Download chapter 22: the origin of species

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
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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
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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.
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.
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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
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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
Analysis
Synthesis
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Have students explain factors in your locale that can cause allopatric
speciation of a large grazing animal such as deer.
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Have students view genetics.
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Ask students to explain why unrelated organisms such as crabs and fish
use gills to carry out gas exchange with the environment.
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Have students analyze how urban sprawl around major cities contributes
to allopatric speciation.
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Ask students to explain how agriculture takes advantage of allopatric
speciation.
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Ask students to hypothesize about the impact of global climate change on
the diversity of organisms in your area.
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Ask students how exposure to hazardous chemicals can affect the
population genetics of the organism.
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Have students assess the impact of invasive species on the biodiversity of
native organisms.
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Evaluation
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Ask students design an experiment to show that evolutionary change in
bacteria is not gradual.
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Ask students to evaluate the effects on the releasing pet birds and fish into
the environment.
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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.
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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
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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/specidem
o.html
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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-hoxgene/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.
a. Students should be provided with the following materials to perform this open-ended
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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.
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