Locomotor performance in the Drosophila brain mutant drop-dead.

Mutation of the drop-dead gene in Drosophila causes early death of the adult animal. After hatching from pupae, drop-dead mutants increasingly lose body control and typically die within ten days. Drop-dead carries an X-chromosomal recessive mutation that causes brain degeneration, due to a loss in glia function. Recent results attribute this functional deficiency to a component required to form the tracheolar respiratory apparatus and thus to a reduction of tracheal oxygen supply. If the reduction of respiratory capacity is the primary reason for brain degeneration, locomotor capacity of drop-dead should be significantly impaired. We thus determined running performance and locomotor motivation of drop-dead(1) mutants at ages between one and five days. The mutant achieves similar mean and maximum forward speeds during running of approximately 1.5 and 10 mms(-1), respectively, as wild type flies. Thus metabolic capacity required for running seems not to be compromised. Drop-dead(1) flies, however, are significantly more active (34%) and also have a higher motivation (33%) to initiate running. Heading instability during forward running was increased by 17% compared to wild type and tended to increase with age. These findings are consistent with the previously reported loss in body control in the mutant and thus demonstrate the significance of the drop-dead gene for running behaviour in Drosophila.