Mark A. Townley

Changes in composition of spider orb web sticky droplets with starvation and web removal, and synthesis of sticky droplet compounds

SUMMARY 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 spiders 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.

Water extraction by the major ampullate duct during silk formation in the spider, Argiope aurantia Lucas

Abstract The water, K+ and Na+ content of naturally produced major ampullate silk as well as silk mechanically drawn from the spider Argiope aurantia have been compared to that of the major ampullate gland. It is demonstrated that water is extracted by the major ampullate duct and that this process is accompanied by an exchange of K+ for Na+. The significance of these observations is discussed.

Detection and isolation of proctolin-like immunoreactivity in arachnids: Possible cardioregulatory role for proctolin in the orb-weaving spiders Argiope and Araneus

Abstract Proctolin-like immunoreactivity was detected in the prosoma of four species of araneid spiders. Proctolin levels as determined by radioimmunoassay ranged from 3.2 ± 0.6 ng proctolin per prosoma in Argiope aurantia to 8.7 ± 0.9 ng proctolin per prosoma in Araneus cavaticus . Immunohistochemical staining of prosomal sections revealed proctolin-positive tracts, fibres and varicosities in both the supraoesophageal and suboesophageal ganglia of Argiope aurantia and Araneus cavaticus . Using whole-mount preparations of spider hearts, proctolin immunoreactive fibres and varicosities were also observed in association with the myocardium. Proctolin-like bioactivity in partially purified prosomal extracts of Argiope aurantia and Araneus cavaticus co-eluted with synthetic proctolin using high-performance liquid chromatography. Application of 10 −7 M synthetic proctolin to the neurogenic spider heart typically caused increases in the strength and rate of heart contractions, and occasionally produced a sustained contracture of the myocardium. Responses were similar in all four species examined. These data suggest that an endogenous proctolin-like peptide in these arachnids may act as a cardioregulatory neuromodulator or as a neurotransmitter in the central nervous system.

VARIATION IN THE CHEMICAL COMPOSITION OF ORB WEBS BUILT BY THE SPIDER NEPHILA CLAVIPES (ARANEAE, TETRAGNATHIDAE)

Abstract 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.

ON THE USE OF AMPULLATE GLAND SILKS BY WOLF SPIDERS (ARANEAE, LYCOSIDAE) FOR ATTACHING THE EGG SAC TO THE SPINNERETS AND A PROPOSAL FOR DEFINING NUBBINS AND TARTIPORES

Abstract The means by which female wolf spiders attach an egg sac to their spinnerets was investigated using scanning electron microscopy. In four Pardosa species, we observed that silk fibers emerging from ampullate gland spigots had been affixed to the surface of the egg sac. More specifically, primary (1°) and secondary (2°) major ampullate (MaA) glands and 1° and 2° minor ampullate (MiA) glands all contributed fibers for this purpose. The diameters of the 2° MaA and 2° MiA fibers were greater than those of the 1° MaA and 1° MiA fibers and, correspondingly, the widths of the 2° ampullate spigots were clearly greater than those of the 1° ampullate spigots. Larger 2° ampullate spigots were also observed in adult females of species from three other lycosid genera. Thus, 2° ampullate glands, which in araneoids function only in juveniles during proecdysis, are not only functional in adult female lycosids (and adult females of several other families), but they appear to play a greater role than the 1° ampullate glands in egg sac attachment. Observations made on the 1° and 2° ampullate spigots of adult females from species belonging to several other families are also presented. Cuticular structures referred to as nubbins and tartipores are present in some spinning fields on spinnerets. A proposal is made for defining these terms by a criterion, namely their different origins, which differs from that applied previously.

The independent regulation of protein synthesis in the major ampullate glands of Araneus cavaticus (Keyserling)

Abstract The effect of mechanical silking on the rate of protein synthesis in the major ampullate glands of the spider Araneus cavaticus has been investigated. Silking of one of the paired glands results in a greater rate of protein synthesis than in the unpulled control gland; in both in vivo and in vitro experiments. Our data indicate that the rate of protein synthesis can be regulated independently in the two silk glands. Radioisotopic label appears in the orb web more rapidly than one would expect were older silk drawn before newly synthesized silk.

