Papers in the Biological Sciences


Date of this Version

May 2005


Published in Behavioral Ecology 16:1 (2005), pp. 75–82; doi 10.1093/beheco/arh133 Copyright © 2004 International Society for Behavioral Ecology; published by Oxford University Press. Used by permission.


Complex signals are common throughout the animal kingdom, consisting of one or more signals in one or more sensory modalities presented within a single display. I tested an efficacy-based backup hypothesis of complex signal function using the bimodal courtship signaling wolf spider Schizocosa uetzi. This hypothesis predicts that the visual and vibratory courtship displays function as backups to each other in the presence of environmental variability. I compared mating frequencies across four environmental treatments in which the visual and vibratory environments were manipulated independently in a 2 × 2 design with visual treatments of light/dark (i.e., visual signal present/absent) and vibratory treatments of filter paper substratum/granite substratum (i.e., vibratory signal present/absent). Results did not match the predictions of an efficacy-based backup hypothesis. The vibratory environment affected mating frequency, with more mating occurring in the vibration-present treatments compared to the vibration-absent treatments, but the visual environment had no effect on mating frequency. A second experiment was then conducted to test for an inter-signal interaction. Using the video-playback technique, I presented females with manipulated video sequences simultaneous with a controlled vibratory signal to test the hypothesis that the presence of a vibratory signal alters a female’s response to the visual signal. In the presence of a vibratory courtship signal, females were more receptive to more visually ornamented males. This increased receptivity to increased visual ornamentation was not seen in a previous study conducted on S. uetzi in the absence of a vibratory signal, suggesting a potential inter-signal interaction. In a third experiment, I tested whether a female’s visual attention was altered by the vibratory signal by examining female response to a visual “predator” while exposed to all possible combinations of male courtship signals. Females were more likely to get caught, and thus less likely to notice a predatory visual stimulus when exposed to a courtship vibration, supporting the hypothesis that the vibratory signal alters a female’s visual attention.