Artificial and natural selection for two behavioral traits in Drosophila pseudoobscura.

In an attempt to elucidate the genetic architecture of two behavioral traits, populations of Drosophila pseudoobscura were selected for positive and for negative phototaxis and geotaxis. The selected populations diverged rapidly in their behavior (Figs. 1 and 2). The selection was relaxed after 20 generations in the phototactic, and after 30 generations in the geotactic populations. The relaxation resulted in convergence almost as rapid as was the divergence under selection. The average phototactic and geotactic neutrality of natural populations is an adaptive trait protected by genetic homeostasis. This does not preclude rapid responses to artificial, and presumably to natural, selection.