De Gregorio Chiara, Valente Daria, Cristiano Walter, Carugati Filippo, Prealta Michela, Ferrario Valeria, Raimondi Teresa, Torti Valeria, Ratsimbazafy Jonah, Giacoma Cristina, Gamba Marco
Department of Life Sciences and Systems Biology, University of Torino, Torino 10123, Italy.
Department of Psychology, University of Warwick, Coventry CV4 7A, UK.
Philos Trans R Soc Lond B Biol Sci. 2025 Apr 3;380(1923):20240021. doi: 10.1098/rstb.2024.0021.
Animal vocalizations contain a varying degree of nonlinear phenomena (NLP) caused by irregular or chaotic vocal organ dynamics. Several hypotheses have been proposed to explain NLP presence, from unintentional by-products of poor vocal technique to having a functional communicative role. We aimed to disentangle the role of sex, age and physiological constraints in the occurrence of NLP in the songs of the lemur , which are complex harmonic vocal displays organized in phrases. Age and sex affected the presence and type of NLP in songs. In particular, the proportion of the phenomena considered decreased with age, except for subharmonics. Subharmonics potentially mediate the perception of lower pitch, making signallers appear larger. Subharmonics and frequency jumps occurred in lower-pitched notes than regular units, while chaos and sidebands occurred in higher-pitched units. This suggests that different types of NLP can be associated with different vocal constraints. Finally, indris might present short-term vocal fatigue, with units occurring in the last position of a phrase having the highest probability of containing NLP. The presence of NLP in indris might result from proximate causes, such as physiological constraints, and ultimate causes, such as evolutionary pressures, which shaped the communicative role of NLP.This article is part of the theme issue 'Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions'.
动物发声包含由不规则或混乱的发声器官动态引起的不同程度的非线性现象（NLP）。已经提出了几种假说来解释NLP的存在，从发声技巧不佳的无意副产品到具有功能性的交流作用。我们旨在厘清性别、年龄和生理限制在狐猴歌声中NLP出现过程中的作用，狐猴的歌声是由短语组成的复杂和声发声展示。年龄和性别影响了歌声中NLP的存在和类型。特别是，除了次谐波外，所考虑的现象比例随年龄增长而降低。次谐波可能介导对较低音高的感知，使信号发出者显得更大。次谐波和频率跳跃出现在比常规单元音调更低的音符中，而混沌和边带出现在音调更高的单元中。这表明不同类型的NLP可能与不同的发声限制相关。最后，大狐猴可能会出现短期发声疲劳，短语最后位置出现的单元包含NLP的可能性最高。大狐猴中NLP的存在可能源于近端原因，如生理限制，以及最终原因，如进化压力，这些因素塑造了NLP的交流作用。本文是主题为“脊椎动物发声中的非线性现象：机制与交流功能”的一部分。
