Modeling-Based Integrated Life Science Technology Curriculum Project and
Publications:
Sexual Selection
Jonathan and Shane
03/07/2011
EDC 746
Final Draft
Learning Outcomes
Science Content Standards From the National Science Education Standards
Content Standard A
As a result of activities in grades 9–12, all students should develop
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Abilities necessary to do scientific inquiry
Understandings about scientific inquiry
Developing Student Abilities and Understanding
For students to develop the abilities that characterize science as inquiry, they must actively
participate in scientific investigations, and they must actually use the cognitive and
manipulative skills associated with the formulation of scientific explanations. This standard
describes the fundamental abilities and understandings of inquiry, as well as a larger framework
for conducting scientific investigations of natural phenomena.
In grades 9-12, students should develop sophistication in their abilities and understanding of
scientific inquiry. Students can understand that experiments are guided by concepts and are
performed to test ideas. Some students still have trouble with variables and controlled
experiments. Further, students often have trouble dealing with data that seem anomalous and
in proposing explanations based on evidence and logic rather than on their prior beliefs about
the natural world.
One challenge to teachers of science and to curriculum developers is making science
investigations meaningful. Investigations should derive from questions and issues that have
meaning for students. Scientific topics that have been highlighted by current events provide
one source, whereas actual science- and technology-related problems provide another source
of meaningful investigations. Finally, teachers of science should remember that some
experiences begin with little meaning for students but develop meaning through active
involvement, exposure, and growing skill and understanding.
A critical component of successful scientific inquiry in grades 9-12 includes having students
reflect on the concepts that guide the inquiry. Also important is the prior establishment of an
adequate knowledge base to support the investigation and help develop scientific explanations.
The concepts of the world that students bring to school will shape the way they engage in
science investigations, and serve as filters for their explanations of scientific phenomena. Left
unexamined, the limited nature of students' beliefs will interfere with their ability to develop a
deep understanding of science. Thus, in a full inquiry, instructional strategies such as smallgroup discussions, labeled drawings, writings, and concept mapping should be used by the
teacher of science to gain information about students' current explanations. Those student
explanations then become a baseline for instruction as teachers help students construct
explanations aligned with scientific knowledge; teachers also help students evaluate their own
explanations and those made by scientists.
Students also need to learn how to analyze evidence and data. The evidence they analyze may
be from their investigations, other students' investigations, or databases. Data manipulation
and analysis strategies need to be modeled by teachers of science and practiced by students.
Determining the range of the data, the mean and mode values of the data, plotting the data,
developing mathematical functions from the data, and looking for anomalous data are all
examples of analyses students can perform. Teachers of science can ask questions, such as
''What explanation did you expect to develop from the data?" "Were there any surprises in the
data?" "How confident do you feel about the accuracy of the data?" Students should answer
questions such as these during full and partial inquiries.
Public discussions of the explanations proposed by students is a form of peer review of
investigations, and peer review is an important aspect of science. Talking with peers about
science experiences helps students develop meaning and understanding. Their conversations
clarify the concepts and processes of science, helping students make sense of the content of
science. Teachers of science should engage students in conversations that focus on questions,
such as "How do we know?" "How certain are you of those results?" "Is there a better way to
do the investigation?" "If you had to explain this to someone who knew nothing about the
project, how would you do it?" "Is there an alternative scientific explanation for the one we
proposed?" "Should we do the investigation over?" "Do we need more evidence?" "What are
our sources of experimental error?" "How do you account for an explanation that is different
from ours?"
Questions like these make it possible for students to analyze data, develop a richer knowledge
base, reason using science concepts, make connections between evidence and explanations,
and recognize alternative explanations. Ideas should be examined and discussed in class so that
other students can benefit from the feedback. Teachers of science can use the ideas of students
in their class, ideas from other classes, and ideas from texts, databases, or other sources—but
scientific ideas and methods should be discussed in the fashion just described.
