Article

Evidence suggests that modified setae of the crab spiders Stephanopis spp. fasten debris from the background

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Abstract

Crab spiders (Thomisidae) are known by their ability to change their body colouration via change in epithelial pigments. However, the crab spider genus Stephanopis appears to match the colouration of the bark they are sitting on by having debris attached to its dorsal cuticle. The functional morphology, colouration, and evolution of this phenomenon were investigated in Stephanopis cf. scabra and S. cambridgei. Analysis under the microscope revealed that debris originated from the bark they were sitting on. Using scanning electron microscopy, three different types of setae likely related in the retention of debris were found in S. cf. scabra and one in S. cambridgei. These setae are branched and possess barbs, unlike the more filiform setae found in other crab spider species. In addition, the presence of debris improved the brightness background matching of spiders against the bark, but not hue and chroma matching. Ancestral character state reconstruction suggested that presence of debris evolved two to three times within Thomisidae. The evolution of both masking and colour change among crab spiders indicates that they are under a strong selection to avoid detection.

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... Although the family is indeed comprised of many flower-dwelling species, the majority of species use other substrata on which they capture their prey. For instance, the genera Stephanopis and Tharpyna in Australia (Mascord 1970;Gawryszewski 2014), or Xysticus and Ozyptila in Holarctic Region, inhabit leaf litter and tree bark (Jiménez-Valverde and Lobo 2007), whereas Sidymella, Hedana, and Runcinia are commonly found on foliage or low vegetation (Mascord 1970;Calero-Torralbo and Rodriguez-Gironés 2012). Crab spiders usually match the color of their background (Mascord 1970;Morse 2007). ...
... Crab spiders usually match the color of their background (Mascord 1970;Morse 2007). Some species even have debris attached to their bodies, making them more similar to their bark background (Gawryszewski 2014), whereas some flowerdwelling species change their body color to that of their flower (Packard 1905;Gabritschevsky 1927;Théry 2007;Morse 2007;Insausti and Casas 2009). The best-studied crab spider, Misumena vatia, changes its body coloration over 10-20 days when transferred from white to yellow flowers and vice versa (Packard 1905;Gabritschevsky 1927). ...
... The reflectance data of some crab spider species (Thomisus spectabilis, Stephanopis spp. and Diaea evanida) collected for this study have already been published elsewhere Gawryszewski et al. 2012;Gawryszewski 2014;Gawryszewski et al. 2015). ...
Article
The evolution of a visual signal will be affected by signaller and receiver behaviour, and by the physical properties of the environment where the signal is displayed. Crab spiders are typical sit-and-wait predators found in diverse ambush sites, such as tree bark, foliage and flowers. Some of the flower-dweller species present a UV(+) -white visual lure that makes them conspicuous and attractive to their prey. We hypothesised that UV(+) -white colouration was associated with the evolution of a flower-dwelling habit. In addition, following up on results from a previous study we tested whether the UV(+) -white colouration evolved predominantly in flower-dwelling species occurring in Australia. We measured the reflectance of 1149 specimens from 66 species collected in Australia and Europe, reconstructed a crab spider phylogeny, and applied phylogenetic comparative methods to test our hypotheses. We found that the flower-dwelling habit evolved independently multiple times, and that this trait was correlated with the evolution of the UV(+) -white colouration. However, outside Australia non-flower-dwelling crab spiders also express a UV(+) -white colouration. Therefore, UV(+) -white reflectance is probably a recurring adaptation of some flower-dwellers for attracting pollinators, although it may have other functions in non-flower-dwellers, such as camouflage. This article is protected by copyright. All rights reserved.
... scabra L. Koch, 1874 and S. cambridgei Thorell, 1870 and found 3 different types of setae that are finger-shaped with dentation. The dentate structure of the setae is related to the fact that they live among the debris and use these debris as camouflage (Gawryszewski, 2014). ...
... Considering the spider families examined, lanceolate, spatulate, and plumose setae are commonly observed in spiders. There are almost no studies covering setae morphology in members of the family Thomisidae (Townsend & Felgenhauer, 1998;Gawryszewski, 2014;Baltayeva et al., 2024). According to these studies, Baltayeva reported that there are no cover setae in species Synema plorator (O. ...
Article
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The present study aims to determine the covering setae in the two crab spiders using scanning electron microscopy (SEM). The setae on the prosoma of Runcinia grammica (C. L. Koch, 1837) and Thomisus onustus Walckenaer, 1805 were examined. This study reveals the existence of a new type of covering setae in Thomisidae group.
... 78, state 2; see Fig. 13f) as the only unambiguous synapomorphy. This group was also recovered by the presence of barbed clavate setae on their opisthosoma (Fig. 16b), which according to Gawryszewski (2014) are positively related to the effectiveness of becoming camouflaged through debris retention. This author found three different types of setae in St. altifrons and St. cambridgei that seem to be specialized for retaining organic particles. ...
... While St. altifrons present all three types of elongated and branched setae (generalized here as "needle-shaped"), St. cambridgei have just one, which we coded as "clavate", while Gawryszewski (2014) describes it as cuneiform, barbed and dorsally striated. We agree with Gawryszewski (2014) that this variation in setae morphology could be related to selection for retaining different types of debris, which might indicate niche partitioning. The paraphyletic relationship between these clades can also be observed through differences in sexual traits. ...
... 78, state 2; see Fig. 13f) as the only unambiguous synapomorphy. This group was also recovered by the presence of barbed clavate setae on their opisthosoma (Fig. 16b), which according to Gawryszewski (2014) are positively related to the effectiveness of becoming camouflaged through debris retention. This author found three different types of setae in St. altifrons and St. cambridgei that seem to be specialized for retaining organic particles. ...
