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.性相关性状（如婚赠 (nuptial gifts)）具有成本代价，且通常依赖于个体生理状态。雄性个体应在自然选择压力下，在不损害自身繁殖成功率的前提下降低此类成本。蜘蛛的婚赠通常为蚕丝包裹的食物，但也可能是无价值（无营养）的馈赠：此类馈赠虽可成功促成交配，但其交配时长更短。无价值的婚赠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（即生理状态不佳）无法产出合格婚赠的结果。除非能量制约限制了蚕丝的投入量，否则雄性应在无价值婚赠上使用更多蚕丝，以弥补其较低的繁殖价值。本研究以狡蛛 (Pisaura mirabilis) 为研究对象，旨在解答两个问题：1）无价值婚赠是否依赖于个体生理状态；2）雄性是否会根据婚赠类型（合格 vs 无价值）策略性地调控蚕丝投入量。我们通过采集野外获取的婚赠，以及让雄性个体在不同喂食条件下于实验室中产出婚赠，检验了雄性生理状态是否会影响其婚赠策略，并对比了不同类型婚赠的蚕丝包裹量。本研究结果显示，生理状态不佳或资源受限并不会促使雄性产出无价值婚赠。相反，无价值婚赠实则是一种演化形成的欺骗策略：雄性借此机会主义式地降低合格婚赠的成本，同时获取营养优势，且实施欺骗的雄性可获得更多体质量。无论雄性自身生理状态或喂食状态如何，其都会在无价值婚赠上投入更多蚕丝，这表明即便蚕丝投入存在成本，雄性仍可策略性地调控蚕丝用量。通过掩盖婚赠内容并延长雌性的进食时长，蚕丝对于维持欺骗策略至关重要，这一现象可能源于雄性欺骗与雌性评估之间的演化军备竞赛。