Characterization and evolutionary history of larval photobehavior in Drosophila

Drosophila melanogaster larvae are generally repelled by white light. I have shown that an isofemale line, which was originally classified as D. melanogaster, is in fact Drosophila simulans. I have also determined that D. simulans larvae are unresponsive or weakly responsive to white light. This weak photoresponse is stage- and modality-specific. Analysis of F1 hybrids from crosses of D. melanogaster and D. simulans suggests that a weak photoresponse is due to recessive gene(s) on the autosomes.; Larvae from the other members of the melanogaster species subgroup were tested in the larval photokinesis assay and found to be unresponsive or weakly responsive to white light. In addition to the melanogaster subgroup species, other outgroup species were also tested in the larval photokinesis assay. Larvae from different species had different responses to light. D. willistoni was weakly responsive to light, while the two strains of D. pseudoobscura tested, D. immigrans , and D. virilis were all strongly repelled by white light. Adults from each of these species were also tested in a phototaxis assay. No correlation between the strength of the larval photoresponse and the strength of the adult photoresponse was observed.; Phylogenetic analysis of the larval photoresponse suggests that, as a minimum, three changes in the larval photoresponse have occurred since Drosophila species have evolved from a common ancestor. It was not possible to determine whether the ancestral species had a strong or weak larval photoresponse.; Larvae from all of the species that responded weakly to light were also tested in an "apple-assay". The results suggest that the ability to respond strongly to light is not required for larvae to distribute in a food source.