BIOLOGICAL EVOLUTION
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Species evolve over time. Evolution is the consequence of the interactions of (1) the
potential for a species to increase its numbers, (2) the genetic variability of offspring due
to mutation and recombination of genes, (3) a finite supply of the resources required for
life, and (4) the ensuring selection by the environment of those offspring better able to
survive and leave offspring.
The great diversity of organisms is the result of more than 3.5 billion years of evolution
that has filled every available niche with life forms.
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Natural selection and its evolutionary consequences provide a scientific explanation for
the fossil record of ancient life forms, as well as for the striking molecular similarities
observed among the diverse species of living organisms.
The millions of different species of plants, animals, and microorganisms that live on
earth today are related by descent from common ancestors.
Biological classifications are based on how organisms are related. Organisms are
classified into a hierarchy of groups and subgroups based on similarities which reflect
their evolutionary relationships. Species is the most fundamental unit of classification.
Students will:
1. Investigate and explain the selective pressures that result in sexual selection in a
species.
2. Identify key differences between natural and sexual selection.
3. Analyze data and determine if sexual selection is taking place.
4. Utilize computer-based technological resources to access and share materials
5. Students will formulate conclusions from model-based activities from data.
6. Students will learn how to use the resources provided to them to create explanatory
models to explain data
7.
7. Students will operate in teams to produce an online reference source based on
conclusions made from modeling exercises. .
Student Misconceptions
Most of the student misconceptions that concern sexual selection stem from preexisting conceptions involving heredity. Misconceptions involving heredity as listed from an
article in the MSTA Journal
Berthelsen, B. (1999). Students Naïve Conceptions in Life Science. MSTA Journal, 44(1)
(Spring’99), pp. 13-19. http://www.msta-mich.org

This article provides research based misconceptions concerning heredity which relate to
sexual selection
They are as follows:

Students think variation between species is a result of adaptation to environment
instead of inheritance. The theory of inheritance of acquired characteristics for species
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states that physiological changes acquired over the life of an organism (such as the
enlargement of a muscle through repeated use) may be transmitted to offspring.
Students do not distinguish between sexual and asexual reproduction. Students need to
understand
Students believe that transmitted characteristics are acquired during the life time of the
animal.
Students believe that individuals can adapt to a changing environment. These
adaptations are heritable.
Students can apply chance and probability to assigned genetics problems, but not to
human situations in families.
Students do not understand the relationship between DNA, genes, and chromosomes.
Students do not understand that DNA is the carrier of genetic information (genes) and
that genes, which make up the portion of DNA that is used for instructions such as
making proteins, are packaged into chromosomes.
Teaching and Learning Activities For Teacher
Note: These notes for use as a background for the instructor. The background should
only be used for students as a review.
According to Darwinian evolution, traits that increase an organism’s fitness (the ability
to survive and reproduce) will become more common in a population over time. Often this
process results in descendants with enhanced ability to hunt prey, avoid predators, or resist
infection in the environment that their ancestors were selected in. However, in some cases
evolutionary traits arise in a population not as result of competition for survival, but as a result
of enhanced relative ability of individuals in terms of passing on genetic information to
subsequent generations. This type of competition occurs between individuals of the same
species and is referred to as sexual selection. It can occur in two forms: intrasexual selection, in
which males fight amongst themselves for access to the passive females; and intersexual
selection, in which females choose their mates and males compete for attention. In some rare
cases, the roles of the males and females are reversed.
Traits that enable an organism to gain a sexual advantage over members of the same
species but are not actually utilized in reproduction are called secondary sexual characteristics.
For intrasexual selection, these can include horns, tusks, or other ‘weapons’ used to defeat
rivals, and for intersexual selection we see examples such as brilliant coloration of birds and
fish.
This inquiry based-unit suitable for two to three 40-minute class periods, consisting of
7th-9th graders. Within this unit, technology is used as a delivery mechanism for the information
and as a medium for compiling the students’ creations and interactions into a single resource.
Day One: Widowbirds
Lesson Format
1. Formative Assessment
Students will be given several minutes to answer the following questions (perhaps projected on
an overhead) on a sheet of paper, to be collected by the teacher upon completion.
