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.

尽管雄性动物常于混合物种聚集群中开展求偶展示，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。本研究旨在探究捕食与寄生风险是否会因与异种信号展示者的空间距离而发生变化。本研究依托两种常共享栖息池塘的物种——泡蟾（túngara frogs）与沙漏树蛙（hourglass treefrogs）的鸣声开展野外回放实验，对两项假说进行验证：（1）当在易被信号窃听者察觉的异种信号展示者附近鸣叫时，会引来更多捕食性蝙蝠与寄生摇蚊的关注（附带伤害假说（Collateral Damage hypothesis））；（2）当在异种信号展示者附近鸣叫时，个体面临的捕食与寄生风险会降低，因为窃听的捕食者与寄生者会被异种个体吸引（安全阴影假说（Shadow of Safety hypothesis））。实验结果显示，邻近鸣叫个体并未对蝙蝠的到访频次产生影响。但当沙漏树蛙的鸣声与泡蟾鸣声同步回放时，吸引到的蛙类吸血摇蚊数量提升了三倍，这一结果支持附带伤害假说。由此可见，与异种信号展示者的空间距离可显著改变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，同资源种团内异种个体间的相互作用，可能会影响信号展示策略的演化，以及物种在局域乃至更大尺度上的分布格局。