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Abstract

Spider web research bridges ethology, ecology, functional morphology, material science, development, genetics, and evolution. Recent work proposes the aerial orb web as a one-time key evolutionary innovation that has freed spider-web architecture from substrate constraints. However, the orb has repeatedly been modified or lost within araneoid spiders. Modifications include not only sheet- and cobwebs, but also ladder webs, which secondarily utilize the substrate. A recent nephilid species level phylogeny suggests that the ancestral nephilid web architecture was an arboricolous ladder and that round aerial webs were derived. Because the web biology of the basalmost Clitaetra and the derived Nephila are well understood, the present study focuses on the webs of the two phylogenetically intervening genera, Herennia and Nephilengys, to establish ontogenetic and macroevolutionary patterns across the nephilid tree. We compared juvenile and adult webs of 95 Herennia multipuncta and 143 Nephilengys malabarensis for two measures of ontogenetic allometric web changes: web asymmetry quantified by the ladder index, and hub asymmetry quantified by the hub displacement index. We define a ‘ladder web’ as a vertically elongated orb exceeding twice the length over width (ladder index ≥ 2) and possessing (sub)parallel rather than round side frames. Webs in both genera allometrically grew from orbs to ladders, more so in Herennia. Such allometric web growth enables the spider to maintain its arboricolous web site. Unexpectedly, hub asymmetry only increased significantly in heavy-bodied Nephilengys females, and not in Herennia, challenging the commonly invoked gravity hypothesis. The findings obtained in the present study support the intrageneric uniformness of nephilid webs, with Herennia etruscilla webs being identical to H. multipuncta. The nephilid web evolution suggests that the ancestor of Nephila reinvented the aerial orb web because the orb arises at a much more inclusive phylogenetic level, and all intervening nephilids retained the secondarily acquired substrate-dependent ladder web. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 849–866.

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... Kuntner et al. (2008bKuntner et al. ( , 2010a and Kuntner and Agnarsson (2009) termed a similar formula the ladder index (calculated as the ratio of web height to web width; Peters, 1937 named this Große Achse/Kleine Achse), which tends to the value of one in symmetrical webs, but may reach values above five in strongly vertically elongated webs (e.g. Herennia; Kuntner et al., 2010b). The hub asymmetry of an orb web quantifies the displacement of the hub from web's geometric centre (Blackledge and Gillespie, 2002) and is calculated as: ...
... Cyclosa or Deliochus in Kuntner et al., 2008a;Nakata, 2010b). Similar indexes were termed hub displacement (Kuntner et al., 2008b(Kuntner et al., , 2010b and asymmetry index (Nakata and Zschokke, 2010). The former index show values of 0.5 in webs with a symmetric hub, and correspondingly closer to 1 in upward, and closer to zero in downward eccentric webs, and the latter equals zero in webs with a symmetric hub, but shows differently scaled values to hub asymmetry in asymmetrical ones. ...
... Small instar juveniles make tiny symmetric orb webs. Web shape then changes allometrically as the spiders mature, becoming increasingly ladder shaped in adults (Japyassu and Ades, 1998;Kuntner and Agnarsson, 2009;Kuntner et al., 2008bKuntner et al., , 2010b. ...
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Spiders are the preeminent silk craftsmen among arthropods and are best known for producing aerial orb webs that snare flying insects. Orb web spiders are ubiquitous predators in terrestrial ecosystems and are popular models for behavioural and ecological research, in part due to the ease of characterizing the shapes of orb webs. Orb webs are composite structures built from multiple types of silks, each with its own unique molecular structure and mechanical function, such that orb webs also link together evolutionary research from the genes coding for silk proteins to whole web function in the environment. Yet, orb webs are only intermediate structures in the evolutionary diversification of silk use among spiders, acting as stepping stones facilitating the origin of new web types and increased spider diversification. Here, we review the current research on the form and function of spider orb webs. We provide a comprehensive introduction to all aspects of orb web biology, suitable for any new investigation into orb web biology. While other reviews exist individually for webs, silk, and spider evolution, we hope that the synthetic nature of this review will facilitate a more integrated approach by future investigators. Finally, we explore in more detail some of the most dynamic areas of orb web biology to suggest promising venues for the next decade of research on these fascinating creatures and their silken snares. In particular, we discuss how spider webs might drive speciation, the dramatic growth in our understanding of the molecular ecology of spider silk, and the importance of a greater role for spider biology per se in silk biomimicry.
... The web architectures of spiders varies though ontogeny [57][58][59]. Accordingly, web architecture may be considered an extended phenotype depicting ontogeny. Allometric variations in silk production, the capacity to build webs, or to capture prey within webs, explain the variations in webs as spiders grow [59]. ...
... In some species these ontogentic changes are thought to reflect its phylogenetic history, the socalled "biogenic law" [65,70,71]. However, in other species this has proven to be not the case [58,59,72]. In any event, a combination of web architecture, silk properties and use of additional components are good indicators of ontogeny in many spiders. ...
... Phylogenetic studies of extended phenotypes may assist studies into the evolution and co-evolution of key phenotypic and behavioural innovations [4,135,136]. Indeed, phylogenetic analyses of spider web designs have been instrumental in enabling the identification of factors, such as predator diversification, predator and prey visual perceptibilities, and microenvironments, as drivers of the spider evolution and the diversification of web architectures [43,58,90,136,137]. While there remains controversy pertaining to the conclusions of these studies and whether or not evolution has acted directly on the structures, or the structures represent an "end-product" of a complex suite of physiological and behavioural traits that selection acts on [5,138], the work on spider webs serves as a good template for the examination of the selection pressure and constraints acting on the diversification of animals and their structures. ...
Article
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An animal's structure is an expression of its genotype beyond the confines of the body, so is considered an extended phenotype. The fitness consequences of extended phenotypes are not well defined because extended phenotypes affect fitness via interactions with both the environment and the somatic phenotype and these interactions are not well understood. Here I illustrate that web-building spiders make ideal models for testing hypotheses regarding the functional significance and adaptive benefits of extended phenotypes. A review of the literature reveals that spider webs, silks and additional components, e.g. decorations, decoys and barrier webs, represent expressions of (i) a multitude of behaviours including foraging and courtship, (ii) the spider's ontogeny, (ii) the sensory capacities of the spider and/or its predators and prey, and (iv) the phenotypic expression of any infecting parasitoids. I herein assess the adaptive benefits of expressing webs as extended phenotypes and outline the feedback cycles that influence spider fitness. Niche construction is an under explored aspect of extended phenotypes. I thus describe how it might play a role in enhancing spider fitness. I will lastly outline some research applications of using the 'web as an extended phenotype' model, in investigations of: (i) invasive and conservation biology of spiders, (ii) spider phylogenetics, and (iii) using webs for biomonitoring, among others.
... The web architectures of spiders varies though ontogeny [57][58][59]. Accordingly, web architecture may be considered an extended phenotype depicting ontogeny. Allometric variations in silk production, the capacity to build webs, or to capture prey within webs, explain the variations in webs as spiders grow [59]. ...
... In some species these ontogentic changes are thought to reflect its phylogenetic history, the socalled "biogenic law" [65,70,71]. However, in other species this has proven to be not the case [58,59,72]. In any event, a combination of web architecture, silk properties and use of additional components are good indicators of ontogeny in many spiders. ...
... Phylogenetic studies of extended phenotypes may assist studies into the evolution and co-evolution of key phenotypic and behavioural innovations [4,135,136]. Indeed, phylogenetic analyses of spider web designs have been instrumental in enabling the identification of factors, such as predator diversification, predator and prey visual perceptibilities, and microenvironments, as drivers of the spider evolution and the diversification of web architectures [43,58,90,136,137]. While there remains controversy pertaining to the conclusions of these studies and whether or not evolution has acted directly on the structures, or the structures represent an "end-product" of a complex suite of physiological and behavioural traits that selection acts on [5,138], the work on spider webs serves as a good template for the examination of the selection pressure and constraints acting on the diversification of animals and their structures. ...
Article
Mimicry is a natural phenomenon which never ceases to amaze, involving one organism taking on characteristics of another, to gain evolutionary advantage. These strategies based on "deceit" carry with them advantages to the mimic (or deceiver) either in the form of heightened protection from potential predators (as in the case of Batesian or Müllerian mimicry), or easier access to prey (aggressive mimicry). Mimics exploit different sensory channels, including visual, acoustic or chemical systems, by looking, sounding or "smelling" like a model organism, respectively. Certain characteristics of model organisms are favorable to mimics, especially when the mimicry is a form of protection from predators. Among insects, an ideal group of model organisms are the ants, as they are numerous, often aggressive and unpalatable for many other animals. Ant mimicry is therefore common in several invertebrate families. In spiders, ant mimicry occurs in at least 13 different families. Here, ant mimicry in spiders will be outlined, briefly describing the main findings to date of this vast and fascinating topic.
... Fourth, there is strong evidence that the six species currently recognized are globally fully allopatric [10,11], which hints at their geographic, ecological and behavioral exclusivity. Finally, these extremely sexually dimorphic nephilid spiders are becoming model organisms in a range of disciplines [11][12][13][14] and thus predicting their habitat suitability, or even future occurrence would facilitate further research of their biology. Figure 1 shows the currently known ranges for all six Nephilengys species, which are i) tropical, and ii) show a range in inhabited areas from limited island distributions, such as in N. livida (Vinson, 1863), N. borbonica (Vinson, 1863) and N. dodo , to a wider distribution over several islands as in N. papuana Thorell, 1881, and to extremely wide distributions over vast areas as seen in N. malabarensis (Walckenaer, 1841) and N. cruentata (Fabricius, 1775), the latter being even spread intercontinentally. ...
... However, their establishment in new areas and consequently their fine scale distribution depends on the proximity, accessibility, and, primarily, the ecological suitability of the available space. Their natural history suggests that they need hard vertical surfaces (trees) to anchor their large webs [10,14]. As any terrestrial organism, they further need spaces of suitable elevation, year round temperature and sufficient precipitation. ...
... We believe these facts reflect both species synanthropic habits. Nephilengys malabarensis is common in coastal and higher elevation areas over SE Asia, where its habitat ranges from native forest to introduced tree stands to houses [14], which is also accurately reflected by our model predicting high habitat suitability in wet areas of the mixed land cover types. Despite its apparent absence from the areas that biogeographically represent Australasia (e.g. ...
Article
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Background: Although numerous studies model species distributions, these models are almost exclusively on single species, while studies of evolutionary lineages are preferred as they by definition study closely related species with shared history and ecology. Hermit spiders, genus Nephilengys, represent an ecologically important but relatively species-poor lineage with a globally allopatric distribution. Here, we model Nephilengys global habitat suitability based on known localities and four ecological parameters. Methodology/principal findings: We geo-referenced 751 localities for the four most studied Nephilengys species: N. cruentata (Africa, New World), N. livida (Madagascar), N. malabarensis (S-SE Asia), and N. papuana (Australasia). For each locality we overlaid four ecological parameters: elevation, annual mean temperature, annual mean precipitation, and land cover. We used linear backward regression within ArcGIS to select two best fit parameters per species model, and ModelBuilder to map areas of high, moderate and low habitat suitability for each species within its directional distribution. For Nephilengys cruentata suitable habitats are mid elevation tropics within Africa (natural range), a large part of Brazil and the Guianas (area of synanthropic spread), and even North Africa, Mediterranean, and Arabia. Nephilengys livida is confined to its known range with suitable habitats being mid-elevation natural and cultivated lands. Nephilengys malabarensis, however, ranges across the Equator throughout Asia where the model predicts many areas of high ecological suitability in the wet tropics. Its directional distribution suggests the species may potentially spread eastwards to New Guinea where the suitable areas of N. malabarensis largely surpass those of the native N. papuana, a species that prefers dry forests of Australian (sub)tropics. Conclusions: Our model is a customizable GIS tool intended to predict current and future potential distributions of globally distributed terrestrial lineages. Its predictive potential may be tested in foreseeing species distribution shifts due to habitat destruction and global climate change.
... AI values were zero for a perfectly symmetric web. AI is analogous to hub asymmetry (Blackledge & Gillespie 2002) and hub displacement (Kuntner et al. 2008b(Kuntner et al. , 2010b, but these metrics are different. The values of hub asymmetry are also zero for symmetric webs, but are differently scaled to AI; specifically hub asymmetry is negative when a web has a larger upper part. ...
... However, another study did not find any additional cost to laying a sticky spiral in the upper part of webs (Coslovsky & Zschokke 2009). Alternatively, the constraint may be ontogenetic, and a phylogenetic constraint may restrict ontogenetic change in web asymmetry (Kuntner et al. 2010b). Many authors have shown that as spiders grow the downward bias in the webs increases (Japyassú & Ades 1998;Graf & Nentwig 2001;Kuntner et al. 2008b;Kuntner & Agnarsson 2009;Hesselberg 2010). ...
