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![Phylogeny for spider groups analyzed in this study. Phylogeny is based on [2,48]. doi:10.1371/journal.pone.0038084.g001](publication/228116401/figure/fig7/AS:667188092497920@1536081445007/Phylogeny-for-spider-groups-analyzed-in-this-study-Phylogeny-is-based-on-2-48.png)
Phylogeny for spider groups analyzed in this study. Phylogeny is based on [2,48]. doi:10.1371/journal.pone.0038084.g001
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![Phylogeny is based on [2], [48].](publication/228116401/figure/fig1/AS:214211079741441@1428083309696/Phylogeny-is-based-on-2-48_Q320.jpg)
Silk spinning is essential to spider ecology and has had a key role in the expansive diversification of spiders. Silk is composed primarily of proteins called spidroins, which are encoded by a multi-gene family. Spidroins have been studied extensively in the derived clade, Orbiculariae (orb-weavers), from the suborder Araneomorphae ('true spiders')...
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... few species have been sampled for their silk genes. While most silk research has focused on derived members of Araneomorphae (''true spiders''), we present silk genes from Paleocribelletae (a basal araneomorph clade), increase sampling for Mygalomorphae (trapdoor spiders, tarantulas, and their kin; the sister group to Araneomorphae), and record silk sequences from Mesothelae (segmented spiders; the sister suborder to all other spiders; Figure 1; [2]). Mesotheles and mygalomorphs exhibit profound differences in silk use compared to most araneomorph spiders [3,4]. ...
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... used the tree based on the maximum likelihood (ML) analysis with constraints (Figures 3, S1; Table S1) for reconcili- ation analysis and reconstruction of the evolution of continuous characters (Table S2). While tubuliform, aciniform, pyriform, and flagelliform spidroins were each recovered as monophyletic in all ML and Bayesian analyses, without these constraints, monophy- letic groupings of neither major ampullate spidroins nor minor ampullate spidroins were recovered. ...
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... monophyly of both major ampullates and minor ampullates is supported by a previous Bayesian analysis of combined N and C-terminal data [23]. The ML constrained and unconstrained trees were identical at 46 of 58 nodes ( Figure S1). Conflicting relationships were restricted to weakly supported nodes (Table S1). ...
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... N- terminal region of Liphistius fib1 has not been characterized, but there are three cysteines in the C-terminal region that may allow for disulfide bonds with the ECPLs, as well as between fib1 monomers. Phylogenetic analyses did not recover a close relationship between Liphistius fib1 and TuSp1, indicating that TuSp1 is the result of spidroin duplication after the split of Opisthothelae from Mesothelae (Figures 1, 3). This implies that ECPs evolved prior to TuSp1. ...
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... many cases, closely related spidroin proteins may be used in the construction of very different web architectures. For example, Aliatypus spiders construct trapdoors, yet their spidroin is most closely related to the spidroins of Hexura and Megahexura, which construct sheet-webs (Figures 3, S1). On the other hand, very similar architectures may be built from very divergent spidroins. ...
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... and Bayesian analyses were also conducted with constraints placed for each gland-associated spidroin group (i.e., minor ampullate, major ampullate, flagelliform, tubuliform, pyriform, and aciniform gland types; Figure S1; Table S1). Our higher-level sampling was not intended to establish monophyly of each of the gland associated spidroin groups; rather we aimed to determine the phylogenetic placements of the gland associated spidroin groups among spidroins from across the spider phylogeny. ...
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... punctuated average model was favored if the data was indicated to have evolved from branching events where the branch lengths were 100 or, more conservatively, 1000 times longer than their corresponding sister branch lengths (CoMET User's Guide, Feb. 2006). Figure S1 Spidroin gene tree based on ML analysis of the carboxy-terminal encoding region. In the analysis, gaps were coded as binary characters and monophyly of some groups was constrained (see Methods). ...
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Citations
... Although the types of core genes among spiders and insects were different, GMC genes were partially or entirely conserved. As spiders evolved, the types of silk refined and increased 47 . Mygalomorphae spiders are known to retain a higher number of ancestral states and are more primitive than the Araneomorphae. ...
The spider of Ectatosticta davidi, belonging to the lamp-shade web spider family, Hypochilidae, which is closely related to Hypochilidae and Filistatidae and recovered as sister of the rest Araneomorphs spiders. Here we show the final assembled genome of E. davidi with 2.16 Gb in 15 chromosomes. Then we confirm the evolutionary position of Hypochilidae. Moreover, we find that the GMC gene family exhibit high conservation throughout the evolution of true spiders. We also find that the MaSp genes of E. davidi may represent an early stage of MaSp and MiSp genes in other true spiders, while CrSp shares a common origin with AgSp and PySp but differ from MaSp. Altogether, this study contributes to addressing the limited availability of genomic sequences from Hypochilidae spiders, and provides a valuable resource for investigating the genomic evolution of spiders.
