Male courtship reduces the risk of cannibalism in web-building spiders but varies in structure

Male courtship serves multiple functions in addition to inducing females to accept them as a mate. In predatory species, male courtship can function to reduce the risk of sexual cannibalism. This is particularly important in web-building spiders in which males risk being mistaken for prey when they enter the female's predatory trap – the web – in order to commence courtship. Male spiders generate vibrations by shuddering in the female's web. Shudder vibrations can delay female aggression, even toward prey struggling in the web. We predicted that shudder vibrations are highly conserved across species of web-building spider as males all face the same constraint of not being mistaken for prey by females. We examined how conserved shudder vibrations are across web-building spiders by testing whether female Trichonephila plumipes delay aggressive behaviour toward real prey struggling in the web during playback of conspecific or heterospecific (Argiope keyserlingi) male shudder vibrations. We found that while conspecific shudder vibrations do indeed delay female predatory behaviour, heterospecific male shudder vibrations do not. There is evidence of shudder or shudder-like vibrations in male courtship behaviour across web-building spider families, but these vary in structure. This suggests that despite strong constraints on courtship signal design to separate predatory responses from sexual responses, there is additional selection driving the divergence of signals across distantly related spider species.Response latencies of female spiders in Experiments 1 and 2 are censored (females were given a maximum of 10 minutes to respond to prey). Recordings of male courtship were used to test for the presence of shudder courtship elements, rather than to comprehensively characterise male courtship behaviour. Cells marked 'NA' indicate measurements that were not applicable.Experiment 1: Female Trichonephila plumipes were presented with live crickets in their webs during playbacks of male T. plumipes shudder vibrations, white noise or a silent control. Their responses were compared. Experiment 2: Female Trichonephila plumipes were presented with live crickets in their webs during playbacks of male A. keyserlingi shudder vibrations, white noise or a silent control. Their responses were compared. Shudder recordings: Recordings of male shudders from 8 species of web-building spider were analysed for peak frequency (Hz), duration (ms) and inter-shudder duration (s). Species included were: Argiope aetherea, A. katherina, A. keyserlingi (note, recordings from Wignall & Herberstein 2013a), A. radon, Cryptachaea sp., Phonognaetha graffei, Plebs eburnus, Trichonephila plumipes. A subset of these recordings were compared in a linear discriminant analysis