Abstract
How can deceptive communication signals exist in an evolutionarily stable signalling system? To resolve this age-old honest signalling paradox, researchers must first establish whether deception benefits deceivers. However, while vocal exaggeration is widespread in the animal kingdom and assumably adaptive, its effectiveness in biasing listeners has not been established. Here, we show that human listeners can detect deceptive vocal signals produced by vocalisers who volitionally shift their voice frequencies to exaggerate or attenuate their perceived size. Listeners can also judge the relative heights of cheaters, whose deceptive signals retain reliable acoustic cues to interindividual height. Importantly, although vocal deception biases listeners’ absolute height judgments, listeners recalibrate their height assessments for vocalisers they correctly and concurrently identify as deceptive, particularly men judging men. Thus, while size exaggeration can fool listeners, benefiting the deceiver, its detection can reduce bias and mitigate costs for listeners, underscoring an unremitting arms-race between signallers and receivers in animal communication.
Highlights
How can deceptive communication signals exist in an evolutionarily stable signalling system? To resolve this age-old honest signalling paradox, researchers must first establish whether deception benefits deceivers
While earlier theories saw animal communication as a cooperative exchange of information[10], the production of animal signals during communication between unrelated individuals is predominantly regarded as a selfish behaviour[2,10], whereby signallers attempt to manipulate the responses of receivers
We combine acoustic analysis of vocal signals, produced by men and women attempting to sound physically larger or smaller, with a series of psychoacoustic playback experiments conducted on a representative sample of 200 human listeners. Their task was to judge the heights of these vocalisers, and to attempt to discriminate among honest, exaggerated, or attenuated vocal signals of body size. Using this innovative approach we address long-standing questions about the evolution of deceptive signals in animal communication: Does deceptive size signalling retain an element of honesty? Can listeners detect size deception and do they correct for it when judging height? If so, does it still benefit vocalisers to exaggerate their perceived size? Are there sex differences, as predicted by sexual selection[11,25], in the production and perception of exaggerated signals? Our results offer a unique lens into the conflict between deceivers and receivers, showing that while deceptive vocal signals can effectively bias listeners’ judgements of body size, such signals remain constrained and retain some reliable information
Summary
How can deceptive communication signals exist in an evolutionarily stable signalling system? To resolve this age-old honest signalling paradox, researchers must first establish whether deception benefits deceivers. Selection operates on receivers to evade deception, for example by leading them to ignore deceptive signals or to recalibrate their responses Both individuals in a dyadic exchange are expected to behave in ways that maximise their own fitness[2], giving rise to an evolutionary arms race that is most apparent when interests diverge (e.g., mate choice) or are entirely opposed (e.g., resource contests)[11]. Researchers can directly measure the effects of this deception on human receivers using controlled psychoacoustic experiments, offering a full picture of the signaller–receiver communication chain (Fig. 1) We apply this paradigm to study an ecologically relevant vocal signalling system observed across the animal kingdom—vocal communication of body size
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