Ovulation stimulating substances in Drosophila biarmipes males: their origin, genetic variation in the response of females, and molecular characterization.

Ovulation responses of Drosophila biarmipes females to an injection of methanolic extract from conspecific males vary with the strains of females. This strain difference seems to be controlled by a small number of autosomal genes, with low responsiveness being recessive. Strangely, all D. biarmipes strains show a high level of ovulation after mating. We pursued the reason for this discrepancy and found that D. biarmipes males produce two different substances with ovulation-inducing activity. One of them is derived from the accessory glands and effective in females of all strains. Another originates in the ejaculatory duct and is inactive in some strains. In an active HPLC fraction of the ejaculatory duct extract, we found a peptide consisting of 32 amino acids. Its C-terminal region has a striking similarity to the sex-peptide of D. melanogaster, but the N-terminal region was entirely different. Evolutionary implications of these findings are discussed.