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Structure and composition of the spider Argiope amoena egg case

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Author(s): JIANG Ping | XIAO Yong-Hong | ZHOU Bing | LIAO Xin-Jun | GUO Cong

Journal: Acta Zoologica Sinica
ISSN 0001-7302

Volume: 54;
Issue: 5;
Start page: 918;
Date: 2008;
Original page

Keywords: Argiope amoena | Egg case structures | Amino acid composition | SEM

ABSTRACT
The egg case of the spider A. amoena is composed of multiple layers of silk, including a frame of yellow silk, an outer cover with layers of gray-green, pale brown, and white silk, and an inner cover of brown silk. SEM shows the outer cover threads consist of six large diameter (4.8–6.8 µm) cylindrical gland monofilaments with numerous smaller diameter (0.26–0.76 µm) fibers. The number of small-diameter fibers varies with layer; it is high in outer layers and decreases in inner layers. Small diameter fibers are absent from the inner cover, which consisted entirely of fibers made with six strands of large diameter (5.2 µm) cylindrical gland monofilaments. The chemical makeup (mole fraction of alanine, serine, and glycine) of the outer cover strands is intermediate between that of inner cover silk and aciniform gland silk. These observations support Matthew's (2002) hypothesis that the small diameter fibers are produced by the aciniform glands. Spiders appear to use relatively few gland silks in varying combinations to achieve different physical, chemical (e.g. color, diameter, amino acid composition) and functional (mechanical properties, resistance, etc) characteristics in different layers of the egg case providing protections for eggs or spiderlings [Acta Zoologica Sinica 54 (5): 918 – 927, 2008].
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