Allocrine modulation of feeding behavior by the Sex Peptide of Drosophila

Abstract

Mating elicits a dramatic reprogramming of female behavior in numerous insect species. In Drosophila, this postmating response (PMR) comprises increased egg-laying rate and reduced sexual receptivity and is controlled by the products of the male accessory glands, a family of approximately 80 small peptides transferred in the male seminal fluid . Here, we show that copulation strongly stimulates female food intake. Remarkably, this change is abolished if the males lack a single, small seminal protein, the Sex Peptide (SP). Ectopic expression of SP in virgin females mimics the effect of mating on feeding behavior, demonstrating that SP is the main agent controlling this behavioral paradigm. Our observations identify enhanced feeding behavior as a novel component of the Drosophila PMR and suggest that SP represents a molecular link between energy acquisition and reproductive investment.

Figure 1

Mating Stimulates Female Food Intake (A) Virgin and mated females after feeding on red-dyed medium for 2 hr. (B) Feeding rate of virgin (− dye, n = 42; + dye, n = 39) and mated (− dye, n = 40; + dye, n = 36) females allowed to feed on medium with or without red dye for 30 min following 12 hr of wet (water-only) starvation. Shown is the average per fly ± standard deviation (SD) of three replicates. Y axis represents values of optical density (OD) of abdomen homogenate (assayed at 630 nm). (C and D) Induction of feeding rate upon mating is female specific. Ingestion volume of [α-32P]dCTP-labeled food over a 24 hr period by ad-libitum-fed virgin and mated females (C) and males (D). Results are expressed as volume of food intake (in μl) over 24 hr averaged per fly ± SD of four replicates of 15 animals per condition. ** indicates p < 0.01; *** indicates p < 0.0001, two-tailed t test.

Figure 2

SP Is Necessary for Postcopulatory Induction of Female Food Intake (A) Genetic ablation of male accessory-gland main cells abolishes stimulation of feeding behavior. Experimental males carry a construct in which the Acp95EF main-cell promoter is fused to the modified coding sequence of diphtheria toxin subunit A (DTA) [5]. Control males have identical genetic background but do not bear the DTA construct (one-way ANOVA, p = 0.0021). (B) Males that lack SP (SP⁰) but produce and transfer normal amounts of remaining Acps and sperm fail to stimulate female appetite. Experimental males carry the null mutant allele SP⁰ (introduced by homologous recombination) over the Δ¹³⁰ deletion, which uncovers the SP locus. Control males have identical genetic background but carry a wild-type copy of SP over Δ¹³⁰ [8] (one-way ANOVA, p = 0.0001). All values are expressed as volume of food intake (in μl) over 24 hr averaged per fly ± SD of three replicates of 15 animals per condition.

Figure 3

Ectopic Expression of SP in Virgin Females Mimics the Effect of Copulation (A) Constitutive fat-body expression of SP in virgins by means of the yolk protein 1 (yp1) enhancer stimulates feeding to mated-like levels. Isogenic control strain is cinnabar; rosy (cn; ry). (B and C) Effect on feeding behavior of expression of a UAS-SP construct driven by the 9Y- (B) or C370- (C) GAL4 driver lines. All values are expressed as volume of food intake (in μl) over 24 hr averaged per fly ± SD of three replicates of 15 animals per condition. * indicates p < 0.05; ** indicates p < 0.01; *** indicates p < 0.0001, two-tailed t test.