The question
Name: ______________________ Date: ____________ Mating trials between separated populations (4 points)
Experimental setup
Fruit flies raised on two foods
Researchers split one laboratory population of fruit flies into four cages. Flies in cages S1 and S2 were fed a starch-based food; flies in cages M1 and M2 were fed a maltose-based food. Everything else was the same. After 40 generations, the researchers plan mating trials. In each trial they will place 12 unmated females and 12 males in a vial: 6 females and 6 males from one cage, and 6 females and 6 males from another cage, marked with colored dust so the cage of each fly is known. They will record each mating pair as same-cage or different-cage. Trials will be run for the pairs S1 with M1, S2 with M2, S1 with S2, and M1 with M2, 20 trials each.
(a) State the null hypothesis for the trials that pair a starch cage with a maltose cage. [1 point]
(b) Identify the independent variable and the dependent variable in the mating trials. [1 point]
(c) Justify including trials that pair S1 with S2 and M1 with M2. [1 point]
(d) Predict the results of the starch × maltose and the same-food trials if a prezygotic barrier has begun to evolve between the starch and maltose lines, and explain how such a barrier could lead to speciation if these were populations in the wild. [1 point]