Sexual selection and adaptive function of gibbon vocalizations: Do testosterone-driven males sing their own praises, but pay a cost in immuno competence?

在哺乳动物中，复杂的发声是相当罕见的。然而，最著名的例外之一是长臂猿(Hylobatidae)，这是东南亚的一种小而灵活的类人猿。在这个灵长类动物群体中，两性都会唱歌，但当雌性发出刻板的歌曲时，雄性则会精心制作独唱，其功能仍然是个谜。长臂猿歌曲中的性别差异表明，它可能是通过为雄性提供最精致的歌曲而进化出来的，比它们的竞争对手具有繁殖优势。因此，这项研究的目的是研究性选择是否驱动了野生白手长臂猿(Hylobates Lar)种群中雄性发声的进化。我们将要调查的种群呈现了大量习惯性动物的独特性，它们既生活在社会一夫一妻制的群体中，也生活在一夫多妻的群体中。我们将调查男性发声是否和在多大程度上不同于男性，以及它们是否可能作为性信号发挥作用。特别是，通过非侵入性的方法，我们将(I)测试雄性雄性的睾丸素水平，并研究它们的生理特征是否会导致雄性歌曲的声音结构发生变化；通过测量长臂猿的寄生虫负载，我们将(Ii)评估男性歌唱是否有助于宣传身体状况；以及(Iii)我们将使用遗传亲子分析方法，调查“歌曲质量”的变化是否与雄性繁殖成功率的变化有关。

Among mammals, elaborate vocalizations are quite rare. However, one of the best known exceptions are the gibbons (Hylobatidae), the small and agile apes of South-East Asia. In this primate group, both sexes sing but while females utter stereotyped songs, males sing elaborate solos, the function of which still remains enigmatic. Sex differences in gibbons’ songs suggest that it may have evolved by providing males with the most elaborate song with a reproductive advantage over their rivals. Thus, the aim of this study is to investigate whether sexual selection has driven the evolution of male vocalizations in a population of wild white-handed gibbons (Hylobates lar). The population we will investigate presents the uniqueness of a very large number of habituated animals which live in both socially monogamous and polyandrous group. We will investigate whether and to what extent male vocalizations vary between males and whether they may function as sexual signal. In particular, by using non-invasive methodologies, We will (i) test males for testosterone levels and examine whether their physiological characteristics may drive variation in the acoustic structure of male song; by measuring gibbons’ parasite load, we will (ii) assess whether male singing serves to advertise physical condition; and (iii) we investigate, using genetic paternity analysis, whether variation in ‘song quality’ is related to variation in male reproductive success.