Modeling-Based Integrated Life Science Technology Curriculum Project and Publications:

Sexual Selection

Jonathan and Shane

0203/2207/2011

EDC 746

Final Draft

Background 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 superior 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 due to competition not for survival, but for theas a result of enhanced relative ability of individuals in terms of privilege 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 two2 to -three3 40-minute class periods, consisting of 7th-9th graders. We have decided that rather than using technology as a tool for demonstrating the principles of sexual selection, which do not lend themselves to that format, we will be focusing on usingWithin this unit, technology is used as a delivery mechanism for the information and as a medium for compiling the students’ information creations and interactions into a single resource.

Learning OutcomesScience Content Standards From the National Science Education Standards

Content Standard A

As a result of activities in grades 9–12, all students should develop

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 small-group 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

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.

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.[1.] Identify key differences between natural and sexual selection.3.[2.] Analyze data and determine if sexual selection is taking place.4.[3.] Utilize computer-based technological resources to access and share materials[4.] Students will using problem-solving methods to evaluate the data gained from the

technology resourcesformulate conclusions from model-based activities from data.[5.] Students will learn how to use the resources provided to them by this model-based

unit to guide themselves tocreate explanatory models conclusions based on those resourcesto explain data

[6.] Operate in teams to produce an online reference source for themselves and their classmates who are interested in the subject

5. 7. Students will operate in teams to produce an online reference source based on conclusions made from modeling exercises. .

Student MisconceptionsMost of the student misconceptions that concern sexual selection stem from pre-

existing conceptions involving heredity. Misconceptions involving heredity as listed from an article in the MSTA Journal (cited in the references section).

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 Vvariation between species is a result of adaptation to environment instead of inheritance. The theory of inheritance of acquired characteristics for species 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 Iindividuals 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

L e s s o n F o r m a t

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 would you delineate betweenwhat is natural selection? What is and sexual selection? How do they differ?

[B.] In what way could intrasexualIf 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? selection be working on 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?about intersexual selection.

A.[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 widowbirds?

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 engage help them begin to build their conceptual model of with the idea 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 to work on how to make a Wwikispaces listing is provided in the references section of this unit.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****

[1.] Describe your initial thoughts about how tail length would impact male widowbirds, from both positive and negative perspectives.

[2.] Identify the independent and dependent variables.2. What are the researchers trying to determine by collecting this data? Identify the

independent and dependent variables.3. 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:

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

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.

4. 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?

[5.] Using your knowledge of sexual selectionUsing 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 red-shouldered 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)

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.

5.[6.] 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?

6.[7.] Why do you think the investigators chose to perform this addition to their study?[8.] 9. Do you think that the results support the idea that sexual selection is taking place

in ???? Explain.[9.] 10. 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.

http://evolution.berkeley.edu/evosite/evo101/IIIE3aRunawayselec2.shtml

Within this article, students will bes show be instructed to describe how the actual 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.

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 from normal 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 choosepick and explain a real-life example of sexual selection to put on their Wwikispace.

EXAMPLES OF SEXUAL SELECTION IN NATURE (if needed)

1. Plumage of male peacocks2. Necks of Giraffes3. Courtship ritual of birds of paradise4. Bowers of bowerbirds5. Tusks of Walruses6. Horns of Mountain Goats7. Antlers of Deer8. “Mustache” of guppy Poecilia sphenops (seriously!)9. Coloration of Mandrills10. Canine size of baboons

Example of Wikispace Page

WIKISPACES 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 on-task 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 non-breeding 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.

L e s s o n F o r m a t

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 attempting to 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 a “gift” of 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 prefer 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???evidently, 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 “gifts”spermatophores from multiple males, use the nutritious resources contained within for their own benefit, and then pick their preferredinfluence

what genes for will be passed to their offspring. The females, themselves the product of many years of species evolution, pick spermatophores that give their want their offspring to have 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 prefer 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?

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

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 and Additional Resources

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.

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

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.

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.] What are the researchers trying to determine by collecting this data? Identify the independent and dependent variables.

The purpose of collecting this data is to observe the effects of tail length on fitness. 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 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.

[4.] 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.

[5.] Using your knowledge of sexual selection, 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.

[6.] 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.

[7.] 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.

[8.] 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.

[9.] 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.

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.