Fig 3.

The difference between the experimental and control lines in the mean proportion of eggs laid on the “correct” medium (orange in odd-numbered, pineapple in even-numbered generations). Separate regression lines were fitted for the two testing periods (period 2 and period 3). Because selection was suspended at generations 27–31, regression lines for generations 1–26 and 32–51 were fitted separately; for generations 1–26, the lines were forced through the origin. For generations 1–26, both regression slopes are significantly positive (P < 0.001); after generation 32, only the regression for period 2 is significantly positive (P < 0.01).