A. In your own words, how what is natural selection? What is sexual selection? How do
they differ?
B. If members of one sex of the widowbird population compete (such as a physical fight) to
have the ability to mate with the opposite sex, how could this affect the widowbird
population? Answer the same question but what if one sex of the widowbird species will
only mate with the other sex if they have specific physical qualities that are wanted for
mating?
C. What advantages could be provided for a male bird by growing an extremely long tail
before mating season? What about disadvantages?
D. How could you test your theories about the function of extremely long tails in male
birds?
2. Investigation – Is Selection Occurring?
Students will be presented with the following information in student activity worksheets 1-3.
As they move through the data, they will be tasked with answering multiple high-level
questions designed to help them begin to build their conceptual model of sexual selection as a
process.
3. Team Assembly and Wiki Briefing
Students will be organized into teams of three to four. These teams will work together over the
next two classes as they explore and analyze data relating to sexual selection and continue
building their conceptual model of the process. Upon completion of these tasks, the teams will
collaborate to create a Sexual Selection Wiki using the Wikispaces program.
Wikispaces is quite simple to use and edit, but it will probably be useful to give a brief
demonstration of how to use the on-line software in order to post the students’ findings. The
link below can help when setting up wikispace sites for students. Also an example
Wikispaces for Educators How to Site: http://www.wikispaces.com/content/for/teachers
This is the resource page for educators who are new to Wikispaces. The FAQ explains how
educators can use the site and have it be a safe online space with restrictions and accessibility
options for the classroom.
Student Activity Worksheet 1
NAME:______________________________
DATE:____________
1. Describe your initial thoughts about how tail length would impact male widowbirds,
from both positive and negative perspectives.
Tail Length Study
In an initial field study, researchers compared the number of active nests and date of the first
egg production in a nest among males with different tail lengths. Results of the study are given
in Figures 3 and 4.
Number of Active Nests vs. Male Tail Length (mm)
Figure 3. Number of active nests for males with different tail lengths (y = 0.038x − 4.84;
F1,40 = 17.3, r2 = 47.4%, p < 0.001). Data based on Pryke et al. 2001.
Note: A p-value is a probability measure that is used to decide if an assumed "fact" is false. The
"assumed fact" is the formalized statement about a parameter, or Null Hypothesis, in a
hypothesis test. In the hypothesis testing process you use existing data to determine if the
observed estimate of the parameter is consistent with the hypothesized value. The p-value is
the probability that measures the likelihood of the data occurring if the Null Hypothesis true. If
the p-value is small (<5%) it is unlikely that the Null Hypothesis is true.
Day of First Egg in Nest vs. Male Tail Length (mm)
Figure 4. Date of first egg laid in the nest for males with different tail lengths. (y = 0.085x + 27.32, F1,40 = 9.3, r2 = 30.0%, p = 0.0003) Data based on Pryke et al. 2001.
****Answer Key to the Discussion Questions For the Rest of This Activity Are At The End of The
UNIT. Questions 1-9****
2. Identify the independent and dependent variables.
3. What are the researchers trying to determine by collecting this data?
4. What conclusions can you draw from the information presented in the two graphs
shown above? Make sure to discuss the relationship of the independent and
dependent variables when answering.
Student Activity Worksheet 2
NAME:______________________________
DATE:____________
Tail Length Manipulations
In a different study, researchers studied the long-tailed widowbird (Euplectes progne). They
started by counting the number of active nests (a nest with birds or eggs present)among four
groups of nine male birds with similar tail lengths (Figure 5). Next, researchers manipulated the
four groups of males as follows:
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Group 1—tails shortened
Group 2—tails uncut
Group 3—tails cut and re-glued onto the male, length unchanged
Group 4—tails elongated by gluing on the length cut from Group 1 males
The number of new active nests in the territories of males in the four groups after treatment is
given in Figure 6.
Mean Number of Active Nests vs. Treatment
Figure 5. Mean number of active nests (± standard error) for nine males in four different
treatment groups before tail length manipulation. There are no significant differences in mean
number of nests among groups. Data based on Andersson 1982.
