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

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).File Descriptions: --analysis_exps_1-5,7.R-- This file contains the R code, for all statistical analyses of experiments 1-5,7, and well as the code to generate Fig. 3. The metadata for "exp_1.csv - exp_5.csv, exp_7.csv" are also fully described in this file. --exp_1.csv - exp_4.csv-- These files contain the response data from the y-tube olfactory experiments (exp. 1-4) testing the effect of web reduction on the response of male false black widow spiders to female webs. --exp_5.csv-- This file contains the behavioural responses of male and female false black widow spiders from mating trials in which half of the males had their spinneretes occluded with super glue. --exp_7.csv-- This file contains the durations of upward and downward abdominal movement of male false black widow spiders from high speed video recordings of mating trials. --weight and size regression.R-- This file contains the R code used to fit a regression of weight and tibial length in false black widow spider males and females and calculate a "condition index" (residuals) for each spider. This file also contains the code necessary to generate Fig. S2. --(fe)male weights and sizes.csv-- Weight and tibial length measurements of the entire pool of either male or female spiders used to calculate the "condition index" (weight and tibial length residuals). Metadata descriptions are the same as those described in "analysis exps 1-4.R"