... Dragline silk has been understood to be composed primarily of two spidroins, MaSp1 and MaSp2, that have similar but distinct evolutionary histories and structural properties. Nearly all spidroins are encoded by large genes that belong to a single gene family that has undergone substantial diversification throughout the evolutionary history of spiders [11][12][13][14]. Spidroins share a common structure characterized by short conserved N-and C-terminal regions flanking a long repetitive region in which repeat units are often highly homogenized [15,16]. ...
... genes appear to be replaced largely by serine residues (S4 Fig) and the two V. arenata MaSp2.1 sequences (Fig 7) that lack QQ repeats also have a high serine composition (11.6% and 9.1%). A similar trade-off between glycine and serine was found across multiple spidroins spanning the Araneae [11]. Overall, given the dramatic shift in QQ motif representation within MaSp2 evolutionary history, it will be critical for future studies to isolate the functional properties of this motif. ...
The evolutionary diversification of orb-web weaving spiders is closely tied to the mechanical performance of dragline silk. This proteinaceous fiber provides the primary structural framework of orb web architecture, and its extraordinary toughness allows these structures to absorb the high energy of aerial prey impact. The dominant model of dragline silk molecular structure involves the combined function of two highly repetitive, spider-specific, silk genes (spidroins)—MaSp1 and MaSp2. Recent genomic studies, however, have suggested this framework is overly simplistic, and our understanding of how MaSp genes evolve is limited. Here we present a comprehensive analysis of MaSp structural and evolutionary diversity across species of Argiope (garden spiders). This genomic analysis reveals the largest catalog of MaSp genes found in any spider, driven largely by an expansion of MaSp2 genes. The rapid diversification of Argiope MaSp genes, located primarily in a single genomic cluster, is associated with profound changes in silk gene structure. MaSp2 genes, in particular, have evolved complex hierarchically organized repeat units (ensemble repeats) delineated by novel introns that exhibit remarkable evolutionary dynamics. These repetitive introns have arisen independently within the genus, are highly homogenized within a gene, but diverge rapidly between genes. In some cases, these iterated introns are organized in an alternating structure in which every other intron is nearly identical in sequence. We hypothesize that this intron structure has evolved to facilitate homogenization of the coding sequence. We also find evidence of intergenic gene conversion and identify a more diverse array of stereotypical amino acid repeats than previously recognized. Overall, the extreme diversification found among MaSp genes requires changes in the structure-function model of dragline silk performance that focuses on the differential use and interaction among various MaSp paralogs as well as the impact of ensemble repeat structure and different amino acid motifs on mechanical behavior.
... The appearance of the MaSp2 proteins seems to represent a major evolutionary breakthrough that is used to distinguish two different lineages within the Entelegynae [14]: RTA-clade and Araneoidea. Both lineages spin MAS fibers with comparable values of tensile strength (up to a true stress, σ, of σ ≈ 1500 MPa), but the silk produced by the Araneoidea tends to show larger values of strain at breaking (up to a true strain, ε, of ε ≈ 1.5), when compared with the maximum value of true strain, ε ≈ 0.5 attained by RTA-clade representatives [5]. ...
Two different polyglycine-rich fragments were selected as representatives of major ampullate gland spidroins (MaSp) 1 and 2 types, and their behavior in a water-saturated environment was simulated within the framework of molecular dynamics (MD). The selected fragments are found in the sequences of the proteins MaSp1a and MaSp2.2a of Argiope aurantia with respective lengths of 36 amino acids (MaSp1a) and 50 amino acids (MaSp2.2s). The simulation took the fully extended β-pleated conformation as reference, and MD was used to determine the equilibrium configuration in the absence of external forces. Subsequently, MD were employed to calculate the variation in the distance between the ends of the fragments when subjected to an increasing force. Both fragments show an elastomeric behavior that can be modeled as a freely jointed chain with links of comparable length, and a larger number of links in the spidroin 2 fragment. It is found, however, that the maximum recovery force recorded from the spidroin 2 peptide (Fmax ≈ 400 pN) is found to be significantly larger than that of the spidroin 1 (Fmax ≈ 250 pN). The increase in the recovery force of the spidroin 2 polyglycine-rich fragment may be correlated with the larger values observed in the strain at breaking of major ampullate silk fibers spun by Araneoidea species, which contain spidroin 2 proteins, compared to the material produced by spider species that lack these spidroins (RTA-clade).
