Further Observations on Polymegaly in Species of the \u3ci\u3eDrosophila affinis\u3c/i\u3e Subgroup

Polymegaly, or the production of two or more size class of sperms by the same male, has been known in Drosophila for more than a decade. More recently polymegaly (dimegaly, or two size classes) was found in the Drosophila affinis subgroup. Additional observations on polymegaly in six D. affinis subgroup species: D. affinis, D. algonquin, D. athabasca, D. azteca, D. narragansett, and D. tolteca are reported here. The two kinds of sperms differ strikingly in the nature of the head, which is elongate (threadlike) in long sperms, short and dense in short sperms. Ultraviolet fluorescence following treatment with 4\u27, 6-diamidino-2-phenylindole (DAPI) made it possible to recognize these distinctive heads in developing spermatids and in mature sperms. Investigations of spermatids were supplemented with observations of Feulgen-stained preparations and by electron microscopy. Short sperms were found to be much more numerous than long ones in the seminal vesicles of males and in the uteri of recently inseminated females. However, the proportions of short sperms were greatly reduced in the sperm storage organs of mated females. Inspection of squash preparations of newly laid eggs revealed flagella of long sperms but no unequivocal evidence of short sperms