Changes in composition of spider orb web with starvationm,,

Changes in composition of spider orb web with starvationm,,...

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1463 Introduction In the construction of its orb web an araneoid spider first builds a non-sticky scaffolding using ampullate silk gland fibers and piriform silk gland junctional cements/attachment disks. One part of the scaffolding, the radii, are arranged like the spokes of a wheel. Subsequently, the sticky spiral (or adhesive or viscid spiral, among other names) (Zschokke, 1999) is attached to the radii. The sticky spiral consists of a pair of flagelliform silk gland fibers coated with an adhesive, aqueous secretion from the aggregate glands (Sekiguchi, 1952; Peters, 1955). This aggregate gland secretion contains organic and inorganic low-molecular-mass compounds (LMM; <200 Da), at least one high-molecular-mass phosphorylated glycoprotein and, likely, lipids (see references in Higgins et al., 2001; Schulz, 2001). Organic LMM include 11 of the 12 compounds monitored in this study; GABamide (4- aminobutyramide; GAB), N -monoacetylputrescine (NAP), isethionic acid (2-hydroxyethane sulfonic acid; Ise), N - acetyltaurine (NAT), glycine (Gly), choline (Cho), glycine betaine (Bet), alanine (Ala), proline (Pro), putrescine (Put), taurine (Tau) (Fischer and Brander, 1960; Tillinghast and Christenson, 1984; Vollrath et al., 1990; Townley et al., 1991; Higgins et al., 2001). The aggregate gland secretion, initially deposited as an unstable liquid cylinder, spontaneously redistributes into a pattern of linked droplets (Boys, 1889; Warburton, 1890; Edmonds and Vollrath, 1992; Ball, 1999). Concurrent with droplet formation is the formation of discrete nodules at the center of the droplets that contain the aforementioned glycoprotein (Vollrath and Tillinghast, 1991). While it is believed the nodules are the principal adhesive agents in the droplets (Richter, 1956; Vollrath and Tillinghast, 1991), the The sticky spiral of araneoid spider orb webs consists of silk fibers coated with adhesive droplets. The droplets contain a variety of low-molecular-mass compounds (LMM). Within a species, a fairly consistent ratio of LMM is often observed, but substantial variability can exist. To gain insight into factors influencing LMM composition, spiders of three araneid species were starved and LMM from their webs were analyzed for changes in composition. To determine if these changes were consistent with the spider’s ability to synthesize the different organic LMM, synthetic capacities were estimated following the feeding of radiolabeled metabolites. Some changes in droplet composition were broadly consistent with differing synthetic capacities: molar percentages of less readily synthesized compounds (e.g. choline, isethionate, N - acetyltaurine) typically declined with starvation, at least during a portion of the imposed fast, while more readily synthesized compounds (e.g. GABamide, glycine) tended to increase. Most striking was the apparent partial substitution of N -acetylputrescine by the more readily synthesized GABamide in fasting Argiope trifasciata .
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Changes in composition of spider orb web with starvationm,,...

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