Mean Number of Active Nests vs. Treatment
Figure 6. Mean number of new nests (± standard error) for nine males in four different
treatment groups after tail length manipulation. Groups with different letters above them are
significantly different from one another (p < 0.05). Data based on Andersson 1982.
5. The two graphs above represent a before and after scenario of a selection of birds
that have had their tails experimentally modified. Why do you think the researchers
chose to include one group that has been “cut and reglued” with no change in
length?
6. Using the idea that individuals have varying reproductive success based on
competition for mates, how do you explain the difference between the two graphs?
Student Activity Worksheet 3
NAME:______________________________
DATE:____________
Follow Up Study
Having conducted the studies described above in two long-tailed species, the researchers
conducted a similar tail manipulation experiment in a closely related species, the redshouldered widowbird (Euplectes axillaris). Although males in this species have distinctive
breeding plumage colors, they do not produce a long tail. Data from this experiment are given
in Figures 7 and 8.
Number of Males vs. Tail Length (cm)
Figure 7. Number of males with different tail lengths in a population of red-collared
widowbirds. Data based on Pryke and Andersson 2002.
Mean Number of Active Nests vs. Tail Length (cm)
Figure 8. Mean number of active nests (± standard error) in a population of red-shouldered
widowbirds that had tails shortened (6 cm), elongated (8 cm), or super-elongated (22cm).
Groups with different letters above them are significantly different from one another (p < 0.05).
Data based on Pryke and Andersson 2002.
7. The information in these last two graphs was obtained from a population of birds
very closely related to widowbirds, but who do not naturally display the exaggerated
tail length. What does this data demonstrate?
8. Why do you think the investigators chose to perform this addition to their study?
9. Do you think that the results support the idea that sexual selection is taking place in ????
Explain10. If longer tails equate to greater success in males, why don’t you think that the tails
continue to get even longer as…????
Day 1 Discussion Questions Answer Key
1. Describe your initial thoughts about how tail length would impact male widowbirds,
from both positive and negative perspectives.
Responses may vary. We can see from the data that longer tails have a positive
correlation with number of nests and a negative correlation with the number of days
before the first egg appears, indicating that longer tails enhance reproductive
fitness. However, students may note that a longer tail surely makes the bird more
noticeable to predators and may affect their in-flight maneuverability.
2. Identify the independent and dependent variables.
The independent variable in this situation would be the length of the tails being
observed, and the dependent variables include whatever the graph is comparing tail
length with. This can be number of active nests or days before the first egg appears.
3. What are the researchers trying to determine by collecting this data?
The purpose of collecting this data is to observe the effects of tail length on fitness.
4. What conclusions can you draw from the information presented in the two graphs
shown above?
Students should note that increased tail length seems to lead to greater reproductive
success in the widowbirds.
5. The two graphs above represent a before and after scenario of a selection of birds
that have had their tails experimentally modified. Why do you think the researchers
chose to include one group that has been “cut and reglued” with no change in
length?
This sample creates a control for the experiment. Researchers would be concerned
that the actual process of alteration of tail length could perhaps psychologically
affect the birds’ fitness, casting doubt on whether it was actually the tail length that
affected the outcome of the experiment. By including this group, the researchers can
compare the “cut and reglued” group with the primary control group to determine
whether their results are valid.
6. Using the idea that individuals have varying reproductive success based on
competition for mates,, how do you explain the difference between the two graphs?
Students should observe that the group of birds that had their tails experimentally
lengthened demonstrated a dramatic increase in reproductive success. Based on
their fundamental knowledge of the sexual selection process, it would seem that the
longer tails do, in fact, confer an advantage to the male birds. Since the birds did not
naturally possess this feature, students may hypothesize that simply seeing the
longer tails made the female widowbirds more willing to mate with the males.
Taking this a step farther, students may hypothesize that females are able to assess
a male’s ability to survive despite having a trait that could be detrimental to avoiding
predators.
