STUDIES OF ESTERASE 6 IN DROSOPHILA MELANOGASTER. VI. EJACULATE COMPETITIVE ABILITIES OF MALES HAVING NULL OR ACTIVE ALLELES

Recent studies of the function of the polymorphic seminal fluid enzyme, esterase 6, of Drosophila melanogaster suggested that it may act in the process of sperm displacement (Gilbert, Richmond and Sheehan, 1981a). This report examines the competitive ability of ejaculates from males homozygous for null or active alleles of esterase 6 under three experimental conditions that model aspects of sexual selection affecting males. The results demonstrate no significant difference in ejaculate competition between esterase 6 null or active male types, but marker males used for paternity identification had poorly competitive ejaculates. The proportion of second-male progeny, P  2, used as an index of competition is primarily influenced by second-male genotype and uninfluenced by female genotype. P2 can change with time from remating and be unaffected by different intensities of competition, which suggests a complex ejaculate competition mechanism.