CHAPTER 22: THE ORIGIN OF SPECIES

WHERE DOES IT ALL FIT IN?

Chapter 22 applies the principles of Chapters 20 and 21 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 22 is essential to explain the biodiversity information covered throughout the book 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

·  Define and differentiate between sympatric and allopatric speciation.

·  Be able to describe and give an example of instantaneous speciation and polyploidy.

·  Know what is meant by the Biological Species Concept and explain why the controversy of hybrid species surrounds it.

·  Distinguish between the Biological Species Concept and the Ecological Species Concept.

·  Differentiate between prezygotic and postzygotic isolating mechanisms.

·  Distinguish between the three types of postzygotic isolating mechanisms.

·  List the six predominant prezygotic isolating mechanisms and give examples of each.

·  Give two ideas that may be explanations for the development of reproductive isolating mechanisms.

·  Explain how geographical isolation influences allopatric speciation.

·  Give examples of how clusters of species reflect rapid evolution through adaptive radiations and character displacement.

·  Develop an appreciation for the importance of the Cambrian explosion and mass extinction events as they have led to species diversity.

·  Describe how extinctions during the Cretaceous led to increased opportunities for mammal diversity.

·  Differentiate between gradualism and punctuated equilibria.

·  Be able to speculate on some possible outcomes of the human species evolutionary future.

·  Describe how the influences of humans can affect the future of evolution.

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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 22 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 the 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 22.

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.

USEFUL INTERNET RESOURCES

  1. Research studies related to species diversity are good for reinforcing the content of Chapter 22. A study called “Drosophila as Monitors of Change in Hawaiian Ecosystems” shows how speciation of organisms can be used as an indicator of environmental disturbance. A website containing detailed data and images of this study is available at http://biology.usgs.gov/s+t/noframe/t233.htm.
  2. Dramatic images of hox gene mutations in flies are available on a German website called Bedeutung der Hox-Gene. Images from the website can be incorporated into a presentation for students to see the ability for simple mutations to cause drastic phenotypic changes. The website can be found at http://www.zum.de/Faecher/Materialien/hupfeld/Genetik/bedeutung-hox-gene/bedeutung-hox-gene.html.
  3. The University of California at Berkeley provides a valuable website on natural selection called Understanding Evolution. It provides resources that can be shared with students that supplement the information covered in Chapter 22. The website is available at http://evolution.berkeley.edu/evolibrary/home.php.
  4. Cases studies are an effective tool for getting students interested in abstract scientific topics. The University of Buffalo provides a teaching case study called “The Story of Dinosaur Evolution”. It has the students apply what they learned in Chapters 21 and 22 to dinosaur evolution. The case study can be found at http://www.sciencecases.org/dinosaur_evolution/dinosaur_evolution_notes.pdf

LABORATORY IDEAS

Diversity with 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.

  1. Students should be provided with the following materials to perform this open-ended experiment.
  2. Sterile Petri plates containing solid Yeast Growth Media or nutrient agar supplemented with glucose at 1 g/l
  3. Packet of bakers or brewer yeast dissolved in 250 ml of sterile nutrient broth supplemented with glucose at 1 g/l
  4. Test reagents for investigating genetic differences
  5. Athletes foot fungicidal powder
  6. Bonide Rotenone-Copper Dust For Gardens
  7. Bonide Sulphur Plant Fungicide
  8. Ortho Multi Purpose Fungicide Daconil
  9. Sterile water in screw-top container
  10. Sterile test tubes covered with culture caps or cotton
  11. Clean graduated cylinders
  12. Droppers
  13. Sterile 1ml pipettes
  14. Microbiology laboratory references
  15. Discuss how yeast can be grown in liquid medium and transferred to Petri plates as a way of determining yeast colonies
  16. Ask students to design an experiment to see if they find yeast, a fungus, that has genes for protecting form fungicidal compounds.
  17. 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.

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