... While St. altifrons present all three types of elongated and branched setae (generalized here as "needle-shaped"), St. cambridgei have just one, which we coded as "clavate", while Gawryszewski (2014) describes it as cuneiform, barbed and dorsally striated. We agree with Gawryszewski (2014) that this variation in setae morphology could be related to selection for retaining different types of debris, which might indicate niche partitioning. The paraphyletic relationship between these clades can also be observed through differences in sexual traits. ...
Article
A matrix of 117 morphological characters scored for 77 terminal taxa was subjected to parsimony analysis under equal and implied weighting schemes and to Bayesian inference in order to test the relationships in and between Stephanopis and Sidymella species, as well as its implications for the systematics of the subfamily Stephanopinae. A sensitivity test was performed to evaluate nodal stability. Our results indicate the polyphyletism of both genera and the topologies obtained allowed the proposition of the following taxonomic acts: The “altifrons clade” is the only group considered as Stephanopis (stricto sensu), with species restricted to the Australian region; most species from the Neotropical region, hitherto attributed to this genus, formed the well-supported “pentacantha clade”, while two of them, restricted to Central America, were recovered as the “championi clade”. The latter shows significative evidences for the revalidation of Paratobiasgen. rev.; the “cambridgei clade” emerged with I. punctata nested within, having all its component species transferred to Isala. None of the Sidymella species with Australian distribution seems to be part of this genus, which occurs in fact only in the Neotropical region and is closely related to Coenypha. This latter has an increment of three species transferred from Stephanopis. Aside from the “lucida clade”, which is considered here as Sidymella (stricto sensu), three other groups and a single species emerged apart from this genus: the “hirsuta clade”, “trapezia clade”, “angularis clade” and Si. rubrosignata. Morphological evidences seem to justify the proposition of all these groups as new genera.
... Debris and sediment-trapping setae vary greatly in size and morphology depending on the type, scale and density of the target 'cloaking' material [83,84]. Nonetheless, finely subdivided cuticular specializations are recurrent adaptations in the trunk of microdebris-and soil-capturing arachnids [85] and insects [79][80][81]. These debris-and sediment-trapping 'splintered setae' occur in terrestrial animals (electronic supplementary material), and as such offer no direct autecological counterparts to Scalidodendron. ...
Article
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Scalidophora, the ecdysozoan group including priapulids, kinorhynchs and loriciferans, comprises some of the most abundant and ecologically important Cambrian animals. However, reconstructions of the morphology and lifestyles of fossil scalidophorans are often hampered by poor preservation of their submillimetre-scale cuticular specializations. Based on exceptionally preserved small carbonaceous fossils (SCFs), we describe a new scalidophoran-grade animal, Scalidodendron crypticum gen. et sp. nov., from the Early to Middle Cambrian Hess River Formation of northern Canada. The Hess River SCFs comprise pharyngeal teeth, coniform sclerites and hook-like sclerites, all closely comparable to known scalidophoran counterparts. The coniform and hook-like sclerites recurrently associate with arborescent cuticular projections that show multiple orders of branching, morphologically unlike those of any known living or fossil scalidophoran. The fine splintering and inferred post-pharyngeal position of these structures argue against locomotory, feeding and defensive roles with direct analogues in extant counterparts. As such, the arborescent structures of Scalidodendron denote a previously cryptic range of morphological variation in Cambrian scalidophorans, paralleling that of coeval panarthropods but expressed at a fundamentally different level of anatomical organization.
... Indeed, Brechbühl et al. (2010b) found that predators' camouflage was ineffective when taking into account the whole community of potential flower-visiting prey (Brechbühl et al., 2010b). Similarly, the lack of avoidance or alterations in the pollinator behavior of some flower visitors may be just the result of not being able to detect predators due to predator body coloration or behavioral crypsis (Chittka, 2001;Théry and Casas, 2002;Théry et al., 2004;Morse, 2007;O'Hanlon et al., 2014;Gawryszewski, 2014). Alternatively, some predators are not cryptic but actively attract their prey by manipulating floral signals, such as through UV reflection in crab spiders or by displaying a flower-like appearance as in the orchid mantis (Heiling et al., 2003;Mizuno et al., 2014). ...
Article
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Foraging behavior of pollinators is shaped by, among other factors, the conflict between maximizing resource intake and minimizing predation risk; yet, empirical studies quantifying variation in both forces are rare, compared to those investigating each separately. Here, we discuss the importance of simultaneously assessing bottom-up and top-down forces in the study of plant-pollinator interactions, and propose a conceptual and testable graphical hypothesis for pollinator foraging behavior and plant fitness outcomes as a function of varying floral rewards and predation risk. In low predation risk scenarios, no noticeable changes in pollinator foraging behavior are expected, with reward levels affecting only the activity threshold. However, as predation risk increases we propose that there is a decrease in foraging behavior, with a steeper decline as plants are more rewarding and profitable. Lastly, in high predation risk scenarios, we expect foraging to approach zero, regardless of floral rewards. Thus, we propose that pollinator foraging behavior follows an inverse S-shape curve, with more pronounced changes in foraging activity at intermediate levels of predation risk, especially in high reward systems. We present empirical evidence that is consistent with this hypothesis. In terms of the consequences for plant fitness, we propose that specialized plant-pollinator systems should be more vulnerable to increased predation risk, with a steeper and faster decline in plant fitness, compared with generalist systems, in which pollinator redundancy can delay or buffer the effect of predators. Moreover, whereas we expect that specialist systems follows a similar inverse S-shape curve, in generalist systems we propose three different scenarios as a function not only of reward level but also compatibility, mating-system, and the interplay between growth form and floral display. The incorporation of trade-offs in pollinator behavior balancing the conflicting demands between feeding and predation risk has a promising future as a key feature enabling the development of more complex foraging models.
