Body size and courtship behaviour in Drosophila melanogaster

Abstract

1. 1. Lines of Drosophila melanogaster selected for large and small body size differ in their courtship. Small males have more and large males less vibration in their courtship than the controls. 2. 2. Flies that were small due to environmental causes did not behave in the same manner as the small selected males. 3. 3. No correlation was found between courtship and size in the F2 progeny crosses between large and small lines. 4. 4. It was therefore concluded that the changes found in the courtship of the selected lines are not the inevitable result of increase and decrease in body size. 5. 5. All the selected lines were less active than the controls. No connection between general activity and the differences in courtship can be postulated. 6. 6. Small males are less successful in obtaining mates than the large or control males when in competition with them. 7. 7. It is therefore suggested that the difference in the small males' courtship is due to selection pressure for increased amounts of vibration to counteract otherwise deficient courtship. 8. 8. This was tested by selecting for large and small body size under conditions where competition between males was eliminated. As predicted no change occurred in the small males' courtship until sexual competition was reintroduced. The large males' courtship diverged as before, showing that changes in their courtship are not due to selection.