Rare Parthenogenesis in Drosophila robusta

1. By screening large quantities of unfertilized eggs laid by unmated females in the laboratory, 14 parthenogenetically-produced individuals of Drosophila robusta were found. All were females. It is suggested that they arose through automictic fusion of haploid products of meiosis in the unfertilized egg. 2. Each of the initial seven females came from a different wild strain, five from Nebraska and two from Missouri. The rate of parthenogenesis in these strains was .93 adult females per million unfertilized eggs laid. 3. Virgin females with one or more parthenogenetic females in their ancestry show a rate of parthenogenesis about 21/2 times that of the original strains. 4. A majority of the parthenogenetic females show reduced fertility, complete sterility and/or morphological abnormalities. 5. The evidence indicates that rare parthenogenesis such as is found in D. robusta, D. parthenogenetica, and D. polymorpha is genetically based and may serve as an example of an evolutionary stage through which the obligatory parthenogenetic species, D. mangabeirai, may have passed during the evolution of its parthenogenesis.