Substrate-dependent signalling success in the wolf spider, Schizocosa retrorsa

Signals used in communication are often hypothesized to be optimally designed for their signalling environment. Here, we explore the importance of signalling substrate on seismic signal efficacy and reproductive behaviour in the wolf spider, Schizocosa retrorsa: a species found on multiple signalling substrates (pine litter and/or red clay or sand). In this multimodal signalling species, simultaneous with conspicuous visual displays, males produce percussive seismic signals via an impulse mechanism which tends to excite a substrate evenly across a wide band of frequencies. We first quantified the transmission characteristics of this broadband percussive signal by playing recorded signals back across three naturally occurring substrates, two of which represent substrates upon which S. retrorsa is commonly found: leaf litter, pine litter and red clay (the latter two exemplify their natural habitat). The substrates varied in their transmission characteristics with respect to both attenuation (higher on red clay) and filtering. Next, we compared copulation success, courtship behaviour and microhabitat choice among these same substrates. Copulation frequency was higher on the natural substrates of pine litter and red clay as compared with leaf litter. Males took longer to initiate courtship on leaf litter, but once initiated, courtship behaviour did not vary across substrates and we were not able to discern any choice with respect to the first, or the most common, substrate chosen. Our results show that while S. retrorsa's percussive signals may not be matched to the specific properties of any one substrate, copulation success was substrate dependent and we discuss potential explanations for this substrate-dependent signalling success.