Semi-aquatic spider silks: transcripts, proteins, and silk fibres of the fishing spider, Dolomedes triton (Pisauridae)

Characterization of the primary structure of the major silk gene, h-fibroin, across caddisfly (Trichoptera) suborders

Larvae of caddisflies (Trichoptera) produce silk to build various underwater structures allowing them to exploit a wide range of aquatic environments. The silk adheres to various substrates underwater and has high tensile strength, extensibility, and toughness and is of interest as a model for biomimetic adhesives. As a step toward understanding how the properties of underwater silk evolved in Trichoptera, we used genomic data to identify full-length sequences and characterize the primary structure of the major silk protein, h-fibroin, across the order. The h-fibroins have conserved termini and basic motif structure with high variation in repeating modules and variation in the percentage of amino acids, mainly proline. This finding might be linked to differences in mechanical properties related to the different silk usage and sets a starting point for future studies to screen and correlate amino acid motifs and other sequence features with quantifiable silk properties.

1000 spider silkomes: Linking sequences to silk physical properties

Spider silks are among the toughest known materials and thus provide models for renewable, biodegradable, and sustainable biopolymers. However, the entirety of their diversity still remains elusive, and silks that exceed the performance limits of industrial fibers are constantly being found. We obtained transcriptome assemblies from 1098 species of spiders to comprehensively catalog silk gene sequences and measured the mechanical, thermal, structural, and hydration properties of the dragline silks of 446 species. The combination of these silk protein genotype-phenotype data revealed essential contributions of multicomponent structures with major ampullate spidroin 1 to 3 paralogs in high-performance dragline silks and numerous amino acid motifs contributing to each of the measured properties. We hope that our global sampling, comprehensive testing, integrated analysis, and open data will provide a solid starting point for future biomaterial designs.

Golden orb-weaving spider (Trichonephila clavipes) silk genes with sex-biased expression and atypical architectures

Spider silks are renowned for their high-performance mechanical properties. Contributing to these properties are proteins encoded by the spidroin (spider fibroin) gene family. Spidroins have been discovered mostly through cDNA studies of females based on the presence of conserved terminal regions and a repetitive central region. Recently, genome sequencing of the golden orb-web weaver, Trichonephila clavipes, provided a complete picture of spidroin diversity. Here, we refine the annotation of T. clavipes spidroin genes including the reclassification of some as non-spidroins. We rename these non-spidroins as spidroin-like (SpL) genes because they have repetitive sequences and amino acid compositions like spidroins, but entirely lack the archetypal terminal domains of spidroins. Insight into the function of these spidroin and SpL genes was then examined through tissue- and sex-specific gene expression studies. Using qPCR, we show that some silk genes are upregulated in male silk glands compared to females, despite males producing less silk in general. We also find that an enigmatic spidroin that lacks a spidroin C-terminal domain is highly expressed in silk glands, suggesting that spidroins could assemble into fibers without a canonical terminal region. Further, we show that two SpL genes are expressed in silk glands, with one gene highly evolutionarily conserved across species, providing evidence that particular SpL genes are important to silk production. Together, these findings challenge long-standing paradigms regarding the evolutionary and functional significance of the proteins and conserved motifs essential for producing spider silks.

Spider Silks: An Overview of Their Component Proteins for Hydrophobicity and Biomedical Applications

Spider silks have received extensive attention from scientists and industries around the world because of their remarkable mechanical properties, which include high tensile strength and extensibility. It is a leading-edge biomaterial resource, with a wide range of potential applications. Spider silks are composed of silk proteins, which are usually very large molecules, yet many silk proteins still remain largely underexplored. While there are numerous reviews on spider silks from diverse perspectives, here we provide a most up-to-date overview of the spider silk component protein family in terms of its molecular structure, evolution, hydrophobicity, and biomedical applications. Given the confusion regarding spidroin naming, we emphasize the need for coherent and consistent nomenclature for spidroins and provide recommendations for pre-existing spidroin names that are inconsistent with nomenclature. We then review recent advances in the components, identification, and structures of spidroin genes. We next discuss the hydrophobicity of spidroins, with particular attention on the unique aquatic spider silks. Aquatic spider silks are less known but may inspire innovation in biomaterials. Furthermore, we provide new insights into antimicrobial peptides from spider silk glands. Finally, we present possibilities for future uses of spider silks.