7. The information in these last two graphs was obtained from a population of birds
very closely related to widowbirds, but who do not naturally display the exaggerated
tail length. What does this data demonstrate?
We can see from this study that even though the males of this new species have not
evolved to have extremely long tails, the trait is still viewed favorably by females and
confers a reproductive advantage. The birds that had their tails showed a higher
average number of active nests, and the birds that had their tails super-elongated
demonstrated a dramatic increase in number of nests. This data supports the
hypothesis that females tend to select males that show visual indications of
increased survivability, even when the females have no prior experience with this
adaptation.
8. Why do you think the investigators chose to perform this addition to their study?
A diverse sampling lends credibility to any experiment. By comparing their initial
findings with a genetically similar species that had not previously displayed the same
type of sexual selection, the researchers were able to demonstrate that their
hypothesis was applicable in other settings outside of a single species. Furthermore,
this data reveals that under the right conditions, sexual selection can take place very
suddenly if a particular phenotype appears to be advantageous for survival.
9. Do you think that the results support the idea that sexual selection is taking place?
Explain.
Responses may vary, but the data seems to provide good support for the theory of
sexual selection. The increased tail length does not provide a survival advantage
(which would indicate natural selection), and may even hamper survivability, and yet
birds with naturally long tails or experimentally enhanced tails were consistently able
to secure more nests and faster offspring production times. Students should follow
proper scientific policy and note that this data does not PROVE anything, but
supports the idea that sexual selection is taking place.
10. If longer tails equate to greater success in males, why don’t you think that the tails
continue to get even longer?
Again, answers may vary, but a good answer would be that the optimum tail length
is a compromise between being as long as possible to attract females without
encumbering the bird so drastically that it is unable to survive long enough to
reproduce.
SIDE NOTE:
If students are still struggling to understand the pressures that lead to sexual selection, the
following excerpt from the Evolution 101 Website may prove useful.Within this article, students
will be instructed to describe how gene variation attributes to the goal of sexual selection.
FROM THE WEBSITE:
http://evolution.berkeley.edu/evosite/evo101/IIIE3aRunawayselec2.shtml

Runaway selection:
Imagine a bird population in which females choose mates at random. Males with slightly
longer tails fly a little more adeptly, avoid predation, and so, survive better than males
with slightly shorter tails. In this situation, a gene for female choosiness (longer tail =
sexier) will be favored, since—by choosing a long-tailed male—she will have sons with
longer tails. This trait will spread through the population until most males have long tails
and most females prefer long-tailed mates. So far so good.
However, once this has happened, the process may run out of control, until the male trait
becomes so exaggerated that it is disadvantageous. In other words, female preference,
instead of survival advantage, may begin to drive the evolution of ever-longer tails, until
males are encumbered by showy plumage that no longer helps them avoid predation.
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Good genes:
Imagine another bird population in which females choose mates at random. Some males
in the population have better genes for survival than others, but it is difficult to tell
whether a male has good genes or not. In this scenario, long tails make it more difficult to
survive—they are costly to produce and maintain. Because they are so costly, only males
with good genes have the extra resources to produce them. In this situation, a long tail is
an indicator of good genes. A gene for female choosiness (longer tail = sexier) will be
favored, since—by choosing a long-tailed/good gene male—she will have sons with good
genes. This trait will spread through the population until most females choose long-tailed
mates and males that are able to produce long tails are favored.
If females choose males with “long and costly” tails, they are guaranteed to get good genes! If
they choose males with “short and cheap” tails, they may get good or bad genes.
4. Collaboration
Having analyzed the above data, students will spend the last 10-15 minutes of class making the
initial entry on their Wiki. Each group will create a page titled “Sexual Selection.” Their
Wikispaces project will consist of two different parts:
1. First, they will compose a paragraph explaining what sexual selection is, how it differs
from and is similar to natural selection, and what factors can lead to its occurrence.
They will then create one entry for their “Examples” section describing what they have
learned about the widowbird.
Secondly, students will be allowed to research and choosea real-life example of sexual selection
to put on their Wikispace.
