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The zebra tarantula Aphonopelma seemanni entangling a silk thread released from the spinneret with its hind leg, while starting to climb a vertical glass wall.Arrows indicate the silk thread.

The zebra tarantula Aphonopelma seemanni entangling a silk thread released from the spinneret with its hind leg, while starting to climb a vertical glass wall.Arrows indicate the silk thread.

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As with all spiders, tarantulas spin silk from specialized structures in the abdomen called spinnerets, which are key features unique to the group. Recently Gorb et al. reported that the zebra tarantula Aphonopelma seemanni also secretes silk from its feet, which might improve its ability to climb on vertical surfaces. Here we show that when the sp...

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Like all spiders, tarantulas (family Theraphosidae) synthesize silk in specialized glands and extrude it from spinnerets on their abdomen. In one species of large tarantula, Aphonopelma seemanni, it has been suggested that silk can also be secreted from the tarsi but this claim was later refuted. We provide evidence of silk secretion directly from...

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... These results were not confirmed by further studies. Finally, Pérez-Miles et al. (2009) and Pérez-Miles and Ortíz-Villatoro (2012) clearly proved that tarantulas do not produce any tarsal silk secretion. On the basis of observations of similar structures in other spider species, Foelix et al. (2012bFoelix et al. ( , 2013 admitted that these setae are in fact sensory setae. ...
Article
The ventral surfaces of tarsi in spiders in the infraorder Mygalomorphae group play a key role in locomotion and burrow and nest construction. In our research, we analyzed the diversity of setae and patterns of sculpturing on tarsi in three species with different life strategies: a burrowing spider Brachypelma smithi (F. O. Pickard-Cambridge, 1897), a ground-dwelling spider, Pterinochilus murinus Pocock, 1897, and a arboreal spider, Poecilotheria regalis Pocock, 1899. We showed the presence of three types of setae on the ventral side of tarsi: plumose setae, short-haired spiniform setae, and spirally striated setae. Plumose setae were differentiated within a tarsus and their apical sections among the studied species, while the microtriched ensiform and spirally striated setae did not differ. All setae were characterized by a similar structure. Little differentiation was observed in the number and location of setae on the tarsi of the studied species. Spirally striated setae were absent in the burrowing spiders. In contrast, the shape and size of the sculpturing pattern varied among the studied species. The greatest differentiation was found in the burrowing and ground-dwelling spiders, while the smallest differentiation was found in the arboreal spider. We discuss our findings in relation to preferred habitats, the biology of the spiders, and adaptation of sculpturing and setae on spider feet to surface type. The morphology and diversity of setae and sculpturing patterns on the ventral side of tarsi in P. murinus was reported for the first time.
... It was rather surprising when some reports claimed that tarantula spiders (Theraphosidae) possess tarsal silk glands that produce fine threads which would aid in the adhesion to smooth vertical surfaces (Gorb et al., 2006;Rind et al., 2011). However, these findings were soon contradicted by behavioral experiments (Pérez-Miles et al., 2009) and more recently by morphological and functional arguments (Foelix et al., , 2012a. Although there was good morphological evidence why the alleged tarsal silk spigots ("ribbed hairs") were chemoreceptors rather than silksecreting spigots, one decisive point was lacking, namely the proof of sensory innervation of those ribbed hairs. ...
... Secondly, no silk glands or ducts were found histologically in the tarsi, quite in contrast to the spinnerets. And, since tarantulas with sealed spinnerets did not leave any silk threads behind while climbing vertical glass plates, there is no physiological evidence for a tarsal silk production (Pérez-Miles et al., 2009;Pérez-Miles and Ortiz-Villatoro, 2012). ...