Free-standing spider silk webs of the thomisid Saccodomus formivorus are made of composites comprising micro- and submicron fibers

Our understanding of the extraordinary mechanical and physico-chemical properties of spider silk is largely confined to the fibers produced by orb-weaving spiders, despite the diversity of foraging webs that occur across numerous spider families. Crab spiders (Thomisidae) are described as ambush predators that do not build webs, but nevertheless use silk for draglines, egg cases and assembling leaf-nests. A little-known exception is the Australian thomisid Saccodomus formivorus, which constructs a basket-like silk web of extraordinary dimensional stability and structural integrity that facilitates the capture of its ant prey. We examined the physical and chemical properties of this unusual web and revealed that the web threads comprise microfibers that are embedded within a biopolymeric matrix containing additionally longitudinally-oriented submicron fibers. We showed that the micro- and submicron fibers differ in their chemical composition and that the web threads show a remarkable lateral resilience compared with that of the major ampullate silk of a well-investigated orb weaver. Our novel analyses of these unusual web and silk characteristics highlight how investigations of non-model species can broaden our understanding of silks and the evolution of foraging webs.

The life aquatic with spiders (Araneae): repeated evolution of aquatic habitat association in Dictynidae and allied taxa

Despite the dominance of terrestriality in spiders, species across a diverse array of families are associated with aquatic habitats. Many species in the spider family Dictynidae are associated with water, either living near it or, in the case of Argyroneta aquatica, in it. Previous studies have indicated that this association arose once within the family. Here we test the hypothesis of a single origin via the broadest phylogeny of dictynids and related ‘marronoids’ to date, using several taxa that were not previously sampled in molecular analyses to provide the first quantitative test of the hypothesis put forth by Wheeler et al. (2016). We sampled 281 terminal taxa from 14 families, assembling a matrix with 4380 total base pairs of data from most taxa. We also assembled an atlas of morphological traits with potential significance for both ecology and taxonomy. Our resulting trees indicate that an aquatic habitat association has arisen multiple times within dictynids. Dictynidae and the genus Dictyna are polyphyletic and the genera Lathys and Cicurina remain unplaced. A review of aquatic habitat associations in spiders indicates that it occurs in members of at least 21 families. With our morphological atlas, we explore characters that have been implicated in aiding an aquatic lifestyle, which in the past may have caused confusion regarding taxon placement. Our results indicate that not all spiders with traits thought to be useful for aquatic habitat associations occupy such habitats, and that some spider taxa lacking these traits are nonetheless associated with water.

Spidroins and Silk Fibers of Aquatic Spiders

Spiders are commonly found in terrestrial environments and many rely heavily on their silks for fitness related tasks such as reproduction and dispersal. Although rare, a few species occupy aquatic or semi-aquatic habitats and for them, silk-related specializations are also essential to survive in aquatic environments. Most spider silks studied to date are from cob-web and orb-web weaving species, leaving the silks from many other terrestrial spiders as well as water-associated spiders largely undescribed. Here, we characterize silks from three Dictynoidea species: the aquatic spiders Argyroneta aquatica and Desis marina as well as the terrestrial Badumna longinqua. From silk gland RNA-Seq libraries, we report a total of 47 different homologs of the spidroin (spider fibroin) gene family. Some of these 47 spidroins correspond to known spidroin types (aciniform, ampullate, cribellar, pyriform, and tubuliform), while other spidroins represent novel branches of the spidroin gene family. We also report a hydrophobic amino acid motif (GV) that, to date, is found only in the spidroins of aquatic and semi-aquatic spiders. Comparison of spider silk sequences to the silks from other water-associated arthropods, shows that there is a diversity of strategies to function in aquatic environments.