Function of a multimodal signal: A multiple hypothesis test using a robot frog.

Area of Science:

• Animal Behavior
• Evolutionary Biology
• Bioacoustics
• Animal Communication

Background:

• Multimodal communication signals can evolve through content-based, efficacy-based, or inter-signal interaction selection.
• Understanding the function of combined signals, like aggressive calls and toe flags in frogs, is crucial for evolutionary insights.

Purpose of the Study:

• To investigate the function of multimodal signals (aggressive calls + toe flags) in territorial contests of the frog Crossodactylus schmidti.
• To test hypotheses related to content-based (quality, redundant signal), efficacy-based (efficacy backup), and inter-signal interaction (context) selection.

Main Methods:

• Exposed resident male frogs to robot simulations of aggressive calls and toe flags, individually and combined.
• Measured male quality traits and environmental factors (noise, light intensity).
• Derived and tested unique predictions for each selective hypothesis.

Main Results:

• Toe flags alone did not elicit a receiver response, supporting the context hypothesis.
• Combined signals evoked different responses than calls alone, suggesting context-dependent modification.
• No evidence found for quality or redundant signal hypotheses.
• No support for efficacy backup hypothesis across varying environmental conditions.

Conclusions:

• Toe flags accompanying aggressive calls provide contextual information that modifies receiver response and potentially increases contest escalation.
• Highlights the importance of considering multiple selective pressures, especially inter-signal interaction, in multimodal signal evolution.
• Context-dependent multimodal signals are rare, underscoring the need for broader hypothesis testing in signal research.