... Specialised chaetotaxy may aid faecal retention in the faecal retaining chrysomelid clades. Specialised setae to hold on to debris have been described in unrelated beetles (Leschen and Carlton 1993;Leschen 1994;Yoshida and Leschen 2020), in other insects (e.g., Reduviidae, Weirauch 2006), and in other animals (e.g., spiders, Duncan et al. 2007;Gawryszewski 2014). In Uraba caterpillars (Fig. 9), it is a question how the old head capsules become stacked on the living caterpillar's head, since the head capsule typically splits first during the moulting process, then becomes distorted as it is pushed posteriad, and the larva propels forward to exit its old exoskeleton. ...
Article
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Animal constructions are the outcomes of complex evolutionary, behavioural, and ecological forces. A brief review of diverse animal builders, the materials used, and the functions they provide their builders is provided to develop approaches to studying faecal-based constructions and faecal-carrying in leaf beetles (Coleoptera: Chrysomelidae). Field studies, rearing, dissections, photography, and films document shields constructed by larvae in two species in two tribes of the subfamily Cassidinae, Calyptocephala attenuata (Spaeth, 1919) (Spilophorini), and Cassida sphaerula Boheman, 1853 (Cassidini). Natural history notes on an undetermined Cassidini species and Stolas cucullata (Boheman, 1862) (Tribe Mesomphaliini) outline the life cycle of tortoise beetles and explain terms. Commonly, the cassidine shield comprises exuviae onto which faeces are daubed, producing a pyramidal-shaped shield that can cover most of the body (up to the pronotum). In Cal. attenuata the larval shield comprises only exuviae, while in Cass. sphaerula , instar 1 initiates the shield by extending its telescopic anus to apply its own faeces onto its paired caudal processes; at each moult the exuvia is pushed to the caudal process base but remains attached, then more faeces are applied over it. The larva’s telescopic anus is the only tool used to build and repair the shield, not mouthparts or legs, and it also applies chemicals to the shield. Pupae in Cal. attenuata retain part of the exuviae-only shield of instar VI, while pupae in Cass. sphaerula retain either the entire 5 th instar larval shield (faeces + all exuviae) or only the 5 th larval exuvia. The caudal processes are crucial to shield construction, shield retention on the body, and as materials of the central scaffold of the structure. They also move the shield, though the muscular mechanism is not known. Altogether the faecal + exuviae shields may represent a unique morpho-behavioural synapomorphy for the crown-clade Cassidinae (10 tribes, ~ 2669 species) and may have been a key innovation in subsequent radiation. Defensive shields and domiciles may help explain the uneven radiation of chrysomelid subfamilial and tribal clades.
... Comparable uses of external materials for decoration have been explored for terrestrial animals, mostly among larvae of several insect species (Nakahira & Arakawa, 2006;Jackson & Pollard, 2007;Khan, 2020). Spider species across several families have evolved setal microstructures that render them cryptic (Duncan, Autumn & Binford, 2007;Gawryszewski, 2014) by retaining debris in the case of Stephanopis (Thomisidae) and sand particles in Sicarius (Sicariidae) and Homalonychus (Homalonychidae) genera. In all these instances, the decorations are added to the animal's body. ...
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Many ecological interactions of spiders with their potential prey and predators are affected by the visibility of their bodies and silk, especially in habitats with lower structural complexity that expose spiders. For instance, the surface of tree trunks harbours relatively limited structures to hide in and may expose residents to visual detection by prey and predators. Here we provide the first detailed description of the novel retreat building strategy of the tree trunk jumping spider Arasia mullion . Using fields surveys, we monitored and measured over 115 spiders and 554 silk retreats. These spiders build silk retreats on the exposed surface of tree trunks, where they remain as sedentary permanent residents. Furthermore, the spiders decorate the silk retreats with bark debris that they collect from the immediate surrounding. We discuss the role of silk decoration in the unusual sedentary behaviour of these spiders and the potential mechanisms that allow A. mullion to engineer their niche in a challenging habitat.
... Photos a-c, h-i by Nicky Bay; d-e by Thomas Shahan; and f-g by Dinesh Rao pattern colouration (Defrize et al. 2010), attaching debris from the microhabitat to special setae in the cuticle as seen in Stephanopis spp. (Gawryszewski 2014), or even changing the body colouration according to the background, as seen in many crab spider species (Insausti et al. 2012). Several studies have evaluated spider crypsis through body colouration from the perspective of a predator in a visual ecology context using spectrophotometry (Théry and Casas 2002;Théry et al. 2005;Clark et al. 2011) or digital imaging (Robledo-Ospina et al. 2021). ...
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Many animals use visual traits as a predator defence. Understanding these visual traits from the perspective of predators is critical in generating new insights about predator–prey interactions. In this paper, we propose a novel framework to support the study of strategies that exploit the visual system of predators. With spiders as our model taxon, we contextualise these strategies using two orthogonal axes. The first axis represents strategies using different degrees of conspicuousness to avoid detection or recognition of the spider and deter predator attacks. The second axis represents the degree of honesty of the visual signal. We explore these issues with reference to the three main vision parameters: spectral sensitivity, visual acuity, and temporal resolution, as well as recent tools to study it, including multispectral digital imaging.
... Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society. (Gawryszewski, 2014). Individuals with attached bark debris were observed on bark with darker colours and individuals without debris were found on lighter-coloured bark, in both cases improving background-matching camouflage. ...
Article
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Camouflage – adaptations that prevent detection and/or recognition – is a key example of evolution by natural selection, making it a primary focus in evolutionary ecology and animal behaviour. Most work has focused on camouflage as an anti‐predator adaptation. However, predators also display specific colours, patterns and behaviours that reduce visual detection or recognition to facilitate predation. To date, very little attention has been given to predatory camouflage strategies. Although many of the same principles of camouflage studied in prey translate to predators, differences between the two groups (in motility, relative size, and control over the time and place of predation attempts) may alter selection pressures for certain visual and behavioural traits. This makes many predatory camouflage techniques unique and rarely documented. Recently, new technologies have emerged that provide a greater opportunity to carry out research on natural predator–prey interactions. Here we review work on the camouflage strategies used by pursuit and ambush predators to evade detection and recognition by prey, as well as looking at how work on prey camouflage can be applied to predators in order to understand how and why specific predatory camouflage strategies may have evolved. We highlight that a shift is needed in camouflage research focus, as this field has comparatively neglected camouflage in predators, and offer suggestions for future work that would help to improve our understanding of camouflage.
... However, live specimens are colored in a wide spectrum of shades of green and orange, depending on the substrate where the spider is found (Fig. 1A-D). According to Gawryszewski (2014) S. altifrons (senior synonym of S. scabra) match the colouration of the bark they are sitting on by having debris attached to their dorsal cuticle. These debris are retained on the spider's body due to their modified branched setae. ...
Article
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Here we present a revision of the Australian species of Stephanopis. The type species S. altifrons is redescribed and S. aspera, S. depressa, S. monticola, S. elongata and S. scabra are considered its junior synonyms. Males of S. altifrons, S. angulata, S. nigra, S. armata, S. fissifrons and S. longimana are described for the first time. We propose neotypes for S. nigra and S. barbipes and describe the female of the latter. Nine species are considered species inquirendae, S. thomisoides as nomen dubium and S. cheesmanae is transferred to Phrynarachne. Seven new species are described, new distribution records are provided and comments are made about the validity of the genus and its relationship with Sidymella species and other Stephanopinae genera from the Australian region.
... In spiders of the genus Cryptothele (Zodariidae), soil particles are mechanically held in place by curved setae covered by long barbs . In some crab spiders ( Thomisidae ), environmental particles, detritus and growing fungi cover the body, attached by barbed club-like setae and papillate microtrichia; an adhesive secretion may also be involved (Ramírez 2014 ;Gawryszewski 2014 ). Soil crypsis is also known from some burrowing mygalomorphs (Paratropidae, some Nemesiidae). ...
Book
This book surveys attachment structures and adhesive secretions occurring in this class of animals and discusses the relationships between structure, properties, and function in the context of evolutionary trends, and biomimetic potential. Topics comprise mechanical attachment devices, such as clamps, claws, hooks, spines and wraps, as well as hairy and smooth adhesive pads, nano-fibrils, suction cups, and viscid and solidifying adhesives. Attachment is one of the major types of interactions between an organism and its environment. There are numerous studies that deal with this phenomenon in lizards, frogs, insects, barnacles, mussels and echinoderms, but the second largest class of animals, the Arachnida, was highly neglected so far. The authors demonstrated that most arachnid adhesive structures are highly analogous to those of insects and vertebrates, but there are also numerous unique developments with some intriguing working principles. Because arachnid attachment organs have a very strong potential of technological ideas for the development of new materials and systems, inspirations from biology could also be interesting for a broad range of topics in materials and surface engineering.
... In spiders of the genus Cryptothele (Zodariidae), soil particles are mechanically held in place by curved setae covered by long barbs . In some crab spiders ( Thomisidae ), environmental particles, detritus and growing fungi cover the body, attached by barbed club-like setae and papillate microtrichia; an adhesive secretion may also be involved (Ramírez 2014 ;Gawryszewski 2014 ). Soil crypsis is also known from some burrowing mygalomorphs (Paratropidae, some Nemesiidae). ...
Chapter
Rigid cuticular structures that generate high friction by mechanical interlocking with substrate protuberances are the most abundant attachment devices in arthropods. Here we review the different types of such structures in arachnids. The claws of appendages are primarily to increase foothold on walking and climbing substrates, but may also be important means of prey capture, which often comes with structural modifications. Claws are often supported by spines and microtrichia, all of which have different tip diameters. Such a set of differently sized interlocking devices may generate friction on a broad range of substrate roughness from very fine to rather coarse. Other examples of interlocking mechanisms are hooks and platelets on different body parts, some types of genital sealing (mating plugs), and silk threads interlocking with protuberances of substrate surfaces. Clamps and pincers are muscle-driven attachment devices, which are abundant means of prey capture and food handling: the chelicerae, the pedipalpal chelae of scorpions and pseudoscorpions, the raptorial legs (spinated legs or pedipalps for prey capture), and the cucullus (‘hood’) of Ricinulei. Other mechanical attachment devices are expansion anchors that are first pierced into a substrate, such as prey cuticle, plant epidermis or host skin, and interlocked there. They are represented by some specialized mouth parts. Lock-and-key is a system, in which two specific co-adapted structures interlock with each other. They can be found in some copulation organs. Wrapping around the substrate is an effective means of attachment, as it can highly enhance the action of friction. This mechanism is frequently used by long-legged harvestmen, when walking on thin cylindrical surfaces like grass or herb stems. It is further utilized by some spiders which tightly wrap their prey in silk.
