Abstract
BackgroundUnderstanding the diversity of animal signals requires knowledge of factors which may influence the different stages of communication, from the production of a signal by the sender up to the detection, identification and final decision-making in the receiver. Yet, many studies on signalling systems focus exclusively on the sender, and often ignore the receiver side and the ecological conditions under which signals evolve.Methodology/Principal FindingsWe study a neotropical katydid which uses airborne sound for long distance communication, but also an alternative form of private signalling through substrate vibration. We quantified the strength of predation by bats which eavesdrop on the airborne sound signal, by analysing insect remains at roosts of a bat family. Males do not arbitrarily use one or the other channel for communication, but spend more time with private signalling under full moon conditions, when the nocturnal rainforest favours predation by visually hunting predators. Measurements of metabolic CO2-production rate indicate that the energy necessary for signalling increases 3-fold in full moon nights when private signalling is favoured. The background noise level for the airborne sound channel can amount to 70 dB SPL, whereas it is low in the vibration channel in the low frequency range of the vibration signal. The active space of the airborne sound signal varies between 22 and 35 meters, contrasting with about 4 meters with the vibration signal transmitted on the insect's favourite roost plant. Signal perception was studied using neurophysiological methods under outdoor conditions, which is more reliable for the private mode of communication.Conclusions/SignificanceOur results demonstrate the complex effects of ecological conditions, such as predation, nocturnal ambient light levels, and masking noise levels on the performance of receivers in detecting mating signals, and that the net advantage or disadvantage of a mode of communication strongly depends on these conditions.
Highlights
Airborne sound as a communication channel is used in a variety of taxa, and has been well studied in birds, frogs, and insects
We describe the changes in the mode of communication in a katydid with the lunar cycle, and the consequences for signal detection
In our survey on the site fidelity of D. gigliotosi for the bromelid A. magdalena we regularly found some plants occupied by spiders of the genus Cupiennius, which prey upon katydids [39]
Summary
Airborne sound as a communication channel is used in a variety of taxa, and has been well studied in birds, frogs, and insects (reviews in [1,2]). Due to the conspicuousness of the songs, they do not remain private to the intended receivers, but are subject to eavesdropping by unintended receivers, with potentially dramatic consequences for the signallers’ survival if the eavesdropper is a parasitoid or a predator [3,4,5,6,7]. The result of this strong selection pressure often is facultative predator avoidance behaviour, such as reduced activity and feeding, or reduced or modified communication. Many studies on signalling systems focus exclusively on the sender, and often ignore the receiver side and the ecological conditions under which signals evolve
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