Complex signals and comparative mate assessment in wolf spiders: results from multimodal playback studies

Complex signals of animals involve multiple sensory modes and contain multiple structural components, and teasing apart how these modes and components interact in receiver decision making is an experimental challenge. Females of many species have ordered preferences for increased size or expression of male indicator traits. However, studies also suggest other species may exhibit comparative evaluation of mates rather than absolute preference hierarchies. We examined mate assessment by female wolf spiders, Schizocosa ocreata, using digital playback of video and vibratory/seismic signals in preference and choice tests of male trait differences. In playback experiments, female wolf spiders showed ordered preferences for male condition indicating traits (leg tuft size, vibration signal amplitude) in both individual sensory modes and multimodal (combined) signals. Tests with single modes and multimodal signals showed that trait expression in either signal mode affects outcome of mate choice. Females exhibited transitive preferences, consistently choosing males with larger tuft size or higher amplitude vibration in no-choice and two-choice tests. Thus, female S. ocreata do not necessarily need to compare mates to exhibit preferences for particular traits. Choice tests with multimodal playback showed that females made predicted choices when male traits covaried positively, but in 'cue-conflict' (negative trait covariance) choice tests, females showed a bias for visual signal trait expression (tuft size), displaying priority for visual signals over vibratory signals when in conflict. These studies demonstrate that under controlled experimental conditions, differences in behavioural responses to manipulation of digital video and vibration playback can provide valuable insights about recognition and interpretation of complex signals and their components.