蜘蛛位置对成功捕获猎物和球型网图案的影响

静坐在球型网的中心,蜘蛛可能遭受天敌的攻击并暴露在不利的天气条件下,如风和雨。然而,栖居于网的中心使蜘蛛比隐藏在隐蔽场所中的蜘蛛能更迅速地察觉并捕获猎物,这是因为猎物的位置仅能被位于网中心的蜘蛛所确定。对在隐蔽场所中的蜘蛛而言,提高对猎物捕获率的方式之一是尽量减少隐蔽所与网中心的距离。而且,网中心与隐蔽所之间较短的距离使蜘蛛能更迅速地逃离危险境况。我使用既在网中心、又在隐蔽场所的硬类肥蛛(Larinioides sclopetarius Clerck),来检验这两种行为如何影响对猎物的捕获成功率。隐藏在隐蔽场所中的蜘蛛更经常忽略猎物,使猎物也有比较多的逃离机会,这样,与在网中心的蜘蛛相比,猎物的损失率就更高。另外,研究了隐蔽场所的位置对球型网图案的影响。在大多数球型网中,网中心上方的区域比网下方小,丝也比较少,形成了结构不对称的网;隐蔽场所通常在网的上方。当隐蔽场所的位置在实验中被倒转时,就形成了非典型的球型网。最后,L．sclopetarius建造的网有很突出的边缘非对称性,与隐蔽场所相邻的区域面积较小,而远离隐蔽场所的区域面积较大,这也可解释为减少了隐蔽场所和网中心之间的距离[动物学报50(4)：559-565．2004]。     

Forces in the spider orb web

Summary Pretensile forces were measured in individual threads of intact spider webs. In the orb web of Araneus diadematus forces decrease from mooring threads to frame threads and radii, a typical ratio being 1071. The smaller number of radii in the upper than in the lower half of the orb is paralleled by force ratios of 21 to 31. A similar difference between radii built first during web construction and radii added after completion of the frame underlines the importance of the former as part of the scaffolding. High tensions in the auxiliary spiral stabilize the radii in addition to providing a pathway for the spider when inserting the sticky spiral. Radial pretension (F) changes with spider mass (m). F/m is similar for different animals indicating an adaptation of radial forces to those resulting from spider mass. Several observations suggest tension control by the spider. When forced to anchor its web to thin flexible rods tension in the threads remains in the normal range. Tension values are similar in the webs of A. diadematus, Zygiella x-notata, Nuctenea umbratica, and Nephila clavipes indicating independence from details of web geometry. Only the mooring threads of Nephila show unusually large forces suggesting a narrower working range of tensions for the catching area than for the scaffolding.     

How Did the Spider Cross the River? Behavioral Adaptations for River-Bridging Webs in Caerostris darwini (Araneae: Araneidae)

Background

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.

Methodology

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.

Conclusions

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.     

Vertical asymmetries in orb webs

In almost all vertical orb webs the hub is above the geometric centre and consequently, the extent of the capture area is larger below the hub than above. In addition to this vertical web‐extent asymmetry, orb webs show vertical asymmetries in number of spiral loops, mesh widths, and angles between radii. However, it was unknown whether these asymmetries are adaptations to the web‐extent asymmetry or whether they are linked to gravity in a different way than through web‐extent asymmetry. We reviewed known vertical asymmetries of orb webs, and we analysed the asymmetries of webs built by four different Cyclosa species, which show large intra‐ and inter‐specific variation in web‐extent asymmetry. We found all analysed structural asymmetries to be linked both to web‐extent asymmetry and to gravity: Larger web extents below the hub and gravity both led to more sticky‐spiral loops and to smaller angles between radii below the hub, whereas web‐extent asymmetry and gravity had opposing effects on mesh width (mean and peripheral). Independent of web‐extent asymmetry, almost all analysed webs had narrower peripheral meshes and smaller angles between radii below the hub than above. We interpret the narrow peripheral meshes along the web's lower edge as an adaptation to prevent tumbling prey from escaping, and the small angles between radii as an adaptation to prevent the sticky‐spiral lines in these narrow meshes to come into contact with each other. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 659–672.     

Cues that Spiders (Araneae: Araneidae,Tetragnathidae) Use to Build Orbs: Lapses in Attention to One Set of Cues because of Dissonance with Others?

Even for small animals such as spiders, behavioral decisions are sometimes influenced by multiple cues. Orb webs constitute exquisitely precise records of the stimuli the spider experienced and the decisions that it made while building its web. In addition, because spiders appear to sense their webs largely by touch, direct behavioral observations can determine which stimuli they probably sense. Previous studies have shown that when an orb‐weaving spider decides how far apart to space successive sticky lines during orb construction, it responds to at least five different kinds of stimuli, all of which apparently use a cue from the web, the location of the previous, inner loop of sticky spiral (IL location), as a point of reference. Here we show that two additional cues from the web, which are related to the position of the temporary spiral (TS), also influence sticky spiral spacing. A combination of direct observations of spider movements, analyses of complete and partially complete webs, and responses to experimental modifications of the web of two species in different families, Micrathena duodecimspinosa (Araneidae) and Leucauge mariana (Tetragnathidae), indicate that both the TS‐IL distance itself and the short‐term memory of the change in TS‐IL distance compared with that on other recently encountered radii correlate with sticky spiral spacing. When the TS‐IL distance was large, the spiders apparently ceased to attend to other cues. Thus, even the relatively stereotyped behavior of orb construction includes variation that stems from attention‐like mental processes.     

