of yeast growth over the term of the experiment. e. Students should be able to compare yeast grown at various alcohol concentrations to a control LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. 1. Have students design do a poster for a library on Darwin’s voyage on the Beagle. 2. Have students tutor high school students covering natural selection in a biology class. 3. Have students do a presentation about artificial selection for a FFA or 4H group. 4. Have design educational materials on the artificial selection of antibiotic resistant bacterial for distribution in the community. ETYMOLOGY OF KEY TERMS adapt to make fit (from the Latin ad- toward and aptus- fit) analogous showing similarity of function but different origins (from the Greek ana- up and logos- thought, ratio) bio- life or relating to living organisms (from the Greek bios- mode of life) evolution change (from the Latin evolvere – to unroll) geo- earth (from the Greek ge- earth or land) homeo- likeness; resemblance; similarity (from the Greek homoios- like) ortho straight (from the Greek orthos- straight) para- beside; next to (from the Greek para- beside) CHAPTER 21: THE ORIGIN OF SPECIES WHERE DOES IT ALL FIT IN? Chapter 21 applies the principles of Chapters 19 and 20 to explain the origins of organismic diversity. This chapter also requires knowledge of meiosis, inheritance, and development to build a model of diversity due to natural selection. Chapter 21 is essential to explain the biodiversity information covered throughout the book and forms the basic paradigm of biological reasoning. SYNOPSIS The term “species” is difficult to define and how a species becomes a new species is even more complex. The concept of a species must account for the distinctiveness of all the species that occur within a single location, yet connect populations of the same species that exist in geographically separated areas. Mayr’s Biological Species Concept defines species in terms of reproductive isolation and is more applicable to animals than to plants. One substantial problem with the Biological Species Concept involves the formation of hybrids. If biological species are indeed reproductively isolated by definition hybrids should be rare – they are not. Therefore, species distinctions may be additionally maintained by natural selection and countered by gene flow. As yet, there seems to be no universal explanation that represents the diversity of all living organisms, adding to the dynamic nature of evolutionary biology. The term sympatric refers to different species living in the same areas but maintain their species identity because of their habitat utilization and behavior. Species identity is retained by either prezygotic or postzygotic mechanisms. The former prevents the formation of the zygote and includes geographical, ecological, behavioral, temporal, prevention of gamete fusion, and mechanical isolation. Postzygotic mechanisms may prevent proper development of zygotes to adults or, if adults form, they may be sterile. Reproductive isolation may indirectly be caused by selection or it may occur due to a completely random event. Partial reproductive isolation may allow for the formation of hybrids between two closely related species. If the hybrid is at a disadvantage compared to either parent, reinforcement will occur as selection favors alleles in the parent populations that prevent future hybrid formation. Adaptation and speciation are often related since with adaptation species develop differences that lead to reproductive isolation. Change in just a few genes may be sufficient to result in speciation. In many plants polyploidy is often involved in the formation of new species, whereas this is not the case with animals species. Clusters of related species provide ample data supporting rapid evolution and speciation in isolated areas. Among the best known examples are Darwin’s finches, Hawaiian Drosophila, Lake Victoria chichlids, and New Zealand alpine buttercups. Until recently, the diversity of eukaryotes increased steadily over billions of years. The greatest spurt occurred during the Cambrian explosion, followed by five great extinction events. The activities of humans may produce a sixth great extinction. At current rates, 25% of all species may be lost within the next 50 years! The controversy between gradualism and punctuated equilibrium continues, but it is safe to say that the evolution of different groups occurs at different rates. Large populations are often in stasis for long periods, small isolated populations usually experience rapid evolution. The future of evolution is not just confined to other species, humans are also subject to the pressures of natural selection. Certainly improvements in medicine, medical treatments, diet, and new ideas on the vast frontier of genetics offer ample opportunity for future generations to witness natural selection within the human population. LEARNING OUTCOMES 21.1 The Biological Species Concept Highlights Reproductive Isolation 1. Explain the basis for the biological species concept. 2. Distinguish among the various forms of prezygotic isolating mechanisms. 3. Differentiate between postzygotic and prezygotic isolating mechanisms. 4. Explain the weakness of the biological species concept. 21.2 Natural Selection May Reinforce Reproductive Isolation 1. Explain how natural selection can reinforce reproductive isolation. 21.3 Natural Selection and Genetic Drift Play Key Roles in Speciation 1. Compare how natural selection and genetic drift affect speciation. 21.4 Speciation Is Influenced by Geography 1. Compare allopatric species with sympatric species. 2. Explain the conditions required for sympatric speciation to occur. 21.5 Adaptive Radiation Requires Both Speciation and Habitat Diversity 1. Describe how a key innovation can lead to adaptive radiation. 2. Explain how character displacement may promote sympatric speciation. 3. Describe examples of adaptive radiation. 21.6 The Pace of Evolution Varies 1. Compare stasis, gradual evolutionary change, and punctuated equilibrium. 21.7 Speciation and Extinction Have Molded Biodiversity Through Time 1. Define mass extinction and identify when major mass extinctions have occurred. 2. Evaluate the contention that we are in the midst of a mass extinction today. