Data from: Costs and benefits of lifetime exposure to mating rivals in male Drosophila melanogaster

Theory predicts that males should evolve mechanisms to assess competition and allocate resources accordingly. This requires phenotypic plasticity, to accurately match responses to the environment. Plastic responses in males to sexual competition are diverse and widespread. However, our ability to understand and predict how they evolve is limited because their benefits are rarely measured, and costs are, as yet, entirely unquantified. In the fruit fly Drosophila melanogaster, males that anticipate strong competition for matings or fertilisations subsequently mate for longer and transfer more of two key seminal fluid proteins. This results in significantly elevated reproductive output. In this study we examined the fitness effects of male responses to rivals across the entire male lifespan. Males were exposed to rivals or not throughout life whilst controlling mating opportunities. Males showed significant responses to rivals throughout their lifetimes, associated with significant early-life fitness benefits. However, these disappeared after the third mating. There were also significant costs – males exposed to rivals took significantly fewer mating opportunities in later life and had significantly shorter lifespans than controls. The data suggest that there are substantial costs for males of mounting plastic responses to the threat of sexual competition.

理论预测，雄性生物会演化出评估竞争状况并据此分配资源的机制，这需要表型可塑性（phenotypic plasticity）以精准匹配环境变化调整自身响应。雄性针对性竞争的表型响应多样且普遍存在，然而，由于这类响应的收益鲜有量化，且其代价迄今仍完全未被测定，我们理解并预测其演化规律的能力受到了限制。在黑腹果蝇（Drosophila melanogaster）中，预先感知到交配或受精存在激烈竞争的雄性，后续的交配时长会更长，且会传递更多的两种关键精浆蛋白（seminal fluid proteins），这会显著提升其繁殖产出。本研究在雄性个体的整个生命周期中，探究了其针对竞争对手的响应对适合度（fitness）的影响，研究过程中我们控制了交配机会，让雄性在整个生命周期中分别处于有竞争对手暴露和无竞争对手暴露的两种环境下。雄性在整个生命周期中均对竞争对手表现出显著响应，且该响应伴随显著的早期适合度收益，但这类收益在第三次交配后便消失无踪，此外还存在显著代价：相较于对照组，暴露于竞争对手的雄性在生命后期获得的交配机会显著更少，且寿命也明显更短。本研究数据表明，雄性针对性竞争威胁做出表型响应，需付出高昂的代价。