Larval foraging behaviour and competition in Drosophila melanogaster.

Populations of Drosophila melanogaster derived by bidirectional selection for high (HA) and low (LA) aggregated oviposition behaviour differ significantly in the duration of the larval period and adult size because of differences in the developmental profiles for feeding rate over successive phases of larval growth. Feeding rates of HA larvae are significantly lower than those of LA larvae during the flexible period of growth which precedes attainment of critical mass for pupation. Consequently the HA larvae have a slower mean rate of development. In the fixed postcritical period of development the feeding rates of HA larvae are significantly higher than those of LA larvae. This causes a greater postcritical growth increment and larger adult flies. HA and LA larvae respond adaptively by changing the expression of components of their foraging behaviour depending on whether they are in or out of food. LA larvae exhibit a more flexible pattern of response and are also more successful competitors when food resources are limiting.