Sexual selection in complex choruses : the interplay of male signal variation, social structure, and female mate choice
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Females in many species assess variation among males’ sexual signals when choosing mates. Despite substantial empirical data demonstrating this, the role of mate choice in the evolutionary elaboration of signals among natural systems is not well understood. A major challenge is that mate choice often occurs within complex, dynamic social networks such as leks and choruses, scenarios that combine multiple interacting males, multiattribute signals, and the emergence of spatial relationships, all with the potential to influence females’ decisions. I examined the interplay of males’ social associations and females’ mate choices in túngara frogs (Physalaemus pustulosus), a model system for female mate choice but for whom interactions between male competition and mate choice were unexplored. My aim was to understand ways in which this complexity might influence the relative mating success of advertising males and ultimately, sexual signaling evolution. I conducted field studies and behavioral experiments to deconstruct spatial and neighbor association preferences among males. I found that males are highly tuned to features of their competitors’ calls, exhibiting association biases that roughly paralleled females’ mate preferences, thus supporting a dual function of advertisement calls. I tested classic chorus formation models invoking conspecific association preferences and found that phonotaxis preferences support a central role for highly attractive “hotshot” males in social structuring. I then examined consequences of these interactions for females’ mate preferences. I first tested the importance of signalers’ spatial positions, showing centrality outweighs bout-leading benefits and substantially increases inferior males’ success. I then tested females’ susceptibility to “decoy effects” and demonstrated that mate preferences were similarly reversible by presenting females with an irrelevant third option. Finally, I explored preference patterns among multiattribute signals between males and females; I found that transitivity in females’ preferences broke down among superior signals, suggesting that cyclical competition may play a fundamental role in maintaining signal diversity. Females’ preferences, in contrast with theoretical assumptions, exhibit substantial context-specificity, often paralleled by males’ strategies. These studies highlight the inextricable linkage between male competition and female mate choice and the importance of integration when assessing the opportunity for, and potency of, sexual selection via mate choice.