State-dependent decisions in nest site selection by a web-building spider

Foraging decisions may reflect a trade-off between food intake and safety and can also be influenced by the animal's internal state. Foraging in the web-building spider Stegodyphus lineatus depends on a capture web associated with a retreat (the nest). The relocation of nests, including the take-over of conspecific nests, may be viewed as a foraing decision, which depends on risk of exposure, cost of silk production and hunger state. We investigated a possible state-dependent trade-off in nest site choice of S. lineatus spiderlings. The philopatric nature of S. lineatus implies a high risk of encounters with potentially cannibalistic conspecifics and a potential loss of inclusive fitness because encountered conspecifics are likely to be kin. To test for state dependence of foraging decisions, we compared preferences of well-fed and hungry spiders for their own nests and those of siblings and nonsiblings. We expected satiated spiders to prefer their own to conspecific nests and hungry spiders to choose the risky option of a conspecific nest. Since S. lineatus is less aggressive towards kin, we tested the ability of spiders to discriminate kin by silk-bound cues. Because of this reduced aggression, preference for kin nests should be safer than preference for nonkin nests. A strong preference for self-nests demonstrated self-recognition in well-fed spiders. However, neither well-fed nor hungry spiders discriminated between nests of siblings and nonsiblings. Well-fed spiders preferred self-nests to empty chambers, but showed no discrimination between nonself-nests and empty chambers. Hungry spiders showed a reduced preference for self-nests, suggesting that hunger elicits a more risky foraging strategy. A tendency of hungry spiders to adopt the nests of conspecific spiders may reflect a silk-saving strategy. We conclude that S. lineatus spiders show state-dependent decision making in nest site selection. (C) 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.