Sexually antagonistic coevolution of the male nuptial gift and female feeding behaviour in decorated crickets

The evolution of nuptial gifts has traditionally been considered a harmonious affair, providing benefits to both mating partners. There is growing evidence, however, that receiving a nuptial gift can be actively detrimental to the female. In decorated crickets (Gryllodes sigillatus), males produce a gelatinous spermatophylax that enhances sperm transfer but provides little nutritional benefit and hinders female post-copulatory mate choice. Here, we examine the sexually antagonistic coevolution of the spermatophylax and the female feeding response to this gift in G. sigillatus maintained in experimental populations with either a male-biased or female-biased adult sex ratio. After 25 generations, males evolving in male-biased populations produced heavier spermatophylaxes with a more manipulative combination of free amino acids than those evolving in female-biased populations. Moreover, when the spermatophylax originated from the same selection regime, females evolving in male-biased populations always had shorter feeding durations than those evolving in female-biased populations indicating the evolution of greater resistance. Across populations, female feeding duration increased with the mass and manipulative combination of free amino acids in the spermatophylax suggesting sexually antagonistic coevolution. Collectively, our work demonstrates a key role for interlocus sexual conflict and sexually antagonistic coevolution in the mating system of G. sigillatus.

Methods
We manipulated the intensity of interlocus sexual conflict in replicate experimental population by manipulating the adult sex ratio to be either male -biased (increased conflict) or female-biased (reduced conflict). This was done for 25 generations of evolution. We then measured the manipulative properties of the male nuptial gift (the spermatophylax) in these populations (spermatophylax dry mass and amino acid composition), as well as female feeding duration on these gifts (as a measure of resistance to manipulation). We present the raw data and population mean data for these traits. Spermatophylax dry mass was measured using an electronic balance. Spermatophylax amino acid composition was measured using GC-MS. Female feeding behaviour was measured in behavioural assays.

传统上，求偶礼物（nuptial gift）的演化通常被视为一种和谐过程，可为交配双方带来收益。然而，越来越多的研究证据表明，接收求偶礼物可能会主动对雌性个体造成不利影响。在装饰蟋蟀（Gryllodes sigillatus）中，雄性会分泌一种凝胶状的精护垫（spermatophylax），该结构可促进精子转移，但几乎无营养益处，且会阻碍雌性交配后的配偶选择。本研究针对该物种的精护垫与雌性对该礼物的取食反应之间的性拮抗共演化展开探究，实验种群设置为雄性偏性成年性别比与雌性偏性成年性别比两组。经过25代演化后，相较于在雌性偏性种群中演化的雄性，在雄性偏性种群中演化的雄性所产生的精护垫更重，且其游离氨基酸组合更具操控性。此外，当精护垫源自相同的选择体系时，在雄性偏性种群中演化的雌性，其取食时长始终短于在雌性偏性种群中演化的雌性，这表明前者演化出了更强的抵抗能力。跨种群分析显示，雌性取食时长随精护垫的重量及其游离氨基酸操控性组合的提升而增加，这印证了性拮抗共演化的存在。综上，本研究证实了基因座间性冲突与性拮抗共演化在装饰蟋蟀的交配系统中发挥着关键作用。

方法
我们通过调整成年性别比，设置雄性偏性（性冲突加剧）与雌性偏性（性冲突减弱）两组重复实验种群，以此操控基因座间性冲突的强度。该处理持续了25代演化周期。随后，我们测定了这些种群中雄性求偶礼物（精护垫）的操控相关特性（包括精护垫干重与氨基酸组成），以及雌性对该礼物的取食时长（以此作为抵抗操控能力的衡量指标）。本文附带了这些性状的原始数据与种群均值数据。精护垫干重通过电子天平测定。精护垫氨基酸组成通过气相色谱-质谱联用仪（GC-MS）测定。雌性取食行为通过行为学实验测定。