Data from: Sacrificial males: the potential role of copulation and predation in contributing to copepod sex-skewed ratios

Predation is thought to play a selective role in the emergence of behavioural traits in prey. Differences in behaviour between prey demographics may, therefore, be driven by predation with select components of the population being less vulnerable to predators. While under controlled conditions prey demography has been shown to have consequences for predation success, investigations linking these implications to natural prey population demographics are scarce. Here we assess predator-prey dynamics between notonectid predators (backswimmers) and Lovenula raynerae (Copepoda), key faunal groups in temperate ephemeral pond ecosystems. Using a combination of field and experimental approaches we test for the development and mechanism of predation-induced sex-skewed ratios. A natural population of L. raynerae was tracked over time in relation to their predator (notonectid) and prey (Cladocera) numbers. In the laboratory, L. raynerae sex ratios were also assessed over time but in the absence of predation pressure. Predation success and prey performance experiments evaluating differences between L. raynerae male, female, gravid female and copulating pairs exposed to notonectid predation were then examined. Under natural conditions, a female dominated copepod population developed over time and was correlated to predation pressure, while under predator-free conditions non sex-skewed prey population demographics persisted. Predator-prey laboratory trials showed no difference in vulnerability and escape performance for male, female and gravid female copepods, but pairs in copula were significantly more vulnerable to predation. This vulnerability was not shared by both sexes, with only female copepods ultimately escaping from successful predation on a mating pair. These results suggest that contact periods during copula may contribute to the development of sex-skewed copepod ratios over time in ecosystems dominated by hexapod predators. This is discussed within the context of vertebrate and invertebrate predation and how these dissimilar types of predation are likely to have acted as selective pressures for copepod mating systems.捕食被认为在猎物行为性状的演化中发挥选择作用。因此，猎物种群不同类群间的行为差异可能由捕食压力驱动，即种群中特定组分对捕食者的抵御能力更弱。尽管在可控条件下，猎物种群统计特征已被证实会影响捕食成功率，但将这些影响与自然猎物种群统计特征联系起来的研究仍较为匮乏。本研究针对温带临时池塘生态系统中的关键动物类群——仰泳蝽科捕食者（backswimmers）与雷氏罗文猛水蚤（Lovenula raynerae，Copepoda）之间的捕食者-猎物动态展开评估。本研究结合野外调查与实验手段，探究捕食诱导的性比偏斜现象的形成过程与潜在机制。研究人员对雷氏罗文猛水蚤的自然种群进行长期跟踪，同步记录其捕食者（仰泳蝽科）与猎物（枝角类（Cladocera））的种群数量。在实验室环境中，本研究同样对雷氏罗文猛水蚤的性比进行长期监测，但此时捕食压力缺失。随后，本研究开展了捕食成功率与猎物行为表现实验，评估暴露于仰泳蝽捕食压力下的雷氏罗文猛水蚤雄体、雌体、怀卵雌体以及交配成对个体间的差异。在自然条件下，桡足类种群的雌性占比随时间推移逐渐升高，且与捕食压力呈显著相关；而在无捕食者的环境中，猎物种群统计特征始终未出现性比偏斜。捕食者-猎物室内实验结果显示，雄体、雌体与怀卵雌体桡足类的被捕食风险与逃逸能力并无显著差异，但处于交配状态的成对个体被捕食风险显著更高。这种被捕食风险并非两性均等：在交配成对个体的捕食事件中，仅雌性桡足类最终得以逃脱。上述结果表明，交配过程中的接触时长可能是导致以六足类捕食者为主导的生态系统中，桡足类种群性比随时间偏斜的重要因素。本研究将在脊椎动物与无脊椎动物捕食的研究框架下，探讨这两类不同的捕食模式如何作为选择压力，对桡足类的交配系统演化产生影响。