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.

尽管雄性个体常于多物种混合的聚集群中开展求偶炫耀，但此前尚未有研究探讨邻近异种个体对性信号展示相关生存风险的影响。我们针对两种常于同一池塘中开展求偶炫耀的蛙类——泡蟾（túngara frogs）与沙漏树蛙（hourglass treefrogs）的鸣唱开展野外鸣唱回放实验，以此检验两个假说：（1）若异种信号展示者能够吸引窃听型天敌，则在其附近鸣唱会提升捕食性蝙蝠与寄生蠓的关注程度（附带损害假说（Collateral Damage hypothesis））；或（2）若窃听型天敌会被异种个体吸引，则在其附近鸣唱可降低个体面临的捕食与寄生风险（安全阴影假说（Shadow of Safety hypothesis））。实验结果显示，捕食性蝙蝠的到访频次并未受邻近鸣唱个体的影响。然而，当沙漏树蛙的鸣唱邻近泡蟾鸣唱播放时，被其吸引的噬蛙蠓（frog-biting midges）数量增长了三倍，这一结果支持附带损害假说。本研究表明，与异种信号展示者的空间邻近关系可大幅改变鸣唱展示的绝对风险，以及捕食与寄生压力的相对强度。通过上述作用机制，异种功能群成员间的相互作用或可影响信号展示策略的演化，以及局域乃至更大空间尺度下的物种分布格局。