Exposure to sperm competition risk improves survival of virgin males

Abstract

Sperm competition between the ejaculates of multiple males for the fertilization of a given set of ova is taxonomically widespread. Males have evolved remarkable adaptations to increase their reproductive success under postcopulatory sexual selection, which in many species includes the ability to modify behaviour and ejaculate characteristics plastically to match the perceived level of sperm competition. Males of the model species Drosophila melanogaster increase mating duration and modify seminal fluid composition in response to short-term changes in sperm competition risk. If these responses increase a male's total investment in reproduction, he must either trade-off this cost against other life-history traits or suffer reduced survival. We tested whether mounting a plastic sperm competition response bears an instantaneous survival cost, and instead found that male D. melanogaster exposed to a high risk of sperm competition survive 12 per cent longer than those at low risk, equating to a 49 per cent reduction in the hourly hazard of death. This striking effect was found only among virgins: the high cost of mating in this species eliminates any such benefit among non-virgin males. Our results suggest that the improvement in survival found among virgins may be a product of males' tactical responses to sperm competition.

Flirtation reduces males’ fecundity but not longevity

“…; Moatt et al. ) but these two parameters are not positively correlated in some species (e.g., Gilchrist and Partridge ; the present study). Fifth, sperm production mediated by mean SCR and SCI levels may increase in both male‐biased and female‐biased conditions because males may gain reproductive fitness by increasing sperm production after exposure to rivals (Wedell et al.…”

“…Third, in many SC studies authors measure various parameters for only one mating event rather than lifetime reproductive activities (e.g., Bretman et al 2009;Bretman et al 2010;Lize et al 2012;Price et al 2012;Bretman et al 2013a;Bretman et al 2013b;Worthington et al 2013). Fourth, copulation duration is usually considered an accurate measure of sperm allocation (e.g., Bretman et al 2011a;Price et al 2012;Moatt et al 2013) but these two parameters are not positively correlated in some species (e.g., Gilchrist and Partridge 2000; the present study). Fifth, sperm production mediated by mean SCR and SCI levels may increase in both male-biased and female-biased conditions because males may gain reproductive fitness by increasing sperm production after exposure to rivals (Wedell et al 2002;Parker and Pizzari 2010) and additional mates (Abe and Kamimura 2015).…”

“…; Moatt et al. ). During copulation in E. kuehniella , the male produces a spermatophore in his internal sac and pushes it to the female's bursa (Xu and Wang ).…”

“…Several additional points are also worth mentioning. First, although females may play important roles in male reproductive plasticity (Bretman et al 2011a;Requena and Alonzo 2014;Abe and Kamimura 2015), they are often conditioned (e.g., virgin females reared in groups) before mating while the impact of such treatment on SC predictions is not considered (e.g., Price et al 2012;Moatt et al 2013;Bretman et al 2013b;Worthington et al 2013). Second, the effect of different life history strategies of study species on research outcomes (and thus predictions) is rarely considered in SC studies (Ingleby et al 2010).…”

Male–male competition leads to less abundant but more attractive sperm

“…One taxonomically widespread strategy is the adjustment of ejaculate investment according to the presence of rival males to maximize fertilization success [2,3]. Plastic responses to the risk of pre-or post-copulatory male-male competition can increase male fitness, as shown for instance in Drosophila melanogaster [4,5]. Commonly, the response to male-male competition involves adjustment of ejaculate size or the number of ejaculates.…”