Case Study 4_Part One worksheet

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Jan 9, 2024

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BIOL*2400DE – Evolution Case Study 4: Part One Trait evolution Worksheet Step 1: Using evolution’s explanatory toolkit to understand the origin of traits For this step, you will be revisiting the material on the various processes and concepts that are involved in understanding how complex adaptive traits evolve, with specific reference to eye evolution and by identifying specific examples of those processes and concepts. Be sure that you have viewed the video “ Evolution’s explanatory toolkit ” on Courselink before you start, and make a point of thinking about the different explanations you have available and when they would be applicable. You will need to consult the paper that was assigned in Unit 07: Gregory, T.R. (2008). The evolution of complex organs. Evolution: Education and Outreach 1: 358-389. This paper is part of a special open access issue of the journal on the topic of the evolution of eyes. You can access all the papers in the special issue here: https://link.springer.com/journal/12052/volumes-and-issues/1-4 Using the assigned paper and others from the special issue for reference, answer the following questions about the concepts and processes involved in the evolution of complex traits like eyes. There are many misconceptions about how complex organs like eyes evolve. Sometimes these are reflected in questions that people ask (along the same lines as “If we’re descended from monkeys, why are there still monkeys?”). How would you answer the questions below? Question #1 – “How can something as complicated as the eye evolve by chance?” The evolution of complex organs like the eye is not based on random chance alone. It involves a combination of random genetic variations and natural selection, with each small improvement providing a functional advantage. Over time, these incremental changes accumulate, leading to the development of more sophisticated structures.

Question #2 – “What good is half an eye?” Each stage in the evolution of complex organs like the eye provides a functional advantage, even if it is not fully developed. The process is gradual, with each incremental improvement increasing survival and reproduction chances. Over time, these small changes accumulate, leading to the development of more advanced structures. In what ways are the eyes of vertebrates and those of cephalopod molluscs the same? How are they different? Why are they different? The eyes of vertebrates and cephalopod molluscs share similarities in having photoreceptor cells, a lens, a retina, and a nerve pathway. However, they differ in eye structure, placement, retina organization, and colour vision. These differences are due to their distinct evolutionary histories and adaptations to their respective environments and visual needs. List some imperfections and limitations of vertebrate eyes. Why did the eyes of vertebrates evolve to be like this? Why aren’t vertebrate eyes optimal? Imperfections and limitations of vertebrate eyes include a blind spot, optical aberrations, sensitivity to light, and a limited field of view. The eyes of vertebrates evolved this way due to trade-offs and evolutionary constraints, and they are not considered optimal because evolution does not guarantee perfection but rather functional adaptations for survival and reproduction. Not all animals have eyes. What are some possible explanations for why a lineage of animals may lack eyes? (Hint: a lack of eyes could be because they never had them, or because they had eyes but then lost them). Possible explanations for the absence of eyes in a lineage of animals include evolutionary loss, adaptation to other senses, reduction in energy costs, or the lineage never having eyes to begin with. Step 2: The Great Clade Race – using traits to reconstruct phylogeny

“The Great Clade Race” is an activity originally designed by D.W. Goldsmith (2003) to help biology students understand and practice cladistics and the creation of phylogenetic trees. It takes a simple, real-life scenario that is not immediately related to biology and allows us to create an analogy to apply these evolutionary concepts. Here, we will use it to provide a very basic illustration of how traits can be used to reconstruct evolutionary trees. In Part Two, we will flip this around and use phylogenies to understand trait evolution. Instructions: Imagine a race through the woods with six runners (A-F). All the runners start at the same single starting line, but at various places the course forks, and runners are free to choose either path. The paths never converge again (once two runners pick different paths, they can never meet up again). To help keep track of the race, each runner carries a card that gets stamped at check-in stations distributed at various places in the course. The following rules apply: • Runners cannot backtrack • Runners are required to collect a stamp from each check-in station. • Each check-in station uses only one stamp. • No two check-in stations use the same stamp All six runners finish the race carrying their cards, each crossing at a different finishing line. After the race, the organizers admit they have lost the original map of the woods. You realize that you can use the information in the cards collected from the six runners to reconstruct the course and the placements of the check-in stations. The final cards for the six runners are provided on the next page.

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With the starting point at the bottom and 6 possible finishing lines at the top, reconstruct the full course with all the paths and check-in stations (with the symbol of the stamp they use), and indicate which runner finishes at each finishing line.

In thinking about the analogy to evolution, what would the various elements of the race represent? The runners, the check-in stations and stamps, the forks in the paths, etc.? In the race analogy for evolution: Runners represent individual organisms or species. Check-in stations and stamps symbolize the environment and selective pressures. Forks in the paths represent evolutionary branching or divergence. The finish line represents a significant milestone in evolutionary history. Winning runners are those that successfully adapt and thrive in their environment.