EXAMPLES OF SEXUAL SELECTION IN NATURE (if needed)
1. Plumage of male peacocks
2. Necks of Giraffes
3. Courtship ritual of birds of paradise
4. Bowers of bowerbirds
5. Tusks of Walruses
6. Horns of Mountain Goats
7. Antlers of Deer
8. “Mustache” of guppy Poecilia sphenops (seriously!)
9. Coloration of Mandrills
10. Canine size of baboons
Example of Wikispace PageWIKISPACES TUTORIAL
1. When you first access the site at www.wikispaces.com, you will be prompted to create an account.
It’s easy to sign up and there is even an option for teacher to get a free upgrade. When you create your
account, choose to create a new wiki. We have named ours “kirbyrogers” but you can name yours after
your classroom. You will now have a page that looks like this:
2. In order for students to join, they will need to create accounts as well. To invite a student, click the
“Manage Wiki” button on the left side of the screen and then choose “Invite People,” shown below with
an arrow pointing at the icon.
3. Once students have access to the wiki, they can begin to create pages. This is accomplished by clicking
on the “New Page” button on the left side of the screen. Be sure pop-ups are enabled on the computers,
because they will get a new screen that allows them to create and edit information. We have entered in
the title for this one:
4. Adding text is really easy. Students can simply type into the box as if they are using a word processor.
Adding images is a bit trickier, because you can’t just copy and paste them. When students find an
image they want to use, they need to save it to their flash drive or the computer’s hard drive, and then
upload it with the File button:
5. Now just browse your hard drive until you find the image, and then double click on it to upload it to
your page:
6. Just click “Save” to store the wiki page in its current form. Students can continue to add additional
pages, or edit existing pages by pressing the Edit button in the upper right hand side of the screen.
7. As more pages accumulate, you will see links to them appear on the left side of your wiki’s home
screen. Be sure to edit the home screen to contain information about your class! Here’s what ours looks
like now, with an arrow indicating the links to the other pages:
8. Congratulations! You are on your way to having a large collection of data about different species that
engage in sexual selection. Wikispaces is a very powerful tool with many options for making a
professional-looking site, but this should be enough to get you started!
WIKISPACES GRADING RUBRIC
Students can earn a total of 20 points on their Wikis.
Criteria
0
1-2
3-4
5
INFORMATION
Wiki fails to
describe the
animal in
question.
Wiki attempts to
describe the
animal, but little
to no effort is
made to link it to
sexual selection
Wiki describes
animal in detail, but
relation to sexual
selection is vague or
lacking key
information
Wiki contains detailed
description of the
animal and its sexual
selection behavior,
including identification
of intrasexual or
intersexual selection
DESIGN
The wiki
contains
numerous
formatting
errors and no
use of images
The wiki contains
at least one
image, but is
poorly designed
and difficult for
readers to follow
The wiki
incorporates only
one image, but the
page is laid out
attractively and has
a logical flow
Wiki is attractively and
logically laid out, and
incorporates at least
two images of the
animal into the
description of the
behavior
CITATION
The wiki does
not include
citations of
any sources
The wiki only
includes one
citation, and
errors in
formatting may be
present
The wiki cites at
least two sources,
but fails to
document the
citations according
to MLA format
The wiki contains
citations of at least two
sources, and citations
are accurately listed at
the end of the page in
MLA format
INDIVIDUAL
EFFORT
Student gave
no
meaningful
contribution
to the group
whatsoever
Student
participated in
creation of the
wiki, but failed to
remain on-task
and contribution
was negligible
Student participated
in creation of the
wiki but contributed
less than a fair share
of the work
Student remained ontask during the in-class
portion of the
assignment, and
participated fairly in the
creation of the wiki
To access how well students understand sexual selection from the modeling exercises, students
will be presented with the following case study written and designed by J. Phil Gibson from the
University of Oklahoma Department of Zoology and Department of Botany and Microbiology.
Student Activity Worksheet 4
NAME:______________________________
DATE:____________
Figure 1. Long-tailed widowbirds showing breeding and non-breeding plumage. (Long-Tailed Whydah, 1899.
