The genetic basis of the geographically variable photoperiodic diapause in Drosophila littoralis

Abstract

The variation and inheritance of the photoperiodic adult diapause in females was studied in eight Drosophila littoralis strains originating from latitudes ranging from 42° N to 69° N. The extent of genetic variation was from photoperiodic neutrality (no diapause) to complete short-day diapause with critical daylengths between 13.0 to 17.6 hours light per day. Local populations share a small proportion of the total variation within the species, but are not genetically uniform. Genetic analysis shows that the variation in hybrids indicates a quantitative mode of inheritance. Long critical daylength (northern characteristic) is due to incompletely dominant alleles. The variation corresponds to the segregation of a single, autosomal mendelian unit, indicating at least linkagebetween loci responsible for the daylength measurement. There is enough variation in this unit to form a continuous latitudinal cline in photoperiodic reaction.