Vinicius Matheus Caldart, Maurício Beux dos Santos, Glauco Machado

1. Mate choice in females is influenced by intrinsic and extrinsic factors, including signal conspicuity, receiver body condition, and environmental properties. These factors interact in complex ways to modulate the choice of mates. Multimodal signals are more conspicuous than their unimodal components and therefore should elicit a stronger response. However, variations in female body condition and background noise can modify their responsiveness to signals of varying conspicuity.
2. Males of the diurnal stream-dwelling frog Crossodactylus schmidti emit unimodal e multimodal signals under variable noisy conditions, and the females vary greatly in body condition. We tested hypotheses on how signal type (unimodal or multimodal) interacts with female body condition and background noise to modify female responses. In a field experiment using a male mimicking robot frog, females were randomly exposed to acoustic-only (call, A), visual-only (toe flag, V), and multimodal (call + toe flag, M) stimuli, while female body condition was estimated and data on background noise was taken.
3. Females exhibited three types of response: emission of acoustic signals, emission of visual signals, and movements toward the robot. All stimuli elicited responses, with a higher percentage of females responding to M, an intermediate percentage to A, and a lower percentage to V. Females in better physical condition exhibited a decreased probability of acoustic response, emitted signals at a lower rate, and took more time to emit signals or move towards the robot. With increasing noise, females exhibited decreased probability of responding with a visual signal to both the visual and multimodal stimuli, but when stimulated by the acoustic stimulus, females exhibited a higher probability of visual response as the noise increased. Finally, females at noisier sites also emitted signals at a higher rate but took more time to respond with visual signals and to move towards the robot.
4. The results suggest that the multimodal signal had the highest female responsiveness. The negative effect of body condition and the positive effect of background noise on the response occurred because better-conditioned females were more selective in their choice, while noisy environments negatively interfered with mate assessment. Our study highlights the complex and context-dependent nature of female mate choice, influenced by signal conspicuity, female body condition, and noise levels.