... mino acids; Hinman et al. 1992;Ayoub and Hayashi 2007) and consist of strongly conserved amino (N)-and carboxyl (C)terminal regions flanking a highly repetitive central region (Garb et al. 2010;Xu and Lewis 1990). Unlike the N-and C-terminal regions, the sequences of the highly repetitive central regions vary greatly across spidroin family members (Starrett et. al 2012;Babb et. al 2017). Comparative analyses of the repetitive regions of major ampullate spidroin (MaSp) sequences have identified amino acid motifs that are believed to confer structural and mechanical properties to MA silk fibers. Most generally, poly-alanine (poly-A) blocks within the repetitive regions have been demonstrated to assemble ...
Spider dragline fibers exhibit incredible mechanical properties, outperforming many synthetic polymers in toughness assays, and possess desirable properties for medical and other human applications. These qualities make dragline fibers popular subjects for biomimetics research. The enormous diversity of spiders presents both an opportunity for the development of new bioinspired materials and a challenge for the identification of fundamental design principles, as the mechanical properties of dragline fibers show both intraspecific and interspecific variations. In this regard, the stress–strain curves of draglines from different species have been shown to be effectively compared by the α* parameter, a value derived from maximum-supercontracted silk fibers. To identify potential molecular mechanisms impacting α* values, here we analyze spider fibroin (spidroin) sequences of the Western black widow (Latrodectus hesperus) and the black and yellow garden spider (Argiope aurantia). This study serves as a primer for investigating the molecular properties of spidroins that underlie species-specific α* values. Initial findings are that while overall motif composition was similar between species, certain motifs and higher level periodicities of glycine-rich region lengths showed variation, notably greater distances between poly-A motifs in A. aurantia sequences. In addition to increased period lengths, A. aurantia spidroins tended to have an increased prevalence of charged and hydrophobic residues. These increases may impact the number and strength of hydrogen bond networks within fibers, which have been implicated in conformational changes and formation of nanocrystals, contributing to the greater extensibility of A. aurantia draglines compared to those of L. hesperus.
... Pioneering work by Gatesy et al. (14) identified and analyzed spidroin sequences from several spider lineages, including basal spider groups, thus enabling a glimpse into the complex evolution of spidroin sequences. Subsequently, there have been a large number of studies that have explored the subject of spidroin sequence diversity and evolution, including focused studies on various spidroin paralogs (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29), and those from more phylogenetic perspective (7,(30)(31)(32)(33)(34), predominantly based on the conserved terminal sequences. On the other hand, the mechanical properties of silk fibers are governed largely through the repetitive regions that dominate the silk protein sequence, and the study on the diversity of spidroin repetitive regions, particularly in the more evolutionarily divergent taxa, has been limited to date. ...
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.
... The evolution of spider silk has received considerable attention [17,[20][21][22][23]. More derived spiders possess multiple distinct silk glands, which are serially homologous. ...
... We identified sequences belonging to the seven major spidroin clades (aciniform, aggregate, flagelliform, major ampullate, minor ampullate, piriform, and tubuliform), as well as three uncharacterized spidroins with homology to genes that had previously been identified only in the orb-weaving genus Trichonephila (Sp-5803, Sp-907/74867, and Sp-1339) [14,38]. Phylogenetic conflict can occur between spidroin N-and C-termini, and N-termini generally contain more phylogenetic signal [21,39]. Nonetheless, the only major topological difference between our two trees is that the N-terminal tree recovers a sister relationship between aciniform and tubuliform (as in [21]), whereas the C-terminal tree places aciniform sister to (flagelliform + aggregate). ...
... Phylogenetic conflict can occur between spidroin N-and C-termini, and N-termini generally contain more phylogenetic signal [21,39]. Nonetheless, the only major topological difference between our two trees is that the N-terminal tree recovers a sister relationship between aciniform and tubuliform (as in [21]), whereas the C-terminal tree places aciniform sister to (flagelliform + aggregate). Note that with our data, we have no way of knowing which Nand C-terminal sequences belong to the same physical gene. ...
