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.

School breakfast improves verbal fluency in undernourished Jamaican children.

School feeding programs exist in many countries, but few have been properly evaluated. In this study, the short-term effects of breakfast on children's cognitive functions were examined. The subjects were 97 undernourished (weight-for-age < or = -1 SD of reference) and 100 adequately nourished (weight-for-age > -1 SD) children in four primary schools in rural Jamaica. The children were randomly assigned to a group provided with breakfast or a group given a quarter of an orange as a placebo, and then given a battery of four cognitive function tests. After a few weeks the treatments were reversed and the tests repeated. Undernourished children's performance improved significantly on a test of verbal fluency when they received breakfast, whereas that of the adequately nourished children did not change (breakfast x group interaction, P < 0.05). There were no other effects of breakfast on test scores. The findings extend those of a previous Jamaican study conducted under more controlled conditions, and support the targeting of school meals to undernourished children.

Behavioural correlates of selection for oviposition by Drosophila melanogaster females in a patchy environment.

The behaviour of females from lines selected for high (H) and low (L) aggregated oviposition was compared in an environment consisting of discrete patches of resource available for larval development. Oviposition behaviour was influenced by the conformation and by the texture of the substrate, but this does not account for the selective differences in levels of aggregation which are under genetic control. The distribution of males of both selected populations tends to be overdispersed across resource patches. This observation is consistent with male territorial behaviour. The dispersal patterns of females of the two selected populations differ significantly. H females show a contagious distribution whereas the distribution for L females is more nearly random. Differences in adult female dispersion are likely to be a significant factor contributing to aggregated oviposition. The level of aggregated oviposition affects the pattern of progeny survival when the unit of resource in each patch is small.