No abstract

As part of an effort to understand the changes that piriform (Pi) and aciniform (Ac) silk glands undergo throughout the molt-intermolt cycle, spinnerets from all instars of two Mimetus Hentz, 1832 and one Araneus Clerck, 1757 species were examined by scanning electron microscopy. Especially informative were scans of spinning fields from the same individual over two or more consecutive stadia. These allowed us to determine that, in both genera, the Pi and Ac glands in use during a given stadium could be divided into two categories: (1) those with ducts accommodated by tartipores during proecdysis and (2) those not so accommodated and thereby apparently not functional during proecdysis. A silk gland in the former category, once developed, could presumably be used, at most, in every other stadium, whereas one of the latter category could potentially be used in every stadium. Unexpectedly, Pi glands of the latter category were constant in number [two per anterior lateral spinneret (ALS); four in total] throughout the ontogenies of both genera, and their spigots occupied the same location in the Pi spinning field in both genera. By contrast, tartipore-accommodated Pi glands increased in number from one stadium to the next in both genera. Of the Ac glands that had their spigots located on the posterior median spinnerets, none were tartipore-accommodated in either genera but, of the Ac glands with spigots on the posterior lateral spinnerets (PLS), some were tartipore-accommodated and some were not. All of them increased in number during the ontogenies of both genera. Adult males of three Mimetus species had two unusual spigots of unknown function on each ALS, which we interpret as modified Pi (MoPi) spigots. Their number and position raise the possibility that they serve (presumably modified) versions of the Pi glands that were not accommodated by tartipores during proecdysis. No spigots fully matching the description of Mimetus MoPi spigots were observed in adult males of four Australomimetus Heimer, 1986 or five Ero C. L. Koch, 1836 species. However, two of the Ero species did show a pair of Pi spigots on each ALS that, although not as conspicuous as Mimetus MoPi spigots, had wider openings than other Pi spigots. A minority of juvenile Mimetus specimens, and no adults, had a protuberance on one or both of their PLS, in a position similar to that of the aggregate (Ag)-flagelliform (Fl) spigot triad of araneoids, which may represent a phylogenetic vestige of a Fl or Ag spigot or one of their homologues.

Orb web hygroscopicity was examined in three species of araneid spiders, Argiope aurantia, Argiope trifasciata, and Araneus cauaticus. Both whole webs and fractions generated from them (water-soluble and -insoluble fractions; ethanol-soluble and -insoluble subfractions [Etsol and -insol]) were examined a t various relative humidities. In general, the water-soluble fraction, consisting of low molecular weight components (LMW) of the adhesive spiral cover, was more hygroscopic than the water-insoluble (protein) fraction. As the Et-sol of the water extract was typically more hygroscopic than the Et-insol, it appears that organic LMW are more responsible for water adsorption by the adhesive spiral cover than inorganic LMW. Hygroscopicity measurements made on individual synthetic or commercially obtained LMW compounds known to be in the web (both organic and inorganic) agree with this interpretation.As a first attempt toward correlating web hygroscopicity with composition, the water-soluble web fractions from the three species were examined by proton nuclear magnetic resonance ('H-NMR) spectroscopy and the molar percentages of the organic LMW were estimated. To accomplish this, it was necessary to identify the principal organic LMW in the web of A . trifasciata (since, unlike the situation in other araneids which have been studied, GABamide is not the principal organic LMW in A. trzfasczata). Using 'H-NMR and thin layer chromatography this compound was identified as N-acetylputrescine. While considerable interspecific variation in the molar percentages of GABamide, N-acetylputrescine, isethionic acid, and N-acetyltaurine was observed, interspecific differences in Et-sol hygroscopicities were not apparent.

SummaryThe 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. However, departures from expected compositional shifts demonstrated that synthetic capacity alone does not adequately predict sticky droplet compositional shifts with starvation. Moreover, feeding controls exhibited some changes in composition similar to starving spiders. As the webs of both feeding and starving spiders were removed for chemical analysis and could not be recycled, the loss of LMM contained in these webs likely contributed to similarities between treatments. In addition, feeding spiders molted, oviposited, and/or built heavier webs. The added metabolic demands of these activities may have contributed to changes in composition similar to those resulting from starvation.

