Do you see what I see?

Transcription

1 Do you see what I see? Light, sight, and natural selection Lesson 6: Why do guppies have a favorite color? I. Overview In this lesson, students examine how natural and sexual selection can help explain why guppies are attracted to different colors. Students are prompted to ask questions about the different selective pressures that guppies might be exposed to, such as traits to help find food, avoid predators, or attract a mate. By playing The Guppy Game students investigate how fish with a variety of traits are affected by the environments in which they try to survive and reproduce. By analyzing data generated by the game, students begin to understand the selective pressures that drive the evolution of guppies. Finally, students create a scientific explanation that addresses these concepts. Connections to the driving question While playing the guppy game, students learn how the guppies attraction to a color impacts survival in a given environment and thus is influenced by the environment. This lesson helps students understand what conditions lead differences in guppies vision. Connections to previous lesson In the previous lesson, students designed experiments and tested hypotheses about what color guppies prefer. Based on Dr. Becky Fuller s and others research, students found that guppies had a color preference. Now students will explore the evolutionary mechanisms that have resulted in that color preference. The culminating scientific explanation helps pull these concepts together. II. Standards Next Generation Science Standards Science and Engineering Practices o Developing and Using Models o Analyzing and Interpreting Data Disciplinary Core Ideas o LS3.B: Variation of Traits o LS4.B: Natural Selection o LS4.C: Adaptation Crosscutting Concepts o Patterns o Stability and change 1

2 III. Learning Objectives Learning Objective Assessment Criteria Location in Lesson Explain how natural and Explanation can include: Explanation in conclusion sexual selection affect variation of traits. Frequency of a trait can change over time if it has a genetic basis and either increases or decreases an organism s ability to reproduce. of lesson. Give examples of natural selection pressures Describe the impact of sexual selection on the observed frequency of traits. Give examples of traits that are subjected to sexual selection. Discuss how sensory systems and fish coloration evolve to match different environments. Examples can include: Predators Food availability Mating Descriptions can include: Sexual selection can increase the frequency of traits such as bright coloration in male guppies if it offers them a reproductive advantage Examples can include: Fin color, brightness Responses can include: Sensory systems evolve to make it easier to find food Coloration evolves to make it easier to find a mate Discussion during data analysis collected through playing the game. Discussion during data analysis collected through playing the game. Discussion during data analysis collected through playing the game. Discussion during data analysis collected through playing the game. IV. Adaptations/Accommodations Students with special needs might require assistance with some of the tasks of the game. Consider assigning a group leader to assist with rolling the dice and tracking scores if necessary. Safety There are no additional safety concerns, other than those that would be reasonably expected in the science classroom, associated with this lesson. V. Timeframe for lesson Opening of Lesson Review previous lessons 5 minutes 2

3 Main Part of Lesson Activity 1: The Guppy Game o Learning the rules of the game 10 minutes o Gamplay and Data Collection minutes Conclusion of Lesson Data Analysis and Interpretation 10 minutes VI. Advance prep and materials Students play the game in groups of four. If the groups are smaller than four, then some students will play two guppy cards. Activity 1: The Guppy Game Materials: Each group will need: One six-sided die (if available, more die per group will decrease time to play game) One set of guppy and habitat cards, printed in color and double-sided on cardstock (U1_L6_Cards_GuppyGame.pdf) Six Group Score Cards, one for each habitat (but extras are good), printed in black and white (U1_L6_Cards_Scorecards.pdf) One quick rules document, printed in color (U1_L6_StudentSheet_QuickRules.pdf). It might be helpful if each student has a sheet for reference. Preparation: Print and cut enough card sets and Quick Rules documents. To make long-lasting card sets, laminate the guppy and habitat card set before cutting. You can print additional scorecards for every class as necessary. Know how to play the game. Know the game relates to evolution. Homework and Assessments Materials No additional materials. VII. Resources and references Resources The materials for this lesson can be downloaded for free from the Project NEURON website: Background knowledge for teachers, U1_L5_TeacherResource_BackgroundKnowledge.docx 3

4 Supplemental Guppy Lab Online. Retrieved from References Bishop, B., & Anderson, C. (1990). Student conceptions of natural selection and its role in evolution. Journal of Research in Science Teaching. 27,