... Anatomically and physiologically, there is no evidence that any silk threads originate from those "ribbed hairs" (rather, fine "threads" of an unknown substance, perhaps receptor lymph). Behaviorally, it has been shown repeatedly that tarantulas with sealed spinnerets do not leave any silk threads behind after they had walked over clean glass plates (Pérez-Miles et al., 2009;Pérez-Miles and Ortiz-Villatoro, 2012). It thus seems inevitable to dismiss the idea of tarantulas "shooting silk from their feet"; and consequently it is very unlikely that tarantulas have an adhesive system in addition to their claw tufts that would "help these huge spiders to avoid catastrophic falls" (Gorb et al., 2006). ...
... Silk-like secretion by tarantula legs was initially questioned by Pérez-Miles et al. (2009), who observed tarantulas climbing with experimentally sealed spinnerets. When the spinnerets were sealed, they did not observe silk threads on any surface, discarding tarsal secretion of silk. ...
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Theraphosid tarantulas are large spiders that bear dense hairy adhesive pads on the distal parts of their legs: scopula and claw tufts. These structures allow them to climb on vertical smooth surfaces and contribute to prey capture. While adult females and juveniles remain most of the time in their burrows, adult males actively walk searching for females during the reproductive period. Adhesion and locomotion thus play important roles in the ecology and reproduction of these animals. In this paper, we review the current state of the knowledge on adhesion and locomotion in tarantulas, focusing on functional and evolutionary morphology.
... These events were later questioned by Pérez-Miles et al. (2009), who observed tarantulas climbing with free and experimentally sealed spinnerets. When the spinnerets were sealed, they did not observe silk threads on any surface, discarding leg secretion of silk. ...
... Rind et al. (2011) fueled the controversy of tarsal silk by inducing a slight slipping of the tarsi and observing fine silk threads that emerge from ribbed "spigots" on the ventral tarsi. These structures were also reported by Gorb et al. (2006), but Pérez-Miles et al. (2009) found no structures interpretable as silk glands or silk conduits with transverse cuts. ...
... These authors used tarantulas with both free and sealed spinnerets on larger vertical surfaces and induced them to slip, shaking gently the surfaces. They confirmed the results by Pérez-Miles et al. (2009), denying the presence of a silk trail on the legs (when the spinnerets are sealed) and suggested that silk is a light sticky fiber that can easily adhere to a surface. Consequently, passive contamination with spinneret silk is the most likely explanation to the traces found in the studies of Gorb et al. (2006) and Rind et al. (2011). ...
Chapter
Tarantulas are large spiders with adhesive setae on their legs, which enable them to climb on smooth vertical surfaces. The mechanism proposed to explain adhesion in tarantulas is anisotropic friction, where friction is higher when the leg pushes compared to when it pulls. The static friction of live theraphosid spiders on different surfaces and at different inclines was measured and compared between burrowing and arboreal species to test the hypothesis of higher friction in arboreal tarantulas. We analyzed the complementary participation of claw tufts and scopulae of anterior and posterior legs when the tarantula climbs. We also considered the morphology of scopulae and claw tufts setae and compared with similar structures in other families. Adhesive setae, as well as some other setae types found on ventral tarsi are described and characterized. The adhesive face of setae varied in the orientation in different parts of the tarsi, and this variation is more conspicuous in the spiders that have only claw tufts or scopulae. The mechanics of climbing in association with the biological characteristics of the species are analyzed. We discuss the association of adhesive scopulae and claw tufts with burrowing/cursorial mygalomorphs as within Theraphosidae, as was suggested for free-hunter spiders. The morphology, functions, and evolution of scopula and claw tufts are discussed in this chapter.
... These authors also described the "ribbed hairs", i.e., setae, which according to them bear a strong resemblance to the spigots through which silk is emitted onto the surface of spinnerets. However, these findings were called into question by behavioural experiments (Perez-Miles, Panzera, Ortiz-Villatoro, and Perdomo, 2009) as well as morphological and histological studies of the feet of tarantulas (Foelix, Rast, and Peattie, 2012;Foelix, Erb, and Rast, 2013). ...
