Variation in fertility of two wild type strains of Drosophila melanogaster meigen

Initial observations of low fertility, reduced sexual activity of males, and a high frequency of abnormalities in sperm differentiation of the wild type strain (Sevelen, Zürich) of Drosophila melanogaster, normally used in this laboratory, have lead to a study of this phenomenon and its causes. The abnormalities occur during all spermiogenetic stages and are not unique but are found with much lower frequency in normally fertile flies (Oregon R). Growth of Sevelen flies at high but sublethal temperatures (30°C) results in complete sterility, highly abnormal sperm differentiation, and a failure to recover fertility after return to normal temperatures (25° C) in the time period in which normal flies recover. — The principal factor, or factors, controlling normal sperm differentiation are located on the Y chromosome, but are thus far not precisely localized. Expression of the phenotype is modified by genetic background in which the Y chromosome is found.