Data from: Silk wrapping of nuptial gifts aids cheating behaviour in male spiders

Sexual traits, such as nuptial gifts, are costly and often condition-dependent. Males should be under selection to reduce these costs without impairing their reproductive success. Spider gifts consist of silk-wrapped food, but may also consist of worthless (non-nutritive) donations that successfully lead to mating, despite yielding shorter copulations. Worthless gifts may either represent a cheaper cheating strategy or the inability to produce genuine gifts due to resource limitations (i.e. poor body condition). Unless energetic constraints limit expenditure in silk, males should apply more silk to worthless gifts to compensate for their lower reproductive value. We ask whether in Pisaura mirabilis 1) worthless gifts are condition-dependent and 2) males strategically use silk based on gift type (genuine vs worthless). We tested whether male body condition explains the gift-giving strategy and compared silk amounts covering each gift type, in gifts collected from the field and produced in the laboratory by males given different feeding regimes. Our findings show that worthless gifts are not promoted by poor body condition or limited resources. They rather result from a cheating strategy evolved to opportunistically reduce the costs of genuine gifts while ensuring nutritional advantages, with cheaters gaining body mass. Males applied more silk to worthless gifts regardless of their body condition or feeding state, suggesting they can strategically adjust silk expenditure despite its costs. By masking gift contents and prolonging female feeding, silk is crucial for the maintenance of cheating, likely resulting from an evolutionary arms race between male deception and female assessment.

诸如婚赠礼（nuptial gifts）这类性特征，往往代价高昂且具有状态依赖性。雄性个体应在自然选择压力下降低此类代价，同时不损害自身繁殖成功率。蜘蛛的婚赠礼通常由丝线包裹的食物构成，但也可能包含无价值（无营养）的赠品：这类赠品虽能成功促成交配，却会缩短交配时长。无价值赠礼可能是一种成本更低的欺骗策略，也可能是雄性因资源限制（即身体状态不佳）无法产出真实赠礼的结果。除非能量约束限制了丝线投入量，否则雄性应为无价值赠礼包裹更多丝线，以弥补其较低的繁殖价值。

本研究以奇异盗蛛（Pisaura mirabilis）为研究对象，旨在解答两个问题：1）无价值赠礼是否具有状态依赖性？2）雄性是否会根据赠礼类型（真实赠礼 vs 无价值赠礼）策略性地调整丝线投入量？我们通过采集野外样本，以及在实验室中为雄性提供不同饲喂方案以诱导其产赠礼，检验了雄性身体状态是否会影响其赠礼策略，并对比了不同类型赠礼的丝线包裹量。

研究结果显示，无价值赠礼并非由雄性身体状态不佳或资源受限所导致。相反，此类赠礼是一种演化形成的欺骗策略：雄性借此机会降低真实赠礼的成本，同时获得营养收益，而实施欺骗的雄性个体体重会有所增加。无论雄性自身身体状态或饲喂状态如何，其都会为无价值赠礼包裹更多丝线，这表明尽管丝线投入存在代价，雄性仍能策略性地调整丝线用量。丝线通过掩盖赠礼内容、延长雌性的取食时长，在维持欺骗策略中发挥关键作用，这一现象可能源于雄性欺骗与雌性甄别之间的演化军备竞赛。