DOI: 10.5061/dryad.41ns1rnfd
title: Function of a multimodal signal: a multiple hypothesis test using a robot frog

description: 1. Multimodal communication may evolve because different signals may
 convey information about the signaller (content-based selection), increase
 efficacy of signal processing or transmission through the environment
 (efficacy-based selection), or modify the production of a signal or the
 receiver’s response to it (inter-signal interaction selection). 2. To
 understand the function of a multimodal signal (aggressive calls + toe
 flags) emitted by males of the frog Crossodactylus schmidti during
 territorial contests, we tested two hypotheses related to content-based
 selection (quality and redundant signal), one related to efficacy-based
 selection (efficacy backup), and one related to inter-signal interaction
 selection (context). For each hypothesis we derived unique predictions
 based on the biology of the study species. 3. In a natural setting, we
 exposed resident males to a robot frog simulating aggressive calls
 (acoustic stimulus) and toe flags (visual stimulus), combined and in
 isolation, and measured quality-related traits from males and local levels
 of background noise and light intensity. 4. Our results provide support to
 the context hypothesis, as toe flags (the context signal) are insufficient
 to elicit a receiver’s response on their own. However, when toe flags are
 emitted together with aggressive calls, they evoke in the receiver
 qualitatively and quantitatively different responses from that evoked by
 aggressive calls alone. In contrast, we found no evidence that toe flags
 and aggressive calls provide complementary or redundant information about
 male quality, which are key predictions of the quality and redundant
 signal hypotheses, respectively. Finally, the multimodal signal did not
 increase the receiver’s response across natural gradients of light and
 background noise, a key prediction of the efficacy backup hypothesis. 5.
 Toe flags accompanying aggressive calls seem to provide contextual
 information that modify the receiver’s response in territorial contests.
 We suggest this contextual information is increased motivation to escalate
 the contest, and discuss the benefits to the signallers and receivers of
 adding a contextual signal to the aggressive display. Examples of
 context-dependent multimodal signals are rare in the literature, probably
 because most studies focus on single hypotheses assuming content- or
 efficacy-based selection. Our study highlights the importance of
 considering multiple selective pressures when testing multimodal signal
 function. 
description: These are data from a field experiment in which we exposed
 resident males to a robot frog simulating aggressive calls (acoustic
 stimulus) and toe flags (visual stimulus), combined and in isolation, and
 measured quality-related traits from males and local levels of background
 noise and light intensity. The data gathered in the experiment were used
 to test four hypotheses: two related to content-based selection (quality
 and redundant signal), one related to efficacy-based selection (efficacy
 backup), and one related to inter-signal interaction selection (context).
 To test these hypotheses we used different sets of response and predictor
 variables and built linear regression models, generalized mixed-effects
 models (GLMMs), and Cox-Proportional Hazards (CPH) models.
description: There are sixteen dataset files (in csv format) and a ReadMe file
 (in xlsx format). Please refer to the <em>1. ReadMe.xlsx</em>
 file to understand which datasets were used for which models. If you have
 any questions or difficulties in using any file, please contact
 us.