Abstract
The study of tradeoffs between the attraction of mates and the attraction of eavesdropping predators and parasites has generally focused on a single species of prey, signaling in isolation. In nature however, animals often signal from mixed-species aggregations, where interactions with heterospecific group members may be an important mechanism modulating tradeoffs between sexual and natural selection, and thus driving signal evolution. Although studies have shown that conspecific signalers can influence eavesdropper pressure on mating signals, the effects of signaling heterospecifics on eavesdropper pressure, and on the balance between natural and sexual selection, are likely to be different. Here, we review the role of neighboring signalers in mediating changes in eavesdropper pressure, and present a simple model that explores how selection imposed by eavesdropping enemies varies as a function of a signaling aggregation’s species composition, the attractiveness of aggregation members to eavesdroppers, and the eavesdroppers’ preferences to attack different member types. This approach can be used to model mixed-species signaling aggregations, as well as same-species aggregations, including those with non-signaling individuals, such as satellites or females. We discuss the implications of our model for the evolution of signal structure, signaling behavior, mixed-species aggregations, and community dynamics.
Highlights
While the use of conspicuous sexual signals to attract mates is pervasive across animal taxa, these signals come with a cost (Olson and Owens, 1998; Andersson et al, 2002; Andersson and Simmons, 2006; Bradbury and Vehrencamp, 2011)
The locally adapted signal is the result of a balance between sexual selection imposed by females and natural selection imposed by eavesdropping enemies (Tuttle and Ryan, 1981; Endler, 1983, 1995a; Beckers and Wagner, 2012; Trillo et al, 2013)
We have limited our discussion to one side of the tradeoff between mate-choice and eavesdropper pressure, the model we present here should be adept at predicting the effects of neighboring heterospecific and conspecific signalers on female attention garnered by a focal signaler
Summary
While the use of conspicuous sexual signals to attract mates is pervasive across animal taxa, these signals come with a cost (Olson and Owens, 1998; Andersson et al, 2002; Andersson and Simmons, 2006; Bradbury and Vehrencamp, 2011). Taking a more extreme approach, we can set R = 0, to simulate a system in which type 2 individuals do not attract enemies to the aggregation but may still be attacked Parameterizing the model this way estimates risks to a signaling individual in an aggregation that includes non-signaling “satellite” males (Rowell and Cade, 1993), females (Segami et al, 2016), or callers of a second species whose calls do not attract eavesdroppers at a distance (e.g., because they are imperceptible to the eavesdroppers). Setting P1, the eavesdropper’s expressed preference to attack individuals of type 1 vs 2, to values less than one promotes a shadow of safety effect on type 1, whereas P1 > 1 promotes collateral damage to prey of type 1 if type 2 signalers attract eavesdroppers. Compared to signaling alone, signaling near a heterospecific can confer either a shadow of safety or collateral damage, depending both on the difference in attractiveness between the two species (R) and the difference in the enemies’ expressed preferences once they arrive at the aggregation (P1)
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