Article
Orb webs built by spiders are an extended phenotype, and spiders can modify their morphology when rebuilding them. Internal and external environmental conditions can affect how spiders rebuild. Most spiders that build vertical orb webs wait for prey at the web hub and orient downwards. Moreover, their webs exhibit up-down size asymmetry; specifically, the area below the hub is larger than the area above it. However, some spiders reverse this asymmetry in their webs. To examine the relationship between phenotypic plasticity and web asymmetry reversal and whether spiders elongate their webs upwards in response to prey capture in the upper web, I manipulated prey capture location in two closely related spider species. Cyclosa octotuberculata build webs with typical asymmetry (larger area below the web hub). Cyclosa argenteoalba build webs with reversed asymmetry, a derived phenotype, and wait in a reversed orientation, facing upwards. I found that, when spiders fed in the lower part of the web, both species elongated their webs downwards and that C. argenteoalba webs lost their asymmetry and became symmetrical. In contrast, webs were not elongated in the upward direction when spiders of either species were fed in the upper part of the web. These results provided evidence that the up-down asymmetry of Cyclosa webs is a plastic trait regardless of whether spiders build webs with typical or reversed asymmetry. However, no significant upward elongation of webs indicates that there is no evidence of a relationship between plasticity in the extended phenotype and web asymmetry reversal.
... (1) or downward-divergent side frames (2). Similar to side frame curvature (round, subparallel, parallel) sensu Kuntner et al. (2010), this character describes . Note absence of the free sector, with investigated parameters: webwidth (a), web-height (b), top to hub distance (c), free sector (d), retreat (R), vertical number of sticky spirals (SS), and non-circulating SS above and below hub. ...
... Highly asymmetric webs with (sub)parallel side frames, the so called ladder webs, evolved convergently in araneids and nephilids, probably to exploit new habitats or food sources (Eberhard 1975;Kuntner 2005Kuntner , 2006Kuntner et al. 2008aKuntner et al. , b, 2010Harmer & Framenau 2008). Although S. stroemi webs are not on average twice the height over width, which defines ladders (Kuntner et al. 2010), they come closest to this among Zygiella s.l. The limiting spatial factor on a tree is its circumference -the horizontal website availability (Kuntner 2005(Kuntner , 2008a. ...
Article
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The species classically grouped in the genus Zygiella F.O. Pickard-Cambridge 1902 are thought to all possess a characteristic orb web feature — a spiral-free sector in the upper part of the orb. Zygiella s.l. has recently been split into four genera, Zygiella s.s., Leviellus Wunderlich 2004, Parazygiella Wunderlich 2004 and Stroemiellus Wunderlich 2004, and proposed to belong to family Zygiellidae, rather than the classical Araneidae. To find orb web features that could potentially diagnose these species and/or genera, we investigated female web architectures of L. thorelli, P. montana, S. stroemi, Z. keyserlingi and Z. x-notata. We investigated a total of 278 female webs and compared 16 characters emphasizing web size, web and hub asymmetry, as well as radial and spiral counts. The free sector may be present in all species but its prevalence in female webs varied from 41% in Z. keyserlingi to 94% in P. montana. Various combinations of web architecture characters may diagnose those species that in our sample represented all four genera: Zygiella s.s. may be diagnosed by the median number of non-circulating sticky spirals below hub, Stroemiellus by the small web size with small mesh width and the non-circulating spirals above hub, Parazygiella by few primary radii and sticky spirals, and Leviellus by a pronounced vertical hub displacement. This suite of diagnostic features may provide preliminary support for the current taxonomy of Zygiella s.l., although the ultimate test, i.e., a phylogeny, is needed to test the validity of the genera. Seven out of 16 web characters are potentially phylogenetically informative because they show a statistically significant shared variation among species. Our study, which pioneers the quantification of web data to distinguish species, implies that the interspecific variation in webs may turn out to reflect phylogenetic relationships among Zygiella s.l.
... Environmental factors that can be ascribed as influential over the relative number and size of orb-web architectural components include: (i) the presence of predators, (ii) ambient temperature, wind, and light levels, and (iii) prey availability, prey types, and prey nutrient value (Heiling and Herberstein 2000;Boutry and Blamires 2013). Change in web architecture has also been documented across ontogeny in orb-web spiders (Hesselberg 2010;Kuntner et al. 2010;Escalante 2013). ...
... Web plasticity may influence web structural variation across the spider phylogeny (Blackledge et al. 2009Kuntner et al. 2010). Accordingly, some clades might exhibit relatively minor variability in web forms across species, environments, and ontogeny. ...
Chapter
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Web building has been such a highly successful foraging innovation among spiders that the vast majority of extant spiders are web builders. The structure of spider webs varies substantially between species, and web building has even been lost completely in some clades. Examples of different web forms include the classic orb webs, which may be orientated vertical to the ground or horizontal, sheet webs, and cobwebs, which consist of three-dimensional meshwork and ascending sticky threads for support and capture of prey. The architecture of webs may also vary within clades and even within species. This may be a consequence of: (i) individuals adapting their web structures to the environment; e.g., larger webs are built in areas where more space is available, (ii) spiders varying their webs to tune its performance, e.g., when spiders are exposed to different prey, or (iii) silk expression constraints, e.g., when on diets lacking certain nutrients. We review the literature, focusing on contributions from the Neotropical region, showing that spider webs vary in structure and function at multiple levels and so must be considered a dynamic, variable, extended phenotype of its builder. Webs accordingly depict the foraging, mating, and defensive strategies, and physiological status, of the spider.
... Here, we examine whether similar scaling occurs ontogenetically within a species. A variety of studies demonstrate ontogenetic changes in web architecture, with juveniles spinning more symmetric orbs and adults typically shifting to more specialized architectures (Eberhard, 1985Eberhard, , 1986 Eberhard, Barrantes & Madrigal-Brenes, 2008; Kuntner & Agnarsson, 2009; Kuntner, Kralj-Fisěr & Gregoricˇ,Gregoricˇ, 2010). For example, Epeirotypus pulls its orb shaped web into a cone and does so much more pronouncedly when it becomes an adult (Eberhard, 1986), which may be associated with higher energy of recoil when the web is released onto the prey. ...
Article
Body size increases greatly during ontogeny in most animals and is often accompanied by dramatic shifts in foraging strategies and hence food resources. Orb-weaver spiders provide an interesting case, where a relatively homogeneous foraging strategy, aerial silk webs, is employed across all ontogenetic stages. Orb webs are spun soon after spiders emerge from the egg sac through growth of up to two orders of magnitude in body size. The sizes of prey targeted by the spiders are also likely to increase as spiders develop. Here, we examine how relative silk investment, web architecture, and the material properties of silk in webs change during ontogeny in the orb-weaver Neoscona arabesca. We also quantify two emergent properties of web performance – prey stopping potential and stickiness. We find that silk investment increases isometrically with body size, with the exception of greater than expected glue production in larger spiders. Larger spiders spin larger webs, with smaller radii, but the increased volume of all silk types and greater toughness of the capture spiral silk result in the isometric scaling of stopping potential. The strength and toughness of sticky capture spiral thread increases with diameter and hence also with ontogeny, a size scaling pattern that mirrors an evolutionary pattern across spider species. Dragline thread material properties do not change over ontogeny. The improved material properties of capture spiral threads and the increased absolute stopping potential of webs are consistent with the hypothesis that rare, large prey items play a crucial role in spiders reaching adulthood and in maximizing fecundity of female orb-weaver spiders.
... For example, they commonly select microhabitats with high prey encounter rates (Olive 1980; Gillespie 1981; McKay 1982; Uetz 1986; Gillespie and Caraco 1987; Spiller 1992), favorable microclimates (Almquist 1970Almquist , 1973 Riechert 1976), or sites with low pre-existing population densities (Smallwood 1993). Although habitat choice is imposed on all individuals as juveniles, forced web abandonment is not uncommon in adults as the result of intra-and interspecific antagonism (Riechert 1978), ontogenetic shifts in behavior (Hill and Christenson 1981; Kuntner et al. 2010), web damage (Biere and Uetz 1981), repeated encounters with predators (Tolbert 1977), hunger (Wise 1975; McKay 1982), and spatial or structural limitations (Lubin and Robinson 1982). In this study, we ask the following questions: (1) Do female L. hesperus exhibit consistent individual differences in choosiness towards cues of habitat quality? ...
Article
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Research on consistent individual differences in behavior, or “behavioral syndromes”, continues to grow rapidly, and yet, the aspects of behavior under consideration have remained remarkably limited. Here, we consider individual variation in consistency of choice (termed here “choosiness”), as expressed during habitat choice. We repeatedly tested the responses of female Western Black Widows, Latrodectus hesperus, to two cues of habitat quality: prey chemical cues and variation in web site illuminance. We estimated females’ response by the distance they positioned themselves from (1) the source of prey chemical cues and (2) the darkest edge of our test arena. Individuals with low variance in their responses are deemed more “choosy”, whereas individuals with high variance are deemed less “choosy”. Generally, most females initiated web construction near the source of the prey chemical cues and tended to place themselves in low-light conditions. However, we detected strong, repeatable differences in females’ intensity of response, and within-individual variance of response (i.e., choosiness) was correlated across situations: females with highly consistent responses towards cricket chemical cues also exhibited highly consistent responses towards variation in light conditions. When deprived of food for extended periods, females were indistinguishable in their responses towards prey chemical cues, but tended to initiate web construction in brighter lighting conditions. Food-deprived females universally exhibited higher variance and diminished consistency in their responses (i.e., they were less choosy). Additionally, higher choosiness was associated with greater mass loss during choice trials, suggesting choosiness is energetically costly. Our results demonstrate that consistency of response to environmental cues is yet another element of behavior that varies among individuals and variation in choosiness could beget speed/quality trade-offs during animal decision making.
... For example, larger epigean species tend to prey on larger prey (Brown, 1981) which is also evident when comparing M. merianae and M. menardi. The functional relation between different web architecture, which is thought to be mostly genetically determined (Eberhard, 1982;Kuntner et al., 2010, but, see Tso et al., 2007Harmer and Herberstein, 2009), and the prey size, as well as partial foraging of M. menardi on walls (Eckert and Moritz, 1992;Smithers, 1996Smithers, , 2005a, has been empirically confirmed to influ- ence the efficacy of prey capture. Although experimental evidence suggests that orb webs with small mesh size may capture larger prey than those with larger webs (Blackledge and Zevenbergen, 2006), our data suggest that the pattern may be different in Meta and Metellina. ...
Article
Hypogean habitats are relatively simple exhibiting low diversity, low production and relative constancy of environmental factors, and are therefore appropriate for studying species coexistence in situ. We investigated the coexistence of two closely related, similarly sized orb-weaving spider species, Meta menardi and Metellina merianae, living syntopically in a Slovenian cave. We studied the annual dynamics of both species within a mixed population, and the impact of the ambient temperature, relative humidity, airflow and illumination, and compared their trophic niches to legacy data on prey of both species from 55 caves in Slovenia. We predicted a large overlap in their spatial niches and substantial differences in their temporal and trophic niches. We found that their spatial niches overlap greatly with few exceptions, mostly on the dates of notable meteorological changes in the cave but that their temporal niches differ significantly with r-strategy resembling epigean annual dynamic in M. merianae and a steady low abundance course in M. menardi within the cave. We also found that different predatory strategies significantly segregate their trophic niches: M. merianae uses a typical orb-weaving hunting strategy, while M. menardi combines web hunting with off-web hunting. Our findings suggest that both the diverse dynamics and trophic niches enable the coexistence of M. menardi and M. merianae despite their similar spatial niches, and that M. menardi, in particular, is optimally adapted to the epigean/hypogean ecotone.
... The orb web's evolutionary origin defines a single clade, Orbiculariae, a large and diverse group with more than 12.000 species[9][10][11][12]. Architectural evolution of orb webs through time has resulted in novel web types[9,13,14], such as the linyphiid sheetwebs and theridiid cobwebs[10,15,16], the deinopid casting web[17], as well as many modifications of the classical orb web[7,9,[18][19][20]. Because spiders build orb webs using highly stereotypical behaviors that are evolutionarily conserved and phylogenetically informative[13,20], the evolution of new web architectures are expected to coincide with novel behaviors. ...
Article
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Interspecific coevolution is well described, but we know significantly less about how multiple traits coevolve within a species, particularly between behavioral traits and biomechanical properties of animals' "extended phenotypes". In orb weaving spiders, coevolution of spider behavior with ecological and physical traits of their webs is expected. Darwin's bark spider (Caerostris darwini) bridges large water bodies, building the largest known orb webs utilizing the toughest known silk. Here, we examine C. darwini web building behaviors to establish how bridge lines are formed over water. We also test the prediction that this spider's unique web ecology and architecture coevolved with new web building behaviors. We observed C. darwini in its natural habitat and filmed web building. We observed 90 web building events, and compared web building behaviors to other species of orb web spiders. Caerostris darwini uses a unique set of behaviors, some unknown in other spiders, to construct its enormous webs. First, the spiders release unusually large amounts of bridging silk into the air, which is then carried downwind, across the water body, establishing bridge lines. Second, the spiders perform almost no web site exploration. Third, they construct the orb capture area below the initial bridge line. In contrast to all known orb-weavers, the web hub is therefore not part of the initial bridge line but is instead built de novo. Fourth, the orb contains two types of radial threads, with those in the upper half of the web doubled. These unique behaviors result in a giant, yet rather simplified web. Our results continue to build evidence for the coevolution of behavioral (web building), ecological (web microhabitat) and biomaterial (silk biomechanics) traits that combined allow C. darwini to occupy a unique niche among spiders.
