Abstract
BackgroundMammal vocal parameters such as fundamental frequency (or pitch; fo) and formant dispersion often provide information about quality traits of the producer (e.g. dominance and body size), suggesting that they are sexually selected. However, little experimental evidence exists demonstrating the importance of these cues in intrasexual competition, particularly fo. Male Fallow deer (bucks) produce an extremely low pitched groan. Bucks have a descended larynx and generate fo well below what is expected for animals of their size. Groan parameters are linked to caller dominance, body size and condition, suggesting that groans are the product of sexual selection. Using a playback experiment, we presented bucks with groans that had been manipulated to alter vocal cues to these male characteristics and compared the response to the same, non-modified (natural) groans.ResultsWe experimentally examined the ability of bucks to utilise putative cues to dominance (fo), body size (formant frequencies) and condition (groan duration), when assessing competitors. We found that bucks treated groans with lowered fo (more dominant), and lowered formant frequencies (larger caller) as more threatening. By contrast, groans with raised formant frequencies (smaller caller), and shorter durations (more fatigued caller) were treated as less threatening.ConclusionsOur results indicate that intrasexual selection is driving groans to concurrently convey caller dominance, body size and condition. They represent the first experimental demonstration of the importance of fo in male competition in non-human mammals, and show that bucks have advanced perception abilities that allow them to extract information based on relatively small changes in key parameters.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0429-7) contains supplementary material, which is available to authorized users.
Highlights
Mammal vocal parameters such as fundamental frequency and formant dispersion often provide information about quality traits of the producer, suggesting that they are sexually selected
The fundamental frequency or pitch of male voices negatively correlates with levels of circulating testosterone [8,9,10,11], while taller men typically speak with lower formant dispersion [10, 12,13,14,15]
Because fallow buck groans appear to be the product of strong sexual selection for low fo, low formant dispersion, long duration and high groaning rate [4, 5, 31, 33, 35, 37, 38], we experimentally investigated whether bucks use acoustic cues to dominance, size and condition to assess competitors
Summary
Mammal vocal parameters such as fundamental frequency (or pitch; fo) and formant dispersion often provide information about quality traits of the producer (e.g. dominance and body size), suggesting that they are sexually selected. The fundamental frequency or pitch (fo) of male voices negatively correlates with levels of circulating testosterone [8,9,10,11], while taller men typically speak with lower formant dispersion [10, 12,13,14,15]. Fo is a good indicator of dominance in fallow bucks [4, 5] and crested macaques (Macaca nigra) [28] Despite this correlational evidence, to our knowledge, no study has successfully demonstrated the importance of fo in male intrasexual competition in a nonhuman mammal using playback experiments
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