Not every student will draw the map in exactly the same way even if everyone accurately reconstructs the relative locations of the check-in stations. Why might there be differences in the way the course maps are drawn even if no one makes any mistakes in interpreting the available data? Differences in the way the course maps are drawn, even if the relative locations of the check- in stations are accurately reconstructed, can occur due to individual interpretation and subjective factors. Factors such as perspective, artistic style, personal biases, and individual creativity can influence how each student visually represents the map, leading to variations in the drawn maps. What happens to your ability to reconstruct the course if some runners erase some stamps from their cards? If some runners erase stamps from their cards, it would hinder the ability to accurately reconstruct the course. The missing stamps would result in incomplete information, making it more challenging to determine the sequence and order of the check-in stations. The erasure of stamps introduces uncertainty and gaps in the data, which can affect the accuracy and completeness of reconstructing the course. Step 3: Cute cuddly Caminalcules – explaining trait differences within and between species Caminalcules are made-up organisms created by Joseph Camin (the name is a play on words as a portmanteau of “Camin” and “animalcules”, an older term for microscopic organisms). They have been used as part of various hands-on activities used to teach concepts of phylogenetics and classification (Sokal 1983; McComas and Alters 1994; Gendron 2000). We will be using the Caminalcules in a different way, because they provide an excellent opportunity to practice using our explanatory toolkit to account for the evolution of traits within and between species.

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1) Differences between species The males of two closely related species, Examplus uni and Examplus deuxi , are shown below. Identify a major morphological difference between the males of these two species, and propose an evolutionary hypothesis to account for this difference between the two species. (Don’t just make up a story about them. Connect your hypothesis to specific concepts and processes that you have learned about in the course). The major morphological difference between the males of these two species is the presence or absence of elaborate ornamentation. The difference can be explained by sexual selection and intrasexual competition, where intense competition for mates leads to the evolution of exaggerated traits in one species, while less competition results in the lack of elaborate ornamentation in the other species. Describe some additional data that you would need in order to test your hypothesis. Be sure to explain how the new information would be useful in this regard. To test the hypothesis, additional data would be needed, including observations of mating behaviour, investigation of female mate choice, genetic analysis of the ornamentation traits, and examination of historical data on the evolutionary history of the species. These data

would provide insights into the role of intrasexual competition, female preferences, genetic basis, and temporal patterns, helping to test and refine the hypothesis. Briefly provide two possible reasons for why the differences in this trait between E. uni and E. deuxi are not even greater than they are. Two possible reasons for why the differences in this trait between E. uni and E. deuxi are not even greater could be: There might be genetic limitations or constraints that prevent the trait from evolving further in either species. These constraints could be related to the available genetic variation, developmental pathways, or genetic interactions that restrict the magnitude of change in the trait. The differences in the trait might be constrained by the ecological factors or selective pressures acting on both species. Environmental conditions, resource availability, or interactions with other organisms could limit the extent of divergence in the trait. The trait might already be optimized for the specific ecological niche or functional demands, reducing the scope for further differentiation. 2) Differences within species The images below depict the male and female of the same species.

Identify a trait that differs between males and females, then present TWO hypotheses for how this difference could have evolved in this species. One hypothesis should relate to ecological selection, and the other should be based on sexual selection (remember: there are four different types of sexual selection!). Description of the trait: A trait that is different in males and females is the spots on top of the male which makes it stand out. The size of the male is bigger than the female which also differentiates the two sexes. The variation in claws between the two sexes shows how males have more bigger limbs and sharper claws whereas females do not. Hypothesis #1 – Ecological selection: The spots on the males could have been an adaptation overtime for a beneficial purpose for the males. The larger body size of males could be a positive factor for aiding in fighting and aggressive behaviour that could be a natural Hypothesis #2 – Sexual selection:

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The spots could be an attractive trait that the females would choose to mate with. It could be a trait of indirectly benefitting offspring fitness that the females would choose. Larger body size could have a positive impact as it is a trait of direct intrasexual competition where it shows an increase in reproductive success. This aids with fighting and aggressive behaviour that could help in winning over females and food. Sharper claws are also another a trait of indirect benefitting offspring fitness where the female find it a positive factor to mate with. 3) Practice, practice, practice! Download the papers with Caminalcules from Courselink. Choose any two Caminalcules and come up with hypotheses for how they evolved their different traits. This is an excellent exercise to do with a partner: you can take turns choosing two Caminalcules and giving the type of explanation that your partner should use. Or you can choose two Caminalcules and together come up with as many different possible explanations as you can think of, and talk about how you could test your hypotheses. NOTE: You can totally use Caminalcules as the basis for your term project if you want to develop a new way to use them in teaching an evolutionary concept! Step 4: Reflection Answer the following questions about your experience with this case study. 1. What aspects of this case study did you find most challenging or confusing? Yes, the question in step 2 and 3. 2. Did you learn anything or gain a clearer understanding of any specific concepts while completing this case study? No, I did not.

3. Was there anything that you found particularly interesting or surprising in this case study? No, there was not. Once you have completed this worksheet, upload it to Courselink and then proceed to the Case Study 4 – Part One quiz on Courselink.

Case Study 4_Part One worksheet

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