Chromolithograph after Frederick William Frohawk, printed by Brumby & Clark Ltd. in Hull and published in
Frohawk’s Foreign Finches in Captivity, 1899. Image courtesy of ancestryimages.com.)
Widowbirds are small, finch-like birds in the genus Euplectes. They are striking members of the
bird community in grasslands and shrubby savannas of southern and eastern Africa. This group
is noted for the pronounced sexual dimorphism between males and females. During the nonbreeding season, both male and female widowbirds have a brownish or buff coloration that
blends with the grass and other vegetation. During the breeding season, however, males molt
and produce black feathers on most of their body. Males also produce characteristic bright red
and/or yellow epaulets and chevrons on their wings. Additionally, males of several widowbird
species grow elaborately long tail feathers that can be up to half a meter in length (see Figures
1 and 2).
During the breeding season, males secure and defend a territory from other males where they
then build multiple nest frames. Males then perform a flight display that has a “bouncy rowing”
appearance with loops and exaggerated wing beats to attract females to their territory.
Females choose a male for breeding, line a nest frame in his territory with fine grass, and then
incubate the eggs and feed the nestlings in that frame. After the breeding season, males molt
to return to their pre-breeding coloration and appearance. Beyond initially building the nest
frame, males do not participate further in raising their offspring.
These elaborate behaviors and the striking seasonal sexual dimorphism in male widowbirds
have provided researchers with an intriguing system in which to study how natural selection
can shape traits of a species.
Figure 2. Male long-tailed widowbird during courtship display flight. (Photograph ©Callie de Wet/Wild Images.)
The bright breeding coloration and long tails produced by male widowbirds are thought to be
adaptations to attract the attention of female widowbirds. Reproductive systems in which
individuals differentiate among potential mates and choose one based upon some
characteristic(s) is a form of natural selection called sexual selection. The fundamental idea of
sexual selection is that choosing the best mate increases the probability of producing high
quality offspring who will pass on the parental genes to the next generation. Intrasexual
selection occurs when members of one sex compete with one another for the opportunity to
mate with members of the opposite sex or through actively securing and protecting a territory
and its resources. Intersexual selection, frequently referred to as female choice, occurs when
females choose among males based upon some criterion reflecting resources the male can
provide or the quality of his genes.
Day 2: Utetheisa Moth & More
From the previous lesson, students will understand the basics of sexual selection and have
examples from nature to use and draw from to complete Day 2’s activities. We continue our
investigation by exploring possible chemical factors that lead to the process of sexual selection.
Students will reform their groups and begin by analyzing the following information derived
from the article The Chemistry of Sexual Selection by Eisner and Meinwald.
Lesson Format
Student Activity Worksheet 5
NAME:______________________________
DATE:____________
1. Biochemical Nature of Sexual Selection
The moth Utetheisa ornatrix presents an interesting link between sexual selection and
chemoreception. In brief, this moth possesses a defensive adaptation against predation
in the form of chemical compounds called pyrrolizidine alkaloids (henceforth PAs).
These chemicals are extremely bitter and deter predators from eating them.
Like many other insects, these moths reproduce via passing spermatophores from males
to females. A spermatophore is a capsule created by the male which contains the
sperm, and is passed into a specialized receptor organ on the female called the ovipore.
In addition to the actual sperm, the spermatophore usually contains nutrients which the
female can ingest and utilize as an energy source for herself or her eggs. In the case of
Utetheisa, the spermatophore contains some of the PAs which will be passed into the
eggs to enhance the defensive capabilities of the larva.
The males produce a pheromone called hydroxydanaidal (HD), which is produced from
his supply of PA, and is used as a signal to females indicating that he is ready to pass on
a spermatophore. Males with a larger supply of PA are able to produce more HD, as
well as transfer more PA to the female with the spermatophore. Therefore, females
tend to select males with a larger PA supply as mates, since they will be able to pass
more of the bitter alkaloids on to their offspring and improve their chances of survival.