Article
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The study focused on the specialised tarsal setae of tarantulas Avicularia metal-lica and Heteroscodra maculata, and the fibrous and non-fibrous material produced by them. When irritated spiders moved along smooth, perpendicularly-oriented glass walls not covered in silk, the claw tuft setae, located at the tips of the tarsal segments, left behind footprints containing two types of fibrous material. Using electron scanning microscopy, it was discovered that these represent fragments of parallelly oriented bundles of hollow fibres forming the shafts of the setae and their lateral branches (1), as well as clusters of contracted nanofibrils which aggregated at the ends of these fibres (2). During climbing, this fibrous material was detected both on the substratum on which the spiders were moving, and also on their claw tuft setae. The climbing activity of irritated tarantulas is also associated with the secretion of a fluid which dries on contact with air. This secretion acts as an adhesive and facilitates the movement of tarantulas on smooth surfaces, but while doing so it also glues together the distal, lamellar parts of the groups of setae which are in contact with the substratum during climbing. There are no such claw tuft setae morphological changes observed in undisturbed tarantulas, moving freely around their tube-like shelters and on the surfaces of objects covered with silk which they have produced. The sources of the air-drying secretion are probably the tubular fibres forming the shafts of pretarsal setae. The bundles of hollow fibres are an example of a system that produces secretions via a surficial pathway. The spinnerets and silk-producing glands associated with them, located in the opisthosoma, represent a system that produces silk via a systemic pathway. However, the results of observational studies have not confirmed the ability of tarantulas' feet to produce silk fibres of the same, or at least similar ultrastructure to that of the silk fibres produced by the activity of spinnerets and spinneret-associated silk glands.
... They supported their proposal by indicating the presence of silk lines associated to spider legs and the occurrence of specialized setae on spider tarsi. Pérez-Miles et al. (2009) experimentally tested this possibility in theraphosid spiders with the spinnerets sealed with wax. These authors did not find silk line in footprints, and they interpreted the specialized tarsal setae as sensory traits. ...
... These authors also proposed that those fine silk threads would prevent falls when the spider slips when walking on smooth surfaces. In contrast with Pérez-Miles et al. (2009) andOrtíz-Villatoro (2012), in all those experiments the tarantulas had normally functioning spinnerets. Peattie et al. (2011) also studied the adhesion of spiders, solpugids, and mites during locomotion. ...
Chapter
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The infraorder Mygalomorphae comprises almost 3000 species. It is widely distributed all over the world, and about one third of the species included in this infraorder is represented in the Neotropics. The knowledge on several aspects of the biology of Mygalomorphae is relatively scarce in comparison with the Araneomorphae. However, recent studies developed all over the world, but especially in the Neotropical region, are continuously contributing to add information on foraging strategies, communication, reproductive biology, habitat selection, and defenses against natural enemies, minimizing the differences in the status of knowledge between these groups. In this chapter, we review some the main topics on Mygalomorphae biology, including behavior and ecology.
... Criticism to the hypothesis arose as it was postulated the nozzle-like structures were not spigots but thermosensors (Pérez-Miles et al. 2009) or chemoreceptors (Foelix et al. 2012). While Pérez-Miles et al. (2009) were not able to find any secretion after sealing the spinnerets with paraffin, Foelix et al. (2012) observed secretions directly correlated with the ribbed hairs found on the theraphosid tarsus. ...
... Criticism to the hypothesis arose as it was postulated the nozzle-like structures were not spigots but thermosensors (Pérez-Miles et al. 2009) or chemoreceptors (Foelix et al. 2012). While Pérez-Miles et al. (2009) were not able to find any secretion after sealing the spinnerets with paraffin, Foelix et al. (2012) observed secretions directly correlated with the ribbed hairs found on the theraphosid tarsus. As chemosensory hairs are known to be filled with proteinaceous fluid (e.g. ...
