Females mate multiply despite numerous costs. It is well established that polyandry can result in sexual conflict, favoring male adaptations that prevent sperm competition often to the disadvantage of the female. Such adaptations are extreme in spiders with one-shot genitalia of which parts break off and act as mating plugs, rendering them dysfunctional. In the spider Argiope bruennichi, mating plugs effectively prevent further males from inseminating and males that inseminate and plug both genital openings of a female secure exclusive paternity. However, females frequently prevent monopolization by attacking and cannibalizing males during their first copulation, leaving their second spermatheca free for another male. Here, we test whether the high frequency of sexual cannibalism evolved as a female adaptation to resist monopolization and secure indirect benefits of polyandry. To standardize conditions, we double-mated females either with the same or two different males and prevented male consumption. Using a split-brood design, we raised offspring to maturity under poor and rich food conditions and measured their survival, duration of juvenile phase, and adult body mass. Under low food, daughters of polyandrous mothers matured later but slightly heavier than daughters of monandrous females. Since the adaptive value of this combination is unclear, these findings lend no conclusive support to our hypothesis. We discuss the stereotypic nature of the female attack in the context of antagonistic co-evolution considering previous studies that found modest direct benefits of cannibalism as well as a potential for non-additive benefits. Sexual conflict is extreme in spiders where sexual cannibalism impairs male mating rates. Males of the spider Argiope bruennichi possess one-shot genitalia which they break off to plug female genital openings. They gain exclusive paternity with a female if two copulations are achieved and both genital openings plugged. Females, however, stereotypically attack every male at the onset of copulation, limiting most males to single copulation but retaining the option to secure potential benefits of polyandry. Previous studies revealed weak direct and non-additive indirect benefits of multiple mating. In this study, we tested for the presence of additive genetic benefits but again found only inconclusive evidence for adaptive differences in offspring quality between monandrous and polyandrous females. All results combined, we here speculate that the stereotypic female attack might be a ghost of a past antagonistic co-evolution.

中文翻译：

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性同类相食是否确保了大小二态蜘蛛的一妻多夫的遗传优势？

尽管付出了很多代价，但雌性交配成倍增加。众所周知，一妻多夫会导致性冲突，有利于防止精子竞争的男性适应性，通常对女性不利。这种适应在具有一次性生殖器的蜘蛛中是极端的，其部分断裂并充当交配插头，使它们功能失调。在蜘蛛 Argiope bruennichi 中，交配插头有效地阻止了更多的雄性受精，而雄性受精并堵塞了雌性的两个生殖器开口，从而确保了唯一的亲子关系。然而，雌性在第一次交配时经常通过攻击和蚕食雄性来防止垄断，将第二个受精囊留给另一只雄性。这里，我们测试了高频率的性同类相食是否演变为一种女性适应，以抵抗垄断并确保一妻多夫的间接利益。为了标准化条件，我们将雌性与相同或两个不同的雄性进行双交，并阻止雄性食用。使用分裂育雏设计，我们在贫瘠和丰富的食物条件下将后代抚养至成熟，并测量了它们的存活率、幼年期的持续时间和成年体重。在低食条件下，一妻多夫的女儿成熟较晚，但比一夫多妻的女儿略重。由于这种组合的适应性价值尚不清楚，因此这些发现对我们的假设没有决定性的支持。考虑到先前的研究发现同类相食的适度直接好处以及非附加利益的潜力，我们讨论了在对抗性共同进化的背景下女性攻击的刻板性质。蜘蛛的性冲突是极端的，性同类相食会损害雄性交配率。蜘蛛 Argiope bruennichi 的雄性拥有一次性生殖器，它们会折断以堵塞雌性生殖器的开口。如果实现两次交配并且两个生殖器开口都被堵塞，它们将获得与女性的专属父权。然而，雌性在交配开始时刻板地攻击每个雄性，将大多数雄性限制为单次交配，但保留选择以确保一妻多夫的潜在好处。先前的研究揭示了多重交配的弱直接和非加性间接益处。在这项研究中，我们测试了是否存在额外的遗传益处，但再次发现只有一夫多妻和一妻多夫雌性之间后代质量适应性差异的非决定性证据。所有结果结合起来，我们在这里推测刻板的女性攻击可能是过去对抗性共同进化的幽灵。