... Crab spiders appear to the human eye to be highly camou- flaged, and it has previously been assumed that their camouflage was an advantage used to aid spiders in capturing unsuspecting prey or to avoid predation (Angus, 1882;Bristowe, 1958;Heiling et al., 2005;Th?ry, 2007). Crab spiders have evolved a variety of mechanisms to facilitate apparent camouflage, includ- ing a chemical-based colour change to match a background (Insausti & Casas, 2007), background matching through the choice of foraging location (Anderson & Dodson, 2015), and attaching plant detritus to themselves (Gawryszewski, 2014). However, experiments designed to test whether camouflage aids crab spiders in prey capture have found no evidence that insect flower-visitors are more likely to visit inflorescences with crab spiders that are well matched to their background (Brechb?hl et al., 2010a;Peixoto et al., 2012). ...
... Fossil reduviids used anchor setae on the dorsum to adhere dust and debris ( fig. S2, G to I), which is a particle capture mechanism that independently evolved in certain reduviids and extant spiders (24)(25)(26). Debris-carrying was previously only known in extant higher Reduviidae (22,24); however, our findings show that such an adaptation is an ancient characteristic that has repeatedly evolved (or has been lost) during the early evolution of this group (Fig. 5B). ...
Article
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Insects have evolved diverse methods of camouflage that have played an important role in their evolutionary success. Debris-carrying, a behavior of actively harvesting and carrying exogenous materials, is among the most fascinating and complex behaviors because it requires not only an ability to recognize, collect, and carry materials but also evolutionary adaptations in related morphological characteristics. However, the fossil record of such behavior is extremely scarce, and only a single Mesozoic example from Spanish amber has been recorded; therefore , little is known about the early evolution of this complicated behavior and its underlying anatomy. We report a diverse insect assemblage of exceptionally preserved debris carriers from Cretaceous Burmese, French, and Lebanese ambers, including the earliest known chrysopoid larvae (green lacewings), myrmeleontoid larvae (split-footed lacewings and owlflies), and reduviids (assassin bugs). These ancient insects used a variety of debris material, including insect exoskeletons, sand grains, soil dust, leaf trichomes of gleicheniacean ferns, wood fibers, and other vegetal debris. They convergently evolved their debris-carrying behavior through multiple pathways, which expressed a high degree of evolutionary plasticity. We demonstrate that the behavioral repertoire, which is associated with considerable morphological adaptations, was already widespread among insects by at least the Mid-Cretaceous. Together with the previously known Spanish specimen, these fossils are the oldest direct evidence of camouflaging behavior in the fossil record. Our findings provide a novel insight into early evolution of camouflage in insects and ancient ecological associations among plants and insects.
... Duncan et al. [30] show that two unrelated desert-dwelling spiders have independently evolved very similar setal morphology that aids in the retention of sand over the body and presumably acts in concealment. The presence of exogenous material (soil, sand, debris, etc.) on the cuticle has been reported across several spider families [31]. This article reported that modified setae of the crab spiders Stephanopis spp. ...
Article
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Many animals decorate themselves through the accumulation of environmental material on their exterior. Decoration has been studied across a range of different taxa, but there are substantial limits to current understanding. Decoration in non-humans appears to function predominantly in defence against predators and parasites, although an adaptive function is often assumed rather than comprehensively demonstrated. It seems predominantly an aquatic phenomenon-presumably because buoyancy helps reduce energetic costs associated with carrying the decorative material. In terrestrial examples, decorating is relatively common in the larval stages of insects. Insects are small and thus able to generate the power to carry a greater mass of material relative to their own body weight. In adult forms, the need to be lightweight for flight probably rules out decoration. We emphasize that both benefits and costs to decoration are rarely quantified, and that costs should include those associated with collecting as well as carrying the material. © 2015 The Author(s) Published by the Royal Society. All rights reserved.
Chapter
Despite being widely known as a diverse group of predators, spiders are also a regular prey item of several vertebrate and invertebrate predators. Some of these organisms (e.g., wasp species and araneophagic spiders) are spider-hunting specialists. A number of morphological structures and behaviours in spiders have been proposed to be anti-predator adaptations. They comprise strategies such as background matching, disruptive patterns, web decorations, mimicry, masquerading, aposematism, urticating bristles, spines, retreats, barrier webs, group living, and dropping from webs. In this chapter, spider anti-predator strategies are presented, and the correlational and causal evidence of anti-predator adaptations are critically discussed in light of potential costs and benefits they may entail. Studies involving Neotropical species are presented to illustrate most strategies.
