Small organic solutes in sticky droplets from orb webs of the spider Zygiella atrica (Araneae; Araneidae): β-alaninamide is a novel and abundant component

In northeastern North America, Zygiella atrica often build their orb webs near the ocean. We analyzed individual field-built Z. atrica webs to determine if organic low-molecular-mass solutes (LMM) in their sticky droplets showed any unusual features not previously seen in orb webs of other species living in less salty environments. While two of the three most abundant organic LMM (putrescine (butane-1,4-diamine) and GABamide (4-aminobutanamide)) are already well-known from webs of inland spiders, the third major LMM, β-alaninamide (3-aminopropanamide), a homolog of GABamide, has not been detected in sticky droplets from any other araneoid spiders (27 species). It remains to be established, however, whether or not use of β-alaninamide is related to proximity to saltwater. We observed variability in organic LMM composition in Z. atrica webs that appeared to be influenced more by an undetermined factor associated with different collecting locations and/or collection dates than by different genders or instars. Shifts in composition when adult females were transferred from the field to the laboratory were also observed. Structural similarities and inverse correlations among β-alaninamide, GABamide, and N-acetylputrescine suggest that they may form a series of LMM fulfilling essentially the same, as yet unknown, role in the webs of those species in which they occur.

The Adhesive Glycoprotein of the Orb Web of Argiope Aurantia (Araneae, Araneidae)

A phosphorylated, glycoprotein preparation has been obtained from orb webs of the araneid spider Argiope aurantia. This preparation probably contains proteins from more than one gland type, but resolution of these proteins has not yet been achieved. Nevertheless, a major component appears to be the adhesive glycoprotein(s) from the adhesive spiral. A product of the aggregate glands, this glycoprotein(s) occurs as discrete nodules along the core fibers of the adhesive spiral, within the viscid, aqueous droplets.

The glycoprotein preparation has a high apparent molecular weight (> 200 kDa) and is polydisperse. The only monosaccharide constituent identified by gas-liquid chromatography or in lectin studies is N-acetylgalactosamine and this is at least primarily O-linked to threonine. By electron microscopy, linear, unbranched and apparently flexible filaments are observed. Phosphorylated serine and threonine residues are present in the preparation and glycine, proline and threonine together account for about 57 mole % of the preparation's amino acid content. Thus, in some, but not all, respects, this glycoprotein preparation is reminiscent of a secretory mucin.

Moult-related changes in ampullate silk gland morphology and usage in the araneid spider Araneus cavaticus

Major ampullate (MaA) and minor ampullate (MiA) silk glands of juvenile Araneus cavaticus (third to penultimate instars) were examined by dissection at various times relative to ecdysis. Several days before ecdysis the larger pairs of MaA and MiA glands become non-functional and remain so until ecdysis. Nevertheless, proecdysial spiders are able to draw ampullate fibres due to the presence of smaller pairs of MaA and MiA glands which are functional at this time. Indeed, it appears that these smaller ampullate glands are intended for use only during proecdysis. Thus, larger MaA and MiA glands and smaller MaA and MiA glands are typically not used concurrently (a brief transitional period is an exception). The smaller ampullate glands functioning in one juvenile stadium regress in the following stadium and become (what have previously been referred to as) accessory MaA and MiA glands. These nonfunctional accessory ampullate glands do not re-develop into functional smaller ampullate glands until the following stadium. Thus, a given pair of smaller MaA or MiA glands is only functional in every other juvenile stadium. However, because there are two sets of smaller/accessory MaA and MiA glands which function alternately, the spider is able to produce ampullate fibres during the proecdysial portion of each stadium. A new terminology for the larger, smaller and accessory ampullate glands is proposed which emphasizes the kinship between the two sets of smaller/accessory ampullate glands.

Structure and cytochemistry of the silk glands of the mygalomorph spider Antrodiaetus unicolor (araneae, antrodiaetidae)

Dissection and a variety of absorption and fluorescent cytochemical methods have demonstrated that Antrodiaetus unicolor females have only one type of silk gland and spigot and, consequently, the simplest silk production system of any spider yet investigated histochemically. The small spherical to pear-shaped glands are grouped into four clusters, each cluster serving one of the four spinnerets. The spigots are long, slender, and slightly bent distally. Although all gland cells are structurally similar, each gland simultaneously produces two different secretory products, the secretion of the distal hemisphere being rich in basic protein and sulfhydryl groups, and the proximal hemisphere secretion being an acidic protein containing a high concentration of histochemically demonstrable C-terminal carboxyl groups. The two products remain segregated as they pass through the duct, where the acidic protein forms a thin outer layer around a core of basic protein. It is suggested that this segregation may persist in the silk strand after it exits from the spigot and that the outer acidic protein may be an adhesive agent.