Data from: Collateral damage or a shadow of safety? The effects of signaling heterospecific neighbors on the risks of parasitism and predation

Although males often display from mixed-species aggregations, the influence of nearby heterospecifics on risks associated with sexual signaling has not been previously examined. We tested whether predation and parasitism risks depend on proximity to heterospecific signalers. Using field playback experiments with calls of two species that often display from the same ponds, túngara frogs and hourglass treefrogs, we tested two hypotheses: (1) Calling near heterospecific signalers attractive to eavesdroppers results in increased attention from predatory bats and parasitic midges (Collateral Damage hypothesis); or (2) Calling near heterospecific signalers reduces an individual’s predation and parasitism risks, as eavesdroppers are drawn to the heterospecifics (Shadow of Safety hypothesis). Bat visitation was not affected by calling neighbors. The number of frog-biting midges attracted to hourglass treefrog calls, however, rose threefold when played near túngara calls, supporting the collateral damage hypothesis. We thus show that proximity to heterospecific signalers can drastically alter both the absolute risks of signaling and the relative strengths of pressures from predation and parasitism. Through these mechanisms, interactions between heterospecific guild members are likely to influence the evolution of signaling strategies and the distribution of species at both local and larger scales.尽管雄性个体常集群于混合物种种群中开展展示行为，但此前尚未有研究探讨邻近异种个体对性信号展示相关风险的影响。我们测试了捕食与寄生风险是否取决于与异种信号展示者的空间距离。我们针对两种常共享同一池塘进行展示的蛙类——泡蟾（túngara frogs）与沙漏雨蛙（hourglass treefrogs）的鸣声开展野外回放实验，以此验证两项假说：其一，在对窃听者具有吸引力的异种信号展示者附近鸣叫，会导致捕食性蝙蝠与寄生性蠓的关注增加（附带损害假说，Collateral Damage hypothesis）；其二，在异种信号展示者附近鸣叫可降低个体面临的捕食与寄生风险，因为窃听者会被异种个体所吸引（安全阴影假说，Shadow of Safety hypothesis）。研究结果显示，鸣叫邻居并未对蝙蝠的到访频次产生影响。然而，当沙漏雨蛙的鸣声与泡蟾鸣声同步回放时，被吸引的蛙吸血蠓（frog-biting midges）数量增加了三倍，这一结果支持了附带损害假说。由此我们证明，与异种信号展示者的空间距离可显著改变性信号展示的绝对风险，以及捕食与寄生压力的相对强度。通过上述机制，异种功能群成员间的相互作用可能会影响信号展示策略的演化，以及局部乃至更大尺度下的物种分布格局。