Convergent Evolution in Animal Locomotion Convergent Evolution in Animal Locomotion Purpose Students take simple measurements to model the procedure by which a group of researchers discovered an unexpected example of convergent evolution. Through data analysis and critical thinking, students learn how natural selection can result in the evolution of striking similarities among very different animals. Audience This lesson was designed to be used in an introductory high school biology course. The first section, where students take measurements and calculate proportions, may also be appropriate for a math course. Lesson Objectives Upon completion of this lesson, students will be able to: ஃ define convergent evolution and apply its definition to the question of why proportions of propulsors (wings, tail fins, etc.) are similar across different groups of animals. ஃ define adaptation and understand the criteria used to determine whether a trait is an adaptation or not. ஃ describe the mechanism by which adaptations spread in populations. ஃ explain and apply the use of ratios when comparing measurements at different scales. Key Words adaptation, convergent evolution, fitness, heritable, natural selection, propulsor, ratio Big Question This lesson addresses the Big Question ​“Where did we come from?” Standard Alignments ஃ Science and Engineering Practices ஃ SP 4. ​Analyzing and interpreting data ஃ SP 5. ​Using mathematics and quantitative thinking ஃ MA Science and Technology/Engineering Standards (2016) ஃ HS-LS4-1.​ Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence, including molecular, anatomical, and developmental similarities inherited from a common ancestor (homologies), seen through fossils and laboratory and field observations. Convergent Evolution in Animal Locomotion 1 ஃ HS-LS4-2.​ Construct an explanation based on evidence that Darwin’s theory of evolution by natural selection occurs in a population when the following conditions are met: (a) more offspring are produced than can be supported by the environment, (b) there is heritable variation among individuals, and (c) some of these variations lead to differential fitness among individuals as some individuals are better able to compete for limited resources than others. ஃ NGSS Standards (2013) HS-LS4-1. ​Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence. Misconceptions Addressed ஃ This lesson addresses two common misconceptions about evolution and natural selection, including: ஃ The “fittest” is the strongest, fastest, or fiercest. (Question 5) ஃ All of an organism’s traits are adaptations. (Question 5) ஃ Further information about student misconceptions on this topic can be found ​here. Primary Sources ஃ Bite ​“Fins, Wings, and...Fractions?” ​based on: Lucas KN, Johnson N, Beaulieu WT, Cathcart E, Tirrell G, Colin SP, Gemmell BJ, Dabiri JO, and Costello JH. 2014. ​Bending rules for animal propulsion​. ​Nature Communication​ 5(3293). doi: 10.1038/ncomms4293 ஃ Nature​ ​News article about this paper Ball, Philip. "​Wing and Fin Motions Share Universal Principles.​" Nature News. February 18, 2014. Accessed June 12, 2018. ​doi:10.1038/nature.2014.14728 ஃ Misconceptions Anderson, Diane I., Kathleen M. Fisher, and Gregory J. Norman. 2002. ​“Development and Evaluation of the Conceptual Inventory of Natural Selection.”​ ​Journal of Research In Science and Teaching​ 39(10): 952–978. doi: ​10.1002/tea.10053 Materials ஃ Copy of Student Document and Science Bite for each student (note: color copies of the animal images would be helpful, but are not necessary) ஃ Ruler and calculator for each student Time This lesson should take approximately one 50-minute class period. Convergent Evolution in Animal Locomotion 2 Student Prior Knowledge Students should have been introduced to the process of natural selection prior to this lesson. Some specific background on adaptations, fitness, or convergent evolution could be helpful but is not required. This lesson could serve as an introduction to convergent evolution or a synthesis/review of natural selection. Instructions and Teacher Tips ஃ General Procedure ஃ Hand out the student documents, rulers, and calculators. Individually or in small groups, have students read the introduction, make their measurements (see note below), and complete Analysis Questions 1 and 2. ஃ Hand out the Fins, Wings, and…Fractions? Science Bite. ஃ Have students read the Bite and complete Analysis Questions 3–7. ஃ Optionally, conclude with a class discussion based on student answers to questions 6–7. See the Big Question Discussion section below for tips. ஃ Tips, Variations, and Extensions ஃ To increase accuracy and precision, advise students to measure to the nearest tenth of a millimeter and to measure from the centers of each dot. ஃ Shapes have been used in Science Bite FIgures 1 and 3 to help differentiate animal groups when printing in black and white, however, we recommend projecting the images in color or having a few color copies available if at all possible. ஃ To begin, you may want to have students