Abstract
ABSTRACTAmong the triad spinning units for capture thread producing system in the orb-web spiders, aqueous gluey substances are produced from two pairs of aggregate silk glands (ASG). Although biochemical analysis of glue substance is produced by way of their passage through the ASG, its structural modifications in the nodular area have been nearly neglected till now. This paper focused on identifying the fine structural characteristics of the aggregate nodules in the golden orb-web spider Nephila clavata using both of light and transmission electron microscopes. The ASG in N. clavata is composed of a multi-lobed secretory region and a thick excretory duct surrounded by large irregular nodules. Histological analysis of the nodules demonstrates that the nodule forming cells have extensive membrane-bound tubular system that is continuous with the surface membrane. In particular, the nodule forming cells contain numerous mitochondria and glycogen particles within their cytoplasms, and they are surrounded by the same sheath of thin connectives. As previously described, each gluey droplet is formed of a central glycoprotein mass surrounded by an aqueous covering components, the nodular organization in N. clavata indicates that the extensive membrane system is thought to have a function for gluey silk production in spider. The results of this study also strengthen the premise that spider glues are made of glycoproteins, and the aggregate nodule functions as a key component for the spider web glue production.
Highlights
Capture threads in spiders are basically distinguished into two types with respect to the properties whose suitability for holding prey is based upon either a covering with a viscous glue or a covering with extremely fine fibrils (Peters 1987)
Histologic preparation of the opisthosoma is shown that the sticky capture threads are produced from a pair of triad silk glands which composed of a flagelliform silk gland (FSG) and two aggregate silk glands (ASG) (Figure 1(A,B))
By the light microscopic observation embedded in the plastic EM-bed medium, the posterior spinneret in female spider is filled with four kinds of silk glands including FSG, ASGs, tubuliforms, and aciniforms
Summary
Capture threads in spiders are basically distinguished into two types with respect to the properties whose suitability for holding prey is based upon either a covering with a viscous glue (gluey capture threads) or a covering with extremely fine fibrils (cribellar capture threads) (Peters 1987). A pair of flagelliform glands produces supporting axial fibers, and two pairs of aggregate glands coat these fibers with an aqueous solution that quickly forms into sticky droplets (Vollrath et al 1990; Peters and Kovoor 1991). It is the flagelliform axial fibers that provide the primary tensile mechanics of the gluey capture threads (Opell and Bond 2000; Becker et al 2003; Blackledge et al 2005; Park and Moon 2014), the aggregate silk secretions make capture threads sticky and can modulate the mechanics of the axial core fibers (Opell and Hendricks 2010; Townley and Tillinghast 2013). The aggregate silk coating of viscid threads spontaneously forms droplets as it is spun (Vollrath et al 1990; Vollrath and Tillinghast 1991; Townley et al 2006), and allows spiders to achieve a greater stickiness per unit area in their webs (Opell 2002). Viscid silk has reduced UV reflectance and this decrease in visibility may make webs more difficult for insects to avoid (Craig et al 1994)
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