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，精细的发声是相当罕见的。然而，最著名的例外之一是长臂猿（长臂猿科），一种生活在东南亚的小而敏捷的类人猿。在这种灵长类动物群体中，两性都唱歌，但雌性唱的是刻板的歌曲，雄性唱的是精心制作的独唱，其功能至今仍是个谜。长臂猿鸣叫的性别差异表明，它可能是通过向雄性提供最精致的鸣叫来进化的，以获得比竞争对手更大的繁殖优势。因此，本研究的目的是调查性选择是否推动了野生白掌长臂猿（Hylobates lar）种群雄性发声的进化。我们将调查的种群呈现出大量习惯动物的独特性，这些动物既生活在社会一夫一妻制中，也生活在多夫制群体中。我们将调查雄性之间的发声是否以及在多大程度上存在差异，以及它们是否可以作为性信号。特别是，通过使用非侵入性方法，我们将(i)测试雄性的睾丸激素水平，并检查它们的生理特征是否可能驱动雄性歌曲声学结构的变化；通过测量长臂猿的寄生虫负荷，我们将（ii）评估雄性鸣叫是否有助于宣传身体状况；（iii）我们使用遗传父权分析来调查“歌声质量”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.