Background
A striking aspect of evolution is that it often converges on similar trajectories. Evolutionary convergence can occur in deep time or over short time scales, and is associated with the imposition of similar selective pressures. Repeated convergent events provide a framework to infer the genetic basis of adaptive traits. The current study examines the genetic basis of secondary web loss within web-building spiders (Araneoidea). Specifically, we use a lineage of spiders in the genus Tetragnatha (Tetragnathidae) that has diverged into two clades associated with the relatively recent (5 mya) colonization of, and subsequent adaptive radiation within, the Hawaiian Islands. One clade has adopted a cursorial lifestyle, and the other has retained the ancestral behavior of capturing prey with sticky orb webs. We explore how these behavioral phenotypes are reflected in the morphology of the spinning apparatus and internal silk glands, and the expression of silk genes. Several sister families to the Tetragnathidae have undergone similar web loss, so we also ask whether convergent patterns of selection can be detected in these lineages.
Results
The cursorial clade has lost spigots associated with the sticky spiral of the orb web. This appears to have been accompanied by loss of silk glands themselves. We generated phylogenies of silk proteins (spidroins), which showed that the transcriptomes of cursorial Tetragnatha contain all major spidroins except for flagelliform. We also found an uncharacterized spidroin that has higher expression in cursorial species. We found evidence for convergent selection acting on this spidroin, as well as genes involved in protein metabolism, in the cursorial Tetragnatha and divergent cursorial lineages in the families Malkaridae and Mimetidae.
Conclusions
Our results provide strong evidence that independent web loss events and the associated adoption of a cursorial lifestyle are based on similar genetic mechanisms. Many genes we identified as having evolved convergently are associated with protein synthesis, degradation, and processing, which are processes that play important roles in silk production. This study demonstrates, in the case of independent evolution of web loss, that similar selective pressures act on many of the same genes to produce the same phenotypes and behaviors.
... The evolution of silk properties and its uses in spiders is related to selective pressures that affect spinning behaviors, ecology, and the physiological production of silk (Vollrath, 1999). Different taxonomic groups of spiders have shown modifications in the use of silk, and the variation is linked to the type of habitat, prey capture strategy, predator deterrence, and mating Garb, 2013;Starrett et al., 2012). Arguably, the most important factor affecting web properties and architecture is the type of prey that the spider catches, which can change as the spider ages (Sensenig et al., 2011). ...
... Arguably, the most important factor affecting web properties and architecture is the type of prey that the spider catches, which can change as the spider ages (Sensenig et al., 2011). Mygalomorphs and Mesothele have a morphologically simple and uniform set of silk glands that are related to a sit-and-wait strategy for subduing prey (Sanggaard et al., 2014;Starrett et al., 2012). On the other hand, Araneomorph orb-weavers represent the widest diversity of silk types that are functionally distinct (Garb, 2013). ...
Spiders are useful models for testing different hypotheses and methodologies relating to animal personality and behavioral syndromes because they show a range of behavioral types and unique physiological traits (e.g., silk and venom) that are not observed in many other animals. These characteristics allow for a unique understanding of how physiology, behavioral plasticity, and personality interact across different contexts to affect spider's individual fitness and survival. However, the relative effect of extrinsic factors on physiological traits (silk, venom, and neurohormones) that play an important role in spider survival, and which may impact personality, has received less attention. The goal of this review is to explore how the environment, experience, ontogeny, and physiology interact to affect spider personality types across different contexts. We highlight physiological traits, such as neurohormones, and unique spider biochemical weapons, namely silks and venoms, to explore how the use of these traits might, or might not, be constrained or limited by particular behavioral types. We argue that, to develop a comprehensive understanding of the flexibility and persistence of specific behavioral types in spiders, it is necessary to incorporate these underlying mechanisms into a synthesized whole, alongside other extrinsic and intrinsic factors. Few studies have explored the mechanisms driving the expression of personality in spiders, and what effects extrinsic and intrinsic factors (and their interactions) have on the expression of personalities. Physiological traits, particularly venom and silk, may play an important role in the expression of personalities and/or behavioral flexibility in spiders
... Silk and webs have featured prominently in studies of spider evolution (e.g., 15,16,18,20,38,48,49,65,99,100). While all spiders produce several types of silk (135), some of these silk types and their associated proteins and genetic machinery are restricted to specific lineages (e.g., 25,31,126). For example, the evolution of viscid sticky silk, a defining trait of the Araneoidea clade (68), has been hypothesized to be a key innovation responsible for the remarkable diversity of this clade, along with a shift from horizontal to vertical capture webs (20). ...
