Probing the function of Drosophila melanogaster accessory glands by directed cell ablation.

Abstract

The female Drosophila melanogaster fly undergoes behavioral changes after mating, including an increase in egg laying and an avoidance of remating. Accessory-gland products elicit these changes transiently when introduced into unmated female flies. We report here the generation and phenotype of flies that lack functional accessory-gland main cells as a consequence of genetically directed delivery of diphtheria toxin subunit A to those ceUls. Only main-cell secretions are essential for the short-term inhibition to remating; no other products of the genital tract can replace their function. Long-term inhibition to remating depends only on the storage of sperm in the female. Both sperm and main-cell secretions have roles in the increase of egg laying by the mated female. In addition to full-strength diphtheria toxin, we used low-activity toxins to kill only those ceUls that express toxin at high levels. These transgenic strains that express diphtheria toxins of different strengths in accessory-gland main cels wiUl be useful in further defining the role of these cells.In insects, mating causes females to undergo physiological and behavioral changes that persist for several days (1, 2). After mating, females lay eggs at a high rate and they reject further male courtship and remating. They store and utilize sperm they receive. In Drosophila melanogaster, these behavioral changes are due in part to sperm and in part to seminal fluid (3-5). Seminal-fluid components have been shown to cause the initial decrease in receptivity, called the "copulation effect" (3), but the long-term decrease in receptivity, called the "sperm effect" (4, 5), is correlated with the presence of sperm in the female's sperm-storage organs.To determine which molecules are responsible for these behavioral changes, we need to know their source. Seminalfluid effects on oviposition (egg laying) rate and receptivity were demonstrated in Hihara's study (3) of mates of males that had depleted their seminal secretions due to multiple prior matings. Hihara (3) postulated that products of the accessory gland, a secretory tissue in the male reproductive tract, caused these behavioral changes. He reasoned this because the accessory glands of multiply mated males were shrunken, apparently due to depletion of their contents, and because transplantation ofaccessory glands (6, 7) or injection of their extracts (for review, see ref.2) was known to cause increases in oviposition and decreases in receptivity. Chen et al. (8) and Aigaki et al. (9) later showed that a single accessory-gland peptide, the sex peptide, is able to induce oviposition and rejection when introduced into female flies.

Cross-generational fitness benefits of mating and male seminal fluid

“…Nor did egg density contribute to daughter fitness because we statistically accounted for vial egg density in all of our analyses of daughter traits. Also, though exposure to Acps increases egg production in virgin females (Kalb et al 1993), we found that additional exposure to Acps did not influence egg production in inseminated females.…”

“…At maternal age day 2, we exposed each female to three fresh virgin Dahomey males for four hours. At maternal age day 4, we randomly assigned the females to one of the three additional mating treatments: no additional mating, additional mating with five fresh males that were sterile and lacked production of main-cell Acps (DTA-E males; Kalb et al 1993), or additional mating with five fresh males that were sterile but produced main-cell Acps (sons of tudor females; Boswell & Mahowald 1985). All of the females were provided with fresh vials and the additional mating treatment females were provided with fresh males every 2 days from maternal age days 4 to 10.…”

Males' evolutionary responses to experimental removal of sexual selection

“…Finally, D. melanogaster males transfer many more sperm than females are capable of storing (Gilbert 1981) and egg laying is known to be in£uenced by seminal proteins rather than by variation in sperm supply (e.g. Chen et al 1988;Kalb et al 1993;Herndon & Wolfner 1995). It is also unlikely that this divergence is the result of di¡erential larval survival brought about through sperm length di¡erences.…”

Seminal fluid causes temporarily reduced egg hatch in previously mated females

“…In addition, male o¡spring of tudor females fail to produce germline cells, and are likewise spermless but produce normal seminal £uid (SchÏpbach & Wieschaus 1986). The results using these males were compared with the results of remating with sterile DTA (which bear a diphtheria toxin transgene) males, which lack an accessory gland and thus produce no seminal £uid proteins (Kalb et al 1993). A third-chromosome extracted line (B3^09) from Beltsville, was used as a control with normal fertility.…”