... For example, Nephilengys cruentata (Fabricius, 1775) inhabits most of tropical Africa where variation in size and colors is tremendous, and the species has also spread into the Neotropics, where it has established permanent synanthropic colonies (Levi and von Eickstedt, 1989;Kuntner, 2007). Similarly, the Asian populations all seem to belong to a single, albeit morphologically variable species, Nephilengys malabarensis (Walckenaer, 1841), which lives synathropically and naturally in forests (Kuntner, 2007;Kuntner et al., 2010). According to the current taxonomic hypothesis, Nephilengys populations inhabiting the islands of the western Indian Ocean islands are thought to belong to only one species, Nephilengys borbonica (Vinson, 1863) (Kuntner, 2007), yet, these populations show a striking pattern of color variation ( Fig. 1; Vinson, 1863;Dahl, 1912;Kuntner, 2007). ...
Article
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The origin of the terrestrial biota of Madagascar and, especially, the smaller island chains of the western Indian Ocean is relatively poorly understood. Madagascar represents a mixture of Gondwanan vicariant lineages and more recent colonizers arriving via Cenozoic dispersal, mostly from Africa. Dispersal must explain the biota of the smaller islands such as the Comoros and the chain of Mascarene islands, but relatively few studies have pinpointed the source of colonizers, which may include mainland Africa, Asia, Australasia, and Madagascar. The pantropical hermit spiders (genus Nephilengys) seem to have colonized the Indian Ocean island arc stretching from Comoros through Madagascar and onto Mascarenes, and thus offer one opportunity to reveal biogeographical patterns in the Indian Ocean. We test alternative hypotheses on the colonization route of Nephilengys spiders in the Indian Ocean and simultaneously test the current taxonomical hypothesis using genetic and morphological data. We used mitochondrial (COI) and nuclear (ITS2) markers to examine Nephilengys phylogenetic structure with samples from Africa, southeast Asia, and the Indian Ocean islands of Madagascar, Mayotte, Réunion and Mauritius. We used Bayesian and parsimony methods to reconstruct phylogenies and haplotype networks, and calculated genetic distances and fixation indices. Our results suggest an African origin of Madagascar Nephilengys via Cenozoic dispersal, and subsequent colonization of the Mascarene islands from Madagascar. We find strong evidence of gene flow across Madagascar and through the neighboring islands north of it, while phylogenetic trees, haplotype networks, and fixation indices all reveal genetically isolated and divergent lineages on Mauritius and Réunion, consistent with female color morphs. These results, and the discovery of the first males from Réunion and Mauritius, in turn falsify the existing taxonomic hypothesis of a single widespread species, Nephilengys borbonica, throughout the archipelago. Instead, we diagnose three Nephilengys species: Nephilengys livida (Vinson, 1863) from Madagascar and Comoros, N. borbonica (Vinson, 1863) from Réunion, and Nephilengys dodo new species from Mauritius. Nephilengys followed a colonization route to Madagascar from Africa, and on through to the Mascarenes, where it speciated on isolated islands. The related golden orb-weaving spiders, genus Nephila, have followed the same colonization route, but Nephila shows shallower divergencies, implying recent colonization, or a moderate level of gene flow across the archipelago preventing speciation. Unlike their synanthropic congeners, N. borbonica and N. dodo are confined to pristine island forests and their discovery calls for evaluation of their conservation status.
... However, ontogenetic changes in the designs of spider webs are well known to show a ''biogenetic'' pattern in which the designs of the webs of younger individuals of a species tend to be more plesiomorphic than those of older individuals in those species in which web design changes as spiders mature. This pattern has been observed in 13 different web-building spider genera with different web designs (summaries in Eberhard 1990;Eberhard et al. 2008a;Kuntner et al. 2008Kuntner et al. , 2010. It is not clear why this pattern should occur, but it is so consistent that it was used ''in reverse'' in a recent study of the theridiid Latrodectus geometricus C.L. Koch 1841 to deduce the probable ancestral web form for theridiids on the basis of ontogenetic changes. ...
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Web designs of young spiders are often less derived than those of older conspecific individuals. This study tested whether this “ontogeny repeats phylogeny” pattern occurs in two species of Latrodectus and two species of the closely related genus Steatoda. This pattern was assumed to occur in a recent study of a third Latrodectus species, L. geometricus, which attempted to deduce a probable evolutionary derivation of gum-foot webs of theridiids on the basis of ontogenetic changes. We found the same basic ontogeny repeats phylogeny ontogenetic pattern in all four species, suggesting that the previous suppositions were justified. As expected, the webs of the young instars of the two Latrodectus species were more similar than those of the adults, and were more similar to those of young than to those of adults of L. geometricus. One apparently derived trait of L. mirabilis, attaching prey remains as camouflage for the spider in the central portion of the web, did not change during ontogeny, and was present in even the webs of first-instar spiderlings. Field observations of L. mirabilis suggest that the ontogenetic change from light to darker abdominal color patterns that occurs in many Latrodectus species may result from changes in selection for camouflage associated with ontogenetic changes in web designs and the spiders' resting sites. The webs of Steatoda also fit the ontogenetic pattern: at least some ontogenetic changes in both species involved younger spiders having less derived traits than those of adults. The webs of young Steatoda spiders were more derived in some respects than those of the early instars of Latrodectus.
... That webs remain circular throughout ontogeny further indicates that increased differences in running speed affect web symmetry, as that difference can only explain the increased hub displacement. Changes in web shape are usually a result of limited web space (Kuntner et al. 2010b; Harmer and Herberstein 2009) or prey adaptation (Eberhard 1975). As L. venusta build webs in unlimited aerial space, and because circular webs are better prey-catching devices than asymmetrically shaped webs (Harmer et al. 2012), web shape was not expected to change through ontogeny. ...
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The biogenetic law posits that the ontogeny of an organism recapitulates the pattern of evolutionary changes. Morphological evidence has offered some support for, but also considerable evidence against, the hypothesis. However, biogenetic law in behavior remains underexplored. As physical manifestation of behavior, spider webs offer an interesting model for the study of ontogenetic behavioral changes. In orb-weaving spiders, web symmetry often gets distorted through ontogeny, and these changes have been interpreted to reflect the biogenetic law. Here, we test the biogenetic law hypothesis against the alternative, the optimal foraging hypothesis, by studying the allometry in Leucauge venusta orb webs. These webs range in inclination from vertical through tilted to horizontal; biogenetic law predicts that allometry relates to ontogenetic stage, whereas optimal foraging predicts that allometry relates to gravity. Specifically, pronounced asymmetry should only be seen in vertical webs under optimal foraging theory. We show that, through ontogeny, vertical webs in L. venusta become more asymmetrical in contrast to tilted and horizontal webs. Biogenetic law thus cannot explain L. venusta web allometry, but our results instead support optimization of foraging area in response to spider size.
... Despite the fact that Nephila is among the most intensively studied spiders in the world, the only species-level phylogeny is based on morphology and behavior (Kuntner et al., 2008). Studies based on this topology include evolution of size (Kuntner and Coddington, 2009), genital complexity (Kuntner et al., 2009a), and web evolution, (Kuntner et al., 2010). Although some of the intra-nephilid relationships from Kuntner et al. (2008) appear very robust, others, especially within the Nephila clade, received low clade support. ...
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The molecular phylogeny of the globally distributed golden orb spider genus Nephila (Nephilidae) was reconstructed to infer its speciation history, with a focus on SE Asian/W Pacific species. Five Asian, two Australian, four African, and one American species were included in the phylogenetic analyses. Other species in Nephilidae, Araneidae, and Tetragnathidae were included to assess their relationships with the genus Nephila, and one species from Uloboridae was used as the outgroup. Phylogenetic trees were reconstructed from one nuclear (18S) and two mitochondrial (COI and 16S) markers. Our molecular phylogeny shows that the widely distributed Asian/Australian species, N. pilipes, and an African species, N. constricta, form a clade that is sister to all other Nephila species. Nested in this Nephila clade are one clade with tropical and subtropical/temperate Asian/Australian species, and the other containing African and American species. The estimated divergence times suggest that diversification events within Nephila occurred during mid-Miocene to Pliocene (16 Mya-2 Mya), and these time periods were characterized by cyclic global warming/cooling events. According to Dispersal and Vicariance Analysis (DIVA), the ancestral range of the Asian/Australian clade was tropical Asia, and the ancestral range of the genus Nephila was either tropical Asia or Africa. We conclude that the speciation of the Asian/Australian Nephila species was driven by Neogene global cyclic climate changes. However, further population level studies comparing diversification patterns of sister species are needed to determine the mode of speciation of these species.
... For these parameters, as well as for the outermost sticky spiral loop, I calculated the asymmetry in the same way as above, [i.e., (upper -lower)/(upper + lower)], yielding the values of sticky spiral ratio, spiral spacing asymmetry, and web asymmetry, respectively. Note that web asymmetry (like hub asymmetry sensu Blackledge & Gillespie 2002) is based on the position of the hub relative to the outermost sticky spiral loop, whereas the similar metric hub displacement (sensu Kuntner et al. 2008) is based on the position of the hub relative to the web frame (Kuntner et al. 2010). Web asymmetry here is used in the same way as in Zschokke (1993) and Coslovsky & Zschokke (2009), whereas Blackledge & Gillespie (2002) used the term web asymmetry index to quantify web shape (deviation of the outermost sticky spiral from a circle). ...
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Most orb webs are vertically asymmetric with larger lower than upper parts, even though the basic structure of orb webs with concentric sticky spiral loops implies a round shape with the hub in its geometric centre. Spiders are known to modify the basic, round web structure to achieve asymmetric webs by placing the sticky spiral loops eccentrically around the hub and by inserting additional sticky spiral threads below the hub. In addition, spiders could increase asymmetry by building larger meshes below than above the hub. In the present paper, I analyzed these web modifications quantitatively in webs of Araneus diadematus Clerck 1757. In addition, I assessed the influence of gravity on the different web modifications during web building by laying some webs horizontally during auxiliary and/or sticky spiral building, and I also assessed how the web modifications influenced each other during web building. I found that web orientation during auxiliary spiral building influenced auxiliary spiral eccentricity, which in turn influenced sticky spiral eccentricity and overall web asymmetry. Web orientation during sticky spiral building only influenced – together with web asymmetry and spiral ratio – mesh size asymmetry. I conclude that A. diadematus uses the auxiliary spiral as a guiding line during sticky spiral building and that it employs different rules to build the two spirals.
... Study species. For this experiment, we focused on N. malabarensis, a highly sexually size dimorphic nephilid/araneid 29,62 that is common in Singapore and easily recognised in juvenile stages due to its highly characteristic web built on trees ( Supplementary Fig. 9) 72 . We collected juveniles and subadults in Singapore and reared them to maturity (for rearing details, see the "comparative study" section). ...
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When sexual conflict selects for reproductive strategies that only benefit one of the sexes, evolutionary arms races may ensue. Female sexual cannibalism is an extreme manifestation of sexual conflict. Here we test two male mating strategies aiming at countering sexual cannibalism in spiders. The “better charged palp” hypothesis predicts male selected use of the paired sexual organ (palp) containing more sperm for their first copulation. The “fast sperm transfer” hypothesis predicts accelerated insemination when cannibalism is high. Our comparative tests on five orbweb spider species with varying levels of female sexual cannibalism and sexual size dimorphism (SSD) reveal that males choose the palp with more sperm for the first copulation with cannibalistic females and that males transfer significantly more sperm if females are cannibalistic or when SSD is biased. By supporting the two hypotheses, these results provide credibility for male mating syndrome. They, however, open new questions, namely, how does a male differentiate sperm quantities between his palps? How does he perform palp choice after assessing his cannibalistic partner? By conducting follow-up experiments on Nephilengys malabarensis, we reveal that it is sperm volume detection, rather than left-right palp dominance, that plays prominently in male palp choice.
... Moths are, nevertheless, difficult to capture in two-dimensional orb webs, as their wing scales do not stick to the spirals and they readily fall out under gravity (Nentwig 1987). Moth specialization has accordingly been hypothesized to drive the evolution of many variations in spider web forms, including the evolution of "ladder webs" and "bolases" (Eberhard 1990;Yeargen 1994;Kuntner et al. 2010). Henceforth, it may be plausible that, in addition to avoiding predators, more efficient moth capture may drive the use of three-dimensional structures among orb-web spiders. ...
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Animal structures come at material, energetic, time, and expression costs. Some orb-web spiders add three-dimensional barrier structures to their webs, but many do not. Predator protection is considered to be the principal benefit of adding these structures. Accordingly, it remains paradoxical why some orb-web spiders might construct the barriers while others do not. Here, we experimentally determined whether the barrier structure added to the horizontal orb web of the spider Cyrtophora moluccensis deters predators at the cost of reducing the amount of prey captured in the field. We conducted experiments by day and night to assess whether the effects vary with the time of day. We found that the three-dimensional barriers not only offered protection from predatory wasps by day but also enhanced the amount of prey captured by day and night. Moreover, the barrier structure appears particularly useful at catching moths, the largest and most energetically profitable prey that it encounters. We, therefore, concluded that reducing the energetic and time costs associated with producing and depositing extra silk threads is the principal reason why barrier structures are used intermittently among orb-web spiders.