Logically, and confirmed via scientific study???, larger males are able to produce and
pass on more PA than smaller males because their supply is larger, and they can also
produce more female-attracting HD for the same reason.
In addition, the female moths have a special adaptation. They can accept
spermatophores from multiple males and store their sperm, then decide later which
sperm to actually use for fertilizing their eggs. This can be extremely advantageous
because they can accept spermatophores from multiple males, use the nutritious
resources contained within for their own benefit, and then influence what genes will be
passed to their offspring. The females, themselves the product of many years of species
evolution, pick spermatophores that give their offspring the best chance of surviving
and reproducing. High PA supply means less chance of predators eating their offspring,
and greater success at reproducing due to having more HD, which all culminates to
mean one thing: females select the sperm of larger males.
Discussion Questions:
1. In your own words, describe how you think sexual selection is occurring in this
species of moth.
2. How is this selective process similar to what you observed with widowbirds? How is
it different?
3. Create a Wiki entry about this moth under your Sexual Selection page.
Day 2 Discussion Questions Answer Key
1. In your own words, describe how you think sexual selection is occurring in this
species of moth.
We know that for intersexual selection, females choose which males to mate with
based on physiological characteristics. In this scenario, females tend to select for
larger males because they know that a larger body enables the individual to store
more PA, which means that their offspring will have better defenses and greater
survivability, and will in turn grow into a large male which will probably have the
same reproductive success.
2. How is this selective process similar to what you observed with widowbirds? How is
it different?
The process is similar because the females are making a choice based on
physiological features. A primary difference is that the moths accumulate sperm
from several males and retroactively choose which one they thought was the best.
Furthermore, the moths are making their decisions based on chemical factors, and
the birds were making their decision based on visual factors.
3. Create a Wiki entry about this moth under your Sexual Selection page.
A good wiki entry should contain the common, genus, and species names of the
animal in question. Students should describe basic physical traits of the organism,
describe any male-female dimorphism, and describe the reproduction of the
organism as it relates to the process of sexual selection. This should take two to
three paragraphs. Ideally, students should include a picture of the organism as well.
2. Wiki Expansion & Post-Assessment
Now that students have explored several examples of sexual selection and can see both
physiological and biochemical factors involved in perpetuating this process, they can begin to
apply their knowledge to an area that interests them and use technology to simultaneously
demonstrate their comprehension of the material and create a useable resource for themselves
and their peers.
For the rest of the class period the students will attempt to complete the following objectives.
1. Research the animal you have chosen from ???and identify the manner in which sexual
selection is taking place on their species.
2. Create a wiki entry describing your animal and detailing the information you have found
related to the sexual selection process. Is the type of sexual selection intrasexual or
intersexual? Does it seem visual, chemical, something else in terms of its basis? Why do
you think that is?
CONCLUSION
Students will be graded on the quality and thoroughness of their wiki entries. Each member of
the ???? group will receive a similar grade, with exceptions being made for instances of
obvious individual effort or the lack thereof. The goal of this project is to have a class-wide (and
eventually spanning multiple classes) compendium of sexual selection in nature. Students will
be required to explore the other groups’ wiki entries to develop a more complete
understanding of sexual selection.
References
National Science Education Standards. (1996)
http://www.nap.edu/openbook.php?record_id=4962

The National Science Education Standards are developed by the National Committee on
Science Education Standards and Assessment. Its purpose is to lay out the
framework needed to engage students in science content.
Eisner, T. and Meinwald, J. The chemistry of sexual selection. PNAS, 92(1), 50-55

This article provides chemistry content to apply to the biology content of sexual
selection. Allows for the topic to be taught in either a biology class, chemistry class, or
as a combined unit in either course.
Fisher, R.A. The Evolution of Sexual Preference. The Eugenics Review, 1915.

This article provides a general background on how sexual selection, with natural
selection, has provided for evolution within different species.
Gibson, Phil. Exaggerated Traits and Breeding Success in Widowbirds.
www.sciencecases.org/widowbirds/widowbirds_notes.asp

This article is necessary as an activity for Day 1 of this unit.