5 VIII. Lesson Implementation Opening of Lesson: Review the results of students experiments in the previous lesson. What is a guppies favorite color? Why do you think that is? Review ideas that came up in the last lesson such as preference for a food or mate. This discussion should continue with questions about what guppy would survive best in a habitat with lots of predators. Additional questions that can be used to help guide the discussion include: How would color impact the survival of the fish? How have the fish that they have observed differed? Would these different colors impact how a fish might survive? How would a brightly colored guppies or drably colored fish survive? What would happen over several generations? Teacher Pedagogical Knowledge Using student responses to address common misconceptions is a useful way to integrate assessment into everyday teaching. Students enter the science classroom with ideas about how the world works. Students should be made aware of their potential misconceptions to help them clarify their thinking about a concept. After this opening discussion, have the students imagine a habitat with very murky water, so murky that it would be difficult to see in. Ask the students: What would happen to the guppies ability to see colors? What would happen over a few hundred generations to fish in these types of waters? Student Misconceptions It is common for students to think that different environments cause individuals to develop new traits in order to survive (Bishop & Anderson, 1990). Help students overcome this misconception by focusing on changes in the prevalence of a trait that happen over long periods of time. Tell students that they will be playing a game that will help them think about these ideas. Main Part of the Lesson Activity 1: Guppy Game 5

6 A good way to introduce the game is by going through a sample round with the Practice Pond habitat. Pass out the Quick Rules (one for each student), Guppy Game cards (one set for every group of four), and Score Cards (a small handful for each group), and dice (one per group or one per student for faster gameplay). Teacher Pedagogical Content Knowledge The Guppy Game has been designed to be a game that will motivate student learning. The game is designed to parse the subtle evolutionary algorithm into a more easily understandable package. The key to presenting this lesson is to start with a discussion of evolutionary forces by posing a series of questions about different habitats and species found in the introduction to the activity. 1. Introduce the guppies. Tell students that each one of them will play as a guppy. Ask each student to claim a guppy card and look at it. There is a Female Fancy Guppy, Male Fancy Guppy, Female Wild Guppy, and Male Wild Guppy. Students record their guppy on their Student Sheet. Ask students: What kind of guppies are there? o Male and female, wild and fancy (artificially bred to have bright colors). What kind of traits to the female guppies have? o Females have a Strength of Color Preference score. Fancy females are very picky whereas wild females are not as picky. What kind of traits do the male guppies have? o Males have a Brightness score. Fancy males are brighter than wild males. 2. Examine the guppies traits. Ask students to think about how these traits could affect the drivers of evolution: survival and reproduction. Students work within their small groups to fill out the advantages and disadvantages for each guppy in a table in their Student Sheet (suggested answers are in the Answer Key). Scaffold this thinking process if necessary: How do you expect the female s strength of color preference score to influence survival and/or reproduction? (Scaffolded) If you are a picky female guppy, when would this be an advantage? o When you are trying to find food (survival). (Scaffolded) If you are a picky female guppy, when would this be a disadvantage? o When you are trying to choose a mate maybe none of the males will be bright enough for you (reproduction). How do you expect the male s brightness score to influence survival and/or reproduction? o It is an advantage when attracting a mate (reproduction). o It is a disadvantage when trying to hide from predators (survival). 6

7 Thus, every guppy has different advantages and disadvantages in terms of survival and reproduction. Teacher Pedagogical Knowledge It is important for struggling students to go from simple to complex environments in the game. Gradually increasing complexity provides scaffolding for students to learn the concepts being addressed in the game. 3. Examine the habitats. Describe to students that their guppy must try to survive and reproduce in each of the habitats. Direct students to look at the habitat cards. Ask students to fill out the Habitat Information table in their student packets. Scaffold the process if necessary, discussing each habitat one at a time and posing questions to the students. These are just general ideas, to get students thinking (they are not expected to know the mechanisms of the game in a highly sophisticated matter). 4. Practice Round with the Practice Pond. Next ask students to look at their habitat cards, and locate the Practice Pond. Use the Quick Rule document to demonstrate how every round (season) a guppy has a chance to survive and reproduce. Basic Rules of Gameplay 1. Roll a die once for survival. 2. If you succeed at the task (roll above/below threshold for male/female guppies according to the guppy card) you earn a point for surviving. 3. If you do not succeed, turn your guppy card over and wait for the next season (round). 4. If you succeed at surviving, roll again for reproduction. 5. If you succeed at the task (roll above/below threshold for female/male guppies according to the guppy card) you earn another point for reproducing. 6. Thus, a student can only score 0, 1, or 2 points per round. At the end of the round, everyone starts over and tries again for the new season! Do up to four seasons (rounds) for every habitat. Allow students to roll for survival and reproduction using the Practice Pond. As students are practicing, make sure they are recording their points correctly in their table in their student sheet! This will prevent mix-ups with data later. Below is an example of an individual student s table. Habitat Season 1 Season 2 Season 3 Season 4 Season 5 AVERAGE 7