... prey size, Blamires et al. 2010 constraints. It is more efficient to enlarge the lower part of the web because it is easier to catch prey in this region than in other parts of the web due to gravity (Venner and Casas 2005;Kuntner et al. 2010b). This is also an adaptation to environmental structural constraints (Kuntner et al. 2010a;Hesselberg 2013), and this enlargement without increasing silk investment but by increasing mesh height could be interpreted in terms of optimal foraging; it is better for a spider to enlarge this part of its web where prey capture is more efficient (Gregoric et al. 2013). ...
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Very few studies have investigated the influence of regular practice of a stereotyped behaviour on its future expression. In spiders, orb-web construction is a succession of repetitive and stereotyped behaviours and is a relevant model for such study. This study examined if preventing spiders from building influences their future constructions. Spiders were caught in the field and brought back to the laboratory where they were exposed to two different situations; half were maintained in small boxes where web building was not possible, and half were maintained in large enclosures where they could build orb-webs. All spiders were tested twice: 1 week after their capture (test 1) and 12 weeks later (test 2). Their building performance was evaluated by examining silk investment (length of the capture spiral, number of radii, of spiral turns, length of the lower part of the web), web design (mesh height, asymmetry) and the frequency of anomalies in the web. There was no difference in web constructions between the two groups in either test. However, the rearing conditions seemed to affect two parameters: the length of the lower part of the web and the asymmetry were higher for spiders reared in small boxes. We did find also, an overall decrease with time in silk investment (length of the capture spiral, capture area) in both groups as well as an increase in the number of anomalies of the capture spiral from tests 1 to 2. These results suggest that regular web construction does not have a strong effect on web structure or silk investment, but spider age did affect parameters in the two groups. Thus, the lack of practice over a large portion of a spider's adult life does not affect a stereotyped behaviour such as the building of an orb-web.
... Es conocido que la variación estructural de las telas orbiculares, le brinda una mejor adaptación a las condiciones locales (Heiling y Herberstein, 2000). Entre estas condiciones se incluyen el tipo de presa (Sandoval, 1994;Schneider y Vollrath, 1998), la disponibilidad de presas (Herberstein et al., 2000a, Higgins y Buskirk, 1992Sherman, 1994), el estado nutricional de la araña (Crews y Opell, 2006, Mayntz et al., 2009, las condiciones atmosféricas Liao et al., 2009), el tamaño de la araña Herberstein y Heiling, 1999a, b y c), la edad y el desarrollo (Hesselberg, 2010;Kuntner et al., 2010), el suministro de seda (Eberhard, 1988), la experiencia (Heiling y Herberstein, 1999;Nakata y Ushimaru, 1999, la presencia de depredadores y parásitos (Higgins, 1992;Eberhard, 2000Eberhard, , 2010 y la estructura del microhábitat (Krink y Vollrath, 2000;Blamires et al., 2007;Harmer y Herberstein, 2009). ...
Thesis
The spider webs made by juvenile are similar in overall shape to that of adults. However, many details show the existence of different morphometrics and designs in stabilimenta correlated to the instar of the spider and the habitat constraints. This phenomenon may be a reflection of an adaptive strategy by different age groups based on habitat conditions. In this work, we describe the morphological adaptations of both the web and its stabilimenta, made by juveniles, pre-adult and adult Argiope argentata living in the xeromorphic scrub of Siboney-Juticí Ecological Reserve and the Cactus Garden, as well as the grassland of the Botanical Gardens, all three places located in Santiago de Cuba province. Morphometric parameters of the web and design of stabilimenta were recorded from 144 webs and were taken into account the effect of the web height to the soil, the open space of vegetation and spider size on these parameters. The age groups showed the existence of adaptive mechanisms, which was assessed through morphometric variables of the webs and design of stabilimenta. In all age groups, mid-vertical symmetry and web shape were both positively correlated to habitat conditions of each study site. Juveniles used a smaller space in the vegetation, at a lower height and constructed smaller and more symmetrical webs, with a high frequency of discoid-shaped stabilimenta.
... Orb web architecture and function vary widely (12). In nephilids, small juvenile webs are round and symmetric, but older, larger instars spin increasingly asymmetric webs (85,87). In N. pilipes, mass and hub displacement are strongly correlated (84). ...
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Sexual size dimorphism is one of the most striking animal traits, and among terrestrial animals, it is most extreme in certain spider lineages. The most extreme sexual size dimorphism (eSSD) is female biased. eSSD itself is probably an epiphenomenon of gendered evolutionary drivers whose strengths and directions are diverse. We demonstrate that eSSD spider clades are aberrant by sampling randomly across all spiders to establish overall averages for female (6.9 mm) and male (5.6 mm) size. At least 16 spider eSSD clades exist. We explore why the literature does not converge on an overall explanation for eSSD and propose an equilibrium model featuring clade- and context-specific drivers of gender size variation. eSSD affects other traits such as sexual cannibalism, genital damage, emasculation, and monogyny with terminal investment. Coevolution with these extreme sexual phenotypes is termed eSSD mating syndrome. Finally, as costs of female gigantism increase with size, eSSD may represent an evolutionary dead end. Expected final online publication date for the Annual Review of Entomology, Volume 65 is January 7, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... Limited anchor performance may thus in itself be an important constraint in the evolution of web building behavior, and its improvement may have accelerated spider web diversification: web architecture is phylogenetically labile and enormously variable in ecribellate orb-web and cobweb spiders (Blackledge and Gillespie 2004;Eberhard et al. 2008;Kuntner et al. 2010), lineages in which anchor structure has reached the physical optimum. Such a rapid turnover of web building behavior may mask evolutionary histories in these lineages. ...
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Physical structures built by animals challenge our understanding of biological processes and inspire the development of smart materials and green architecture. It is thus indispensable to understand the drivers, constraints and dynamics that lead to the emergence and modification of building behaviour. Here, we demonstrate that spider web diversification repeatedly followed strikingly similar evolutionary trajectories, guided by physical constraints. We found that the evolution of suspended webs that intercept flying prey coincided with small changes in silk anchoring behaviour with considerable effects on the robustness of web attachment. The use of nanofiber based capture threads (cribellate silk) conflicts with the behavioural enhancement of web attachment, and the repeated loss of this trait was frequently followed by physical improvements of web anchor structure. These findings suggest that the evolution of building behaviour may be constrained by major physical traits limiting its role in rapid adaptation to a changing environment. This article is protected by copyright. All rights reserved
... Limited anchor performance may thus in itself be an important constraint in the evolution of web building behavior, and its improvement may have accelerated spider web diversification: web architecture is phylogenetically labile and enormously variable in ecribellate orb-web and cobweb spiders (Blackledge and Gillespie 2004;Eberhard et al. 2008;Kuntner et al. 2010), lineages in which anchor structure has reached the physical optimum. Such a rapid turnover of web building behavior may mask evolutionary histories in these lineages. ...
... The majority of webs from both major orb spider families (Araneidae and Tetragnathidae) are asymmetric with the area below the hub being larger than the area above (Masters & Moffat 1983;ap Rhiziart & Vollrath 1994;Kuntner et al. 2010b). This vertical web asymmetry is primarily thought to arise from an asymmetry in running speed caused by gravity, which allows for faster downwards running speeds than upwards against gravity, as has been observed in a number of araneids in the laboratory (Masters & Moffat 1983;ap Rhiziart & Vollrath 1994;. ...
Article
Vertical asymmetry is a widespread feature of orb webs, with the lower part larger than the upper, although its adaptive value is not fully understood. Gravity is thought to play a major role in the generation of asymmetry through increased running speed downwards from the hub. The relationship between spider orientation and gravity has been relatively well studied. However, webs' inclination from vertical has been less studied. Here we conducted a field study on the tetragnathid orb spider Metellina mengei Blackwall, 1869, which constructs webs that show a marked variation in inclination. Our findings revealed a significant influence of the degree of web inclination and web area on the level of vertical asymmetry, while environmental variables did not have any effect. Thus, our results support the hypothesis that the asymmetry in upwards and downwards running speeds due to gravity is an important determinant of web asymmetry. © 2018 American Museum of Natural History. All rights reserved.
... Web-building spiders are a diverse group of insectivorous terrestrial animals that build and reside in silken webs that they produce to capture prey (Eberhard, 1990;Blackledge et al., 2009). Many webbuilding spiders display ontogenetic shifts in the shape, size, symmetry and dimensionality of their webs as their foraging and defensive demands vary across life stages (Witt, Rawlings & Reed, 1972;Eberhard, 1976Eberhard, , 1986Opell, 1982;Japyass u & Ades, 1998;Blackledge, Coddington & Gillespie, 2003;Lopardo et al., 2004;Eberhard, Barrantes & Madrigal-Brenes, 2008;Kuntner et al., 2008;Hesselberg, 2010;Kuntner, Gregori c & Li, 2010a;Kuntner, Kralj-Fi ser & Gregori c, 2010b). Few studies, nevertheless, have examined whether the material from which a spider's web is produced, silk, also varies across ontogeny (but see Ortlepp & Gosline, 2008;Sensenig, Agnarsson & Blackledge, 2011). ...
... Given the discontinuity of our observations, we were unable to expand this observations to further instars. Nonetheless, this delayed appearance of gumfoot threads may represent a case of the pattern of ontogeny repeating phylogeny that is common in spider webs (Barrantes & Eberhard 2010, Kuntner, Kralj-Fišer & Gregorič 2010. Ontogenetic changes in silk occur in a few phylogenetically scattered families. ...
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Gumfoot threads attached to the substrate may allow spiders to retain prey. These threads were recently discovered in adult females of Pholcidae spiders, and are similar to those in Theridiidae. We report for the first time the presence of gumfoot threads in the webs of immature spiders (fifth instar juveniles) of the pholcid Physocyclus globosus Taczanowski, 1874, and their absence in the webs of first and second instar juveniles and adult males. The bands of adhesive silk were shorter in fifth instar nymphs than in adult females, and had continuous rather than discrete adhesive droplets like the webs of two other adult female pholcid spiders. In Pholcidae, the large spigot on the anterior lateral spinnerets, which presumably produces glue, was relatively thicker in adult females and first instar juveniles than in adult males, which do not produce gumfoot threads. Therefore, we suggest that the ontogenetic origin of gumfoot threads may not be associated with changes in spigot morphology. In addition, the delayed production of gumfoot threads in P. globosus is different to theridiid spiders, in which spiderlings build gumfoot threads from emergence.
... However, while larger spider species use more silk, it is not entirely clear how silk amount scales with spider size, that is, whether different species produce proportionally similar amounts of silk in relation to body size. Furthermore, spiders change web architecture throughout their ontogeny (Eberhard, Barrantes & Madrigal-Brenes, 2008;Kuntner, Kralj-Fišer & Gregorič, 2010), and according to their size and feeding history . They are also quite plastic within individual life stages. ...
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Body size affects almost all aspects of animals' resource use, and its scaling syntheses are well established in most biological fields. In contrast, how behavioral variation scales with body size is understudied. Understanding how body size influences behavior is important as behavior responds more readily to natural selection than many other traits, and foraging effort is a critical behavioral trait. Web spiders are good models for studying foraging effort because webs are physical records of behaviors. Variability in web architectures is well documented, but how spider size scales with foraging effort and web performance is virtually unknown. Here, we investigate behavioral allometry at three phylogenetic scales – broadly across orb-weaving spiders, among a recent radiation of species, and among individuals within species. Conducting a meta-analysis across a wide range of orb weavers, we investigate how foraging effort scales with body size by measuring effort as the volumes of the three silk gland secretions used for building orb webs. We show that volumes of web material scale negatively allometrically with body size, and suggest silk investment is an important limiting factor in evolution of web performance and body size. To assess whether such broad evolutionary trends exist at finer phylogenetic scales, we investigated how foraging effort scales with body size in a group of five closely related Zygiella s.l. species (Araneidae). We find that the general scaling pattern across orb weavers is only partially confirmed. Finally, we examine patterns among individuals within each of the Zygiella species. We find different patterns of silk use in relation to body size, and show that both web architecture and silk investment need to be quantified to estimate total foraging effort. In conclusion, we find support for the prediction that behavioral traits scale differently to body size at different phylogenetic scales and at the individual level.
... Thus, the origin of the spider orb web, and especially whether the orb web evolved more than once, has been the subject of a long debate (Kaston 1964;Kullmann 1972;Eberhard 1982;Coddington 1986a,b;Garb et al. 2006;Blackledge et al. 2009). However, recent advances in both morphological and molecular phylogenetics more or less settled the issue in favour of Coddington's (1986a) hypothesis of a single origin of the orb web, where cribellate capture threads transitioned to viscid capture threads, followed by various modifications of the orb leading to aerial sheet webs, cobwebs and other architectures (Griswold et al. 1998;Eberhard et al. 2008;Kuntner et al. 2008Kuntner et al. , 2010Blackledge et al. 2009). Orbs, therefore, are monophyletic despite substantial diversity in the details of their architectures among various taxa. ...