Spiders (Araneae) make up a remarkably diverse lineage of predators that have successfully colonized most terrestrial ecosystems. All spiders produce silk, and many species use it to build capture webs with an extraordinary diversity of forms. Spider diversity is distributed in a highly uneven fashion across lineages. This strong imbalance in species richness has led to several causal hypotheses, such as codiversification with insects, key innovations in silk structure and web architecture, and loss of foraging webs. Recent advances in spider phylogenetics have allowed testing some of these hypotheses, but results are often contradictory, highlighting the need to consider additional drivers of spider diversification. The spatial and historical patterns of diversity and diversification remain contentious. Comparative analyses of spider diversification will advance only if we continue to make progress with studies of species diversity, distribution, and phenotypic traits, together with finer-scale phylogenies and genomic data.
Expected final online publication date for the Annual Review of Entomology, Volume 66 is January 11, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... These deductions have led researchers to make further inferences about the functional role of MA silk in spider webs and the influence of the expression of the two spidroins on the evolutionary trajectories of spiders and webs. It has been deduced, for instance, that MaSp1 appeared in the MA silks of the earliest web-building spiders, while MaSp2 appeared relatively recently in the silks of the more derived orb-weaving spiders [19,20]. The high extensibility bestowed by a high proline composition within MaSp2 thereupon has been considered integral to the capacity of two-dimensional orb webs to withstand the impacts of fast flying and/or large prey [19,21,22]. ...
... Young's modulus and glycine composition were both greater among basal spider species, whose MA silk is traditionally thought to comprise predominantly MaSp1. MaSp1 is high in glycine because it contains multiple GGX and GA motifs [20]. The GGX motif within the amorphous region of MaSp1 is associated with 3 10 -helical and turn structures containing few inter-molecular hydrogen bonding sights resulting in enhanced fibre stiffness [16]. ...
... Our meta-analysis supports these findings across a broader royalsocietypublishing.org/journal/rsif J. R. Soc. Interface 17: 20200471 spider phylogeny, suggesting that an ecologically driven advent of MaSp2 expression might be integral to the emergence and functionality of different spider web forms [19][20][21][22]. ...
Spider major ampullate (MA) silk, with its combination of strength and extensibility, outperforms any synthetic equivalents. There is thus much interest in understanding its underlying materiome. While the expression of the different silk proteins (spidroins) appears an integral component of silk performance, our understanding of the nature of the relationship between the spidroins, their constituent amino acids and MA silk mechanics is ambiguous. To provide clarity on these relationships across spider species, we performed a meta-analysis using phylogenetic comparative methods. These showed that glycine and proline, both of which are indicators of differential spidroin expression, had effects on MA silk mechanics across the phylogeny. We also found serine to correlate with silk mechanics, probably via its presence within the carboxyl and amino-terminal domains of the spidroins. From our analyses, we concluded that the spidroin expression shifts across the phylogeny from predominantly MaSp1 in the MA silks of ancestral spiders to predominantly MaSp2 in the more derived spiders' silks. This trend was accompanied by an enhanced ultimate strain and decreased Young's modulus in the silks. Our meta-analysis enabled us to decipher between real and apparent influences on MA silk properties, providing significant insights into spider silk and web coevolution and enhancing our capacity to create spider silk-like materials.
... N terminal domains are observed in mygalomorph spidroins, indicating that this feature related to spider silk production has been conserved for at least 240 million years [59]. The discovery of conserved regions in mesothele spidroin sequences, shared with Latrodectus spidroin, suggests the region associated with related spider silk production [73] has been conserved for more than 299 million years based on the recent fossil review of Mesothelae [11]. The intermediate tandem repeats contain one or more distinct subsets of amino acid motifs see (Figure 5) that can form different secondary protein structures such as β-sheets, β-turns, β-spirals (regular spiral-like structure) [74], or 3 10 -helices. ...
... Nonetheless, the phylogenetic relationships of known spidroins can be inferred from their gene sequences and structures. A previous study [73] on the primitively segmented spider family Liphistiidae in the suborder Mesothelae (sister suborder to all other extant spiders, which existed over 380 million years ago) detected a single spidroin (fib1) in Liphistius spiders. The reconstructed spidroin gene tree indicates that Liphistius fib1 is the sister of all other spidroins. ...
... This study also revealed that various spidroin gene duplications occurred after the split between Mesothelae and Opistheothelae (the suborder containing two infraorders, Mygalomorphae and Araneomorphae), and gene duplication had driven the diversification of spidroins. The spidroin gene tree suggests that TuSp and AcSp resulted from gene duplication before the diversification of Araneomorphae, and that Flag, MaSp and MiSp diverged within the Entelegynae clade [73]. In addition, other studies have reported that MaSp4 is derived from the MaSp2 gene [18], and MaSp2 is thought to be derived from an ancestral MaSp1 gene copy [79]. ...
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 preexisting 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.
