Data from: Male spiders reduce pre- and postmating sexual investment in response to sperm competition risk

The interplay between pre- and post-mating responses to intra-sexual competition remains enigmatic. Sperm competition models often assume a trade-off between pre- and post-mating traits that enhance mate acquisition and fertilization success, respectively. However, when males court females through food donations (i.e. nuptial gifts), pre- and post-mating responses may be aligned, as nuptial gifts have the dual function of facilitating both mate acquisition and sperm transfer. In the spider Pisaura mirabilis nuptial gifts consist of silk-wrapped prey. We tested whether males respond to a competitor by altering: 1) pre-mating investment in the gift; 2) post-mating sperm investment; and 3) whether pre- and post-mating responses are coupled and respond to competition in the same direction or not. Under competition risk males silk-wrapped their gifts for significantly shorter time and transferred less sperm to females, pointing to a reduction of both pre- and post-mating responses. Since silk is not a target of female choice, reducing gift construction may speed up mate acquisition. In accordance with models of sperm allocation, perceived high levels of competition and/or sperm priority patterns may explain the reduced patterns of sperm transfer found in our study. Overall, our findings suggest that in competitive environments pre- and post-mating traits are coupled and respond in the same direction.性内竞争下的交配前与交配后响应之间的相互作用，至今仍未得到充分阐释。精子竞争模型通常假定，分别提升配偶获取成功率与受精成功率的交配前、交配后性状之间存在权衡关系。然而，当雄性通过食物馈赠（即婚赠）向雌性求偶时，交配前与交配后响应可能会趋于一致，因为这类婚赠同时兼具促进配偶获取与精子转移的双重功能。在狡蛛（Pisaura mirabilis）中，婚赠由丝质包裹的猎物构成。本研究探究了雄性是否会通过以下方式对竞争者做出响应：1）调整对婚赠的交配前投入；2）调整交配后的精子投入；以及3）交配前与交配后响应是否存在关联，且是否会朝着同一方向响应竞争压力。在存在竞争风险的情境下，雄性包裹婚赠所用的丝质时长显著缩短，且向雌性转移的精子量更少，这表明其交配前与交配后响应均有所降低。由于丝质并非雌性配偶选择的目标性状，缩短婚赠构建时间或许能够加快配偶获取速度。依据精子分配模型，感知到的高强度竞争以及/或精子优先级模式，或许可以解释本研究中观测到的精子转移量降低的现象。总体而言，本研究结果表明，在竞争环境中，交配前与交配后性状存在关联，且会朝着同一方向做出响应。