work in small groups to identify anything the pictured animals have in common (anything goes!). After a few minutes, come back as a group and share their findings with the class. Keep a list on the board. Then, ask them to focus on propulsion and have them eliminate the items on the board that are NOT related to propulsion. They should have identified the propulsors (wings, tails, etc.). Ask them to describe what they think the propulsors might have in common. ஃ Questions 6 and 7 connect this exercise to the Big Question of “Where did we come from.” You may opt to conduct a class discussion. Please be sure to encourage students to be curious and creative, but please keep the discussion productive and civil! Visit the Big Questions section of our website for more ideas on how to integrate this discussion into the classroom, including examples for different formats, such as: Think-Pair-Share, writing pieces and consequent discussion, mock debates, and more. ஃ This lesson is an opportunity to refresh students’ memories about the difference between analogous and homologous traits. Homologous traits are inherited from a common ancestor and may or may not have a similar function among descendants. Analogous traits, on the other hand, were not inherited from a common ancestor, but do have a similar function in the descendants. Through discussion, have students come to the realization that analogous traits are the result of convergent evolution! Convergent Evolution in Animal Locomotion 3 ஃ For an added challenge, have students read the ​Nature Communications ​or ​Nature In the News​ article on this research (see Primary Sources, above) and make a list of unfamiliar terms and questions they have. Go over them in class as a group. Background Information and Research Details ஃ When discussing convergent evolution, be sure that your students understand that just because the trait evolved independently in several lineages, and was therefore not inherited by the common ancestor of ​all​ groups, it was of course inherited by the common ancestor in each ​group. In other words, all whales inherited the ratio from the common ancestor of whales, and all fish inherited it from the common ancestor of fish. However, fish ​and ​whales did ​not ​both inherit the trait from the common ancestor of fish and whales. ஃ The study on which this lesson is based surveyed fifty-nine species of flying and swimming animals. Researchers converted videos into a series of still images to make their measurements. ஃ The “law” of bending uncovered is thought only to apply to swimmers that wave their propulsor in discrete up and down or back and forth motions (like whales and birds), rather than undulate (like eels or sea snakes). ஃ The “law” of bending uncovered is informing engineers on how to make more efficient machines that are propelled through air and water. Researchers are currently building and testing models of flexible animal propulsors to try to understand the physics of how the bending pattern improves swimming, as part of the machine-building process. ஃ In addition to the fifty-nine animal species reported on in the study, the researchers also looked at some of the tiniest animal swimmers in existence—zooplankton. At this tiny size scale (micrometers), water behaves a lot like molasses, and so zooplankton use entirely different physics to swim. At this size scale, the researchers no longer saw the bending pattern. This was cut from the published study due to length constraints. ஃ Before this study, researchers studying animal swimming had done so in isolation, expecting different animals to exhibit very different locomotor styles. Today, more researchers are doing broad comparisons across very different types of animals to find out universal rules in swimming physics. In addition, many researchers are now thinking about how the process of making forces for swimming or flying relates to an animal’s ecology and evolution. ஃ Students interested in pursuing science in college might benefit from hearing about the researchers themselves. Authors Kelsey Lucas, Nate Johnson, Eric Cathcart, and Greg Tirrell were all undergraduates at the time of this study. They all were attending small universities (not famous research schools) but were still able to publish their field-changing research in a very prestigious journal. This is a great example of how college is about what opportunities you pursue, not about how famous the university name is. Big Question Discussion This lesson should get students thinking about the Big Question “​Where did we come from?​” In particular, how did the animals we see around us today become the way they are? If you choose to delve into the Big Question, consider the following ideas: Convergent Evolution in Animal Locomotion 4 ஃ At the beginning of class, review the concepts of fitness and adaptations. Have students discuss in small groups whether adaptations be traits that aren’t directly involved with making gametes or raising offspring, if adaptations are supposed to increase fitness.