Communicative complexity in primates: sociality and multimodal communication in two species of lemurs

动物不仅在类型上表现出惊人的变化，而且在它们产生的信号数量上也表现出惊人的变化。最近，信号多样性的变化在概念上和经验上归因于社会复杂性，生活在更复杂社会中的物种表现出更复杂的信号。然而，如何最好地量化社会和沟通的复杂性是一个持续争论的话题。此外，尽管研究强调了社会和交际复杂性之间的联系，但在大多数研究中，只考虑了一种交际方式，而其他假设，如物种生态学、形态或系统发育位置在塑造交际多样性中的作用，在很大程度上仍未被探索。在本研究中，我们将比较两种近亲狐猴的交流系统，即狐猴和蒙古狐猴，它们在形态和生态上相似，但表现出不同的社会制度。乌拉穆尔生活在多雄性多雌性的群体中，具有高度的社会容忍度，而蒙古乌拉穆尔则是成对生活，雌性比雄性占优势。这两个物种都有明显的声音，产生各种嗅觉信号，但也使用视觉信号进行交流。具体来说，我们的目的是通过考虑不同的社会和沟通复杂性来比较两个物种之间的交流系统，包括声学，嗅觉和视觉以及信号的多模态使用。我们将通过使用各种代理来描述两种物种之间以及两种物种不同群体之间社会结构的变化，并将其与交流系统的变化联系起来，从而实现社会复杂性的操作性。我们建议扩展交际复杂性的社会复杂性假设，同时考虑社会背景的变化，即受众，作为促进信号产生和使用灵活性的社会复杂性的潜在参数。因此，本研究为检验受众效应和研究交际灵活性的主要驱动因素提供了一个新的理论框架。

Animals exhibit stunning variation not only in the type, but also in the number of signals they produce. Recently, variation in signal diversity has been conceptually and empirically attributed to social complexity, with species living in more complex societies exhibiting more complex signals. However, how to best quantify social and communicative complexity is a topic of ongoing debated. Moreover, as compelling as studies highlighting a link between social and communicative complexity are, in most studies only one communicative modality has been considered, and alternative hypotheses, such as the role of a species ecology, morphology or phylogenetic position in shaping communicative diversity, remain largely unexplored. In this study, we will compare the communicative systems of two closely related lemur species, Eulemur rufifrons and E. mongoz, that are similar in morphology and ecology, but which exhibit different social systems. Eulemur rufifrons lives in multi-male multi-female groups characterized by high levels of social tolerance, whereas E. mongoz is pair-living, with females being dominant over males. Both species are conspicuously vocal, produce a variety of olfactory signals, but also use visual signals for communication. Specifically, we aim at comparing the communicative systems, including acoustic, olfactory and visual as well as the multimodal usage of signals, between the two species by taking different measures of social as well as communicative complexity into account. We will operationalize social complexity by using various proxies to characterize variation in social structure between the two species, but also among different groups of both species, and relate it to variation in the communicative system. We propose to extend the social-complexity hypothesis for communicative complexity by also considering variation in social contexts, i.e. the audience, as a potential parameter of social complexity promoting flexibility in signal production and usage. Hence, our study may contribute to a new theoretical framework for testing the audience effect and to study the main drivers of communicative flexibility.