A DEVELOPMENTAL AND BIOMETRICAL ANALYSIS OF LARVAL PHOTORESPONSE OF DROSOPHILA

Young Drosophila larvae (24-28 and 48-52 h old) show a preference for feeding in dark environments, while older larvae (72-76h post-hatching ) prefer more illuminated environments. Changes in the photoresponse d uring larval development are characteristic of D. melanogaster, D. imm igrans, D. hydei and D. virilis. In contrast, larvae of D. simulans, D . gaucha, D. pavani and D. funebris show no change in their response t o light during larval development, both dispersing and feeding in dark environments. A biometrical analysis of the development of larval pho toresponse of D. melanogaster shows that the genetic structure involve d in the expression of this behaviour depends on larval age. At 24-28 h of age, additive, dominant and epistatic components were found. At 4 8-52 h, dominant and epistatic interactions were significant. At 72-76 and 96-100 h of age only non-allelic interactions were important. Thu s, epistasis tends to increase as larval development progresses. The c oncepts of genetic co-adaptation, developmental homeostasis and herita bility are discussed in relation to the development of larval photores ponse in D. melanogaster.