Honey bees respond to multimodal stimuli following the principle of inverse effectiveness.

Multisensory integration is assumed to entail benefits for receivers across multiple ecological contexts. However, signal integration effectiveness is constrained by features of the spatiotemporal and intensity domains. How sensory modalities are integrated during tasks facilitated by learning and memory, such as pollination, remains unsolved. Honey bees use olfactory and visual cues during foraging, making them a good model to study the use of multimodal signals. Here, we examined the effect of stimulus intensity on both learning and memory performance of bees trained using unimodal or bimodal stimuli. We measured the performance and the latency response across planned discrete levels of stimulus intensity. We employed the conditioning of the proboscis extension response protocol in honey bees using an electromechanical setup allowing us to control simultaneously and precisely olfactory and visual stimuli at different intensities. Our results show that the bimodal enhancement during learning and memory was higher as the intensity decreased when the separate individual components were least effective. Still, this effect was not detectable for the latency of response. Remarkably, these results support the principle of inverse effectiveness, traditionally studied in vertebrates, predicting that multisensory stimuli are more effectively integrated when the best unisensory response is relatively weak. Thus, we argue that the performance of the bees while using a bimodal stimulus depends on the interaction and intensity of its individual components. We further hold that the inclusion of findings across all levels of analysis enriches the traditional understanding of the mechanics and reliance of complex signals in honey bees.

Adjusted phonotactic reactions to sound amplitude and pulse number mediate territoriality in the harlequin poison frog.

The information content of signals remains one of the central questions in animal communication. Auditory signals might contain information that allows receivers to estimate the distance as well as the size or the motivational state of senders. Proper differential reactions by receivers could be especially important for territorial species and lead to behavioural adjustments towards intruders according to the threat level: the perceived risk of losing territory. Therefore, territorial individuals should decode signal parameters that indicate the sender's size, distance, and motivation/treat level, reacting accordingly. To test this hypothesis, we studied the phonotactic reaction in territorial males of the poison frog Oophaga histrionica, after analyzing the variability of spectral and temporal parameters of natural calls. Next, we constructed synthetic calls by manipulating sound amplitude (sound pressure level: SPL), gross (inter-call intervals), and fine-temporal (number of pulses) structure of synthetic signals. In this way, we simulated near and far intruders with potentially variable sizes, motivational states, or threat levels. Then, we conducted playback experiments using these synthetic calls to determine 1) how perceived proximity of vocal competitors (determined by SPL) affect the behavior of receivers, and 2) how variation in the temporal structure of calls (inter-call interval and call pulse number) impact the behavior of receivers. We also asked whether signals convey body-size related information by analyzing the relationship between call parameters and body size of the males receiving the experimental stimuli. Consistent with our hypothesis, males recognized the variations in the SPL of calls. Males attacking the simulated opponent increased the number of pulses per call, while those retreating, kept pulse number unchanged (a graded aggressive signal). On the other hand, despite call traits resulted as poor predictors of body size, both SPL and fine temporal call traits might aid to predict whether a contestant will attack an opponent. Our data demonstrate that males discriminate and use SPL to estimate the sender's distance and use the call's fine temporal traits and to adjust the competitive/aggressive reaction using bimodal signals. They further suggest that body size assessment is not always an important factor in vocally- mediated agonistic interactions.