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Animal displays are often limited by the properties of the muscles that generate them. Here, using in situ muscle stimulation, we investigate the twitch properties of the longus colli ventralis (LCv), a primary muscle used protract the head and neck during territorial drumming displays in woodpeckers. Specifically, we test LCv twitch kinetics and endurance in a manner that simulates drum speed (beats s−1) and length (total beats), two signal feature that can evolve independently of each other. We identify a maximum muscle contraction rate that may represent a physiological constraint relevant to drumming speed, but no relevant constraint on the repetition of contractions that might affect drum length. This suggests twitch properties may differentially affect display components. Broadly, our findings highlight how certain display features may freely diversify independent of others due to physiological limits, while pointing to the way complex signals can evolve under partial performance constraints. 

Synopsis Examples of behavioral strategizing exist throughout the animal kingdom, but the quantification and analysis of these complex behavioral patterns remain a challenge. Classic research in this realm often relies either on methods that intentionally simplify complexity or that focus on a subset of abundant behaviors. Unfortunately, these approaches can sometimes eliminate informative details of behavioral strategizing. Here, we demonstrate the utility of a systems-based approach to characterize behavioral patterns in a way that captures the complexity of behavioral strategies and tactics while supporting the generation of relevant, system-specific hypotheses. We accomplish this aim by building upon classic ideas of strategy and tactic, refocusing the theory on behavioral traits, and extending the framework to make sense of patterns of behavior use. In doing so, we outline a more expansive definition of the behavioral tactic, and we provide a methodological roadmap for quantifying multi-behavior and multi-agent tactics. Our goal is to craft a framework for the study of behavioral patterns and encourage researchers to embrace the complexity in their systems. To this end, we provide a case study of territoriality in downy woodpeckers as proof of concept for a network-based systems approach to understanding behavioral strategies. 

Synopsis Sexual selection drives the evolution of a broad diversity of traits, such as the enlarged claws of fiddler crabs, the high-energy behavioral displays of hummingbirds, the bright red plumage of house finches, the elaborated antennae of moths, the wing “snapping” displays of manakins and the calculated calls of túngara frogs. A majority of work in sexual selection has aimed to measure the magnitude of these traits. Yet, we know surprisingly little about the physiology shaping such a diversity of sexually selected behavior and supportive morphology. The energetic properties underlying sexual signals are ultimately fueled by metabolic machinery at multiple scales, from mitochondrial properties and enzymatic activity to hormonal regulation and the modification of muscular and neural tissues. However, different organisms have different physiological constraints and face various ecological selection pressures; thus, selection operates and interacts at multiple scales to shape sexually selected traits and behavior. In this perspective piece, we describe illustrative case studies in different organisms to emphasize that understanding the physiological and energetic mechanisms that shape sexual traits may be critical to understanding their evolution and ramifications with ecological selection. We discuss (1) the way sexual selection shapes multiple integrated components of physiology, behavior, and morphology, (2) the way that sexually selected carotenoid pigments may reflect some aspects of cellular processes, (3) the relationship between sexually selected modalities and energetics, (4) the hormone ecdysone and its role in shaping sex-specific phenotypes in insects, (5) the way varied interaction patterns and social contexts select for signaling strategies that are responsive to social scenes, and (6) the role that sexual selection may have in the exploitation of novel thermal niches. Our major objective is to describe how sexually selected behavior, physiology, and ecology are shaped in diverse organisms so that we may develop a deeper and more integrated understanding of sexual trait evolution and its ecological consequences. 

Synopsis To humans, the diverse array of display behaviors that animals use for communication can easily seem peculiar or bizarre. While ample research delves into the evolutionary principles that shape these signals’ effectiveness, little attention is paid to evolutionary patterning of signal design across taxa, particularly when it comes to the potential convergent evolution of many elaborate behavioral displays. By taking a mechanistic perspective, we explore the physiological and neurobiological mechanisms that likely influence the evolution of communication signals, emphasizing the utilization of pre-existing structures over novel adaptations. Central to this investigation are the concepts of perceptual bias and ritualization that we propose contribute to the convergence of elaborate display designs across species. Perceptual bias explains a phenomenon where pre-existing perceptual systems of receivers, used for innate behaviors such as food and predator recognition, select for certain traits of a communication signal from a signaler. Ritualization occurs when traits with no functional role in communication are co-opted through selection and transformed into a new communicative signal. Importantly, susceptibility for ritualization can be brought about through physiological modifications that occurred early in evolutionary time. In this way, perceptual bias can be a selective force that causes the co-option of non-communicative traits into a new communication signal through ritualization involving pre-existing modifications to physiological systems. If the perceptual bias, non-communicative signal, and physiological modifications that increase susceptibility to ritualization are highly conserved, then we may see the convergent evolution of the new communication signal with unrelated taxa facing similar sensory constraints. We explore this idea here using the foot-flagging frog system as a theoretical case study.