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被归因于社会的复杂性，生活在更复杂的社会中的物种表现出更复杂的信号。然而，如何最好地量化社交和交流的复杂性是一个持续争论的话题。此外，尽管强调社会和交流复杂性之间的联系的研究很有说服力，但在大多数研究中，只考虑了一种交流方式，而其他假设，如物种生态、形态或系统发育地位在塑造交流多样性中的作用，仍在很大程度上未被探索。在这项研究中，我们将比较两个密切相关的狐猴物种，Eulemur rufirons和E.mongoz，它们在形态和生态上相似，但表现出不同的社会制度。Eulemur rufirons生活在具有高度社会容忍度的多雄性多雌性群体中，而E.mongoz是成对生活的，雌性比雄性更占优势。这两个物种的声音都很明显，会产生各种嗅觉信号，但也会使用视觉信号进行交流。具体地说，我们旨在通过考虑社会和交际复杂性的不同衡量标准来比较这两个物种之间的交际系统，包括声音、嗅觉和视觉以及信号的多模式使用。我们将通过使用不同的代理来描述两个物种之间以及两个物种的不同群体之间的社会结构差异，并将其与交流系统的差异联系起来，从而使社会复杂性具有可操作性。我们建议扩展交际复杂性的社会复杂性假设，同时考虑社会语境的变化，即受众，作为社会复杂性的一个潜在参数，促进信号产生和使用的灵活性。因此，我们的研究可能有助于为检验受众效应和研究交际灵活性的主要驱动因素提供一个新的理论框架。

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.