Spiders are among the most successful groups of terrestrial organisms. With more than 42,000 species, spiders are the most numerous predacious arthropod group, only seconded by some insect families such as carabids' beetles or ants. This gives spiders, omnipresent in all terrestrial habitats, a key position in ecological networks and ecosystem functioning. During their evolution of more than 300 million years, spiders developed and improved unique features, the combination of which is regarded as entry for their unrivalled success story. Among the key achievements of spiders at least four have to be mentioned. First, spiders possess up to six different silk gland types that allow them to use silk for a variety of web types not only to catch their prey but also to wrap their victims until they are defenceless. Spiders build silken retreats, sperm webs, cocoons and draglines, thus demonstrating the remarkable material properties of one of the most resistant and elastic biomaterials. Second, spiders are venomous animals and inject defined venom quantities into a prey item to paralyse or kill it. Spider venom is a complex mixture of hundreds of components, consisting of low molecular compounds, peptides and proteins, which target the extracellular matrix, membranes and a variety of receptors, quite often located in the nervous or muscular system. Third, the locomotion of spiders is driven by a combination of muscles and a hydraulic pressure system, since some leg segments only possess flexor muscles. Instead of extensor muscles, the hydraulic pressure of their haemolymph is fine-tuned by a well-balanced system of valves, which provides the necessary back-pressure. This reduces in major parts of the long leg tubes of spiders the muscle system and allows at the same time larger flexors, so that spiders in general are more powerful than comparable insects. Fourth, the distal end of the male pedipalp developed into a complex structure composed of fixed and movable sclerites that are used to transfer sperm to the female seminal receptacles during mating. This key-lock mechanism guarantees safe sperm transfer within the species, largely preventing mating outside the own species, and probably represents a major driver for the fast species radiation we observe in spiders. Ecophysiology is a bridge from functional and evolutionary aspects of morphology, physiology, biochemistry and molecular biology to ecology. Currently, v

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.

The adhesive droplets in the orb webs of araneoid spiders contain, among other constituents, an aqueous solution of organic low-molecular-weight compounds. The chemical composition of this solution has been investigated for pooled web collections from several species, but little is known about how the composition might vary among individuals or among environments. To begin addressing these questions, we analyzed serial collections of orb webs spun by individual juvenile Nephila clavipes from three different populations held first under field conditions and then under laboratory conditions.Our results indicate that the composition of the organic low-molecular-weight solution is not fixed. We found significant differences in the droplet composition among individuals, among populations, and with the transfer of spiders to laboratory conditions. The possible origins and consequences of these differences are discussed.

In the first half of this century, several workers observed small, seemingly glandular structures attached to the ampullate glands of spiders. Hence, they were termed accessory ampullate glands. In juvenile Araneus cavaticus, two pairs of these structures are present (starting at least with third instars), one pair attached to the major ampullate (MaA) glands and the other pair attached to the minor ampullate (MiA) glands. In adults, two pairs of accessory MaA glands and two pairs of accessory MiA glands are present. The two latter-formed pairs of accessory ampullate glands are clearly the remnants of those ampullate glands which atrophy shortly after adulthood is reached. Morphological similarities between these accessory ampullate glands and those present in juveniles provide an indication that the latter also have their origin in functional ampullate glands. A reduction in the number of ampullate glands following the last molt occurs in many spiders. The reason(s) for these reductions is unknown. In penultimate spiders close to ecdysis, we have observed that while the larger pairs of MaA and MiA glands (those that are retained in the adult) are undergoing molt-related changes which apparently render them nonfunctional, their smaller counterparts are seemingly unaffected and functional. This raises the possibility that the principal role of the smaller ampullate glands may be to assume functions during the pre-ecdysial period which are normally in the domain of the larger ampullate glands. If true, then their degeneration after the last molt would make economic sense. The presence of cylindrical spigots in juvenile females starting with fourth instars is documented.