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1. Correlation between protein secondary structure and mechanical performance for the ultra-tough dragline silk of Darwin's bark spider

   https://doi.org/10.1098/rsif.2021.0320  

   Htut, K Zin; Alicea-Serrano, Angela M.; Singla, Saranshu; Agnarsson, Ingi; Garb, Jessica E.; Kuntner, Matjaž; Gregorič, Matjaž; Haney, Robert A.; Marhabaie, Mohammad; Blackledge, Todd A.; et al (June 2021, Journal of The Royal Society Interface)

   null (Ed.)

   The spider major ampullate (MA) silk exhibits high tensile strength and extensibility and is typically a blend of MaSp1 and MaSp2 proteins with the latter comprising glycine–proline–glycine–glycine-X repeating motifs that promote extensibility and supercontraction. The MA silk from Darwin's bark spider ( Caerostris darwini ) is estimated to be two to three times tougher than the MA silk from other spider species. Previous research suggests that a unique MaSp4 protein incorporates proline into a novel glycine–proline–glycine–proline motif and may explain C. darwini MA silk's extraordinary toughness. However, no direct correlation has been made between the silk's molecular structure and its mechanical properties for C. darwini . Here, we correlate the relative protein secondary structure composition of MA silk from C. darwini and four other spider species with mechanical properties before and after supercontraction to understand the effect of the additional MaSp4 protein. Our results demonstrate that C. darwini MA silk possesses a unique protein composition with a lower ratio of helices (31%) and β-sheets (20%) than other species. Before supercontraction, toughness, modulus and tensile strength correlate with percentages of β-sheets, unordered or random coiled regions and β-turns. However, after supercontraction, only modulus and strain at break correlate with percentages of β-sheets and β-turns. Our study highlights that additional information including crystal size and crystal and chain orientation is necessary to build a complete structure–property correlation model. 

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2. The transcriptome of Darwin’s bark spider silk glands predicts proteins contributing to dragline silk toughness

   https://doi.org/10.1038/s42003-019-0496-1  

   Garb, Jessica E.; Haney, Robert A.; Schwager, Evelyn E.; Gregorič, Matjaž; Kuntner, Matjaž; Agnarsson, Ingi; Blackledge, Todd A. (July 2019, Communications Biology)

   Abstract Darwin’s bark spider (Caerostris darwini) produces giant orb webs from dragline silk that can be twice as tough as other silks, making it the toughest biological material. This extreme toughness comes from increased extensibility relative to other draglines. We showC. darwinidragline-producing major ampullate (MA) glands highly express a novel silk gene transcript (MaSp4) encoding a protein that diverges markedly from closely related proteins and contains abundant proline, known to confer silk extensibility, in a unique GPGPQ amino acid motif. This suggestsC. darwinievolved distinct proteins that may have increased its dragline’s toughness, enabling giant webs.Caerostris darwini’sMA spinning ducts also appear unusually long, potentially facilitating alignment of silk proteins into extremely tough fibers. Thus, a suite of novel traits from the level of genes to spinning physiology to silk biomechanics are associated with the unique ecology of Darwin’s bark spider, presenting innovative designs for engineering biomaterials. 

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3. The common house spider, Parasteatoda tepidariorum, maintains silk gene expression on sub-optimal diet

   https://doi.org/10.1371/journal.pone.0237286  

   Miller, Jeremy; Vienneau-Hathaway, Jannelle; Dendev, Enkhbileg; Lan, Merrina; Ayoub, Nadia A. (December 2020, PLOS ONE)

   Signore, Giovanni (Ed.)

