VARIATION IN SPERM DISPLACEMENT AND ITS ASSOCIATION WITH ACCESSORY-GLAND PROTEIN LOCI IN DROSOPHILA-MELANOGASTER

Genes that influence mating and/or fertilization success may be target s for strong natural selection. If females remate frequently relative to the duration of sperm storage and rate of sperm use, sperm displace ment may be an important component of male reproductive success. Altho ugh it has long been known that mutant laboratory stocks of Drosophila differ in sperm displacement, the magnitude of the naturally occurrin g genetic variation in this character has not been systematically quan tified. Here we report the results of a screen for variation in sperm displacement among 152 lines of Drosophilia melanogaster that were mad e homozygous for second and/or third chromosomes recovered from natura l populations. Sperm displacement was assayed by scoring the progeny o f cn;bw females that had been mated sequentially to cn;bw and tested m ales in either order. Highly significant differences were seen in both the ability to displace sperm that is resident in the female's reprod uctive tract and in the ability to resist displacement by subsequent s perm. Most lines exhibited nearly complete displacement, having nearly all progeny sired by the second male, but several lines had as few as half the progeny fathered by the second male. Lines that were identif ied in the screen for naturally occurring variation in sperm displacem ent were also characterized for single-strand conformation polymorphis ms (SSCP) at seven accessory: gland protein (Acp) genes, Glucose dehyd rogenase (GM), and Esterase-6 (Est-6). Acp, genes encode proteins that are in some cases known to be transmitted to the female in the semina l fluid and are likely candidates for genes that might mediate the phe nomenon of sperm displacement. Significant associations were found bet ween particular Acp alleles at four different loci (Acp26Aa/Ab, Acp29B , Acp36DE and Acp53E) and the ability of males to resist displacement by subsequent sperm. There was no correlation between the ability to d isplace resident sperm and the ability to resist being displaced by su bsequent sperm. This lack of correlation, and the association of Acp a lleles with resisting subsequent sperm only, suggests that different m echanisms mediate the two components of sperm displacement.