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Unformatted text preview: BIO152 Laboratory 3: Variability & Selection in Natural Populations of Isopods Before this lab Complete the PRELAB worksheet to prepare for lab. Read the background information on isopods: http://tolweb.org/Isopoda Bring a calculator & ruler to lab Bring a lab coat to lab In this experiment, we will investigate 1) variation in several traits of isopods, a common terrestrial crustacean. 2) whether some traits confer a survival advantage in the presence of simulated predators. 3) whether such survival advantages depend on the kind of predator. Objectives By the end of this exercise, you should be able to: construct a data-collection table to record data for this type of experiment. collect, record, and organize a large number of data points accurately. construct a table to summarize results in a meaningful way & present your data in the appropriate type of graph construct a frequency distribution calculate the mean for a set of values state a hypothesis about which traits confer a survival advantage in a simulated predation experiment and evaluate your hypothesis based on data from experimentation. Thought Questions (For background information use the lab description, course lecture notes and text. Several answers are possible for each question.) 1. How much variation (none, some, a lot) should you expect to see in each of the traits you are to observe and analyze? Why might some traits be more variable than others? 2. What might be the relationship between the amount of variation in a trait and the opportunity for selection in the present? 3. What might be the relationship between the amount of variation in a trait and the intensity of selection on that trait in the past? Summary Many traits vary considerably in natural populations; other traits do not vary at all. Variation in a trait is necessary for that trait to evolve through natural selection, and the amount of variation combined with other evolutionary factors can influence the rate at which the trait evolves. In this lab, we will perform a simulated predation experiment to model selection pressure. We will then measure the amount of variation in the population of prey, to determine which traits are subjected to selection. BIO152 2010 University of Toronto at Mississauga 2-Isopods & Natural Selection page 2 of 8 Figure 1 . External anatomy of a European isopod (or wood louse), Oniscus asellus . (Ruppert and Barnes, 1994, p. 742). Procedure Work in teams of 4 students (half the bench). Remember to record the data on your own sheet. Materials Per team (half bench of about 4 students): spoon forceps paper towel aluminum foil Styrofoam cup Petri-dish Ice-pack isopods (about 30-40) 20 capped vials, sharpie 1 ruler marked in centimeters 1 dissecting microscope with light 1 stopwatch 1 racetrack with cloth to wet & paint brush 1 predation arena with refuge (aluminum foil) 2 plastic containers with lids labeled survivors or victims BIO152 2010 2-Isopods & Natural Selection page...
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- Fall '09