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The higher-level phylogenetic relationships of crab spiders (Thomisidae) are studied from morphological data. 33 taxa are coded for 74 characters (53 binary and 21 multistate). Several analyses using equal, successive and implied weights were carried out. The most parsimonious tree obtained by analysis with successive and implied weights is put forward as the preferred hypothesis of thomisid relationships (length 222 steps, CI 0.74, RI 0.83). Thomisidae emerge monophyletic in all analyses, supported by four unambiguous synapomorphies. It is now apparent that thomisid taxa have been mostly defined on the basis of plesiomorphic character states. A number of taxonomic changes, including the description of new taxa are proposed and the evolution of diverse behaviors of thomisids is studied in light of the new phylogenetic result. Color change behavior evolved once within the family, but eye arrangement patterns of the median ocular quadrangle, thought to be diagnostic for many genera, evolved as much as 10 times independently. The following new species are described: Borboropactus nyerere sp. nov.,Cebrenninus srivijaya sp. nov., Geraesta lehtineni sp. nov. and Geraesta mkwawa sp. nov. The following new generic synonymies are proposed: Bucranium O. P.-Cambridge, 1881 = Aphantochilus O. P.-Cambridge, 1870; Sanmenia Song and Kim, 1992 = Pharta Thorell, 1891 and Cupa Strand, 1906 = Epidius Thorell, 1877. The following species are synonymized: Regillus divergens Hogg, 1914 and Borboropactus hainanus Song, 1993 = Borboropactus bituberculatus Simon, 1884 syn. nov., Epidius ganxiensis (Yin, Peng & Kim, 1999) = Epidius rubropictus Simon, 1909 syn. nov., Geraesta bilobata Simon, 1897 = Geraesta hirta Simon, 1889 syn. nov., Sanmenia kohi Ono, 1995 = Pharta bimaculata Thorell, 1891 syn. nov. and Sanmenia zhengi (Ono & Song, 1986) = Pharta brevipalpus (Simon, 1903) syn. nov. The following new combinations are proposed: Aphantochilus taurifrons (O. P.-Cambridge, 1881) comb. nov., Epidius typicus (Bösenberg & Strand, 1906) comb. nov., Pharta brevipalpus (Simon, 1903) comb. nov., Pharta gongshan (Yang, Zhu and Song, 2006) comb. nov., Pharta nigra (Tang, Griswold & Peng, 2009) comb. nov. and Pharta tengchong (Tang, Griswold & Yin, 2009) comb. nov.
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Spider crabs (family Majidae) often decorate themselves: that is, they put pieces of marine organisms among the hooked setae of the exoskeleton. This behavior can be absent in large crabs or those that live at great depths, on sand or in narrow crevices. Although some species put edible materials on their bodies and later remove and eat them, the majority of the spider crabs decorate themselves to camouflage themselves against predators. A model of the level of decoration is presented, from none at all to complete coverage of the dorsal surface. Important factors that affect the level are the evolutionary state, habitat, size, feeding and particularly the predators of the species of spider crab.
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Immature stages of Reduvius personatus (Linnaeus) and some other Reduviidae are known to camouflage themselves with a range of materials found in their environment. Even though this behavior has been observed in several species, camouflaging structures have never been studied in a comparative way. This study documents for the first time the structure that is involved in the application of camouflaging material, i.e., the hind tarsal fan, and reveals structures that assure the fastening of the camouflaging material, i.e., anchor setae and trichomes, in eight species representing five subfamilies of Reduviidae. Whereas anchor setae assure the attachment of camouflaging material by their mechanical properties, short-projection trichomes, long-projection trichomes, and grouped trichomes are here proposed to secrete a sticky substance for this purpose. Primary homology hypotheses on the three types of trichomes are proposed. At least in some species, short-projection trichomes appear to be responsible for the fastening of the camouflaging layer close to the integument, whereas long-projection trichomes may hold the outer layer of camouflaging material in place.
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A chromaticity diagram which plots the 3 photoreceptor excitations of trichromatic colour vision systems at an angle of 120 is presented. It takes into acount the nonlinear transduction process in the receptors. The resulting diagram has the outline of an equilateral hexagon. It is demonstrated by geometrical means that excitation values for any type of spectrally opponent mechanism can be read from this diagram if the weighting factors of this mechanism add up to zero. Thus, it may also be regarded as a general representation of colour opponent relations, linking graphically the Young-Helmholtz theory of trichromacy and Hering's concept of opponent colours. It is shown on a geometrical. basis that chromaticity can be coded unequivocally by any two combined spectrally opponent mechanisms, the main difference between particular mechanisms being the extension and compression of certain spectral areas. This type of graphical representation can qualitatively explain the Bezold-Brcke phenomenon. Furthermore, colour hexagon distances may be taken as standardized perceptual colour distance values for trichromatic insects, as is demonstrated by comparison with behavioural colour discrimination data of 3 hymenopteran species.
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Cryptic coloration is assumed to be beneficial to predators because of an increased encounter rate with unwary prey. This hypothesis is, however, very rarely, if ever, studied in the field. The aim of this study was to quantify the encounter rate and capture success of an ambush predator, in the field, as a function of its level of colour-matching with the background. We used the crab spider Misumena vatia, which varies its body colour and can thereby match the colour of the flower it hunts upon. We carried out a manipulative field experiment using a complete factorial design resulting in six different colour combinations of crab spiders and flowers differing in their degree of colour-matching. A rich and diverse set of naturally occurring insects visited the flowers while we continuously video-recorded the spider's foraging activity. This enabled us to test the crypsis, the spider avoidance and the flower visitor attraction hypotheses, all three supported by previous studies. Flower visitors of different groups either avoided crab spiders independent of colour-matching, such as solitary bees and syrphid flies, or ignored them, such as bumble-bees and honeybees. Moreover, colour-matched spiders did not have a higher encounter rate and capture success compared to the visually apparent ones. Thus, our results support the spider avoidance hypothesis, reject the two other hypotheses and uncovered a fourth behaviour: indifference to predators. Because flower visitors reacted differently, a community approach is mandatory in order to understand the function of background colour-matching in generalist predators. We discuss our results in relation to the size and sociality of the prey and in relation to the functional significance of colour change in this predator.