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Evolutionary convergence of phenotypic traits provides evidence for their functional success. The origin of the orb web was a critical event in the diversification of spiders that facilitated a spectacular radiation of approximately 12 000 species and promoted the evolution of novel web types. How the orb web evolved from ancestral web types, and how many times orb-like architectures evolved in spiders, has been debated for a long time. The little known spider genus Fecenia (Psechridae) constructs a web that resembles the archetypical orb web, but morphological data suggest that Psechridae (Psechrus + Fecenia) does not belong in Orbiculariae, the ‘true orb weavers’, but to the ‘retrolateral tibial apophysis (RTA) clade’ consisting mostly of wandering spiders, but also including spiders building less regular webs. Yet, the data are sparse and no molecular phylogenetic study has estimated Fecenia's exact position in the tree of life. Adding new data to sequences pulled from GenBank, we reconstruct a phylogeny of Entelegynae and phylogenetically test the monophyly and placement of Psechridae, and in doing so, the alternative hypotheses of monophyletic origin of the orb web and the pseudo-orb versus their independent origins, a potentially spectacular case of behavioural convergence. We also discuss the implications of our results for Entelegynae systematics. Our results firmly place a monophyletic Psechridae within the RTA clade, phylogenetically distant from true orb weavers. The architectural similarities of the orb and the pseudo-orb are therefore clearly convergent, as also suggested by detailed comparisons of these two web types, as well as the spiders' web-building behaviours and ontogenetic development. The convergence of Fecenia webs with true orbs provides a remarkable opportunity to investigate how these complex sets of traits may have interacted during the evolution of the orb.
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Correlated evolution of traits can act synergistically to facilitate organism function. But, what happens when constraints exist on the evolvability of some traits, but not others? The orb web was a key innovation in the origin of >12,000 species of spiders. Orb evolution hinged upon the origin of novel spinning behaviors and innovations in silk material properties. In particular, a new major ampullate spidroin protein (MaSp2) increased silk extensibility and toughness, playing a critical role in how orb webs stop flying insects. Here, we show convergence between pseudo-orb-weaving Fecenia and true orb spiders. As in the origin of true orbs, Fecenia dragline silk improved significantly compared to relatives. But, Fecenia silk lacks the high compliance and extensibility found in true orb spiders, likely due in part to the absence of MaSp2. Our results suggest how constraints limit convergent evolution and provide insight into the evolution of nature's toughest fibers.
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Although the diversity of spider orb web architectures is impressive, few lineages have evolved orb webs larger than 1m in diameter. Until recently, such web gigantism was reported only in a few nephilids and araneids. However, new studies on bark spiders (Caerostris) of Madagascar report a unique case of web gigantism: Darwin's bark spider (C. darwini) casts its webs over substantial water bodies, and these webs are made from silk whose toughness outperforms all other known spider silks. Here we investigate C. darwini web architecture and provide data to begin to answer two intriguing questions to explain these extraordinary web characteristics: 1) Are C. darwini webs specialized to subdue unusually large, perhaps even vertebrate, prey? 2) Do these large, riverine webs allow the spiders to capitalize on catching numerous small semi-aquatic insects? During fieldwork in Madagascar, we studied C. darwini web architecture and ecology, as well as interactions with prey. We characterize C. darwini webs as having relatively simple capture areas with very open sticky spirals and few radial lines. We also compare web features in several sympatric Caerostris species, among which C. darwini represents the most extreme case of web gigantism, with the largest orbs up to 2.76 m2 and longest bridge lines reaching 25.5 m. While preliminary, current data suggest that C. darwini webs are effective snares for semi-aquatic insects such as mayflies and dragonflies, while vertebrate prey were never observed. We suggest that mass emergence of aquatic insects may function analogously to the capture of rare, large prey that recent studies suggest are critical for reproduction in orb weaving spiders.
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The design of orb webs is affected by multiple abiotic (e.g., wind, available space), biotic (e.g., prey availability, predation), and species specific (e.g., spider size) factors. Thus, some features of each spider web are expected to reflect the combined effect of such factors. We compared the relationship of spider size and web inclination on the area of different sections of the orb web and other features (e.g., number or radii) between two sympatric Leucauge species (Leucauge sp., and L. argyra (Walckenaer, 1841), Tetragnathidae). Leucauge sp. was smaller and constructed smaller webs across a wider range of inclinations than L. argyra. Other features of the web, e.g., capture area, and hub area, but not the number of adhesive spiral turns and number of radii, were also larger in webs of L. argyra. The inclination was greater in webs of Leucauge sp., but the asymmetry of webs did not differ between species, though, it correlated negatively with the total area of the web of both species, as in other orb-weavers. The characteristics of each species' web suggest that L. argyra optimizes prey interception, while Leucauge sp. optimizes stopping and retention of large prey.
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The pantropical orb web spider family Nephilidae is known for the most extreme sexual size dimorphism among terrestrial animals. Numerous studies have made Nephilidae, particularly Nephila, a model lineage in evolutionary research. However, a poorly understood phylogeny of this lineage, relying only on morphology, has prevented thorough evolutionary syntheses of nephilid biology. We here use three nuclear and five mitochondrial genes for 28 out of 40 nephilid species to provide a more robust nephilid phylogeny and infer clade ages in a fossil-calibrated Bayesian framework. We complement the molecular analyses with total evidence analysis including morphology. All analyses find strong support for nephilid monophyly and exclusivity and the monophyly of the genera Herennia and Clitaetra. The inferred phylogenetic structure within Nephilidae is novel and conflicts with morphological phylogeny and traditional taxonomy. Nephilengys species fall into two clades, one with Australasian species (true Nephilengys) as sister to Herennia, and another with Afrotropical species (Nephilingis Kuntner new genus) as sister to a clade containing Clitaetra plus most currently described Nephila. Surprisingly, Nephila is also diphyletic, with true Nephila containing N. pilipes + N. constricta, and the second clade with all other species sister to Clitaetra; this "Nephila" clade is further split into an Australasian clade that also contains the South American N. sexpunctata and the Eurasian N. clavata, and an African clade that also contains the Panamerican N. clavipes. An approximately unbiased test constraining the monophyly of Nephilengys, Nephila, and Nephilinae (Nephila, Nephilengys, Herennia), respectively, rejected Nephilengys monophyly, but not that of Nephila and Nephilinae. Further data are therefore necessary to robustly test these two new, but inconclusive findings, and also to further test the precise placement of Nephilidae within the Araneoidea. For divergence date estimation we set the minimum bound for the stems of Nephilidae at 40 Ma and of Nephila at 16 Ma to accommodate Palaeonephila from Baltic amber and Dominican Nephila species, respectively. We also calibrated and dated the phylogeny under three different interpretations of the enigmatic 165 Ma fossil Nephila jurassica, which we suspected based on morphology to be misplaced. We found that by treating N. jurassica as stem Nephila or nephilid the inferred clade ages were vastly older, and the mitochondrial substitution rates much slower than expected from other empirical spider data. This suggests that N. jurassica is not a Nephila nor a nephilid, but possibly a stem orbicularian. The estimated nephilid ancestral age (40-60 Ma) rejects a Gondwanan origin of the family as most of the southern continents were already split at that time. The origin of the family is equally likely to be African, Asian, or Australasian, with a global biogeographic history dominated by dispersal events. A reinterpretation of web architecture evolution suggests that a partially arboricolous, asymmetric orb web with a retreat, as exemplified by both groups of "Nephilengys", is plesiomorphic in Nephilidae, that this architecture was modified into specialized arboricolous webs in Herennia and independently in Clitaetra, and that the web became aerial, gigantic, and golden independently in both "Nephila" groups. The new topology questions previously hypothesized gradual evolution of female size from small to large, and rather suggests a more mosaic evolutionary pattern with independent female size increases from medium to giant in both "Nephila" clades, and two reversals back to medium and small; combined with male size evolution, this pattern will help detect gross evolutionary events leading to extreme sexual size dimorphism, and its morphological and behavioral correlates.
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Orb-web spiders typically construct their webs with a vertical asymmetry: the hub, or meeting point of the radial threads, is often above the geometric center of the web. Previous explanations for this asymmetry involve differences in up/down running speed and mass, but fail to account adequately for ontogenetic changes in vertical asymmetry. The current article argues that the hub location is determined so as to maximize the expected number of prey and is updated, partially, in response to predation experience. A Bayesian model of spider learning from predation experience is presented and shown to be alone a better fit than spider mass to an existing empirical dataset. Combining this Bayesian model with the extant results on spider mass and differential running speeds ought to provide more thorough explanations for observed web asymmetry. The results of this theory-driven work positions orb-web spiders as a potentially ideal study family for animal Bayesian learning: predation experience is manifest in the spider’s orb-web geometry, which is updated frequently, and is readily quantifiable. Spider orb webs ought to facilitate further theoretical and empirical work in animal cognition and learning.
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In the literature on orb-webs and orb-web construction, different terms are used for the same part of the web and - even worse - the same term is used by different authors for different parts of the web. This paper tries to improve the situation by proposing a nomenclature for the different parts of the orb-web. At the same time, it gives an overview of the terms in English, German and French used by various other authors.
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The nephilid 'coin spiders' (Herennia Thorell) are known for their arboricolous ladder webs, extreme sexual size dimorphism and peculiar sexual biology. This paper revises Herennia taxonomy, systematics, biology and biogeography. The widespread Asian Herennia multipuncta (Doleschall) (= H. sampitana Karsch, new synonymy; = H. mollis Thorell, new synonymy) is synanthropic and invasive, whereas the other 10 species are narrowly distributed Australasian island endemics: H. agnarssoni, sp. nov. is known from Solomon Islands; H. deelemanae, sp. nov. from northern Borneo; H. etruscilla, sp. nov. from Java; H. gagamba, sp. nov. from the Philippines; H. jernej, sp. nov. from Sumatra; H. milleri, sp. nov. from New Britain; H. oz, sp. nov. from Australia; H. papuana Thorell from New Guinea; H. sonja, sp. nov. from Kalimantan and Sulawesi; and H. tone, sp. nov. from the Philippines. A phylogenetic analysis of seven species of Herennia, six nephilid species and 15 outgroup taxa scored for 190 morphological and behavioural characters resulted in 10 equally parsimonious trees supporting the monophyly of Nephilidae, Herennia, Nephila, Nephilengys and Clitaetra, but the sister-clade to the nephilids is ambiguous. Coin spiders do not fit well established biogeographic lines (Wallace, Huxley) dividing Asian and Australian biotas, but the newly drawn 'Herennia line' suggests an all-Australasian speciation in Herennia. To explain the peculiar male sexual behaviour (palpal mutilation and severance) known in Herennia and Nephilengys, three specific hypotheses based on morphological and behavioural data are proposed: (1) broken embolic conductors function as mating plugs; (2) bulb severance following mutilation is advantageous for the male to avoid hemolymph leakage; and (3) the eunuch protects his parental investment by fighting off rival males.
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Most adult golden orb weavers (Nephila clavipes) have kleptoparasites of the genus Argyrodes in their webs. The kleptoparasitic load correlates positively with web size. Clustered (interconnected) webs have a more predictable number of kleptoparasites than do solitary webs, but there is no difference in the mean number of kleptoparasites between the two. From the view of the kleptoparasite, host webs are habitat patches or islands. Isolated webs show characteristics of small patches, where web size is a poor indicator of kleptoparasite number and variation is high. The distribution of kleptoparasites in clustered webs, on the other hand, seems to fit the "ideal free distribution" where web size nearly entirely predicts kleptoparasitic load. Thus clustered webs, as a habitat patch, are more than merely the combination of their parts. The predictability of kleptoparasite load in clustered webs may be a function of the stability (longevity) of those habitat patches, and ease of colonization, as neighboring webs act as sources.
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Labelled scanning electron micrographs comprehensively illustrating the spinning fields of Deinopis (Deinopidae), Octonoba (Uloboridae), Araneus (Araneidac), Leucauge (Tetragnathidae), Lalrodeclus and Theridula (Theridiidae), Gaucelmus (Nesticidae), and Frontinella (Linyphiidae) are presented for the first time. Evidence from scanning electron micrographs supports the monophyly of orbweavers (Orbiculariae - Uloboridae, Deinopidae, Araneoidea), the araneid subfamily Cyrtophorinae and the close relationship between Nesticidae and Theridiidae. This evidence is presented in the context of guidelines for the logical taxonomic interpretation of spider spigot morphology. This morphological system, including gross and detailed morphology, location and number of spigots, and serial homology relationships, may be one of the most complex, yet under-utilized, taxonomic character systems in spiders.
