Abstract
Sexual conflict, in which the evolutionary interests of males and females diverge, shapes the evolution of reproductive systems across diverse taxa. Here, we used the fruit fly to study sexual conflict in natural, three-way interactions comprising a female, her current and previous mates. We manipulated the potential for sexual conflict by using sex peptide receptor (SPR) null females and by varying remating from 3 to 48 h, a period during which natural rematings frequently occur. SPR-lacking females do not respond to sex peptide (SP) transferred during mating and maintain virgin levels of high receptivity and low fecundity. In the absence of SPR, there was a convergence of fitness interests, with all individuals gaining highest productivity at 5 h remating. This suggests that the expression of sexual conflict was reduced. We observed an unexpected second male-specific advantage to early remating, resulting from an increase in the efficiency of second male sperm use. This early window of opportunity for exploitation by second males depended on the presence of SPR. The results suggest that the SP pathway can modulate the expression of sexual conflict in this system, and show how variation in the selective forces that shape conflict and cooperation can be maintained.
Highlights
Sexual conflict, in which the evolutionary interests of males and females diverge, is a pervasive selective force for driving evolutionary change
The results show that the sex peptide pathway can modulate the extent of sexual conflict and that variation in traits influenced by sexual conflict can be maintained by the shifting 2 reproductive interests of the individuals involved
Our study shows that the sex peptide pathway can determine the balance of fitness interests in mating males and females
Summary
In which the evolutionary interests of males and females diverge, is a pervasive selective force for driving evolutionary change. We used the fruit fly model system to measure indices of fitness for each individual when a female mated with two males in series This design was used to capture some of the natural complexity of sexual competitions that occur simultaneously between multiple individuals and to allow us to simultaneously measure the fitness interests of all interacting parties. To investigate whether the effect of female SPR status differed among female sperm storage organs we used remating interval, female SPR status and sperm storage organ, and all their interactions as fixed effects in a quasi-Poisson GLM, with sperm stored for each individual (first male, second male, and female) as the response variable in separate models. We conducted post hoc analysis of offspring production to compare the maximum mean for each female genotype (SPRþ and SPR0) using the glht function in the multcomp package (v. 1.4-3; [36] in R v. 3.1.3 [37])
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