Department of Biology, University of York, York YO10 5DD, UK.
Biol Lett. 2013 Feb 27;9(2):20121188. doi: 10.1098/rsbl.2012.1188. Print 2013 Apr 23.
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.
多种雄性的精液之间为争夺特定卵子的受精权而进行的精子竞争在分类上广泛存在。雄性为了在交配后性选择下提高繁殖成功率，进化出了显著的适应机制，包括能够灵活改变行为和精液特征，以适应感知到的精子竞争水平。模型物种黑腹果蝇的雄性会根据短期的精子竞争风险变化，延长交配时间并改变精液成分。如果这些反应增加了雄性在繁殖上的总投资，那么他必须在这一成本与其他生活史特征之间进行权衡，否则就会降低生存能力。我们测试了雄性是否会因做出这种有弹性的精子竞争反应而付出即时的生存代价，结果发现，暴露在高精子竞争风险下的雄性果蝇比处于低风险下的雄性果蝇的存活率高出 12%，这相当于每小时死亡风险降低了 49%。这种显著的效果仅在处女蝇中发现：在这个物种中，交配的高成本消除了非处女蝇雄性中任何这样的益处。我们的研究结果表明，在处女蝇中发现的存活率提高可能是雄性对精子竞争的策略性反应的产物。
