Listening in: the importance of vibratory courtship signals for male eavesdropping in the wolf spider, Schizocosa ocreata

Abstract

Multimodal courtship signals may compensate for environmental interference or loss of signals in some sensory modes but may also increase detection by eavesdroppers. Studies on the wolf spider Schizocosa ocreata (Hentz) have demonstrated that males eavesdrop on visual courtship cues of other males and subsequently initiate courtship. Since S. ocreata males use multimodal courtship signals, we examined responses of males to playback of signals in different sensory modes (visual, vibration, multimodal) to test their relative importance for eavesdropping on courting male rivals. We used a recently developed technique to present male wolf spiders with video and/or vibratory stimuli: (1) a multimodal courting male stimulus, with synchronous visual and vibratory cues; (2) a visual-only courting male stimulus (minus the vibratory cues); (3) vibratory cues only (minus the visual cues); and (4) a control (visual background, no courtship). In single-presentation (no-choice) tests, males displayed more courtship bouts and longer durations of courtship bouts to the vibratory stimulus compared with either the visual or multimodal stimuli. However, in two-choice tests where isolated vibratory cues were paired against visual or multimodal stimuli, test males responded with more courtship bouts and longer durations of courtship bouts to the multimodal and visual stimuli. Results of these experiments suggest that male wolf spiders may vary eavesdropping courtship behaviors to compensate for missing sensory information concerning the location and other distinguishing characteristics of the rival male and the whereabouts of the female. Social eavesdropping is used to exploit information in signals of conspecifics, e.g., as a means of mate competition. Studies on Schizocosa ocreata wolf spiders have shown that males eavesdrop on visual courtship displays of other males and subsequently initiate multimodal courtship. We used video/vibration playback to examine responses of males to signals in different sensory modes (visual, vibration, both) and determine their relative importance for eavesdropping on courting male rivals. Results suggest that depending on sensory modes of their rivals’ signals, males may vary their own courtship displays to compensate for missing information. For example, when signals are presented individually, eavesdropping male response patterns are distinctly different from when presented a choice between modes. Males show more displays with isolated vibratory signals, but given a choice, males more often increase their tapping when multimodal cues were present. Ultimately, eavesdroppers that adjust behaviors in response to available sensory cues would be able to “level the playing field” with rivals and potentially increase the probability of gaining attention of females.