A genetic analysis of diapause in Drosophila melanogaster

Genetic analyses have identified genes which affect such complex behaviours as eclosion, learning, foraging and olfaction. I have applied a multi-faceted approach to the study of the genetics of diapause that is similar to the approach used to study other complex behaviours. Diapause, defined as a neurohormonally mediated, delayed response to future adverse conditions (Danks, H. I987 Insect Dormancy an Ecological Perspective), can occur at any stage of development in an insect. Adult ovarian diapause of Drosophila melanogaster Meigen is triggered by low temperature and short days. Flies in diapause have immature ovaries that remain previtellogenic. I looked for variation in response to these diapause-inducing conditions by scoring the stage of ovary development. Crosses between a natural diapause variant and flies bearing a visible genetic marker suggested that diapause factor(s) reside on chromosome-3.

Recombinant inbred lines bearing neutral roo transposable element markers were used in a quantitative trait locus analysis of diapause. The 97D-E region on chromosome-3 contains gene(s) for diapause. Candidate genes include the Drosophila homologues of known diapause genes. A Caenorhabditis elegans gene affecting dauer formation, age-1, is homologous to Dp110, the Drosophila gene which specifies phosphoinositide-3 kinase (PI3K). I used the GAL-4/UAS system to target the expression of Dp110 to the nervous system and eye. When restricted to the nervous system or R1–R6 photoreceptors, the augmented expression of Dp110 promotes development of the ovaries under diapause-inducing conditions. Furthermore, the wild-type Dp110 transgene when over-expressed in the nervous system promotes significantly less ovarian development than its dominant negative. Dp110, a component of the insulin signalling pathway, plays a role in the adult ovarian diapause of D. melanogaster. My research has identified a region of chromosome-3 in which to search for genes involved in adult ovarian diapause and suggests the neuronal expression of P13K, a component of the insulin-signalling pathway, affects Drosophila diapause.