Clarifying and expanding the social complexity hypothesis for communicative complexity

Abstract

Variation in communicative complexity has been conceptually and empirically attributed to social complexity, with animals living in more complex social environments exhibiting more signals and/or more complex signals than animals living in simpler social environments. As compelling as studies highlighting a link between social and communicative variables are, this hypothesis remains challenged by operational problems, contrasting results, and several weaknesses of the associated tests. Specifically, how to best operationalize social and communicative complexity remains debated; alternative hypotheses, such as the role of a species' ecology, morphology, or phylogenetic history, have been neglected; and the actual ways in which variation in signaling is directly affected by social factors remain largely unexplored. In this review, we address these three issues and propose an extension of the Bsocial complexity hypothesis for communicative complexity^that resolves and acknowledges the above factors. We specifically argue for integrating the inherently multimodal nature of communication into a more comprehensive framework and for acknowledging the social context of derived signals and the potential of audience effects. By doing so, we believe it will be possible to generate more accurate predictions about which specific social parameters may be responsible for selection on new or more complex signals, as well as to uncover potential adaptive functions that are not necessarily apparent from studying communication in only one modality. Significance statement Animals exhibit an astonishing diversity of communicative systems, with important variation in both the nature and the number of signals they produce. The roles of phylogenetic history, genetic drift, environmental factors, and sexual selection in shaping interspecific variation in communicative systems have long been acknowledged, whereas social complexity has only more recently emerged as a potential fundamental factor determining signal diversification. While a number of comparative studies support the key prediction of this hypothesis, i.e., that individuals living in more complex social environments exhibit more signals and/or more complex signals, we discuss several gaps in the current state of the art concerning this hypothesis and point out what we believe are neglected perspectives. By emphasizing the importance of the multimodal nature of communicative systems and the social context in which signals are exchanged, we hope to stimulate the development of new tests and specific questions based on this expanded framework.

The Social Role of Vocal Complexity in Striped Dolphins

“…However, estimating social and communicative complexity faces a rising definition issue across taxa. A system is generally considered more complex if it is made up of more parts, has more connections between parts and vary greatly (Peckre et al, 2019). A first approximation to estimating complexity has been based on the group size, on the number of units and their connections (Peckre et al, 2019), on the counting of discrete behaviors and how they are arranged , or on other social features, such as the type of relationships among organisms (Kappeler, 2019).…”

“…A system is generally considered more complex if it is made up of more parts, has more connections between parts and vary greatly (Peckre et al, 2019). A first approximation to estimating complexity has been based on the group size, on the number of units and their connections (Peckre et al, 2019), on the counting of discrete behaviors and how they are arranged , or on other social features, such as the type of relationships among organisms (Kappeler, 2019). Proxies of communicative complexity were identified especially in the vocal repertoire size, in the number of signaling units, in the call rate and its variability, in the combination of the call (simultaneous or in sequence), in their stereotypy or flexibility, and the tonal sound modulation (Peckre et al, 2019).…”

Catalyzing Transitions to Sociality: Ecology Builds on Parental Care

“…Thus, considering adults as core components of definitions of sociality is in accordance with previous definitions and studies. Second, the emphasis on adult sociality in previous definitions of sociality relates to a qualitative difference between species in which adults are solitary compared to those in which adults engage in regular social interactions with other adults, as for example reflected in studies linking social complexity with communicative complexity and cognition (Dunbar, 2009;Kappeler, 2019;Peckre et al, 2019). Third, equating family living with sociality may preclude the integration of mammals and birds in frameworks on the origins of sociality, since virtually all species have post-birth parental care and would accordingly be classified as social.…”

The Vocal Repertoire of Tibetan Macaques (Macaca thibetana) and Congeneric Comparisons

“…Although communication is undoubtedly multimodal in nature, across the modalities the number of distinct signals or signaling units can be used as a representative of communicative complexity (Peckre et al 2019). For studies investigating the modality of acoustic communication, one possible metric of vocal complexity is repertoire size.…”

“…For studies investigating the modality of acoustic communication, one possible metric of vocal complexity is repertoire size. Repertoire size is defined by the number of call types produced by a species or population (Peckre et al 2019). Therefore, repertoire size is a strictly numeric measure unable to provide any information concerning the function or usage of the calls that constitute them.…”