Sperm competition and sperm loss in Drosophila melanogaster females fertilized by YXY-O males.

T is generally assumed that in animal species all the sperm from a heterozygote, I though genetically different, have the same functional properties; consequently they cannot compete in fertilization, and no selection is possible. This has been interpreted as meaning that genes stop functioning after the first meiotic division (MULLER and SETTLES 1927). An exception to this principle has been described in the mouse where some alleles at the T locus are recovered with higher frequency. This observation is in line with the hypothesis that such a differential recovery might be due to different functional properties which alleles confer on the gametes carrying them (BRADEN 1958). Later experiments (YANAGISAWA, DUNN and BENNETT 1961) seem to have confirmed this hypothesis. Recently, MCCLOSKEY (1966) has extended MULLER and SETTLES' experiments in Drosophila. This author has shown that no competition exists between sperm having two right arms or two left ones of the same autosome and the other arm completely missing. During the last few years we have been examining the question of whether, in Drosophila, sperm carrying both X and Y chromosomes (attached-XY or XY sperm) and sperm without either (0 sperm) have the same physiological properties. The results are in line with the idea that there are functional differences between the two kinds of sperm. A part of this work has already been published in summary form ( OLIVIERI, PICA and OLIVIERI 1964). Since this manuscript was submitted for publication, it was pointed out that similar results were reported in an unpublished thesis for the Master of Arts degree at The University of Oregon by the late J. D. MCCLOSKEY. He used several types of X.Y chromosome in one of which he found results similar to those reported here. In another X.Y type as well as in the male with the normal chromosome arrangement he found no change in the sex ratio with age.