8 Practice Pond Fish Tank Amazon Quiet Brook Murky Pond Clear Stream When students are done with a habitat, they write the average of their data for that habitat on the Group Score Card and give it to the instructor. (They could write the sum, but then the data might be skewed if a group did not complete all seasons. Some groups might work faster than other groups). A sample Group Score Card is shown below. Show the Group Score Card to the students and make sure they understand its purpose. It makes pooling the data easier! As students play the game, enter the data into the Guppy Data Grapher spreadsheet (U1_L6_Resource_GuppyDataGrapher.xlsx). This resource will automatically generate graphs of the data. 5. Continue with gameplay. It is recommended that the class does the habitats in the order on their student sheets. If time is limited, the last two habitats, Murky Pond and Clear Stream, are not necessary. 8

9 Likewise, if time is a limiting factor, students can do three seasons (rounds) instead of five, but it is recommended that they do five to reduce sampling errors. If each student has a die, it will greatly reduce time spent playing. Conclusion of Lesson The conclusion of the lesson enables students to explore the data created by The Guppy Game. 6. Data Analysis. When most students have completed their rounds and the pooled class data is complete (at least the first four habitats), show students the pooled data so they can enter it in their student sheets (if possible, project the spreadsheet on a screen, so students can start recording the data as they complete gameplay). If students have recorded the pooled class data, they can work on making the graph themselves. If class time runs out, students who are familiar with graphing can work on the graph as homework and start the questions. Otherwise, the digitally generated graph can be shown to the students and they can merely copy it into their student sheets, if it is more important to spend class time on data interpretation. 7. Data Interpretation and Questions. This interpretation might be difficult for students, because the data is complicated. If interpreting the data is challenging, look at the answer key (U1_L6_StudentSheet_GuppyGame_ANSWERS.docx) for guidance. The first few questions are about the individual students guppies. Students can share these answers or compare them to their predictions. The questions in the General Analysis start to get at how the data indicate the drivers of evolution, or why guppies have a favorite color. The main points are that: Evolutionary drivers that affect survival tend to be stronger selective pressures than those that affect reproduction--after all, you need to survive in order to reproduce!. o This relates to Helen Rodd s findings (from Lesson 5) in that they suggested that guppy color preference due to finding food (surviving) came before sexual selective pressures to select male guppies for bright spots (reproduction). As students may have predicted, there is a strong selective pressure for female guppies to have a strong for color preference, and there is a strong selective pressure for male guppies to have low brightness. The stronger this pressure is, the higher overall fitness females with high preference and males with low brightness will have across most environments, because surviving will nearly always be the most advantageous. o This effect can be seen if students play the game with the thresholds adjusted to be more extreme (1 s and 6 s) or more lax (3 s and 4 s). o Likewise, the probabilities (available in the Guppy Data Grapher) can be adjusted for students who are curious or would like to manipulate the model. 9

10 Finally, students wrap up their understanding in a scientific explanation. (This scientific explanation can be used instead of the explanation at the end of Lesson 5). Teacher Pedagogical Content Knowledge A scientific explanation should include a claim, evidence, and reasoning (and a rebuttal if appropriate). The evidence is the data students use to support their claim. In this case, the data are from the data tables created as a result of the game. The reasoning is the scientific principle(s) that connect the evidence and the claim to the scientific knowledge being developed by the students throughout the unit. Assessments The following assessments are available in this lesson: Student verbal responses to discussion questions Student answers in student sheet Student written scientific explanations at end of student sheet 10