Data from: Developmental temperature affects the expression of ejaculatory traits and the outcome of sperm competition in Callosobruchus maculatus

The outcome of post-copulatory sexual selection is determined by a complex set of interactions between the primary reproductive traits of two or more males and their interactions with the reproductive traits of the female. Recently a number of studies have shown the primary reproductive traits of both males and females express phenotypic plasticity in response to the thermal environment experienced during ontogeny. However, how plasticity in these traits affects the dynamics of sperm competition remains largely unknown. Here we demonstrate plasticity in testes size, sperm size and sperm number in response to developmental temperature in the bruchid beetle Callosobruchus maculatus. Males reared at the highest temperature eclosed at the smallest body size and had the smallest absolute and relative testes size. Males reared at both the high and low temperature extremes produced both fewer and smaller sperm than males reared at intermediate temperatures. In the absence of sperm competition developmental temperature had no effect on male fertility. However, under conditions of sperm competition, males reared at either temperature extreme were less competitive in terms of sperm offence (P2), whilst those reared at the lowest temperature were less competitive in terms of sperm defence (P1). This suggests the developmental pathways that regulate the phenotypic expression of these ejaculatory traits are subject to both natural and sexual selection: natural selection in the pre-ejaculatory environment and sexual selection in the post-ejaculatory environment. In nature, thermal heterogeneity during development is commonplace. Therefore, we suggest the interplay between ecology and development represents an important, yet hitherto underestimated component of male fitness via post-copulatory sexual selection.

交配后性选择的结果，由两只及以上雄性的主要生殖性状间的复杂相互作用，以及这些性状与雌性生殖性状的相互作用共同决定。近期多项研究表明，雄性与雌性的主要生殖性状，均会在个体发育过程中响应其所经历的热环境而表现出表型可塑性。然而，上述性状的可塑性如何影响精子竞争的动态过程，目前尚不明晰。本研究以豆象甲虫Callosobruchus maculatus为研究对象，阐明了其精巢大小、精子大小与精子数量在响应发育温度时的可塑性变化。在最高温度环境下饲养的雄性，羽化时体型最小，其绝对精巢大小与相对精巢尺寸均为最小。在温度高低极端条件下饲养的雄性，其所产生的精子数量与精子大小，均低于在中等温度环境下饲养的雄性。在无精子竞争的情境中，发育温度对雄性育性无显著影响。然而在精子竞争条件下，任一温度极端组的雄性，其精子进攻能力（P2）均表现更弱；而在最低温度环境下饲养的雄性，其精子防御能力（P1）则相对更弱。这一结果表明，调控这些射精性状表型表达的发育通路，同时受到自然选择与性选择的双重作用：分别对应射精前环境中的自然选择，以及射精后的性选择。在自然环境中，发育阶段的热异质性十分普遍。因此我们认为，生态因子与发育过程间的相互作用，是通过交配后性选择影响雄性适合度的一个重要却此前被低估的关键组分。