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Phylogenies are underutilised, powerful predictors of traits in unstudied species. We tested phylogenetic predictions of web-related behaviour in Clitaetra Simon, 1889, an Afro-Indian spider genus of the family Nephilidae. Clitaetra is phylogenetically sister to all other nephilids and thus important for understanding ancestral traits. Behavioural information on Clitaetra has been limited to only C. irenae Kuntner, 2006 from South Africa which constructs ladder webs. A resolved species-level phylogeny unambiguously optimised Clitaetra behavioural biology and predicted web traits in five unstudied species and a uniform intrageneric nephilid web biology. We tested these predictions by studying the ecology and web biology of C. perroti Simon, 1894 on Madagascar and C. episinoides Simon, 1889 on Mayotte. We confirm predicted arboricolous web architecture in these species. The expected ontogenetic allometric transition from orbs in juveniles to elongate ladder webs in adults was statistically significant in C. perroti, whereas marginally not significant in C. episinoides. We demonstrate the persistence of the temporary spiral in finished Clitaetra webs. A morphological and behavioural phylogenetic analysis resulted in unchanged topology and persisting unambiguous behavioural synapomorphies. Our results support the homology of Clitaetra hub reinforcement with the nephilid hub-cup. In Clitaetra, behaviour was highly predictable and remained consistent with new observations. Our results confirm that nephilid web biology is evolutionarily conserved within genera.
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This study shows that Deinopis spinosus Marx has at least two stereotyped attack behaviors, each elicited by different stimuli. In "backward" strikes the spider expands the net backward over its cephalothorax and away from the substrate; these strikes capture aerial prey. Vibratory stimuli are sufficient to elicit backward strikes. In "forward" strikes the spider expands the web downward and forward against the substrate; these strikes capture walking prey, and visual rather than vibratory stimuli are more effective. We describe the mechanisms underlying each type of strike and the extraordinary extensibility of the web.
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Young juveniles of L. geometricus fit the strong trend for “ontogeny to repeat phylogeny” previously documented in other web-building spiders; younger spiders were less likely to build the derived silk retreats that occur at the edges of webs of adults. Younger individuals also consistently built more highly organized webs, with radial lines that converge on a central, horizontal disc and that support regularly spaced, sticky “gumfoot“ lines. Some details of how radial and gumfoot lines were built suggest that the radial and gumfoot lines and the behavior involved in their construction may be homologous with traits associated with radii and sticky spirals in aranoid orb webs. The numerous convergences between the webs and building behavior of young L. geometricus and the highly modified webs and building behavior of genera of the orb weaving families Theridiosomatidae (Wendilgarda) and Anapidae (Comaroma), which have independently replaced orbs with webs designed to capture prey on surfaces near the web, suggest a new hypothesis for how gumfoot theridiid webs may have evolved from orbs.
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We examined the utility of several popular formulae used to estimate the capture areas of orb webs across a large sample of Cyclosa Menge 1866 and Tetragnatha Latreille 1804 webs. All formulae evaluated contained at least some bias in estimation of the capture areas of webs. We identified two types of asymmetry in orb webs that affect capture area estimation differently. Web asymmetry measures the ratio of the horizontal and vertical diameters of orb webs while hub asymmetry measures the displacement of the hub from the geometric center of a web. An analysis of model webs that varied in web and hub asymmetry showed that most formulae overestimated capture area as web asymmetry increased and that some formulae also overestimated capture area as hub asymmetry increased. Only the “Ellipse−Hub” formula was unaffected by web and hub asymmetry. Although the “Adjusted Radii−Hub” formula provided a slightly more accurate overall estimate of capture area, we recommend that the “Ellipse−Hub” formula be used when comparisons of capture area are made between taxa or individuals that vary in web and hub asymmetry.
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Analise van ekologiese data van die boombewonende nephilid spinnekop Clitaetra irenae Kuntner 2006, endemies tot Maputaland woude in Suid-Afrika, dui die spesie se afhanklikheid van hierdie hoogs bedreigde habitat aan. Ons het C. irenae habitat afhanklikheid via GIS analiese getoets deur die bekende verspreiding teen die suider-Afrikaanse ekologiese streke aan te teken. In die suidelike deel van die verspreiding kom C. irenae in slegs een ekostreek, die Maputaland kusvlakte woude, voor, maar verder noord in die verspreiding kom dit verder in die binneland, in Malawiese bosveld, voor. Ons toets en verwerp die hipotesisse dat C. irenae slegs volgroeide bome bewoon, bome van ‘n spesifieke spesie, bome met gladde bas, boomhabitatte op ‘n sekere hoogte van die grond af, en slegs toe kroonbedekking woude. Die ekologiese nis van C. irenae is aanpasbaar solank daar geskikte bome onder ten minste gedeeltelike toe kroonbedekking beskikbaar is. Ons kwantifiseer C. irenae ontogenetiese webveranderings van ‘n wawiel- na ‘n leerweb en die gelyktydige verskuiwing van die kern na die bokant van die raam. Sulke web allometrie gee die spinnekop die vermoë om die web vertikaal te vergroot sonder horisontale veranderings, wat die spinnekop in staat stel om op dieselfde boom te bly regdeur sy ontwikkeling. Ons sien die leerweb dus as ‘n aanpassing tot boomlewende gewoontes. Volwasse kern verskuiwing, algemeen in spinnekoppe met vertikale webbe, word deur gravitasie verduidelik. C. irenae se web oriëntasie op bome korreleer met kroonbedekking, en kan ‘n aanduider wees van Maputaland woud kwaliteit. Ons stel voor dat nephilid wawiel-web spinnekoppe (Clitaetra en Herennia) se ekologie gebruik word in sistematiese bewarings assesserings in die Ou Wêreld tropiese gebiede.
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Cobweb spiders (Theridiidae) exhibit a rich variety of web designs. Current knowledge of theridiid web architecture and evolution indicates that theridiid web design shows high within-taxon diversity and frequent convergence. Here we redescribe Achaearanea hieroglyphica (Mello-Leitão 1940), including the first description of the male, and document in this species (1) an unusual web design and (2) two dramatically different type of webs.
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We trace the evolution of the web designs of spiders in the large family Theridiidae using two recent, largely concordant phylogenies that are based on mor-phology and molecules. We use previous information on the webs of 88 species and new data on the web designs of 78 additional theridiid species (representing nearly half of the theridiid genera), and 12 other species in related families. Two strong, surprising patterns emerged: substantial within-taxon diversity; and frequent con-vergence in different taxa. These patterns are unusual: these web traits converged more frequently than the morphological traits of this same family, than the web traits in the related orb-weaving families Araneidae and Nephilidae, and than beha-vioural traits in general. The effects of intraspecific behavioural 'imprecision' on the appearance of new traits offer a possible explanation for this unusual evolutionary plasticity of theridiid web designs.
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Orb-weaving spiders depend upon the sticky capture spirals of webs to retain insects long enough to be captured. However, insects often escape from orb webs before the spiders can attack them. Therefore, the architectures of orb webs likely reflect strong selective pressure to increase retention times of insects. We experimentally increased the mesh width of one side of an orb web while maintaining the original mesh width on the other side as a control, and then tested the effect of this manipulation on the retention times of four different taxa of insects. We found evidence that increased mesh width of Argiope aurantia orb webs resulted in a general reduction in the retention times of insects. However, retention times for different taxa of insects were not predicted by any one specific morphological or flight characteristic. The influence of mesh width on the retention times of insects is very complex, but our results suggest that mesh width can act to selectively favor the capture of certain taxa of insect prey over others. This effect may help to explain both species level differences in web-building behaviors and variation in the architectures of webs spun by individual spiders on different days.
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We present the first cladistic analysis focused at the tribal and subfamily level of the orb-weaving spider family Araneidae. The data matrix of 82 characters scored for 57 arancid genera of 6 subfamilies and 19 tribes (and 13 genera from 8 outgroup families) resulted in 16 slightly different, most parsimonious trees. Successive weighting corroborated 62 of the 66 informative nodes on these cladograms; one is recommended as the ‘working’ araneid phylogcny. The sister group of Araneidae is all other Araneoidea. Araneidae comprises two major clades: the subfamily Araneinae, and the ‘argiopoid’ clade, which includes all other subfamilies and most tribes (((Gasteracanthinae, Caerostreae), (((Micratheninae, Xylcthreae), Eruyosaccus), (Eurycorminae, Arciinae)), Cyrlarachninae), ((Argiopinae, Cyrtophorinae), Arachnureae)). Cyrtarachneae and Mastophoreae are united in a new subfamily, Cyr-tarachninae. The spiny orb-weavers alone (Gasteracanthinae and Micratheninae) are not monophyletic. The mimetid subfamily Arciinae and the ‘tetragnathid’ genus Zygiella are araneids, but .Nephila (and other tetragnathids) are not. On the preferred tree, web decorations (stabilimenta) evolved 9 times within 15 genera, and were lost once. The use of silk to subdue prey evolved once in cribellate and four times in ecribillate orb weavers. Sexual size dimorphism evolved once in nephilines, twice in araneids, and reverted to monomorphism five times. Evolution in other genitalic and somatic characters is also assessed; behavioral and spinneret features arc most consistent (male genitalia, leg and prosomal features least consistent) on the phylogeny.
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This phylogenetic analysis of 31 exemplar taxa treats the 12 families of Araneoidea (Anapidae, Araneidae, Cyatholipidae, Linyphiidae, Mysmenidae, Nesticidae, Pimoidae, Symphytognathidae, Synotaxidae, Tetragnathidae, Theridiidae, and Theridiosomatidae). The data set comprises 93 characters: 23 from male genitalia, 3 from female genitalia, 18 from cephalothorax morphology, 6 from abdomen morphology, 14 from limb morphology, 15 from the spinnerets, and 14 from web architecture and other behaviour. Criteria for tree choice were minimum length parsimony and parsimony under implied weights. The outgroup for Araneoidea is Deinopoidea (Deinopidae and Uloboridae). The preferred shortest tree specifies the relationships ((Uloboridae, Deinopidae) (Araneidae (Tetragnathidae ((Theridiosomatidae (Mysmenidae (Symphytognathidae, Anapidae))) ((Linyphiidae, Pimoidae) ((Theridiidae, Nesticidae) (Cyatholipidae, Synotaxidae))))))). The monophyly of Tetragnathidae (including metines and nephilines), the symphytognathoids, theridiid-nesticid lineage, and Synotaxidae are confirmed. Cyatholipidae are sister to Synotaxidae, not closely related to either the Araneidae or Linyphiidae, as previously suggested. Four new clades are proposed: the cyatholipoids (Cyatholipidae plus Synotaxidae), the ‘spineless femur clade’ (theridioid lineage plus cyatholipoids), the ‘araneoid sheet web builders' (linyphioids plus the spineless femur clade), and the ‘reduced piriform clade’ (symphytognathoids plus araneoid sheet web builders). The results imply a coherent scenario for web evolution in which the monophyletic orb gives rise to the monophyletic araneoid sheet, which in turn gives rise to the gumfoot web of the theridiid-nesticid lineage. While the spinning complement of single pairs of glands does not change much over the evolution of the group, multiple sets of glands are dramatically reduced in number, implying that derived araneoids are incapable of spinning many silk fibers at the same time.
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Abstract— Observations of web spinning behavior in Costa Rican Dinopis sp. reveal the same behaviors synapomorphic for orb weavers: specifically frame, radius, non-sticky spiral construction, and sticky spiral construction, as well as more detailed motor patterns. Dinopids are therefore highly derived orb weavers, although the behavioral data do not conclusively indicate whether they are more closely related to the uloborid or araneoid orb weavers. A cladogram of dinopids, uloborids, and araneoids is presented.
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Although behavior is being gradually incorporated into phylogenetic studies, the understanding of the evolution of one of its main characteristics, plasticity or adjustment to environmental features, is still a challenge, mainly due to the lack of comparative data. In this paper we focus on the plasticity of the predatory repertoire of Achaearanea digitus, analyzing its responses to two prey types, and discuss the evolution of behavioral plasticity based on a comparison to the foraging repertoire of other araneoid sheetweavers and on a review of hunting tactics among the larger group of orbweavers. Contrasting with what was observed for other families, spiders of the family Theridiidae (among them A. digitus) show a small set of attack tactics, and a quite stereotyped predatory performance. These spiders regularly attack their prey with a typical sticky silk wrapping tactic, but fail to use other tactics such as bite–wrap or bite–pull out prey, which are commonly used in other spider families. We show that this stereotypy is typical of the foraging repertoire of araneoid sheetweavers. Plotting the mean size of the attack tactics repertoire on the phylogeny of Orbiculariae shows that high predatory stereotypy is a plesiomorphy of the whole araneoidea group, and that evolutionary increases in plasticity occur independently two times in the group, among Araneidae and Nephilidae. The maintenance of a plesiomorphic, stereotyped predatory behavior among theridiids is probably due to the evolution of a special behavioral technique, which includes the simultaneous use of the fourth legs during wrapping attacks. Since the individuals in the species of this group of sheetweavers face less variable environments than do orbweavers, they should indeed evolve more stereotyped phenotypes, but nevertheless their evolved predatory stereotypy contrasts with plasticity in other aspects of their foraging behavior (web building). Since, in this case, both stereotypy and plasticity result from a simplification in the mechanisms underlying behavioral expression, we suggest that less variable environments select not exactly for behavioral stereotypy, but rather to the simplification of these information processing mechanisms.
