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Home , Animal locomotion, Convergent evolution

Convergent in Locomotion

Convergent Evolution in Purpose Students take simple measurements to model the procedure by which a group of researchers discovered an unexpected example of . Through data analysis and critical thinking, students learn how can result in the evolution of striking similarities among very different . Audience This lesson was designed to be used in an introductory high school 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 (, , etc.) are similar across different groups of animals. ஃ define and understand the criteria used to determine whether a trait is an adaptation or not. ஃ describe the mechanism by which spread in populations. ஃ explain and apply the use of ratios when comparing measurements at different scales. Key Words adaptation, convergent evolution, , 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. A​ nalyzing and interpreting data ஃ SP 5. U​ sing 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.

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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. C​ ommunicate 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 ​. N​ ature Communication​ 5(3293). doi: 10.1038/ncomms4293 ஃ ​ N​ ews article about this paper Ball, Philip. "W​ ing and 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.”​ J​ ournal 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.

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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, , etc.). Ask them to describe what they think the propulsors might have in common. ஃ Questions 6 and 7 connect this 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 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!

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ஃ For an added challenge, have students read the ​Nature Communications o​ r ​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 a​ ll ​ groups, it was of course inherited by the common ancestor in each g​ roup. In other words, all inherited the ratio from the common ancestor of whales, and all inherited it from the common ancestor of fish. However, fish a​ nd ​whales did ​not b​ oth inherit the trait from the common ancestor of fish and whales. ஃ The study on which this lesson is based surveyed fifty-nine 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 ), rather than undulate (like or sea ). ஃ The “law” of bending uncovered is informing engineers on how to make more efficient machines that are propelled through air and . 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—. 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 “W​ here 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:

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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. Have students brainstorm how traits like heat tolerance or fast , or anything else you can think of, might connect back to fitness (or not). ஃ After students finish the final question, have them brainstorm other examples of convergent evolution and think about what similar challenges or histories the convergent organisms experience. Answers Sample Table 1 data:

Animal Propulsor Length A Length B Length C Ratio (fin, body and tail, (mm) (mm) (mm) A/C or ) Point 1 to Point 2 Point 2 to Point 3 Point 1 to Point 3

Shark body and tail 31.6 18.5 50.2 0.63

Sea Butterfly fin 7.5 4.9 12.5 0.60

Moth wing 19.8 9.4 29.1 0.68

Eagle wing 19.5 8.6 28.2 0.69

Dolphin body and tail 42.1 17.2 59.3 0.71

1. Look at your data in Table 1. Describe the ratio data. Is there a wide range of values present, or are the data clustered within a small range? Sample answer: T​ he ratios clustered together between 0.60 and 0.71. 2. Were you surprised by your results? Why or why not? Sample answer: I​ was surprised because the animals are all so different. They look different, belong to different groups, and live in different environments. 3. Based on the reading and your data, answer the following questions. a. What is the primary conclusion that the researchers drew from their data? The researchers concluded that the animals all have a bending ratio around 0.67 (2:3) and this was an adaptation that happened through convergent evolution. b. Which of the six groups of animals had the most variation in bending ratio? Which group had the least? How do you know? The fish or the mollusks had the most variation because the fish points had a big range of y​-values and the mollusk points all had big error bars. The marine had the least variation because the y-values were all close together and the error bars were small.

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c. How are their results similar or different from yours? Sample answer: M​ y results were very close to 0.67 but some were slightly smaller, others slightly larger. d. Where do you think differences (if there were any) between your results and theirs could have come from? Sample answer: M​ aybe watching a moving animal instead of looking at a picture let them make better measurements. We only measured one animal in each group but they measured a lot so maybe the ratios average out to closer to 0.67. 4. In your own words, describe convergent evolution. Sample answer: C​ onvergent evolution is when organisms end up having similar adaptations but they don’t get these adaptations from the same common ancestor. 5. Given the definition of adaptation and fitness, explain why the researchers describe the bending pattern they uncovered as an adaptation. The Bite says that an adaptation has to be heritable, have a function, and increase fitness or the chance of having offspring. The bending pattern is heritable within one species, and the researchers think it helps the animals swim/fly better than animals without this ratio. If the animals swim and fly well, they would be able to get food and find mates better than the animals that couldn’t swim or fly as well, and so they would have more offspring and pass the trait on to them. Connect to the Big Question.​ Suppose that you are a scientist using computer models to study how the earliest birds might have flown. You enter all of the data available from fossils into the computer program and discover that according to your models, some of them were good fliers, but others aren’t. Based on your evidence, the birds had bending ratios of 0.4–0.9. The poor fliers had ratios outside of the 0.6–0.7 range we see in modern birds.​. 6. Explain the process that may have led to the 0.6–0.7 ratio range we see in birds today. Sample answer: B​ irds started with a bigger range of ratios, but the birds with ratios in the 0.6–0.7 range were the best at flying, which gave them advantages such as an easier time getting food and finding mates. These birds tended to survive and reproduce more frequently than did the birds with ratios outside of this range.They passed on their bending-ratio trait to their offspring. The proportion of birds in the population with this ratio would increase each generation until only the birds with the 0.6–0.7 ratios were left. 7. Explain how convergent evolution strengthens the core principle of biology that life has evolved by descent with modifications from common ancestors by processes such as natural selection. Sample answer: C​ onvergent evolution is evidence for evolution, particularly for the mechanism of natural selection. According to natural selection, organisms will tend toward traits that increase fitness in their environments. Similar environments would favor similar traits, so you’d expect to find similarities in traits in different groups that live in similar environments. _v2: new note added about vs. , October 2019; _v3: measurements adjusted to reflect new line drawing of animals, November 2019; _v4: rephrased question 1, added measurement tip

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