Reassessment of the effect of biological rhythm mutations on learning in Drosophila melanogaster.

A link between learning deficits and circadian period-lengthening mutations in Drosophila melanogaster previously has been reported. Mutant long-period males performed poorly in two learning assays involving experience-dependent courtship inhibition. In one, normal males that have courted fertilized females subsequently show courtship inhibition with virgin females. In the other, normal males that have courted sexually immature males subsequently fail to court other immature males. Those results have been reassessed in an extended study of genetic variants involving the period gene. 1. Long-period perL1 males demonstrated poor conditioned courtship inhibition when exposed to fertilized females; they showed normal courtship conditioning when exposed to immature males. This could be due to a perL1-associated olfactory deficit with fertilized females, since perL1 males were unable to discriminate behaviorally between fertilized and virgin females. 2. Other long-period males, including perL2 males and transgenic perL1 males bearing a truncated form of the per+ gene, were conditioned normally by fertilized females. Thus, the courtship inhibition defect is specific to the perL1 mutant strain. 3. perL1 (and other per mutant) flies showed normal acquisition and retention of a classically conditioned olfactory avoidance response. 4. Results from a new conditioned courtship inhibition experiment are presented; males exposed to fertilized females during training showed further courtship inhibition during subsequent exposure to fertilized females. From the perspective of learning theory, this can be viewed as a savings experiment.