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We combine statistical and phylogenetic approaches to test the hypothesis that adaptive radiation and key innovation have contributed to the diversity of the order Araneae. The number of unbalanced araneid clades (those whose species numbers differ by 90% or more) exceeds the number predicted by a null Markovian model. The current phylogeny of spider families contains 74 bifurcating nodes, of which 31 are unbalanced. As this is significantly more than the 14.8 expected unbalanced nodes, some of the diversity within the Araneae can be attributed to some deterministic cause (e.g., adaptive radiation). One of the more highly unbalanced (97%) bifurcations divides the orb-weaving spiders into the Deinopoidea and the larger Araneoidea. A simple statistical model shows that the inequality in diversity between the Deinopoidea and the Araneoidea is significant, and that it is associated with the replacement of primitive cribellar capture thread by viscous adhesive thread and a change from a horizontal to a vertical orb-web orientation. These changes improve an orb-web's ability to intercept and retain prey and expand the adaptive zone that orb-weaving spiders can occupy and are, therefore, considered to be "key innovations."
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The relationship between web design and prey capture in orb-web spiders was examined by correlating the mean mesh height with the mean prey length per species taken from existing literature (15 species) and new data (Larinioides sclopetarius and Argiope keyserlingi). Pooling the data from all species, the results revealed no significant relationship. Analysing the data from L. sclopetarius and A. keserlingi separately, no overall significant relationship was found. However, the analyses of the separate observation days showed that mesh height correlated significantly with prey length on one of the five observation days for A. keyserlingi, but not for L. sclopetarius. Consequently, the spacing of the sticky spiral in the orb-web can have a significant effect on the length of the captured prey under certain circumstances, which are discussed in the present paper.
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This paper describes a new kind of ladder-web structure in which there are two ladders, one above and one below a centrally positioned orb. It differs from previously described ladder-webs, not only because of the two ladders but also because of its 24 h (or more) duration, its vertical placement against the trunks of trees, and the fact that it apparently offers the spider protection against parasitism. Both the spider (Araneus atrihastulus) and its ladder-web are ideally adapted to the tree-trunk: the web with regard to its position, shape, and lack of visibility; and the spider in respect of its coloration, daytime posture, and proximity to the snare. It is concluded that the design of this web offers a number of advantages which evidently enhance the spider's survival and increase its capture potential over and above that of the simple orb.
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We combine statistical and phylogenetic approaches to test the hypothesis that adaptive radiation and key innovation have contributed to the diversity of the order Araneae. The number of unbalanced araneid clades (those whose species numbers differ by 90% or more) exceeds the number predicted by a null Markovian model. The current phylogeny of spider families contains 74 bifurcating nodes, of which 31 are unbalanced. As this is significantly more than the 14.8 expected unbalanced nodes, some of the diversity within the Araneae can be attributed to some deterministic cause (e.g., adaptive radiation). One of the more highly unbalanced (97%) bifurcations divides the orb-weaving spiders into the Deinopoidea and the larger Araneoidea. A simple statistical model shows that the inequality in diversity between the Deinopoidea and the Araneoidea is significant, and that it is associated with the replacement of primitive cribellar capture thread by viscous adhesive thread and a change from a horizontal to a vertical orb-web orientation. These changes improve an orb-web's ability to intercept and retain prey and expand the adaptive zone that orb-weaving spiders can occupy and are, therefore, considered to be 'key innovations.'
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The insect-attraction function of silk stabilimenta spun by Argiope spiders was directly tested by examining if isolated stabilimenta will increase insect interception in artificial webs. Artificial webs were made from basswood frames and fine monofilaments coated with a sticky substance and were divided into two groups, experimental and control. In the experimental group, silk stabilimenta isolated from stabilimentum-decorated webs spun by Argiope aurantia were introduced. In the control group, corresponding areas collected from the undecorated webs of A. trifasciata were introduced. A general linear model was used to examine the effect of stabilimenta, web location, and date of data collection on insect interception in artificial webs. When the effects of location and date were simultaneously considered, artificial webs containing isolated stabilimenta intercepted significantly more flying insects (41.6% more) than those in the control group. However, there was no difference in orthopteran interception rates between experimental and control groups. These results indicate that silk stabilimenta of Argiope spiders do attract insects, although not all insects exhibit a strong orientation response to them.
Article
A new genus of orb-web spider (Araneidae Simon), Telaprocera gen. nov., including two new species, T. maudae sp. nov. (type species) and T. joanae sp. nov., are described. Telaprocera gen. nov. differs from all other araneid genera by the presence of a dorsal keel on the male cymbium. The known range of Telaprocera maudae sp. nov. is limited to the east coast of Australia, from far northern Queensland to central New South Wales. The spiders are found in closed can-opy rainforest and adults can be found year round. Telaprocera joanae sp. nov. has been found from central coastal Queensland to far eastern Victoria. They occur in similar habitats, with similar phenology, as T. maudae sp. nov. Both species build highly elongated orb-webs known as ladder-webs. A variety of phylogenetic analyses based on an updated morphological data matrix for orb-web spiders did not provide a conclusive placement of Telaprocera gen. nov. within the Araneidae. Equally weighted analysis placed the genus as sister to Kairo O. P.-Cambridge and Metepeira F. O. P.-Cambridge combined. Strong downweighting of homoplasious characters placed the genus as sister taxon to the traditional Argiopinae Simon. The uncertain phylogenetic position of Telaprocera gen. nov. may reflect the insufficient knowledge of the morphology of Australian taxa-taxa that may possess characters previously not considered in phylo-genetic analyses of the Araneidae.
Article
The relationship between direction of coiling and shape of the auxiliary spiral and that of the capture spiral in orb webs of Araneus diadematus Clerck (Araneidae) was investigated. In most webs, the two spirals had the same direction of coiling and a similar shape, indicating that the auxiliary spiral serves as a guide during construction of the capture spiral. Additionally, it was found that the direction of gravity determined the shape of the auxiliary spiral, whereas the shape of the capture spiral was solely determined by the shape of the auxiliary spiral and was not influenced by the direction of gravity. Possible causes and mechanisms are discussed.
Article
Analysis of orb webs of the garden cross spider (Araneus diadematus) showed that these vertical webs have a significant up/down asymmetry. Experiments demonstrated that the spider runs down faster than up, and thus confers a relatively higher foraging value to sections below the hub. Simulations suggested that the density of capture spiral spacing, prey size, and the density of prey should all affect the capture efficiency of a web. Webs lose effective capture area because of overlap of the capture zone around each thread; the smaller the prey, the finer the mesh can be without losing effective area. Lower sectors of the web have a particular mesh size (height and length of capture spiral segments) throughout, whereas in the upper sectors the mesh size changes, widening from the hub towards the periphery.
Article
The South American spider Scoloderus sp. spins a remarkably elongated ‘ladder’ orb web similar to that of an as yet unidentified New Guinean spider except that it is inverted 180°, with the long part above rather than below the hub. The two webs differ in a number of details, some of which may represent alternate solutions to the special problems associated with extremely long radii. Various details of the web building behaviour of Scoloderus sp. differ from the behaviour of species of Araneus and Zygiella. Immature Scoloderus build less elongate webs which are more similar to the standard araneid orb web. Eustala (?) sp. spins a web similar in many respects to that of the New Guinean spider, except that it is much less elongated, and thus forms an intermediate between typical orb webs and ‘ladder’ webs.
Article
The remarkable, perpendicularly-elongate web of a New Guinea araneid spider is described and illustrated. Its siting and construction are described and the possible origins and functions of the structure are discussed.
Article
Some details of orb web construction and attack behavior are evolutionarily conservative and appear to be useful in defining subfamilies and families and determining relationships. Their patterns of distribution among the at least 148 species in at least 55 genera agree in general with classical taxonomic schemes based on adult morphology. Convergent evolution of orb webs may have occurred in 2 lines (uloborids and araneoids). Certain behaviors appear to constitute autapomorphies for Uloboridae, Nephilinae and Araneinae, while others may be synapomorphies for Theridiosomatidae-Anapidae. -from Author
Article
Stabilimenta are silky structures on the webs of some orb-weaving spiders, whose function is still not well understood. This study tested the prey-attraction hypothesis as a possible function of stabilimenta with the banded garden spidersArgiope trifasciatain southeastern Michigan. Spider webs' stabilimentum length, prey interception rates and web characteristics were recorded daily. The daily insect interception rates and web characteristics were compared between stabilimentum-decorated and undecorated webs. An intra-web comparison was performed between decorated and undecorated halves of webs on the daily insect interception rates and web characteristics. The effects of location and characteristic of webs on insect interception rates were further examined at decorated and undecorated webs. A higher interception rate for flying insects was found in webs decorated with stabilimenta, but orthopteran interception rate was the same when compared with undecorated webs. The decorated web's higher interception rate for flying insects did not seem to result from locations or characteristics of webs. The length of a stabilimentum had little effect on increasing its attractiveness to flying insects.There was no difference in flying insect interception rates between decorated and undecorated halves of webs, but orthopteran interception rates were always higher in lower halves of webs. The results from intra-web comparison indicated that a stabilimentum did not increase insect interception rate of the adjacent area but did increase that of the whole web.
Article
SUMMARY 1. Determinations were made of several physical properties of the viscid and frame silks of the orb-webs built by the spider Araneus sericatus (Cl.). 2. Both types of silk show a breaking stress of approximately 1 GN/m2 and an initial resilience of approximately 0-35. 3. The breaking extension ratio of viscid silk (A = 3*00) is much greater than that of frame silk (A = i#2s), and the viscid silk relaxes to a relatively greater extent. 4. These properties are correlated with the degree of crystallization of the protein from which the silk is made, this factor being controlled by the sequence of amino acids in the protein. 5. The physical properties of the viscid and frame silks allow them to function effectively as shock absorbers and structural elements, respectively; and allow the orb-web to function as an aerial filter with a minimum expen- diture of material and energy.
Article
The uloboridPhiloponella vicina differs from the araneoids Nephila clavipes and Leucauge mariana in one movement made during frame construction, in the ordering of frame construction, in proto-hub removal, and in the highly ordered sequence of operations on adjacent radii just before proto-hub removal. Data from other uloborids suggest that all of these differences may distinguish orb weaving uloborids in general from orb weaving araneoids .N. clavipes differs from the other two species in the order of lines laid during frame construction, in the high variability in the details of frame construction, and in its failure to remove recently laid lines during exploration, radius construction, and frame construction. Frame construction behavior in all three species is more variable than previous reports indicated, and more variable than behavior in later stages of orb construction . In all three species earlier frame construction more often involves breaking lines already present in the web . Similarity between uloborid and araneoid frame construction is more likely to be due to a combination of constructional constraints and inheritance of ancient spinning patterns than previously realized ; it is not clear whether or not it constitutes a synapomorphy uniting the two groups . The failure of N. clavipes to remove recently laid lines during exploration, radius construction, and frame construction is probably plesimorphic . Secondary loss of removal behavior seems unlikely because removal probably confers adaptive advantages . Removal behavior in these contexts and possibly more stereotyped frame construction behavior probably evolved independently in uloborids and araneoids .
Article
In this field study, I tested the insect-attraction hypothesis as one of the functions of stabilimenta spun by Cyclosa conica(Pallas 1772) by examining : (1) if stabilimentum-decorated webs trapped more insects, (2)if a larger web diameter was responsible for the higher insect-trapping rate in decorated webs and, (3) if the differential distribution of insects in spiders' habitats was responsible for the higher insect interception rates of decorated webs . The number of wrapped prey, web diameters and presence of stabilimenta was recorded daily from 13 web locations . The stabilimentum-decorated webs of C. conica trapped significantly more insects (150%more) than undecorated webs, but they had significantly smaller mean web diameter (19% smaller) . Among web locations, there was no significant difference in their insect interception rates, whether the data were collected from decorated or undecorated webs . These results suggest that the higher insect-trapping efficiency of decorated webs spun by C .conicaresulted from the presence of stabilimenta, instead of from larger web diameters or differential distribution of insects .
Article
Marked developmental changes in web pattern provide an opportunity to assess the degree of interdependency between web building routines. The first webs of the tropical orb web spider Nephilengys cruentata are small, closely knit, complete orb webs, built in a great variety of sites. Older spiders built 'incomplete' orbs, which lack upper components (frame, radii, spirals), and in which a silken, cylindrical retreat, placed near a ceiling or a corner, opens into the hub. We studied the transition from the complete orb stage to the semi-orb stage, recording several web parameters and the stages of retreat formation. Two types of ontogenetic changes were identified: global increases in size (allometric growth) and gradual suppression of upper components (vertical asymmetry). The difference between upper and lower parts was evidenced in the curves which describe development: whereas growth in the lower part of the web usually followed linear trends, trends in the upper parts were quadratic, which means decreasing growth rates. Turning points (the temporal threshholds at which upper web parameters passed from increasing to decreasing trends) were not simultaneous: they clustered into two transitional periods. During the first transitional period, number of radii, number of viscid and dry spirals, percentage of orbs with an empty sector and web inclination had turning points; during the second transitional period, horizontal diameter, the length of radii and the percent occurrence of tent-like retreats. Our results (changes in upper and lower parts of the web governed by different ontogenetic rules; asynchrony of changes in the upper part; independence of retreat emergence from web modifications to which it is normally associated) reinforce a modular conception of the control of web building. This conception has implications for the understanding of the evolution of web patterns: aspects or parts of the building program could be independently subjected to selection, leading to specialized webs. The developmental uncoupling between algorithms opens, at the evolutionary level, the possibility of structural novelties in web building.
