ORB-WEBS AS EXTENDED-PHENOTYPES: WEB DESIGN AND SIZE ASSESSMENT IN CONTESTS BETWEEN NEPHILENGYS CRUENTATA FEMALES (ARANEAE, TETRAGNATHIDAE)

In this study I investigate a mechanism underlying size assessment during contests between females of the orb-weaving spider Nephilengys cruentata. Among orb-weaving spiders, some structural parameters of webs have been shown to vary with the size of the web builder, making it theoretically possible for an intruder to gather information about the webʹs resident when initiating a fight. Here I examined whether N. cruentata females are able to assess the size of the web owner during contests by using information from web design. The fighting behaviour of intruders was analysed in two situations: (1) web design indicated the presence of a small resident but actual resident size was large (treatment) and (2) web design cued the presence of a large resident, and actual resident size was also large (control). This was achieved by removing original web builders from their webs and letting newly introduced spiders establish ownership before inducing conflicts. Results were consistent with the hypothesis that web design is used as a cue for web resident size. Strategies adopted by intruders were influenced at an initial stage of the fight mainly by the size of the web builders instead of the size of the newly established residents. The implications of the results for the understanding of fighting behaviour in this species are discussed.