ProcessesOfChange_ProblemSet24

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Biol 241: Evolutionary Biology Spring 2024 Processes of Change Problem Set Problem 1: Tiktaalik Because there are much older fish fossils than land-dwelling vertebrate fossils, scientists have long hypothesized that land-dwelling vertebrates are descended from ancient fish. The fossils in the figure show the transition from living in water to living on land. Researchers had long known about the fossils of the limbed Ichtyostega and Acanthostega (365 million years ago) and those of the finned fish- like Panderichtys (385 million years ago) and Eusthenopteron . By searching in the sediments of the most probable habitat (rivers) and deposited at the most probable time (~380 million years ago), Shubin and colleagues discovered the fossil Tiktaalik , a transitional form with limb-like fins. Read this blog post: https://carlzimmer.com/how-we-got-on-land-bone-by-bone/ And answer based on the post and on your knowledge from the lecture. (a) How does tiktaalik (similarly to other transitional fossils) demonstrate Darwin’s theory of “the gradual diversification of species, potentially into new species, through a mechanism of natural selection”? (b) What is a transitional fossil? Explain why transitional forms provide evidence for the theory of descent with modification. (c) Tiktaalik ’s limb morphology is intermediate to that of fish-like ancestors and land-dwelling descendants. What are some of the structures that are intermediate? 1

(d) Tiktaalik is a transitional fossil. Does that mean it was the actual ancestor of Acanthostega ? Why, or why not? Problem 2: Heritability in the Classroom In this set of questions, you will use the data collected from the class to explore the concept of heritability. Begin by going to the data spreadsheet linked on Canvas (on this week’s page, under “Assignments). Go to ‘File’ on the top left and choose ‘Make a copy’. Now, you have your own copy to work with. In the file, you can find a separate tab for each phenotype. You can see the raw data for the parents and the offspring, and the “midparent value”: this is the average for each pair of parents. (a) We are interested in the relationship between parent and offspring traits. Of the three traits of interest, which do you think are heritable? Why? (b) Next, you will create a scatter plot for the association between offspring’s trait values and midparent trait values, for each of the three traits. To create a scatterplot, choose the midparent and the offspring columns, then click ‘Insert’, and ‘Chart’. Show the trendline and formula by double-clicking on the chart; in the chart editor, click ‘customize’. Under ‘Series’, choose ‘trendline’ and a couple of rows below, under ‘Label’, choose ‘Use equation’. Copy and paste the three scatterplots below, or draw in a rough sketch of each. (c) Heritability (in the narrow sense) is the slope of the regression line (the coefficient of x in the formula). What narrow-sense heritability did you find for each of these traits? (d) Do the numbers you found suggest that any of these traits are heritable? Explain your answer. (e) If a trait is highly heritable according to this analysis, can we definitively conclude that there is a genetic basis to that trait? If not, what else should we consider? 2

Problem 3: Lizard Predator and Prey Anolis sagrei lizards (Fig. 3a) occur on small islands in the Bahamas. Leiocephalus carinatus are ground-dwelling predatory lizards that do not naturally occur on these islands. Jonathan Losos et al. (2004) introduced L. carinatus lizards onto 6 islands where A. sagrei occurred (experimental islands); another 6 islands were studied as controls (no introduction of the predator). Introductions were done in May. The researchers first placed the predators in front of prey lizards to observe whether prey lizards climbed in trees to escape the predators (Fig. 3b); on the control islands the researchers put a control object, rather than a predator, in front of the prey lizards. The researchers then studied how habitat use of A. sagrei lizards changed over time. Fig. 3c shows the percentage of A. sagrei lizards found on the ground on experimental and control islands before (May) and after (Jul/Nov) introduction of the predator; Fig. 3d shows the average height in the vegetation used by A. sagrei in November. Using the data and information provided, answer the following questions. Assume that the prey population size did not change following introduction of the predator and that Anolis generation time is longer than 1 year. 3 Figure 3a Anolis sagrei (prey) Leiocephalus carinatus (predator) Figure 3c Figure 3b Figure 3d

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(a) How does habitat use of the prey ( A. sagrei ) differ during and after the introduction of the predator ( L. carinatus )? Make sure to explain how you come to this conclusion. (b) Are the data more consistent with a behavioral change of A. sagrei (i.e., each lizard changes its own behavior), or with evolution by means of natural selection? Explain. (c) Name three pieces of information that you would need to test whether changes in habitat use could be explained by means of evolution through natural selection. Explain. Problem 4: Seed Size Evolution Large-gape frugivorous birds, fruit-eating birds with large beak openings (such as toucans), require large forested areas to survive. Due to their large gape, they can consume fruit with large seeds, thus facilitating these seeds’ dispersal. Dispersal is fundamental to the trees’ fitness: in order to germinate and grow, these seeds must get somewhere where there is enough light (so right under their tree’s canopy would be a bad spot). In the last century or so, these birds have seen a significant population decline due to hunting, and due to forest fragmentation. In this figure: Seed size variation of the palm (E. edulis) fruits consumed by birds (from left to right): white-necked thrush (Ta, Turdus albicollis), bare-throated bellbird (Pn, Procnias nudicollis), rusty-margined guan (Ps, Penelope superciliaris), spot-billed toucanet and saffron toucanet (Sm, Selenidera maculirostris; Pb, Pteroglossus bailloni), and redbreasted and channel toucan (Rd, Ramphastos 4

dicolorus; Rv, R. vitellinus). The boxes include the mean (horizontal black line), ± 1 SE (gray box), the 95% confidence interval (vertical lines), and outlier values (circles) – yes, this is a rather unorthodox box plot (box plots are usually based on medians and quartiles). (a) What do you predict would be the effect of this population decline on large-seed trees? What would be the effect on small-seed trees? Why? (b) How would you test your predictions? You can use an observational approach, where you don't manipulate anything in the environment, or you can conduct an experiment involving manipulation of one or more aspects of the environment. (c) The figure above describes the seed diameter each bird species consumes (see details below figure). How would the disappearance of small-seed trees affect the bird population? How would the disappearance of large-seed trees affect it? Why? Problem 5: Winter is (Not) Coming 5

Karell et al. (2011) have been studying a population of tawny owls in Finland. The owls have two plumage (feather) coloration morphs: grey and brown (see figure a). The owls feed mostly on voles (tiny rodents that live underground); tawny owls are hunted by large birds of prey, like the eagle owl. (a) The color scoring in figure a is based on brown pigmentation density, where 4 is the lowest level of brown pigmentation and 14 is the highest. Results are shown for 491 owls captured between 1978 and 2008. Describe the trend: which morph is more abundant? (b) Figure b describes survival rates of tawny owls in winter as a function of snow depth. Grey morph survival is denoted by grey circles and brown morph by red diamonds. Describe the trend. (c) Figure c shows snow depth in winter in the tawny owls’ habitat in Finland over the years. Describe the trend. (d) Describe the trend in figure d. (e) The researchers suggest the findings in figure d, supported by the data shown in figures b and c, suggest tawny owls have been undergoing evolution by natural selection. What evidence would be needed to make that argument, and are these all present in the data shown? If they are present, note where. (f) How would you collect the data that is missing to support the natural selection argument? Divide your answer by the different types of data, and be specific (but succinct). (g) Suppose you found that plumage coloration is determined solely by nutrients from owls’ diet. Would you consider the trend shown in figure d a possible indication of evolutionary change? If so, explain why; if not, provide an alternative explanation to the trend based on your new findings. 6

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