Multimodal communication and mate choice in wolf spiders: female response to multimodal versus unimodal signals

Male wolf spiders (Lycosidae) in the genus Schizocosa vary in use of seismic and visual components of courtship display, ranging from unimodal (seismic only) to multimodal (seismic and visual). Studies show that variation in individual modes influences female receptivity, but responses to isolated signals may not be equivalent. To examine redundancy and interaction between modes, we compared female responses to isolated and combined courtship signals from males of two sympatric sibling species that differ in use of visual and seismic modes, S. ocreata and S. rovneri. Females of both species detected multimodal stimuli faster than visual or seismic cues alone, but they differed in responses to cues once they oriented. Female S. ocreata approached males performing isolated visual and seismic cues with equal frequency, but approached males performing multimodal cues more often. A greater proportion of female S. ocreata responded more receptively to multimodal cues than to seismic or visual cues alone, and showed higher rates of receptivity displays with multimodal cues. In contrast, female S. rovneri showed no differences in approaches, but responded more often and with higher display rates to seismic cues alone or multimodal cues, but not visual cues. These results suggest multimodal signalling increases detection of males by females, but that use of signal modes varies between even closely related sibling species. For S. rovneri, male signals in different modes are nonredundant, with seismic cues dominant over visual cues when presented alone or in multimodal signals. In contrast, for S. ocreata, male signals in different modes are redundant (eliciting the same responses from females with similar frequency), while the greatly increased responsiveness to multimodal signals indicates multiplicative enhancement.