January 2005 # Complex signal function: Developing a framework of testable hypotheses Eileen Hebets University of Nebraska - Lincoln, ehebets2@unl.edu Daniel R. Papaj Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ Follow this and additional works at: https://digitalcommons.unl.edu/bioscihebets Part of the Behavior and Ethology Commons Review # Complex signal function: Developing a framework of testable hypotheses Eileen A. Hebets $ ^{*} $ and Daniel R. Papaj $ ^{\dagger} $ $ ^{*} $ Division of Insect Biology, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, USA (Corresponding author) $ ^{\dagger} $ Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA ## Abstract The basic building blocks of communication are signals, assembled in various sequences and combinations, and used in virtually all inter- and intra-specific interactions. While signal evolution has long been a focus of study, there has been a recent resurgence of interest and research in the complexity of animal displays. Much past research on signal evolution has focused on sensory specialists, or on single signals in isolation, but many animal displays involve complex signaling, or the combination of more than one signal or related component, often serially and overlapping, frequently across multiple sensory modalities. Here, we build a framework of functional hypotheses of complex signal evolution based on content-driven (ultimate) and efficacy-driven (proximate) selection pressures (sensu Guilford and Dawkins 1991). We point out key predictions for various hypotheses and discuss different approaches to uncovering complex signal function. We also differentiate a category of hypotheses based on inter-signal interactions. Throughout our review, we hope to make three points: (1) a complex signal is a functional unit upon which selection can act, (2) both content and efficacy-driven selection pressures must be considered when studying the evolution of complex signaling, and (3) individual signals or components do not necessarily contribute to complex signal function independently, but may interact in a functional way. Keywords: multimodal signal, multicomponent signal, communication, signal design, signal interactions ## Introduction Animal signals have received a great deal of attention from scientists across many disciplines, including psychology, neurobiology, ethology, behavioral ecology and evolutionary biology. While this attention has generated a large body of information relating to signal design and evolution, much of the previous research has examined individual signals in isolation and has often focused on sensory specialists (animals that rely predominantly on one sensory modality) [e.g., vision: (Andersson 1982; Bischoff et al. 1985;January 2005 # Complex signal function: Developing a framework of testable hypotheses Eileen Hebets University of Nebraska - Lincoln, ehebets2@unl.edu Daniel R. Papaj Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ Follow this and additional works at: https://digitalcommons.unl.edu/bioscihebets Part of the Behavior and Ethology Commons Review # Complex signal function: Developing a framework of testable hypotheses Eileen A. Hebets $ ^{*} $ and Daniel R. Papaj $ ^{\dagger} $ $ ^{*} $ Division of Insect Biology, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, USA (Corresponding author) $ ^{\dagger} $ Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA ## Abstract The basic building blocks of communication are signals, assembled in various sequences and combinations, and used in virtually all inter- and intra-specific interactions. While signal evolution has long been a focus of study, there has been a recent resurgence of interest and research in the complexity of animal displays. Much past research on signal evolution has focused on sensory specialists, or on single signals in isolation, but many animal displays involve complex signaling, or the combination of more than one signal or related component, often serially and overlapping, frequently across multiple sensory modalities. Here, we build a framework of functional hypotheses of complex signal evolution based on content-driven (ultimate) and efficacy-driven (proximate) selection pressures (sensu Guilford and Dawkins 1991). We point out key predictions for various hypotheses and discuss different approaches to uncovering complex signal function. We also differentiate a category of hypotheses based on inter-signal interactions. Throughout our review, we hope to make three points: (1) a complex signal is a functional unit upon which selection can act, (2) both content and efficacy-driven selection pressures must be considered when studying the evolution of complex signaling, and (3) individual signals or components do not necessarily contribute to complex signal function independently, but may interact in a functional way. Keywords: multimodal signal, multicomponent signal, communication, signal design, signal interactions ## Introduction Animal signals have received a great deal of attention from scientists across many disciplines, including psychology, neurobiology, ethology, behavioral ecology and evolutionary biology. While this attention has generated a large body of information relating to signal design and evolution, much of the previous research has examined individual signals in isolation and has often focused on sensory specialists (animals that rely predominantly on one sensory modality) [e.g., vision: (Andersson 1982; Bischoff et al. 1985;