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All animals are equipped with multiple sensory systems (e.g., visual, chemical, acoustic, tactile, electrical, thermal), and signals perceived via these sensory systems facilitate communication. Such communication often involves displays that incorporate more than one signal from more than one sensory modality, resulting in multimodal signaling. The number of empirical and theoretical studies addressing issues of multimodal signaling is ever-increasing and this chapter highlights why crustaceans, as a taxonomic group, are ideal for advancing such studies. Early classifications of multimodal signaling sought to categorize signal components as either redundant or nonredundant, while more recent classifications lay out specific hypotheses relating to multimodal signal function. Two common empirical approaches used in studying multimodal signaling involve signal isolation and signal playback designs—both of which are extremely amenable to crustaceans.
Chemical communication is considered the oldest and most widespread channel for communication, and as such, it is not surprising that numerous crustaceans incorporate chemical signals into multimodal displays. In this chapter, we review multimodal signaling in crustaceans with a focus on those displays that incorporate a chemical component. Specifically, we highlight examples of taxa that combine chemical and hydrodynamic as well as chemical and visual cues. We conclude that despite the plethora of excellent studies examining crustacean responses to isolated signal components, relatively few studies are couched in a communication framework—ultimately limiting the conclusions that can currently be drawn with respect to multimodal signal evolution and function in crustaceans. We suggest that future studies using a hypothesis-testing framework of multimodal signal function could greatly advance our understanding of multimodal signaling in this group. Furthermore, studies involving signal manipulations and correlations between signaler attributes and variation in signal form could be extremely informative. These avenues are wide open for crustacean biologists. We argue that several aspects of crustacean biology (e.g., their abundance, the ease with which they can be manipulated, the ease with which their environment can be manipulated, their morphological diversity, the diversity of habitats in which they live, etc.) make them ideal for studying multimodal signaling.