   Cobweb weaving spiders and their relatives spin multiple task-specific fiber types. The unique material properties of each silk type result from differences in amino acid sequence and structure of their component proteins, primarily spidroins (spider fibrous proteins). Amino acid content and gene expression measurements of spider silks suggest some spiders change expression patterns of individual protein components in response to environmental cues. We quantified mRNA abundance of three spidroin encoding genes involved in prey capture in the common house spider, Parasteatoda tepidariorum (Theridiidae), fed different diets. After 10 days of acclimation to the lab on a diet of mealworms, spiders were split into three groups: (1) individuals were immediately dissected, (2) spiders were fed high-energy crickets, or (3) spiders were fed low-energy flies, for 1 month. All spiders gained mass during the acclimation period and cricket-fed spiders continued to gain mass, while fly-fed spiders either maintained or lost mass. Using quantitative PCR, we found no significant differences in the absolute or relative abundance of dragline gene transcripts, major ampullate spidroin 1 ( MaSp1 ) and major ampullate spidroin 2 ( MaSp2 ), among groups. In contrast, prey-wrapping minor ampullate spidroin ( MiSp) gene transcripts were significantly less abundant in fly-fed than lab-acclimated spiders. However, when measured relative to Actin , cricket-fed spiders showed the lowest expression of MiSp . Our results suggest that house spiders are able to maintain silk production, even in the face of a low-quality diet. 

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4. Behavior and Bioadhesives: How Bolas Spiders, Mastophora hutchinsoni, Catch Moths

   https://doi.org/10.3390/insects13121166  

   Diaz, Candido; Long, John H. (December 2022, Insects)

   Spiders use various combinations of silks, adhesives, and behaviors to ensnare and trap prey. A common but difficult to catch prey in most spider habitats are moths. They easily escape typical orb-webs because their bodies are covered in sacrificial scales that flake off when in contact with the web’s adhesives. This defense is defeated by spiders of the sub-family of Cyrtarachninae, moth-catching specialists who combine changes in orb-web structure, predatory behavior, and chemistry of the aggregate glue placed in those webs. The most extreme changes in web structure are shown by bolas spiders, who create a solitary capture strand containing only one or two glue droplets at the end of a single thread. They prey on male moths by releasing pheromones to draw them within range of their bolas, which they flick to ensnare the moth. We used a high-speed video camera to capture the behavior of the bolas spider Mastophora hutchinsoni. We calculated the kinematics of spiders and moths in the wild to model the physical and mechanical properties of the bolas during prey capture, the behavior of the moth, and how these factors lead to successful prey capture. We created a numerical model to explain the mechanical behavior of the bolas silk during prey capture. Our kinematic analysis shows that the material properties of the aggregate glue bolas of M. hutchinsoni are distinct from that of the other previously analyzed moth-specialist, Cyrtarachne akirai. The spring-like behavior of the M. hutchinsoni bolas suggests it spins a thicker liquid. 

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5. Temporal Diversification and Evolutionary History of the Cribellum in Marronoid Spiders

   Mottershead, S. D.; Riquelme, F. C.; Esposito, L. A.; Gorneau, J. A. (October 2023, Society for the Advancement of Chicanos/Hispanics and Native Americans in Science - 2023 NDiSTEM)

   Webs play many essential roles in spider biology, including communication, prey capture, locomotion, and reproduction. One interesting morphological feature of many spiders is the cribellum, a plate located near the silk-producing structures called spinnerets, and used to create a special type of matted silk that captures prey mechanically, instead of with glue droplets used by many orb-weaving spiders. The cribellum is hypothesized to have been present in the ancestor of all araneomorph spiders, but lost multiple times over the course of spider evolution. One group of spiders, the ‘marronoids’, shows a pattern of repeated loss and gain of this structure, placing them at a transitional position in the evolution of spider webs, with further implications for the web capture strategy, and other ecological conditions such as water-associated habitat. Studying the timing of the loss of the cribellum may yield insight to the cryptic ecology and morphology of the marranoid clade, and more broadly, araneomorph spiders. We use comparative phylogenetic methods to identify ancestral states of morphological and behavioral characters, and examine divergence dates with fossil calibrations. To do this, 98 representative spiders from the marronoid clade were coded by zoogeographic region, distribution proximity to a body of water and type, web type, and observed aquatic behavior. The morphology of the cribellum and spinnerets was assessed using 42 characters with multiple states. We identified patterns of evolution of the cribellum and aquatic habitat associations in the context of phylogeny, and geologic time. 

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