Multimodal and multifunctional signaling? – Web reduction courtship behavior in a North American population of the false black widow spider

Abstract

Males of widow spiders courting on the web of females engage in web-reduction behavior which entails excising a section of the web, bundling it up, and wrapping it with their silk. Males of the false black widow spider, Steatoda grossa, in European populations also produce stridulatory courtship sound which has not yet been studied in their invaded North American range. Working with a North American population of S. grossa, we tested the hypotheses that (1) web reduction by males renders webs less attractive to rival males; (2) deposition of silk by courting males has an inter-sexual (male-female) signal function that enhances their likelihood of copulation; and (3) stridulatory sound is a courtship signal of males. Testing anemotactic attraction of males in Y-tube olfactometer experiments revealed that reduced webs (indicative of a mated female) and intact webs (indicative of a virgin female) were equally attractive to males. Recording courtship behavior of males with either functional (silk-releasing) spinnerets or spinnerets experimentally occluded on the web of virgin females showed that males with functional spinnerets were more likely to copulate with the female they courted. Although males possess the stridulatory apparatus to produce courtship sound, they did not stridulate when courting or copulating on the web of females. Our data support the conclusion that web-reduction behavior of S. grossa males in their invaded North American range has no long-range effect on mate seeking males. Instead, web-reduction behavior has an inter-sexual signaling function that seems to be linked to functional spinnerets of the courting male. The signal produced by a male likely entails a volatile silk-borne pheromone, but may also embody a gauge of his endurance (the amount of time he engages in web reduction causing web vibrations).

Origin, structure and functional transition of sex pheromone components in a false widow spider

“…Long-distance orientation of male spiders to mate attractant pheromone components emanating from female S. grossa webs was tested in Y-tube, moving-air olfactometers 56 , using web extract (instead of webs) as the test stimulus (Fig. 4a ).…”

“…Sensing contact pheromone, the male essentially behaves as if he were courting on the web of a female. On a web, the male engages in web reduction prior to copulation, a behaviour that entails cutting sections of the female’s web with his chelicerae and wrapping the dismantled web bundle with his own silk pulled from his spinnerets 41 , 56 . Each T-rod apparatus was used only once.…”

Pheromone communication among sexes of the garden cross spider Araneus diadematus

“…The Y-tube olfactometer (connecting arms: 9 cm length; single arm: 12 cm, inner diameter: 1.8 cm) experiment design is described in Fischer et al (2018aFischer et al ( , 2020. The setup was fixed in a polystyrene box (120 × 80 × 80 cm) and the only light source was a cold light lamp (Schott KL 1500 LCD, 2950 K) placed above the centre of the Y-tube.…”

“…For spiders, there is considerable behavioural evidence for the use of chemical communication for mate attraction and mate choice (Huber 2005 ; Gaskett 2007 ; Uhl and Elias 2011 ; Schulz 2013 ; Uhl 2013 ; Fischer et al 2018b , 2020 ; Adams et al 2021 ). Spider sex pheromones not only reveal the presence of a mating partner but may provide cues on age and feeding status of females, judging from differential male reactions (Cory and Schneider 2016 , 2017 , 2018 , 2020 ; Jiang et al 2018 ; Waner et al 2018 ; Fischer 2019 ).…”

Sperm competition when transfer is dangerous

“…Web manipulation (reducing the female's web, wrapping it up in their own silk and sometimes discarding it) is also common. This behaviour may reduce female attractiveness through reduced pheromone dissemination, or release male pheromones that deter other males and decrease female receptivity [55][56][57]. A rather extreme paternity protection strategy evolved independently in Larinia jeskovi and Cyclosa argentoalba.…”