Perceived sperm competition intensity influences seminal fluid protein production prior to courtship and mating.

Sperm competition is a potent postcopulatory selective force where sperm from rival males compete to fertilize a limited set of ova. Considering that sperm production is costly, we expect males to strategically allocate sperm in accordance with the level of competition. Accordingly, previous work has examined a male's strategic allocation in terms of sperm number. However, the seminal fluid proteins (Sfps) transferred along with sperm may also play a crucial role in competition. Surprisingly, the strategic allocation of Sfps has remained largely unexplored. Using Drosophila melanogaster, we examined the expression of three seminal fluid and four spermatogenesis genes in response to perceived sperm competition intensity by manipulating male density in a pre-mating and courtship environment. In the pre-mating environment, we found that males modified Sfp ratios by reducing the production of two spfs when potential rivals were present, while one Sfp and all spermatogenesis genes remained unaltered. In the courtship environment, males did not modify spermatogenesis or Sfp production in response to either rival males or female presence. Our data suggest that perceived competition in the pre-mating environment places a significant influence on Sfp allocation, which may be a general trend in promiscuous animal systems with internal fertilization.

Fedorka KM ，Winterhalter WE ，Ware B 《-》

Sperm wars and the evolution of male fertility.

Simmons LW ，Fitzpatrick JL 《-》

Drosophila seminal sex peptide associates with rival as well as own sperm, providing SP function in polyandrous females.

When females mate with more than one male, the males' paternity share is affected by biases in sperm use. These competitive interactions occur while female and male molecules and cells work interdependently to optimize fertility, including modifying the female's physiology through interactions with male seminal fluid proteins (SFPs). Some modifications persist, indirectly benefiting later males. Indeed, rival males tailor their ejaculates accordingly. Here, we show that SFPs from one male can directly benefit a rival's sperm. We report that Sex Peptide (SP) that a female receives from a male can bind sperm that she had stored from a previous male, and rescue the sperm utilization and fertility defects of an SP-deficient first-male. Other seminal proteins received in the first mating 'primed' the sperm (or the female) for this binding. Thus, SP from one male can directly benefit another, making SP a key molecule in inter-ejaculate interaction.

Misra S ，Wolfner MF 《eLife》

Sperm production responds to perceived sperm competition risk in male Drosophila melanogaster.

Postcopulatory sexual selection arising from female multiple mating leads to the evolution of ejaculates that maximize a male's reproductive success under sperm competition. Where the risk of sperm competition is variable, optimal fitness may be achieved by plastically altering ejaculate characteristics in response to the prevailing sperm competition environment. In the model species Drosophila melanogaster, males expecting to encounter sperm competition mate for longer and transfer more accessory proteins and sperm. Here we show that after being housed with a single rival for one week, the seminal vesicles of male D. melanogaster contain a significantly greater proportion of live sperm than those of males maintained alone, indicating adaptive adjustment of sperm quality in response to the perceived risk of sperm competition. This effect is due to an increase in the number of live sperm produced, indicating that males upregulate sperm production in response to the presence of rivals. Our data suggest that males show plasticity in the rate of spermatogenesis that is adaptive in the context of a fluctuating sperm competition environment.

Moatt JP ，Dytham C ，Thom MD 《-》

Seminal fluid protein allocation and male reproductive success.

Postcopulatory sexual selection can select for sperm allocation strategies in males [1, 2], but males should also strategically allocate nonsperm components of the ejaculate [3, 4], such as seminal fluid proteins (Sfps). Sfps can influence the extent of postcopulatory sexual selection [5-7], but little is known of the causes or consequences of quantitative variation in Sfp production and transfer. Using Drosophila melanogaster, we demonstrate that Sfps are strategically allocated to females in response to the potential level of sperm competition. We also show that males who can produce and transfer larger quantities of specific Sfps have a significant competitive advantage. When males were exposed to a competitor male, matings were longer and more of two key Sfps, sex peptide [8] and ovulin [9], were transferred, indicating strategic allocation of Sfps. Males selected for large accessory glands (a major site of Sfp synthesis) produced and transferred significantly more sex peptide, but not more ovulin. Males with large accessory glands also had significantly increased competitive reproductive success. Our results show that quantitative variation in specific Sfps is likely to play an important role in postcopulatory sexual selection and that investment in Sfp production is essential for male fitness in a competitive environment.

Wigby S ，Sirot LK ，Linklater JR ，Buehner N ，Calboli FC ，Bretman A ，Wolfner MF ，Chapman T ... -  《-》