School of Psychology, University of Sussex, Brighton, United Kingdom.
PLoS One. 2013 Jul 29;8(7):e70279. doi: 10.1371/journal.pone.0070279. Print 2013.
Although the use of formant frequencies in nonhuman animal vocal communication systems has received considerable recent interest, only a few studies have examined the importance of these acoustic cues to body size during intra-sexual competition between males. Here we used playback experiments to present free-ranging male koalas with re-synthesised bellow vocalisations in which the formants were shifted to simulate either a large or a small adult male. We found that male looking responses did not differ according to the size variant condition played back. In contrast, male koalas produced longer bellows and spent more time bellowing when they were presented with playbacks simulating larger rivals. In addition, males were significantly slower to respond to this class of playback stimuli than they were to bellows simulating small males. Our results indicate that male koalas invest more effort into their vocal responses when they are presented with bellows that have lower formants indicative of larger rivals, but also show that males are slower to engage in vocal exchanges with larger males that represent more dangerous rivals. By demonstrating that male koalas use formants to assess rivals during the breeding season we have provided evidence that male-male competition constitutes an important selection pressure for broadcasting and attending to size-related formant information in this species. Further empirical studies should investigate the extent to which the use of formants during intra-sexual competition is widespread throughout mammals.
虽然非人类动物声音交流系统中声道频率的应用最近受到了相当大的关注，但只有少数研究探讨了这些声学线索在雄性个体间的内-性竞争中对体型大小的重要性。在这里，我们使用播放实验向自由放养的雄性考拉播放重新合成的吼叫声，其中声道频率被移频以模拟成年大或小雄性。我们发现，雄性的注视反应并不因播放的声道频率条件而不同。相比之下，当雄性考拉听到模拟体型更大的对手的播放时，它们会发出更长的吼叫声，并且会花更多的时间吼叫。此外，雄性对这种类型的播放刺激的反应速度明显慢于对模拟小体型雄性的播放刺激的反应速度。我们的结果表明，当雄性考拉听到具有较低声道频率指示体型更大对手的吼叫声时，它们会投入更多的努力来做出声音反应，但也表明雄性对代表更危险对手的体型更大的雄性的声音交换反应速度较慢。通过证明雄性考拉在繁殖季节会利用声道频率来评估对手，我们提供了证据表明，雄性间的竞争是对该物种中广播和关注与体型相关的声道频率信息的重要选择压力。进一步的实证研究应该调查在哺乳动物中，声道频率在个体内竞争中的应用广泛程度。
