An Association Between Two Neotropical Spiders (Araneae: Uloboridae and Tengellidae)

Abstract

An interspecific association between two spider species (Araneae, Uloboridae and Tengellidae) was studied over a sixweek period at an Atlantic lowland wet forest site in Costa Rica. The uloborid Philoponella vicina builds orb webs among the frame lines of the platform web constructed by Tengella radiata Kulczynski, the much larger tengellid species. Experiments with marked P. vicina determined that these uloborids actively choose to build in T. radiata webs. Studies of possible advantages the uloborid may derive from inhabiting the web of the tengellid showed that: 1) Associated uloborids persisted at a web site significantly longer than solo uloborids; 2) prey capture was significantly greater for the associated uloborids than for the solo spiders. The association of P. vicina and T. radiata appears to be commensal. As SOLITARY PREDATORS, most spiders are intolerant of conspecifics; even potential mates are sometimes treated as prey. While conspecific associations are known for sub-social, communal, and social spiders (Muma and Gertsch 1964; Pain 1964; Darchen 1965; Dennis 1965; Lubin 1974; Buskirk 1975; Brach 1977; Burgess 1976, 1979; Jackson and Joseph 1973), reports of interspecific associations in the literature are rare and anecdotal (reviewed by Kasto,n 1965). Within the family Uloboridae, however, tolerance olf conspecifics is common (Muma and Gertsch 1964; Eberhard 1971; Buskirk 1981), and several species are known to form commensal and slightly parasitic associations with other spiders (Struhsaker 1969, Bradoo 1972, Opell 1979). I report here on a neotropical association between Philoponella vicina 0. Pickard-Cambridge, a uloborid orb weaver, and Tengella radiata Kulczynski, a tengellid platform weaver, and present evidence that the association is advantageous to, the uloborid. This study attempted to test the nature of the association and addresses the following questions: 1) Do P. vicina actively select T. radiata webs as web sites? 2) Is prey capture in associated uloborids higher than in unassociated (solo) ones? 3) Do tengellid webs offer greater protection from predation than other sites? 4) Do tengellid webs offer uloborids potential site positions in areas where they could otherwise not build? The interspecific association observed may be the result of an active search by uloborids for tengellid webs, or it may result from higher mortality of uloborids which establish themselves outside tengellid webs, or both. An affirmative result of a test of (1) above would indicate that uloborids are using some cue to locate the tengellid webs, and that the association is not merely the result of differential mortality of uloborids. If site selection is an active process in uloborids, one may presume that the spiders derive some advantages in inhabiting the web space of the tengellids. Tests of questions (2), (3), and (4) were designed to determine whether correlates of fitness, such as lower predation or higher rate of prey capture, differ significantly between uloborids building webs inside and outside of ten-