Risks of multimodal signaling: bat predators attend to dynamic motion in frog sexual displays

Abstract

Many sexual displays contain multiple components that are received through a variety of sensory modalities. Primary and secondary signal components can interact to induce novel receiver responses and become targets of sexual selection as complex signals. However, predators can also use these complex signals for prey assessment, which may limit the evolution of elaborate sexual signals. We tested whether a multimodal sexual display of the male túngara frog (Physalaemus pustulosus) increases predation risk from the fringelipped bat (Trachops cirrhosus) when compared with a unimodal display. We gave bats a choice to attack one of two frog models: a model with a vocal sac moving in synchrony with a mating call (multisensory cue), or a control model with the call but no vocal sac movement (unimodal cue). Bats preferred to attack the model associated with the multimodal display. Furthermore, we determined that bats perceive the vocal sac using echolocation rather than visual cues. Our data illustrate the costs associated with multimodal signaling and that sexual and natural selection pressures on the same trait are not always mediated through the same sensory modalities. These data are important when considering the role of environmental fluctuations on signal evolution as different sensory modalities will be differentially affected.

Choosing a mate in a high predation environment: Female preference in the fiddler crab Uca terpsichores

“…In brush‐legged wolf spiders, courting males are significantly more predated by frogs when displaying pronounced decorative traits (Clark, Zeeff, Karson, Roberts, & Uetz, ). The fringe‐lipped bat is more attracted by the multicomponent sexual signal from túngara frogs, call and song sac movement, than by the male's advertisement call alone (Halfwerk et al., ). Conspicuous signals could be selected as an indication of honesty through the handicap principle (Mowles & Ord, ; Zahavi, ) as higher courtship efforts result in elevated predation costs for signallers (Roberts, Taylor, & Uetz, ).…”

Multimodal cues improve prey localization under complex environmental conditions

“…Model parameter estimates, standard errors and t-values are provided for fixed effects that were retained in the minimal adequate models (calculated using REML). test set-up and that they can rely on multiple returning echoes from the moving vocal sac for prey assessment [26]. Spending more time on the perch when prey are calling allows bats to gather more echolocation information, and thereby improve their perceptual scene analyses [42,43].…”

“…The platform was placed 10 cm above the ground, on top of a speaker (Peerless; 2.5 inch). The set-up contained a catheter (Rü sch latex 30 cc balloon) in front of the model (which mimicked the frog's vocal sac) as well as a catheter underneath the Plexiglas platform that functioned as a control for the sound produced by the inflation of the catheter (see [26] for details about this control condition). This control ensured that the bats' behaviour was not influenced by different sound production between the two experimental stimulus presentations.…”

“…We drilled holes in the Plexiglas below the models to allow for sound transfer of the speaker and control catheter. Both catheters were connected with a 3 m tube to a custom-made gas-relay station driving the inflation and deflation of the system in synchrony with the call (see [26] for detailed description of the robotic set-up).…”

“…The fringe-lipped bat (Trachops cirrhosus) is a predator that primarily relies on acoustic mating signals of frogs and insects to find its prey [25][26][27][28]. Once a prey sound is detected and approached, bats can use echolocation for further localization and chemical cues to assess prey palatability [25].…”