Chemical communication of the false widow spiders Steatoda grossa and S. triangulosa (Theridiidae)

The chemical ecology of web-building spiders is poorly understood. Only 12 sex pheromones are known, the side of pheromone production remains elusive, a pheromonal function in female-female conflict has not been described, the effect of male pheromone on male copulatory success has rarely been studied, and there is no report whether female spiders recognize 'self'. Addressing these knowledge gaps, I worked with the false black widow Steatoda grossa, and the triangulate cobweb spider, S. triangulosa.
I found that subadult female S. grossa stay cryptic to mate-seeking adult males, which is likely adaptive to sub-adult females that are in sexual conflict with adult males cohabiting their webs.
Working with adult female S. grossa, I identified three new contact pheromone components: N-4-methylvaleroyl-O-butyroyl-L-serine, N-4-methylvaleroyl-O-isobutyroyl-L-serine and N-4-methylvaleroyl-O-hexanoyl-L-serine. These compounds originate from the posterior aggregate silk gland, induce courtship by males, and web pH-dependently hydrolyse at the carboxylic-ester bond, giving rise to three corresponding carboxylic acids that attract males. A carboxyl ester hydrolase present on webs likely mediates the functional transition of contact sex pheromone components to the carboxylic acid mate attractant pheromone components.
Non-targeted metabolomics helped reveal the contact pheromone components of S. triangulosa: N-4-methylvaleroyl-O-isobutyroyl-L-serine, N-3-methylbutanoyl-O-isobutyroyl-L-serine, and N-3-methylbutanoyl-O-butyroyl-L-serine. Hydrolyses of these serine esters gives rise to butyric and isobutyric acids as mate-attractant pheromone components.
Female S. grossa sense intra-sexual competition via their sex pheromones, and respond to sexual, social and natural selection pressures originating from intra-sexual conflict. In settings of high intra-sexual competition, females adjusted their webs to increase prey capture and lower predation risk. To alleviate mate competition, females deposited more contact pheromone components on their webs and accelerated their breakdown to mate-attractant pheromone components, essentially increasing their webs' attractiveness.
Web reduction behaviour by courting S. grossa males has no long-range effect on mate-seeking males but functions as an inter-sexual signal. Courting males with functional (silk-releasing) spinnerets were more likely to copulate with the female than males with their spinnerets experimentally occluded. The male's signal likely entails a volatile silk-borne pheromone.
Female S. grossa indiscriminately accepted both their own webs and egg sacs and those of conspecific females, likely due to a lack of selection pressure to recognize 'self'.