Experience-dependent development of the adult optic lobe and central brain in Drosophila melanogaster.

The optic lobes, mushroom bodies (MB) and central complex (CC) of Drosophila melanogaster were investigated in order to find out whether rearing in different light regimes affect their size. Flies raised in constant light up for up to four days post eclosion had a lamina that was about 30% larger than in flies kept in constant darkness. A volume difference between light- and dark-reared flies could also be observed for the lobula plate, the MBs, and the CC. When the flies were kept in the dark for the first 12 hours of their adult life and then brought back to constant light for the next 3.5 days, the lamina was as small as the laminae of flies raised for four days in constant darkness. This finding suggests a critical period for lamina development during day one of the imago. Mutant studies suggest that the molecular mechanisms underlying this experience-dependent development might be quite diverse. For example, the structural plasticity of the mushroom bodies is abolished in the dunce mutation, whereas the light-dependent growth of the lamina is not. Finally, studies of optomotor behavior indicate an adaptational role for the structural plasticity in the optic lobe. Surprisingly, dark-reared flies see better under low light conditions than their light-reared counterparts. This suggests that a small lamina is not a bad lamina in the sense that dark-reared animals see worse. They rather adapt to the specific light-conditions they were growing up in.