Genetic analysis of the circadian oviposition rhythm inDrosophila melanogaster: Effects of drift in laboratory strains

Under photoperiodic conditions, flies recently collected in nature exhibit, at the beginning of the scotophase, an oviposition peak which has a higher amplitude in Afrotropical than in European temperate populations. Several old laboratory strains failed, however, to show this peak. In each cross between genetically different strains, the oviposition curves of F₁ and F₂ were usually close to the midparent curve. Ten isofemale lines from an Afrotropical populations were submitted to inbreeding and drift. After 100 generations, two of the four surviving lines had retained the high peak typical of the origin population while the two others had lost it. Chromosome substitutions between these lines demonstrated a polygenic inheritance with a significant effect of the three major chromosomes. Presumably, the variations of amplitude of the oviposition peak were not caused by a modification of the ovarian activity but by a behavioral change toward the external signals of the environment.