Seminal fluid proteins (SFPs) produced in reproductive tract tissues of male insects and transferred to females during mating induce numerous physiological and behavioral postmating changes in females. These changes include decreasing receptivity to remating; affecting sperm storage parameters; increasing egg production; and modulating sperm competition, feeding behaviors, and mating plug formation. In addition, SFPs also have antimicrobial functions and induce expression of antimicrobial peptides in at least some insects. Here, we review recent identification of insect SFPs and discuss the multiple roles these proteins play in the postmating processes of female insects.

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Insect seminal fluid proteins: identification and function.

Scientists perform experiments and gather data to gain evidence for or against various hypotheses about how the world works. This sounds straightforward, but exactly how we use this data to make quantitative statements about various hypotheses requires a bit more care. In fact, there are two related, but philosophically distinct, approaches to scientific inference. To some extent these two approaches parallel the frequency interpretation and the subjective interpretation of probability. “Classical” statistical analysis is most closely allied with the frequency interpretation, whereas “Bayesian” analysis is allied with the subjective interpretation.

https://www.zoology.ubc.ca/biomath/book/Preface.pdf

A Biologist's Guide to Mathematical Modeling in Ecology and Evolution

Mating elicits two major changes in the reproductive behavior of many insect females. The egg-laying rate increases and the readiness to accept males (receptivity) is reduced. These postmating responses last ≈1 week in Drosophila melanogaster. Males that do not transfer sperm but transfer seminal fluid during mating induce a short-term response of 1 day. The long-term response of 1 week requires the presence of sperm (sperm effect). Hence, sperm is essential for the long-term persistence of the postmating responses. Three seminal fluid peptides elicit postmating responses: ovulin, sex-peptide (SP), and DUP99B. Using the technique of targeted mutagenesis by homologous recombination, we have produced males with mutant SP genes. Here, we report that males lacking functional SP elicit only a weak short-term response. However, these males do transfer sperm. Thus, (i) SP is the major agent eliciting the short-term and the long-term postmating responses and (ii) sperm is merely the carrier for SP. The second conclusion is supported by the finding that SP binds to sperm. The 36-aa-encoding SP gene is the first small Drosophila gene knocked out with the method of homologous recombination.

/pdf/sex-peptide-is-the-molecular-basis-of-the-sperm-effect-in-3ntax9a35l.pdf

Sex-peptide is the molecular basis of the sperm effect in Drosophila melanogaster

Mating in many species induces a dramatic switch in female reproductive behaviour. In most insects, this switch is triggered by factors present in the male's seminal fluid. How these factors exert such profound effects in females is unknown. Here we identify a receptor for the Drosophila melanogaster sex peptide (SP, also known as Acp70A), the primary trigger of post-mating responses in this species. Females that lack the sex peptide receptor (SPR, also known as CG16752), either entirely or only in the nervous system, fail to respond to SP and continue to show virgin behaviours even after mating. SPR is expressed in the female's reproductive tract and central nervous system. The behavioural functions of SPR map to the subset of neurons that also express the fruitless gene, a key determinant of sex-specific reproductive behaviour. SPR is highly conserved across insects, opening up the prospect of new strategies to control the reproductive and host-seeking behaviours of agricultural pests and human disease vectors.

A receptor that mediates the post-mating switch in Drosophila reproductive behaviour.

Sex Peptide Causes Mating Costs in Female Drosophila melanogaster

Mating induces profound changes in female insect behavior and physiology In Drosophila melanogaster, mating causes a reduction in sexual receptivity and an elevation in egg production for at least 5 days Injection of the seminal fluid sex peptide (SP) induces both responses in virgin females, but only for 1–2 days The role of SP in eliciting the responses to mating remains to be elucidated Functional redundancy between seminal fluid components may occur In addition, mating with spermless males results in brief (1- to 2-day) post-mating responses, indicating either that there is a “sperm effect” or that sperm act as carriers for SP or other seminal fluid components Here we used RNA interference to suppress SP expression, to determine whether SP is required to elicit full post-mating responses, the magnitude of responses due to other seminal fluid components, and whether SP accounts for the “sperm effect” Receptivity was higher and egg production lower in females mated to SP knock-down males than in controls Comparison with virgins showed that the responses were brief SP is therefore required for normal magnitude and persistence of postmating responses Sperm transfer and use were normal in mates of SP knock-down males, yet their post-mating responses were briefer than after normal matings, and similar to those reported in mates of spermless son-of-tudor males The prolonged “sperm effect” on female receptivity and egg production is therefore entirely attributable to SP, but sperm are necessary for its occurrence

Beth Seifried

Papers

The sex peptide of Drosophila melanogaster: female post-mating responses analyzed by using RNA interference.