Chapter
Walking spiders possess dense tufts of adhesive hairs on the tips of their legs. These tufts, the scopulae, enable spiders to climb smooth, steep surfaces. Spiders with scopulae do not have a third tarsal claw to track the silk thread, as they usually do not build webs for prey capture. In various spider families, additional scopula can be found on the tarsus and metatarsus which are presumably used for prey caption. The attachment system in spiders only recently became interesting again, as indication arose that the hairy system located on the spider legs may not, as previously stated, be operating completely dry. Findings in Mygalomorphae and many other spiders suggest fluid as well as filamentous secretion enhancing adhesion. The noncontinuous secretion of fluids indicates performance of scopulae in wet and dry modes.
... It was rather surprising when some reports claimed that tarantula spiders (Theraphosidae) possess tarsal silk glands that produce fine threads which would aid in the adhesion to smooth vertical surfaces (Gorb et al., 2006;Rind et al., 2011). However, these findings were soon contradicted by behavioral experiments (Pérez-Miles et al., 2009) and more recently by morphological and functional arguments (Foelix et al., , 2012a. Although there was good morphological evidence why the alleged tarsal silk spigots ("ribbed hairs") were chemoreceptors rather than silksecreting spigots, one decisive point was lacking, namely the proof of sensory innervation of those ribbed hairs. ...
... Secondly, no silk glands or ducts were found histologically in the tarsi, quite in contrast to the spinnerets. And, since tarantulas with sealed spinnerets did not leave any silk threads behind while climbing vertical glass plates, there is no physiological evidence for a tarsal silk production (Pérez-Miles et al., 2009;Pérez-Miles and Ortiz-Villatoro, 2012). ...
... Anatomically and physiologically, there is no evidence that any silk threads originate from those "ribbed hairs" (rather, fine "threads" of an unknown substance, perhaps receptor lymph). Behaviorally, it has been shown repeatedly that tarantulas with sealed spinnerets do not leave any silk threads behind after they had walked over clean glass plates (Pérez-Miles et al., 2009;Pérez-Miles and Ortiz-Villatoro, 2012). It thus seems inevitable to dismiss the idea of tarantulas "shooting silk from their feet"; and consequently it is very unlikely that tarantulas have an adhesive system in addition to their claw tufts that would "help these huge spiders to avoid catastrophic falls" (Gorb et al., 2006). ...
Article
Full-text available
Several studies on tarantulas have claimed that their tarsi could secrete fine silk threads which would provide additional safety lines for maintaining a secure foot-hold on smooth vertical surfaces. This interpretation was seriously questioned by behavioral experiments, and more recently morphological evidence indicated that the alleged spigots (“ribbed hairs”) were not secretory but most likely sensory hairs (chemoreceptors). However, since fine structural studies were lacking, the sensory nature was not proven convincingly. By using transmission electron microscopy we here present clear evidence that these “ribbed hairs” contain many dendrites inside the hair lumen – as is the case in the well-known contact chemoreceptors of spiders and insects. For comparison, we also studied the fine structure of regular silk spigots on the spinnerets and found them distinctly different from sensory hairs. Finally, histological studies of a tarantula tarsus did not reveal any silk glands, which, by contrast, are easily found within the spinnerets. In conclusion, the alleged presence of silk spigots on tarantula feet is refuted.
... It was rather surprising when some reports claimed that tarantula spiders (Theraphosidae) possess tarsal silk glands that produce fine threads which would aid in the adhesion to smooth vertical surfaces (Gorb et al., 2006;Rind et al., 2011). However, these findings were soon contradicted by behavioral experiments (Pérez-Miles et al., 2009) and more recently by morphological and functional arguments (Foelix et al., , 2012a. Although there was good morphological evidence why the alleged tarsal silk spigots ("ribbed hairs") were chemoreceptors rather than silksecreting spigots, one decisive point was lacking, namely the proof of sensory innervation of those ribbed hairs. ...