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Inferences about mechanisms at one particular stage of a visual pathway may be made from psychophysical thresholds only if the noise at the stage in question dominates that in the others. Spectral sensitivities, measured under bright conditions, for di-, tri-, and tetrachromatic eyes from a range of animals can be modelled by assuming that thresholds are set by colour opponency mechanisms whose performance is limited by photoreceptor noise, the achromatic signal being disregarded. Noise in the opponency channels themselves is therefore not statistically independent, and it is not possible to infer anything more about the channels from psychophysical thresholds. As well as giving insight into mechanisms of vision, the model predicts the performance of colour vision in animals where physiological and anatomical data on the eye are available, but there are no direct measurements of perceptual thresholds. The model, therefore, is widely applicable to comparative studies of eye design and visual ecology.
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I review the evidence that organisms have adaptations that confer difficulty of detection by predators and parasites that seek their targets primarily using sensory systems other than vision. In other words, I will answer the question of whether crypsis is a concept that can usefully be applied to non-visual sensory perception. Probably because vision is such an important sensory system in humans, research in this field is sparse. Thus, at present we have very few examples of chemical camouflage, and even these contain some ambiguity in deciding whether they are best seen as examples of background matching or mimicry. There are many examples of organisms that are adaptively silent at times or in locations when or where predation risk is higher or in response to detection of a predator. By contrast, evidence that the form (rather than use) of vocalizations and other sound-based signals has been influenced by issues of reducing detectability to unintended receivers is suggestive rather than conclusive. There is again suggestive but not completely conclusive evidence for crypsis against electro-sensing predators. Lastly, mechanoreception is highly understudied in this regard, but there are scattered reports that strongly suggest that some species can be thought of as being adapted to be cryptic in this modality. Hence, I conclude that crypsis is a concept that can usefully be applied to senses other than vision, and that this is a field very much worthy of more investigation.
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Sicarius and Homalonychus are unrelated, desert-dwelling spiders that independently evolved the ability to cover themselves in fine sand particles, making them cryptic against their background. Observations that particles associate with these spiders' setae inspired us to investigate the role of setal microstructure in particle capture and retention. Here we report that Sicarius and Homalonychus convergently evolved numerous high aspect ratio, flexible fibres that we call 'hairlettes' protruding from the setal shaft. We demonstrate that particles attach more densely to regions of Homalonychus with hairlettes than to other regions of the same animal where hairlettes are absent, and document close contact of hairlettes to sand particles that persists after applying force. Mathematical models further suggest that adhesion of hairlettes to sand particles is a sufficient mechanism of particle capture and retention. Together, these data provide the first evidence that hairlettes facilitate sand retention through intermolecular adhesion to particles. Their independent evolutionary origins in Sicarius and Homalonychus suggest that the unique setal structure is adaptive and represents a general biomechanical mechanism for sand capture to cuticle. This discovery has implications for the design of inventions inspired by this system, from camouflage to the management of granular systems.
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Decorating materials in Loxorhynchus crispatus are attached to the hooked setae of the dorsal surface of the exoskeleton. Examination with the scanning electron microscope reveals that the setae bear spinules, a median groove, and a spiralled region. Ablation of these setae prevents the crabs from decorating, but removal of the glands of the first maxillipeds has no effect on the process. Attachment of decorating material appears to be mechanical, not by means of an adhesive secreted by the mouthparts.
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Limitations of linear regression applied on ecological data. - Things are not always linear additive modelling. - Dealing with hetergeneity. - Mixed modelling for nested data. - Violation of independence - temporal data. - Violation of independence spatial data. - Generalised linear modelling and generalised additive modelling. - Generalised estimation equations. - GLMM and GAMM. - Estimating trends for Antarctic birds in relation to climate change. - Large-scale impacts of land-use change in a Scottish farming catchment. - Negative binomial GAM and GAMM to analyse amphibian road killings. - Additive mixed modelling applied on deep-sea plagic bioluminescent organisms. - Additive mixed modelling applied on phyoplankton time series data. - Mixed modelling applied on American Fouldbrood affecting honey bees larvae. - Three-way nested data for age determination techniques applied to small cetaceans. - GLMM applied on the spatial distribution of koalas in a fragmented landscape. - GEE and GLMM applied on binomial Badger activity data.
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The first quantitative phylogenetic analysis of three sequenced genes (16S rRNA, cytochrome c oxidase subunit I, histone 3) of 25 genera of crab spiders and 11 outgroups supports the monophyly of Thomisidae. Four lineages within Thomisidae are recovered. They are informally named here as the Borboropactus clade, Epidius clade, Stephanopis clade and the Thomisus clade, pending detailed morphology based cladistic work. The Thomisus clade is recovered as a strongly supported monophyletic group with a minimal genetic divergence. Philodromidae previously widely considered a subfamily of Thomisidae do not group within thomisids and is excluded from Thomisidae. However, Aphantochilinae previously generally considered as a separate family falls within the Thomisus clade and is included in Thomisidae. The recently proposed new family Borboropactidae is rejected, as it is paraphyletic. © The Willi Hennig Society 2008.
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As a case study of how insects use masks as a defence against vision-guided predators, an experimental study was carried out using Acanthaspis petax, a reduviid bug (‘ant bug’) that covers itself with a ‘mask’, or ‘backpack’, made from carcasses of its preferred prey (ants), and three salticid spider species, Hyllus sp., Plexippus sp. and Thyene sp., salticids being predators with exceptionally acute vision. The ant bugs and the salticids were from the Lake Victoria region of East Africa. In each test, a salticid was presented with a live bug or a lure made from a dead bug, with the mask removed (‘naked’) or intact (‘masked’). Salticids made predatory responses to naked bugs significantly more often than to masked bugs. These findings suggest that salticids readily identify naked bugs as prey, but fail to identify masked bugs as prey.
