Analysis of larval behaviours underlying the pupation height phenotype in Drosophila simulans and D melanogaster

Abstract

Lines of Drosophila melanogaster and D simulans, previously selected for increased and decreased pupation height, have been investigated for larval correlated responses to selection. Larvae of all lines and species showed higher pupation sites when humidity increased from 40 to 100% RH. Pupation height measured in light and in dark revealed that only one out of the nine lines changed its phototactic behaviour during selection. In both species, the high pupation lines showed greater mobility than the corresponding controls. Selection for high pupation sites diminished the digging behaviour in D simulans but not in D melanogaster, whereas selection for low sites augmented the percentage of digging in D melanogaster. A different correspondence between pupation height and gravity response was found in each species. In D simulans, low lines were geopositive and high lines neutral, while low lines were neutral and high lines geonegative in D melanogaster. The results indicate that pupation height is a complex trait determined by other simpler behaviours, so that a given phenotype can be produced by different genetic systems. This question stresses the difficulty of deducing, on biological grounds, the meaning of the genetic architecture of a complex behavioural trait whose underlying basic mechanisms are unknown.