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Unformatted text preview: THE EFFECT OF FOOD AND SILK RESERVE MANIPULATION ON DECORATION-BUILDING OF ARGIOPE AETHEROIDES by I-MIN TSO 1,2) (Department of Biology, Tunghai University, Taichung 407, Taiwan) (Acc. 26-III-2004) Summary In this study I investigated how decoration-building of Argiope aetheroides is proximately controlled. Since decoration silk is produced from the aciniform glands and these glands’ secretion is also used in prey-wrapping, I tested if manipulating the amount of silk in the aciniform glands would lead to changes in the building of decorations. When the aciniform glands of A. aetheroides were supplemented by giving spiders ample prey and silk was not depleted, a significant increase in total area and number of arms of decorations was found. When the aciniform glands were intensively depleted by repeatedly removing the wrapped prey from webs, the size of decorations in subsequent webs was significantly reduced. Spiders building webs with small or no decorations were still able to produce plenty of silk to wrap prey. Therefore, the presence of undecorated webs seemed to result from the silk reserve, which the spiders may invest on decoration-building, being depleted, rather than the aciniform glands being completely emptied. Based on the results, I propose that there is a threshold point in the aciniform glands, and the amount of silk reserve in the glands relative to that threshold determines the size of decorations. Introduction After constructing a regular web, many orb-weaving spiders incorporate ex- tra structures called decorations or stabilimenta on their webs (Nentwig & Heimer, 1987). Investigators have reported several types of decorations made 1) E-mail address: [email protected] 2) Special thanks are given to Thomas Leuteritz, who kindly helped translate Peters (1993), based upon which this study was developed. This work is partially supported by a National Science Council, Taiwan, R. O. C. grant to I.M. Tso (NSC-91-2311-B-029-006). © Koninklijke Brill NV, Leiden, 2004 Behaviour 141, 603-616 Also available online - 604 I-MIN TSO of various material such as silk, egg sacs, prey remain and detritus from at least 12 genera of orb-weaving spiders (Eberhard, 1973; 1990; Levi, 1983; Nentwig & Heimer, 1987). Among various types of decorations the functions of those composed entirely of silk were the focus of most studies. Tradition- ally the functions of silk decorations had been proposed to be stabilizing the web, adjusting web tension, serving as a moulting platform, aiding in ther- moregulation, defending against predators and attracting visually-oriented insects (reviewed in Herberstein et al. , 2000a). Among them, the predator de- fense and prey attraction hypotheses have received the most attention. Many studies demonstrated that decorated webs built by various species of Argiope (Craig & Bernard, 1990; Tso, 1996; 1998a; Herberstein, 2000; Bruce et al. , 2001; Craig et al. , 2001), Cyclosa (Tso, 1998b) and Octonoba (Watanabe, 1999) caught significantly more prey than undecorated ones. Such results1999) caught significantly more prey than undecorated ones....
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- Spring '11
- Ecology, Spider, Spider web, Argiope, argiope spiders