Evidence for Diet Effects on the Composition of Silk Proteins Produced by Spiders

Abstract

Silks are highly expressed, secreted proteins that represent a substantial metabolic cost to the insects and spiders that produce them. Female spiders in the superfamily Araneoidea (the orb-spinning spiders and their close relatives) spin six different kinds of silk (three fibroins and three fibrous protein glues) that differ in amino acid content and protein structure. In addition to this diversity in silks produced by different glands, we found that individual spiders of the same species can spin dragline silks (drawn from the spider's ampullate gland) that vary in content as well. Freely foraging ARGIOPE: argentata (Araneae: Araneoidea), collected from 13 Caribbean islands, produced dragline silk that showed an inverse relationship between the amount of serine and glycine they contained. X-ray microdiffraction of the silks localized these differences to the amorphous regions of the protein that are thought to lend silks their elasticity. The crystalline regions of the proteins, which lend silks their strength, were unaffected. Laboratory experiments with ARGIOPE: keyserlingi suggested that variation in silk composition reflects the type of prey the spiders were fed but not the total amount of prey they received. Hence, it may be that the amino acid content (and perhaps the mechanical properties) of dragline silk spun by ARGIOPE: directly reflect the spiders' diet. The ability to vary silk composition and, possibly, function is particularly important for organisms that disperse broadly, such as Argiope, and that occupy diverse habitats with diverse populations of prey.

Orientational order of Australian spider silks as determined by solid‐state NMR

“…9 Supporting data from positron annihilation spectroscopy, which gives quantitative information about the number and dimensions of free-volume sites, or amorphous regions, 43,44 indicated that the Nephila silk was more crystalline than Argiope silk (A. Hill, personal communication). We have previously shown that diet can vary the amino acid content of Argiope dragline silk 45 and this can show great inter-and intraspecies variation. 2,26,45 Significant mechanical differences are observed in N. clavipes dragline when spiders are fed diets deprived of Ala and Gly.…”

“…We have previously shown that diet can vary the amino acid content of Argiope dragline silk 45 and this can show great inter-and intraspecies variation. 2,26,45 Significant mechanical differences are observed in N. clavipes dragline when spiders are fed diets deprived of Ala and Gly. 46 Nephila appears to be more ordered than Argiope dragline silk when considering the 15 N-Ala spectra.…”

Spider Silk Proteins – Mechanical Property and Gene Sequence

“…Hence, effects, like spider growth, food intake or drawing speed, may play a consideable role in mechanical properties of the spider silk. For example, observations on a group of 29 juvenile Argiope keyserlingi spiders in Brisbane, Australia, show that change in diet might slightly change the amino acid content of the dragline silk (Craig et al, 2000). On the other hand, there was no observed correlation between certain vegetation and amino acid composition.…”

“…On the other hand, there was no observed correlation between certain vegetation and amino acid composition. Eighteen species of Argiope argentata from areas in the Caribbean Islands with various types of vegetation, beachcoconut, beach-acacia and mixed grasses, were studied (by Craig et al, 2000). The amino acid composition of dragline silk in the different spiders turned out to be highly variable, particularly the concentration of glycine and serine.…”

“…Of the remaining amino acids of dragline silk, only 4-25% seemed to have been obtained from the prey. Variation in amino acid composition between observed species was believed to lie in the amorphous fraction, which is the fraction responsible for elasticity (Craig et al, 2000).…”