The combined effects of pre- and postcopulatory processes are masking sexual conflict over mating rate in Gerris buenoi

In polygynandrous animals, postcopulatory processes likely interfere with precopulatory sexual selection. In water striders, sexual conflict over mating rate and postcopulatory processes are well-documented but their combined effect on reproductive success has seldom been investigated. We combine genetic parentage analyses and behavioural observations conducted in a competitive reproductive environment to investigate how pre- and postcopulatory processes influence reproductive success in Gerris buenoi Kirkaldy. Precopulatory struggles had antagonistic effects on male and female reproductive success: efficiently gaining copulations was beneficial for males while efficiently avoiding copulations was profitable for females. Also, high mating rates and an intermediate optimal resistance level of females supported the hypothesis of convenience polyandry. Contrary to formal predictions, high mating rates (i.e. the number of copulations) did not increase reproductive success in males or decrease reproductive success in females. Instead, the reproductive success of both sexes was higher when offspring were produced with several partners and when there were few unnecessary matings. Thus, male and female G. buenoi displayed different interests in reproduction, but postcopulatory processes were masking the effects of copulatory mating success on reproductive success. Given the high mating rates observed, sperm competition could easily counter the effect of mating rates, perhaps in interaction with cryptic female choice and/or fecundity selection. Our study presents a complex but realistic overview of sexual selection forces at work in a model organism for the study of sexual conflict, confirming that insights are gained from investigating all episodes in the reproduction cycle of polygynandrous animals.

在混交制（polygynandrous）动物中，交配后过程大概率会对交配前性选择产生干扰作用。在水黾（water striders）中，关于交配率的性冲突以及交配后过程已有充分的研究记录，但二者对繁殖成功率的联合效应却鲜有探讨。本研究结合竞争性繁殖环境下的遗传亲权分析与行为观察，旨在探究交配前、后过程如何影响布氏黾蝽（Gerris buenoi Kirkaldy）的繁殖成功率。
交配前的争斗对雌雄两性的繁殖成功率存在拮抗效应：雄性若能高效获取交配机会，将有助于提升自身繁殖成功率；而雌性若能有效规避交配，则对自身更为有利。同时，较高的交配率以及雌性呈现中等最优抵抗水平的结果，支持了便利一妻多夫（convenience polyandry）假说。
与既定预测相悖的是，高交配率（即交配次数）并未提升雄性的繁殖成功率，也未降低雌性的繁殖成功率。与之相反，当雌雄个体与多个配偶繁育后代、且不必要交配次数较少时，两性的繁殖成功率均更高。由此可见，布氏黾蝽的雌雄个体在繁殖策略上存在演化利益分歧，但交配后过程掩盖了交配成功对繁殖成功率的直接影响。
鉴于本研究观测到的高交配率，精子竞争很容易抵消交配率的效应，且该过程可能与隐蔽雌性选择（cryptic female choice）和/或繁殖力选择（fecundity selection）存在交互作用。本研究以性冲突研究的模式生物布氏黾蝽为对象，全面呈现了其体内发挥作用的性选择压力的复杂且贴合自然实际的图景，证实了通过探究混交制动物繁殖周期的所有环节，能够获得具有价值的研究见解。