... Secondly, no silk glands or ducts were found histologically in the tarsi, quite in contrast to the spinnerets. And, since tarantulas with sealed spinnerets did not leave any silk threads behind while climbing vertical glass plates, there is no physiological evidence for a tarsal silk production (Pérez-Miles et al., 2009;Pérez-Miles and Ortiz-Villatoro, 2012). ...
... Anatomically and physiologically, there is no evidence that any silk threads originate from those "ribbed hairs" (rather, fine "threads" of an unknown substance, perhaps receptor lymph). Behaviorally, it has been shown repeatedly that tarantulas with sealed spinnerets do not leave any silk threads behind after they had walked over clean glass plates (Pérez-Miles et al., 2009;Pérez-Miles and Ortiz-Villatoro, 2012). It thus seems inevitable to dismiss the idea of tarantulas "shooting silk from their feet"; and consequently it is very unlikely that tarantulas have an adhesive system in addition to their claw tufts that would "help these huge spiders to avoid catastrophic falls" (Gorb et al., 2006). ...
Article
Several studies on tarantulas have claimed that their tarsi could secrete fine silk threads which would provide additional safety lines for maintaining a secure foot-hold on smooth vertical surfaces. This interpretation was seriously questioned by behavioral experiments, and more recently morphological evidence indicated that the alleged spigots ("ribbed hairs") were not secretory but most likely sensory hairs (chemoreceptors). However, since fine structural studies were lacking, the sensory nature was not proven convincingly. By using transmission electron microscopy we here present clear evidence that these "ribbed hairs" contain many dendrites inside the hair lumen - as is the case in the well-known contact chemoreceptors of spiders and insects. For comparison, we also studied the fine structure of regular silk spigots on the spinnerets and found them distinctly different from sensory hairs. Finally, histological studies of a tarantula tarsus did not reveal any silk glands, which, by contrast, are easily found within the spinnerets. In conclusion, the alleged presence of silk spigots on tarantula feet is refuted.
... The few studies that have characterized mygalomorph silk genes indicate that spidroins diversified prior to the mygalomorph/ araneomorph split, and mygalomorphs have the potential for producing multiple spidroins [21,39,40]. The recent controversy regarding silk production in the tarsi (terminal leg segments) of tarantulas also highlights the need for further investigation into the diversity of silk proteins in these spiders4142434445. We constructed cDNA libraries from the silk glands of spiders from Mesothelae, Mygalomorphae, and Paleocribelletae, for the purpose of characterizing the genes encoding their silk proteins. ...
Article
Full-text available
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'). Orbicularians produce a suite of different silks, and underlying this repertoire is a history of duplication and spidroin gene divergence. A second class of silk proteins, Egg Case Proteins (ECPs), is known only from the orbicularian species, Lactrodectus hesperus (Western black widow). In L. hesperus, ECPs bond with tubuliform spidroins to form egg case silk fibers. Because most of the phylogenetic diversity of spiders has not been sampled for their silk genes, there is limited understanding of spidroin gene family history and the prevalence of ECPs. Silk genes have not been reported from the suborder Mesothelae (segmented spiders), which diverged from all other spiders >380 million years ago, and sampling from Mygalomorphae (tarantulas, trapdoor spiders) and basal araneomorph lineages is sparse. In comparison to orbicularians, mesotheles and mygalomorphs have a simpler silk biology and thus are hypothesized to have less diversity of silk genes. Here, we present cDNAs synthesized from the silk glands of six mygalomorph species, a mesothele, and a non-orbicularian araneomorph, and uncover a surprisingly rich silk gene diversity. In particular, we find ECP homologs in the mesothele, suggesting that ECPs were present in the common ancestor of extant spiders, and originally were not specialized to complex with tubuliform spidroins. Furthermore, gene-tree/species-tree reconciliation analysis reveals that numerous spidroin gene duplications occurred after the split between Mesothelae and Opisthothelae (Mygalomorphae plus Araneomorphae). We use the spidroin gene tree to reconstruct the evolution of amino acid compositions of spidroins that perform different ecological functions.