Article
The Pantropical spider clade Nephilidae is famous for its extreme sexual size dimorphism, for constructing the largest orb-webs known, and for unusual sexual behaviors, which include emasculation and extreme polygamy. We synthesize the available data for the genera Nephila, Nephilengys, Herennia and Clitaetra to produce the first species level phylogeny of the family. We score 231 characters (197 morphological, 34 behavioral) for 61 taxa: 32 of the 37 known nephilid species plus two Phonognatha and one Deliochus species, 10 tetragnathid outgroups, nine araneids, and one genus each of Nesticidae, Theridiidae, Theridiosomatidae, Linyphiidae, Pimoidae, Uloboridae and Deinopidae. Four most parsimonious trees resulted, among which successive weighting preferred one ingroup topology. Neither an analysis of an alternative data set based on different morphological interpretations, nor separate analyses of morphology and behavior are superior to the total evidence analysis, which we therefore propose as the working hypothesis of nephilid relationships, and the basis for classification. Ingroup generic relationships are (Clitaetra (Herennia (Nephila, Nephilengys))). Deliochus and Phonognatha group with Araneidae rather than Nephilidae. Nephilidae is sister to all other araneoids (contra most recent literature). Ethological data, although difficult to obtain and thus frequently missing for rare taxa, are phylogenetically informative. We explore the evolution of selected morphological and behavioral characters, discuss and redefine the homology of palpal sclerites, disprove semientelegyny in spiders, trace the newly interpreted evolution of the orb web, and show that nephilid genital morphologies coevolve with sexual behaviors and extreme sexual size dimorphism. Phylogenetic interpretations of behavior suggest new insights into spider biology and avenues for future research.© The Willi Hennig Society 2007.
Article
When there are direct conflicts in resource allocation to foraging effort versus growth and development, the relative allocation to foraging may change in a predictable manner with development. Orb-webs provide a physical record of resource allocation to foraging, and their synthesis requires the investment of physiologically important resources. Spiders in strongly seasonal habitats must complete development prior to the end of the season, and may be expected to alter foraging effort to maximize the probability of successful reproduction. Comparison of populations of the orb-weaving spider Nephila clavipes (Araneae, Nephilidae) in very seasonal versus less seasonal habitats allows testing for changes in allocation of resources to foraging effort during development. Orb-web size increases with increasing spider size, with little variation in slope among populations. However, in univoltine populations inhabiting strongly seasonal habitats, the size of the orb web is not a simple function of spider size: the rate of increase in orb-web size decelerates abruptly at a relatively small juvenile stage. Spiders in a less seasonal habitat did not decelerate foraging investment, and the pattern cannot be explained by changes in other aspects of orb-web structure. I postulate that the decline in relative investment into foraging is related to increased investment into juvenile female growth and development in circumstances where delayed maturation carries heavy fitness penalties.
Article
In this study I investigate a mechanism underlying size assessment during contests between females of the orb-weaving spider Nephilengys cruentata. Among orb-weaving spiders, some structural parameters of webs have been shown to vary with the size of the web builder, making it theoretically possible for an intruder to gather information about the web's resident when initiating a ght. Here I examined whether N. cruentata females are able to assess the size of the web owner during contests by using information from web design. The ghting behaviour of intruders was analysed in two situations: (1) web design indicated the presence of a small resident but actual resident size was large (treatment) and (2) web design cued the presence of a large resident, and actual resident size was also large (control). This was achieved by removing original web builders from their webs and letting newly introduced spiders establish ownership before inducing con icts. Results were consistent with the hypothesis that web design is used as a cue for web resident size. Strategies adopted by intruders were in uenced at an initial stage of the ght mainly by the size of the web builders instead of the size of the newly established residents. The implications of the results for the understanding of ghting behaviour in this species are discussed.
Article
Understanding the web construction behaviour of theridiid (comb-footed) spiders is fundamental to formulating specific evolutionary hypotheses and predictions regarding the reduction of orb-webs. We describe for the first time in detail the web construction behaviour of Achaearanea tepidariorum, Latrodectus geometricus, Theridion sisyphium and T. varians as well as webs of a range of other theridiids. In our survey we distinguish four major web types. Among webs with gumfooted lines, we distinguish between webs with a central retreat (Achaearanea-type) and those with a peripheral retreat (Latrodectus-type). Among webs without gumfooted lines, we distinguish between those which contain viscid silk (Theridion-type) and those with a sheet-like structure, which do not (Coleosoma-type). Theridiid gumfoot-webs consist of frame lines that anchor them to surroundings and support threads which possess viscid silk. Building of gumfooted lines constitutes a unique stereotyped behaviour and is most probably homologous for Nesticidae and Theridiidae. Webs remained in place for extended periods and were expanded and repaired, but no regular pattern of replacement was observed. We suggest that the cost of producing and maintaining viscid silk might have led to web reduction, at least in theridiids. © 2003 The Linnean Society of London. Biological Journal of the Linnean Society, 2003, 78, 293−305.
Article
Both the uloborid Philoponella vicina and the araneid Gasteracantha cancriformis spiders sometimes placed silk stabilimenta on non-orb “resting webs” that consisted of only one or a few lines. These webs completely lacked sticky silk, so their stabilimenta could not function to attract prey. Some non-orbs were built by spiders when their orb webs are damaged. These observations contradict the prey attraction camouflage hypothesis for stabilimentum function, but are compatible with the spider camouflage and web advertisement to avoid web destruction hypotheses. Tanto el ulobórido Philoponella vicina como el aranéido Gasteracantha cancriformis colocan stabilimentos de seda en “telas” no-orbiculares que consisten de una pocas lineas. Estas telas carecen de hilos pegajosos, y no funcionan para capturar presas; por lo tanto, sus estabilimenta no funcionan para atraer presas. Algunas de estas telas no-orbiculares son construidas después de que se daña la tela orbicular. Estas observaciones contradicen la hipótesis de que los estabilimentos funcionan para atraer presas; son compatibles con las hipótesis de que los estabilimentos funcionan para camuflar la araña, ó para avisar a animales grandes y asi evitar que se dañen las telas.
Article
Abstract The nephilid genus Nephilengys, known for its synanthropic habits, large webs with a retreat and the extreme sexual size dimorphism, is revised. Of the twenty-three available names, only four species with a globally allopatric distribution are recognized, illustrated and described from both sexes: N. cruentata (Fabricius, 1775) inhabits tropical Africa and South America, where it has probably been introduced; N. borbonica (Vinson, 1863) is found on Madagascar, Comoros, Seychelles and the Mascarene Islands; N. malabarensis (Walckenaer, 1842) ranges from India and Sri Lanka to China, Japan and eastern Indonesia; N. papuana Thorell, 1881 stat.n. is known from New Guinea and tropical Australia. Nephila instigans Butler, 1876 is the proposed syn.n. of N. borbonica; N. borbonica livida Vinson, 1863 is syn.n. of N. borbonica; N. niahensis Deeleman-Reinhold, 1989 is syn.n. of N. malabarensis; N. rainbowi Hogg, 1899 is syn.n. of N. papuana. N. kenmorei Barrion & Litsinger, 1995, here proposed as a nomen dubium, is an araneid. Nephilengys biology is reviewed and its anatomy summarized for use in a phylogenetic analysis of 197 characters scored for all Nephilengys, selected nephilid species and non-nephilid outgroups. Two new clades are circumscribed, the ‘cruentata species group’ (with N. cruentata and N. borbonica) and the ‘malabarensis species group’ (with N. malabarensis and N. papuana).
Article
This study revises the taxonomy, biology, phylogeny, and biogeography of the basal-most nephilid spider lineage, the Clitaetrinae, with the least known nephilid genus Clitaetra. The five previously known species are redescribed: Clitaetra clathrata Simon from western Africa, C. simoni Benoit from central Africa, C. episinoides Simon from the Comoro Islands and Mayotte, C. perroti Simon from Madagascar, and C. thisbe Simon from Sri Lanka with first descriptions of the males of C. clathrata and C. perroti. Additionally, C. irenae sp. nov. is described in both sexes from southern Africa. Clitaetra biology, so far largely unknown, is presented here based on observations of C. irenae in South Africa, and clitaetrine anatomy is summarized to assess phylogenetic homologies. A species-level phylogenetic analysis of 32 taxa scored for 197 morphological and behavioural characters results in eight most parsimonious cladograms and places Clitaetra as sister to the clade (Herennia+ (Nephilengys+Nephila)). Thus, the orb-weaving spider family Nephilidae Simon contains the (sub)tropical genera Nephila, Nephilengys, Herennia, and Clitaetra, but not Deliochus or Phonognatha. Contra recent cladistic treatments, the nephilines are not tetragnathids, but the sister group to the newly proposed clade, Nephilidae, is ambiguous. The three species clades (subgenera) within Clitaetra show a seemingly old Gondwanan biogeographic pattern: Afroetra subgen. nov., with the three mainland African species, is sister to Clitaetra with the two Indian Ocean island species. Indoetra subgen. nov. contains the unstudied species from Sri Lanka, C. thisbe. Future understanding of the morphology and biology of C. thisbe is important for the polarization of many nephilid features. Vicariance would estimate the clitaetrine subgeneric clades and basal nephilid lineages to be at least 160 Myr old and of Gondwanan origin.
Article
Recent studies demonstrated that orb-weaving spiders may alter web architectures, the amount of silk in webs, or the protein composition of silks in response to variation in amount or type of prey. In this study, we conducted food manipulations to examine three mechanisms by which orb-weaving spiders may adjust the performance of webs to variation in prey by altering the architectures of webs, making structural changes to the diameters of silk threads, and manipulating the material properties or amino acid composition of silk fibers. We fed Nephila pilipes two different types of prey, crickets or flies, and then compared orb structure and the chemical and physical properties of major ampullate (MA) silk between groups. Prey type did not affect orb structures in N. pilipes, except for mesh size. However, MA silk diameter and the stiffness of orbs constructed by spiders fed crickets were significantly greater than for the fly group. MA fibers forcibly silked from N. pilipes fed crickets was significantly thicker, but less stiff, than silk from spiders fed flies. Spiders in the cricket treatment also produced MA silk with slightly, but statistically significantly, more serine than silk from spiders in the fly treatment. Percentages of other major amino acids (proline, glycine, and glutamine) did not differ between treatments. This study demonstrated that orb-weaving spiders can simultaneously alter some structural and material properties of MA silk, as well as the physical characteristics of webs, in response to different types of prey.
Article
Individuals of the orb-weaving spider Nephila clavipesbuild complex webs with a region used for prey capture, the orb, and tangle webs opposite either face, the barrier webs. Barrier webs have been hypothesized to serve a variety of functions, including predator defense, and the primary function of the barrier web should be reflected in the relative size of the barrier to the orb under varying conditions of foraging success and predation risk. To investigate the effects of predation pressure and foraging success on barrier web structure, I conducted a comparative study in three disjunct populations that differed in predation risk and foraging success. Although both the orb web and the barrier webs are silk, there was no indication of a foraging-defense trade-off. Barrier web structure did not change during seasonal shifts in orb web size related to changes in preycapture rate, and barrier web silk density and orb radius were positively correlated. The hypothesis that the construction of barrier webs is in part a response to predation pressure was supported. Barrier webs do deflect attacks by some predators, and barrier webs built by small spiders, suffering frequent predation attempts, had a higher silk density than barrier webs built by larger individuals. Additionally, barrier web complexity decreased at a later age in areas with higher predation risk.
Article
Web-building spiders (Araneae; Theridiidae, Linyphiidae, Araneidae) are catagorized as searchers because they devote a large amount of energy to the construction of the web which constitutes the search phase in the foraging sequence. In this study search energy is equated with the density of threads in a web and the effectiveness of a variety of webs in three broad catagories (tangle webs, sheet webs & orb webs) is tested in the light of current foraging theory. Within each web type there is a distinct thread density at which the number of approaching Drosophila (Diptera; Drosophilidae) that are captured is maximized (Figs. 1, 2, 3). That maximum results from a combination of factors that are a function of the density of threads in the web. The visibility of the web to an approaching Drosophila increases which acts to decrease the number of flies that enter the web (Tables 2, 3, 4). The ability of the web to detain a Drosophila that contacts it (capture efficiency) increases to an asymptote as a function of thread density (Fig. 4). These data support an assumption of many optimal foraging models that with increasing investment in search the predator receives a diminishing return.More Drosophila intercept orb webs than intercept sheet or tangle webs. In addition orb webs detain a greater proportion of the flies that contact them (Fig. 4). Sheet webs are intermediate between orb and tangle webs in their relative abilities to contact and detain Drosophila.