Alleles of Chaser, a dominant modifier of the Drosophila melanogaster foraging gene, are consistent with variegating alleles of the heterochromatic gene spookier.

The relationship between genes and quantitative behavioral traits involves complex regulatory networks. Identifying genes that operate in these regulatory pathways can be challenging, especially when dealing with dominant genetic factors. Our work has focused on a naturally occurring behavioral polymorphism in larval foraging behavior in Drosophila melanogaster. This polymorphism in larval foraging behavior arises from variation in the foraging (for) gene with its rover and sitter naturally occurring variants. The dominant rover allele (forR) results in larvae which move longer distances while foraging compared with larvae with the recessive sitter (fors) alleles. In this article, we report the successful mapping of the Chaser (Csr) gene, a dominant modifier of larval foraging behavior which makes sitter larvae behave in a rover-like manner. We localized Csr by first mapping recessive phenotype tags closely linked to Csr. These phenotype tags mapped to the centromeric heterochromatin on the right arm of chromosome 3. We showed through a combination of deletion mapping, qRT-PCR and feeding of ecdysone hormone to larvae during development that the alleles of Csr are consistent with variegating alleles of the gene spookier (spok). With spok being an essential gene in the synthesis of the molting hormone ecdysone, we have established a link between ecdysone signaling and larval foraging behavior in D. melanogaster.