| Abstract: | In Drosophila melanogaster the polymorphic enzyme Est-6 and a male specific lipid, cis-vaccenyl acetate (cVA), are components of the seminal fluid. It has been suggested that cVA could be a physiological substrate for Est-6, constituting, together with the hypothetical hydrolytic product, cis-vaccenyl alcohol (cVOH), a pheromonal system active in the regulation of the sexual attractiveness of mated females. However, some doubt exists concerning the physiological conversion of cVA to cVOH in females. Est-6 is also known to affect sperm motility, sperm use and female fecundity. The results of a study on qualitative and quantitative effects of topical treatment of females with cis-vaccenyl acetate and cis-vaccenyl alcohol on courtship behaviour are presented. The inhibition of courtship produced by cVOH was more persistent; this was possibly related to its lower volatility. The hypothesis was tested that different Est-6 allozymes could produce different amounts of cis-vaccenyl alcohol in vivo by differential hydrolysis of cis-vaccenyl acetate, and thus affect the timing of remating. For this purpose highly homogeneous Est-6S and Est-6F homozygous lines, with almost certainly identical levels of Est-6 and cVA, were used. They were obtained after 100 generations of inbreeding and selection of the heterozygotes at each generation. The Est-6S and Est-6F products of the Est-6 structural gene did not differentially affect the timing of remating. This could imply that the two allozymes have similar catalytic properties. However, such results could be obtained even if cVA is not converted to cVOH in vivo by Est-6. The effects of Est-6 allozymes on sperm use after remating were also investigated. The general effect of second males was a very high elimination of first male fertilizations. No evidence for a different contribution of the two allozymes to the fitness through sperm predominance was obtained. Remating and sperm predominance experiments were performed at three temperatures: 18, 25 and 30° C. A more general—not species specific—role of cis-vaccenyl esters is suggested by preliminary results on their presence in the ejaculate of other Drosophila species. |