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The nymphs of the West African assassin bugs Paredocla and Acanthaspis spp. disguise themselves with a cover of dust, sand and soil particles (‘dust coat’) and additionally pile a ‘backpack’ of larger objects, such as empty prey corpses and plant parts, on their abdomen. We investigated the effect of this conspicuous camouflage in interactions of the bugs with ants, their main prey, as well as in encounters with their own predators. Experiments with three ant species showed that the dust coat impedes chemical and tactile recognition of the nymphs by ant workers and thus may serve to increase their hunting success. The backpack appeared to play only a minor role in this context. In arena experiments with three potential predators (spiders, geckos and centipedes), camouflaged nymphs were significantly more likely to survive than denuded bugs. Here the observed effect was mainly attributable to the backpack, which enhanced the concealing effect of the dust coat and confused visually orienting predators. In addition, in the case of an attack, it could be shed to distract the enemy while the bug escaped, thus functioning in a similar manner as a lizard’s tail.
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Workers of the tropical ant tribes Basicerotini and Stegomyrmecini possess two dominant forms of setae on the dorsal surfaces of the body and outer surfaces of the legs: longer brush hairs with splintered distal ends, and shorter holding hairs that vary among species from plumose to blade-shaped or filiform. The two usually but not invariably occur together to create a double layer. The brush hairs evidently scrape or otherwise capture fine particles of soil, while the holding hairs help to keep them in place next to the surface exoskeleton. As the worker ages, the soil accumulates as a thin, mud-like layer, greatly enhancing the overall camouflage of the body. The material appears to be primarily or entirely exogenous; no special secretory cells were found (in Basiceros manni, studied for this purpose) that might contribute cryptically colored chemicals or adhesive substances to hold the soil in place.
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The ability to change body coloration is widely used in the context of visual camouflage to hide from predators or prey. Although experimental evidence from human vision shows that background and prey eye colours may trigger adaptive colour change in crab spiders, no study has addressed this hypothesis in the perceptual colour space of either predator or prey. I simultaneously tested the effects of reflected light and prey eye colours on background matching of female crab spiders, Misumena vatia. Using spectror- adiometric measurements and modelling of perceptual colour space of the most frequent prey, I tested whether individual spiders were able to match white and yellow light reflected by artificial backgrounds when fed either white- or red-eyed fruit flies, Drosophila melanogaster. The colour of light reflected by the visual background triggered adaptive camouflage as seen by Hymenopteran prey. In addition, there was a significant effect of prey eye colour within each light colour experiment, with spiders fed white- eyed flies better matching light reflected by the white background, and spiders fed red-eyed flies better matching the yellow reflected light. However, only spiders exposed to yellow reflected light and fed red- eyed flies could approach the colour detection threshold calculated for Hymenoptera. These results provide insights into how colour change is triggered in crab spiders, and indicate that ommochrome pigments in- gested with prey eyes not only are used by crab spiders to adjust their adaptive coloration, but also may indicate the hunting ability of females to potential mates
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Kyoto University (京都大学) 0048 新制・論文博士 博士(理学) 乙第6388号 論理博第994号 新制/理/585 UT51-63-C122 1988-01-23
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The inactivation of a replication protein causes the disassembly of the replication machinery and creates a need for replication reactivation. In several replication mutants, restart occurs after the fork has been isomerized into a four-armed junction, a reaction called replication fork reversal. The repair helicase UvrD is essential for replication fork reversal upon inactivation of the polymerase (DnaE) or the beta-clamp (DnaN) subunits of the Escherichia coli polymerase III, and for the viability of dnaEts and dnaNts mutants at semi-permissive temperature. We show here that the inactivation of recA, recFOR, recJ or recQ recombination genes suppresses the requirement for UvrD for replication fork reversal and suppresses the lethality conferred by uvrD inactivation to Pol IIIts mutants at semi-permissive temperature. We propose that RecA binds inappropriately to blocked replication forks in the dnaEts and dnaNts mutants in a RecQ- RecJ- RecFOR-dependent way and that UvrD acts by removing RecA or a RecA-made structure, allowing replication fork reversal. This work thus reveals the existence of a futile reaction of RecA binding to blocked replication forks, that requires the action of UvrD for fork-clearing and proper replication restart.
Mesquite: a modular system for evolutionary analysis. Version 2 Australian spiders in colour Analysing colors Bird coloration: mechanism and measurements
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A revision of the New Caledonian spider genus Bradystichus (Araneae, Lycosoidea) Descriptions of some new Araneidae of New South Wales
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N, Forster R (1993) A revision of the New Caledonian spider genus Bradystichus (Araneae, Lycosoidea). Am Mus Novit 3075:1–14 Rainbow WJ (1893) Descriptions of some new Araneidae of New South Wales. No. 1. Proc Linnean Soc NSW 7(4):71–476
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Multiple receivers, multiple ornaments, and a trade-off between agonistic and epigamic signalling in a widowbird A spider's world: senses and behaviour Phylogenetics and comparative morphology of crab spiders (Araneae: Dionycha, Thomisidae)
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Chapter 5-The evolution of UV reflectance in Australian crab spiders (Thomisidae)
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Analysing colors Bird coloration: mechanism and measurements
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Change of color and protective coloration in a flower-spider (Misumena vatia Thorell)
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A revision of the New Caledonian spider genus Bradystichus (Araneae, Lycosoidea)
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Australian spiders in colour
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Tomisídeos neotropicais V. Revisão do gênero Onocolus SIMON, 1895 (Araneae
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