Vibratory signalling in two spider species with contrasting web architectures

Spiders provide a fascinating opportunity for the study of animal communication. Web-building spiders build their own signalling environments - the web is the medium that transmits vibrations from prey, predators and potential mates. However, we know little about how information is conveyed through different types of webs, or how spiders distinguish between different types of vibrations. In this thesis, I studied elements of vibratory communication in two species of spiders with contrasting web architecture: the western black widow, Latrodectus hesperus, which builds a tangle-web, and the hobo spider, Eratigena agrestis, which builds a funnel-web. In chapter 2, I document formerly undescribed life history traits of E. agrestis, and conclude that life history traits are robust to differential predator and competitor densities across two study sites in British Columbia. In chapter 3, I present hitherto lacking quantitative descriptions of courtship behaviours in L. hesperus, revealing that web reduction by males correlates with reduced female aggression, and that it may improve mating success of courting males. In chapter 4, I describe how vibration frequencies are transmitted through the webs of L. hesperus and E. agrestis. I found little difference in propagation efficiency between longitudinal and transverse vibrations and that in both species vibration transmission is more variable within webs than between webs, suggesting that specific frequencies play a minor role in signalling. In chapter 5, I tested whether male courtship produces vibratory signals that differ from prey cues. I analysed vibrations produced by courting males and by two types of prey (flies and crickets) on the webs of L. hesperus and E. agrestis, and also played back male and prey vibrations through the webs of L. hesperus. Male vibrations differ more from those of prey in L. hesperus than in E. agrestis. This finding supports the hypothesis that L. hesperus males, faced with aggressive females, produce vibrations that prevent them from being mistaken for prey. The low-amplitude vibrations caused by abdominal tremulations of L. hesperus males may be linked with lowered female aggression.