Selected aspects of spinning apparatus development in Araneus cavaticus (Araneae, Araneidae)

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.

Identification of proctolin in the central nervous system of the horseshoe crab, Limulus polyphemus

A proctolin-like peptide was isolated from the prosomal CNS of the chelicerate arthropod, Limulus, and purified using size exclusion, ion exchange and high performance liquid chromatography. Coincident bioassay (cockroach hindgut) and radioimmunoassay were employed to identify fractions which contained proctolin-like material. Proctolin-like activity coeluted with synthetic proctolin with all three chromatographic techniques employed. When applied to either the Limulus heart or hindgut preparations, purified Limulus proctolin produced excitatory responses which were indistinguishable from those produced by the synthetic peptide. Purified samples of the Limulus proctolin-like peptide were subjected to Edman degradation and tandem mass spectrometry and the amino acid sequence of the Limulus peptide was determined to be identical to that of cockroach proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH). The presence of proctolin in the Limulus CNS and its biological action on the isolated heart and hindgut suggest a physiological role for this peptide in the regulation of cardiac output and hindgut motility.

Aggregate Silk Gland Secretions of Araneoid Spiders

Aggregate silk glands (Ag) of araneoid spiders are unusual because their products are not dry fibers but aqueous secretions, best known for acting as glues that aid in prey capture. We review what is currently known regarding the composition and occurrence of these secretions among builders of orb webs (primarily Nephilidae, Araneidae), cobwebs (Theridiidae), and sheet webs (Linyphiidae) and how the use of these secretions differs among these three lifestyles. For cobweb builders, the separation of the two pairs of Ag into morphologically, compositionally, and functionally distinct “typical” and “atypical” Ag types adds further complexity to an understanding of their secretions. Possible roles played by small molecule components of Ag secretions and aspects of their synthesis are considered. In orb webs and cobwebs, aggregate secretions produce the sticky droplets on the web’s sticky spiral and gumfoot lines, respectively. The droplets, at least in orb webs, are not homogeneous, and we discuss current ideas on organization and function within the droplets. We also review recent work on the physical behavior of sticky droplets in orb webs and cobwebs. This includes the recognition that adhesive force generated in orb webs is attributable to more than just the glycoprotein glue’s adhesion to a surface. Limits imposed by natural selection on the stickiness of the glue are also discussed.

Excitatory Actions of FMRFamide-Related Peptides (FaRPs) on the Neurogenic Limulus Heart

The actions of FMRFamide-related peptides (FaRPs) on the neurogenic heart of the horseshoe crab, Limulus polyphemus, were investigated. Excitatory chronotropic effects were produced by application of TNRNFLRFamide, SDRNFLRFamide, GYNRS-FLRFamide, or pQDPFLRFamide to the intact heart preparation. Effects were dose-dependent with a threshold of 10(-9) M or less. TNRNFLRFamide and SDRNFLRFamide increased the burst rate of the isolated Limulus cardiac ganglion. Synthetic FaRPs produced inotropic excitation of the heartbeat as well. GYNRSFLRFamide, TNRNFLRFamide, SDRNFLRFamide, and pQDPFLRFamide increased heart contraction strength at a threshold dose of approximately 10(-8) M. TNRNFLRFamide and SDRNFLRFamide enhanced electrically evoked contractions of the Limulus myocardium, elicited contracture in some preparations, and increased the excitability of cardiac muscle fibers. The presence of cardioactive FaRPs in the Limulus central nervous system was suggested by reverse phase HPLC of acidified methanol extracts of Limulus nervous tissue. Four peaks of FaRP-like bioactivity were detected with the Busycon radula protractor muscle bioassay. These peaks also contained FaRP-like immunoreactivity. Two of these partially purified peaks produced excitatory chronotropic effects on the intact Limulus heart preparation similar to those produced by synthetic FaRPs.