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 21 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students believe that all genes program for visible traits • Students believe that only the observable phenotype is subject to selection • Students do not fully understand the role of genetic drift in variation • Students believe that vestigial traits disappear over time because of disuse • Students believe that acquired traits are inherited • Student believe evolution is driven to make “better” organisms • Students believe that organisms adapt to change rather than being selected • Students do not take into account mutation in determining population genetics • Students believe selection only kills off weaker individuals • Students believe “fitness” is an absolute set of characteristics • Students believe that species are genetically distinct and fixed • Students believe that a lack of “missing links” disproves evolution • Students believe that all evolution is gradual • Students believe that polyploidy leads to infertile individuals INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE Discuss the rapidity with which populations of feral animals, especially dogs and pigs, return to a wild, generalized appearance. Populations of feral dogs in nearly every country have a similar appearance: coyote-like, forty or so pounds, short fur, brownish coloration, tails that curl over the back. Special strains of many food plants must be continually hybridized to maintain their specific traits. One could relate punctuated equilibrium and gradualism to changes in various styles of clothing, automobiles, architecture, and so forth. It is relatively easy to observe smooth transitions in architecture over a period of time as well as punctuated evolution as in the sudden occurrence of Frank Lloyd Wright buildings. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 21. Application • Have students explain factors in your locale that can cause allopatric speciation of a large grazing animal such as deer. • Have students view genetics. • Ask students to explain why unrelated organisms such as crabs and fish use gills to carry out gas exchange with the environment. Analysis • Have students analyze how urban sprawl around major cities contributes to allopatric speciation. • Ask students to explain how agriculture takes advantage of allopatric speciation. • Ask students to hypothesize about the impact of global climate change on the diversity of organisms in your area. Synthesis • Ask students how exposure to hazardous chemicals can affect the population genetics of the organism. • Have students assess the impact of invasive species on the biodiversity of native organisms. • Ask students design an experiment to show that evolutionary change in bacteria is not gradual. Evaluation • Ask students to evaluate the effects on the releasing pet birds and fish into the environment. • Ask students to investigate the pros and cons of using a biological control strategy in which a non-native fish is introduced in ponds to reduce mosquito populations. • Ask student to evaluate the pros and cons of reintroducing buffalo into areas where they were reduced to near extinction 100 years ago. VISUAL RESOURCES Show photos of humans, dogs, fish, chickens, corn, wheat, members of the broccoli family (including the latest – broccoflower), and so forth to show vast differences in appearance while maintaining species integrity. In contrast, show slides comparing common carp and goldfish or wolves and dogs, animals that are very similar in appearance, but distinctly members of different species. Stress the importance of examining more than gross physical appearance to determine relatedness in living organisms. Obtain photos of areas devoid of life and the rapid radiation of plant and animal life over a period of time, a sort of before and after series. New volcanic islands, Mt. St. Helens, or recent lava flows in the Hawaiian Islands or Yellowstone and Los Alamos, New Mexico after the massive fires would be good subjects. Several good videos have been made on this subject. IN-CLASS CONCEPTUAL DEMONSTRATIONS A. Speciation of Beads Introduction Tangible models of speciation are useful for demonstrating how organisms develop diversity within their populations. Radford University has a simple and easy to understand model that uses beads to represent the population dynamics leading to speciation. This demonstration can be replicated using pop beads or Post-it notes on a board. Materials • Computer with live access to Internet • LCD projector attached to computer • Web browser bookmarked to Radford University site at http://www.radford.edu/~swoodwar/CLASSES/GEOG235/exercises/speciation/specidemo.html Procedure & Inquiry 1. Review the principles of speciation with the class. 2. Tell students they will be viewing a speciation model using beads to represent diversity changes in a population 3. Start the demonstration by going to Step 1: Evolution in prototype common ancestor species. 4. Go through the various parts of Step 1 and then ask the class to think of actual examples where this situation can occur. 5. Next, progress through Step 2: Reproductive isolation occurs between two populations of Ancestor Species A. 6. Now ask the class to think of actual examples where reproductive isolation can occur. 7. Then, finish with Step 3: Independent evolution of isolated populations and speciation. Again, ask the class to think of actual examples where this situation can occur. 8. Have the class answer questions related to what was demonstrated. LABORATORY IDEAS Diversity within populations can be very difficult to measure within a semester-long biology course. Students can be asked to design a simple experiment that investigates the diversity of traits within a microbial population. a. Students should be provided with the following materials to perform this open-ended experiment. a. Sterile Petri plates containing solid Yeast Growth Media or nutrient agar supplemented with glucose at 1 g/l b. Packet of bakers or brewer yeast dissolved in 250 ml of sterile nutrient broth supplemented with glucose at 1 g/l c. Test reagents for investigating genetic differences i. Athletes foot fungicidal powder ii. Bonide Rotenone-Copper Dust For Gardens iii. Bonide Sulphur Plant Fungicide iv. Ortho Multi-Purpose Fungicide Daconil d. Sterile water in screw-top container e. Sterile test tubes covered with culture caps or cotton f. Clean graduated cylinders g. Droppers h. Sterile 1ml pipettes i. Microbiology laboratory references b. Discuss how yeast can be grown in liquid medium and transferred to Petri plates as a way of determining yeast colonies c. Ask students to design an experiment to see if they find yeast, a fungus, that has genes for protecting form fungicidal compounds. d. Students should compare the yeast grown on different fungicides to a control group. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. 1. Have students work with a local environmental group on biodiversity issues. 2. Have students tutor high school students covering evolution in a biology class. 3. Have students prepare an up to date literature review on biodiversity books and websites for a local library. 4. Have students do a biodiversity presentation at a local elementary school science program. ETYMOLOGY OF KEY TERMS inter- between; among (from the Latin inter- between) macro- large; large enough to be seen with the naked eye (from the Greek makros- long) phylo- tribe; race; phylum (from the Greek phyle- tribe, clan) post behind, in the rear (from the Latin post- behind) pre- earlier than (from the Latin prae- in front of) zygote diploid cell created by fertilization (from the Greek zygotes- yoked) Instructor Manual for Understanding Biology Kenneth Mason, George Johnson, Jonathan Losos, Susan Singer 9780073532295, 9781259592416
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