To call or not to call: Persistence of flexible alternative reproductive tactics in a tree cricket

Alternative reproductive tactics (ARTs) are discrete polymorphisms within sexes of a population that help maximise reproductive success. Although flexible ARTs are frequently encountered, theoretical predictions for why flexible ARTs persist over evolutionary time have rarely been empirically tested. We tested the hypothesis that flexible ARTs will persist if they have equal fitness benefits under a range of ecological contexts. Specifically, we investigated how predation risk affects the expression and fitness consequences of two flexible ARTs: acoustic signalling and being silent, expressed by tree cricket <i>Oecanthus henryi</i> males. In large outdoor enclosures, we exposed natural populations of <i>O. henryi</i> to three different abundances of their predator, the green lynx spider <i>Peucetia viridans</i>. Behavioural observations across successive nights revealed that predation risk did not alter the expression levels of the male ARTs. Male crickets demonstrated an equal likelihood of calling or remaining silent on a night. Silent tree crickets spatially associated with callers and acquired 80% of their matings while hearing other callers, suggesting they employ a satellite strategy to improve fitness. Overall, ARTs resulted in similar mating success across differential predation risk, supporting the hypothesis that equal fitness benefits of flexible ARTs under a range of ecological contexts explain their persistence.<br><br>MethodsData collected to address the question of how alternative reproductive tactics persist in a population across variable ecological contexts. Enclosure experiments were performed using 3 different predation treatments that varied in the predator-prey ratio maintained upto 12 nights. Data was collected every night from 1900 hrs to 2130 hrs during which tree crickets are active. Calling and mating was sampled once every 10 minutes (16 times per night). Data is processed at the per individual per night level.

替代性繁殖策略（Alternative Reproductive Tactics，ARTS）是种群内各性别内部存在的离散多态现象，其演化意义在于最大化个体的繁殖成功率。尽管柔性替代性繁殖策略（flexible ARTs）较为常见，但解释其为何能在进化时间尺度上持续存在的理论预测，却鲜有得到实证研究的检验。本研究检验了如下假说：若柔性替代性繁殖策略在一系列生态环境下具备均等的适合度收益，则其能够持续存在于种群之中。具体而言，我们以树蟋属亨利树蟋（Oecanthus henryi）的雄性个体为研究对象，探究了捕食风险如何影响两种柔性替代性繁殖策略的表达及其对应的适合度后果：鸣声信号策略与静默策略。

在大型室外围隔实验中，我们将亨利树蟋的自然种群暴露于三种不同天敌密度的环境中，其天敌为绿色猞猁蛛（Peucetia viridans）。连续多晚的行为观测结果显示，捕食风险并未改变雄性个体所采用的替代性繁殖策略的表达频率。雄蟋在任意一晚选择发出鸣声或保持静默的概率均等。保持静默的树蟋会在空间上聚集于鸣声发出者附近，并在聆听其他个体鸣声的过程中获得了80%的交配机会，这表明它们采用了卫星策略以提升自身适合度。

整体而言，在不同捕食风险条件下，采用替代性繁殖策略所带来的交配成功率并无显著差异，这支持了前述假说：即柔性替代性繁殖策略在一系列生态环境下具备均等的适合度收益，这正是其得以持续存在的原因。

研究方法
本数据集旨在解答“替代性繁殖策略如何在可变生态环境下维持于种群之中”这一科学问题。实验采用室外围隔设置，设置3种捕食处理组，通过调控捕食者与猎物的比例开展实验，实验持续时长最长达12晚。每日19:00至21:30（树蟋的活动时段）开展数据采集。每10分钟对鸣声行为与交配事件进行一次采样（每晚共16次）。所有数据均按逐晚、逐个体的粒度进行整理。