Stabilimenta of Philoponella vicina (Araneae: Uloboridae) and Gasteracantha cancriformis (Araneae: Araneidae): Evidence Against a Prey Attractant Function

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.     

Ladder webs in orb‐web spiders: ontogenetic and evolutionary patterns in Nephilidae

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.     

Design features of the orb web of the spider, Araneus diadematus

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 thanup, and thus confers a relatively higher foraging value to sectionsbelow the hub. Simulations suggested that the density of capturespiral spacing, prey size, and the density of prey should allaffect the capture efficiency of a web. Webs lose effectivecapture area because of overlap of the capture zone around eachthread; the smaller the prey, the finer the mesh can be withoutlosing effective area. Lower sectors of the web have a particularmesh size (height and length of capture spiral segments) throughout,whereas in the upper sectors the mesh size changes, wideningfrom the hub towards the periphery.     

Free amino acids in spider hemolymph

We examined the free amino acid composition of hemolymph from representatives of five spider families with an interest in knowing if the amino acid profile in the hemolymph of orb-web-building spiders reflects the high demands for small organic compounds in the sticky droplets of their webs. In nearly all analyses, on both orb and non-orb builders, glutamine was the most abundant free amino acid. Glycine, taurine, proline, histidine, and alanine also tended to be well-represented in orb and non-orb builders. While indications of taxon-specific differences in amino acid composition were observed, it was not apparent that two presumptive precursors (glutamine, taurine) of orb web sticky droplet compounds were uniquely enriched in araneids (orb builders). However, total amino acid concentrations were invariably highest in the araneids and especially so in overwintering juveniles, even as several of the essential amino acids declined during this winter diapause. Comparing the data from this study with those from earlier studies revealed a number of discrepancies. The possible origins of these differences are discussed.     

Nemertean predation on the tropical fiddler crab Uca musica

We saw 79 predatory interactions between a new speciesof monostiliferous, suctorial hoplonemertean and thefiddler crabs Uca musica (77 cases) and U.stenodactylus (2 cases). At an intertidal sand barin the Pacific entrance of the Panama Canal, worms ateabout 0.1% of the adult crab population per day. Themode of attack and the spatial and temporaldistributions of interactions suggest the worm is anambush predator. When struck by a worms sticky,mucous-covered proboscis, crabs produced copious foamfrom their buccal area. Mucous-laden crabs thatescaped, again foamed indicating that the foam maycounteract the mucus. If the attack led to a kill,the struggling crab soon became quiescent, as istypical in other nemertean-prey interactions. Theworm inverted its proboscis, found ingress to thecrabs body and fed. Crabs escaped by autotomizingappendages entwined by the proboscis, by forcefullypulling away and by remaining quiescent, then movingaway when the worm inverted its proboscis and beforeit entered the crab. Immobility, a response to visualpredators, may falsely indicate paralysis to the wormand cause it to invert its proboscis, therebyproviding the crab with an opportunity to escape. This predator-prey interaction seems to incorporategeneralized predator tactics and fortuitous preydefenses that give worms and crabs about an evenchance of success.     

Homing by path integration in the spider Agelena labyrinthica Clerck

Moving about the web the spider Agelena labyrinthica continuously adjusts the prospective return angle. The amount of path integration was indicated by two compromise angles, return angle e and goal angle (Fig. 2). The spider was primed to one of two perpendicular light azimuths, L1 or L2. Subsequently, the discrete effects of a 90° change in light azimuth on the return direction were recorded (Fig. 3). When primed to L1, and the spider was exposed to L2: (1) while homebound, the deviation from straight home was clockwise and largest, (2) both while outbound and returning, the deviation was smallest (Fig. 4), (3) while outbound, either during the first or second half of the outbound run, the deviations were between those obtained in (1) and (2). When the spider was primed to L1, but given L2 while outbound and L1 again while homebound, Agelena deviated counterclockwise, the most with L2 on during the entire outbound run, and less when L2 was available only during a portion of the outbound run. The degree of adjustment of the home path direction is not correlated with the actual path length but with the shortest distance (bee line) between the two points during which the spider was exposed to one of the two light azimuths.On fellowship leave from Hunter College of the City University of New York, Department of Psychology, New York, NY 10021, USA     

Attack Behavior of Two Wasp Species of the <Emphasis Type="Italic">Polysphincta</Emphasis> Genus Group (Hymenoptera,Ichneumonidae) on their Orb-Weaver Spider Hosts (Araneae,Araneidae)

Species in the Polysphincta genus group, as far as is known, are exclusively koinobiont ectoparasitoids of spiders. These wasps attack their hosts, inflicting a temporary paralysis, and then lay one egg on the host’s abdomen or prosoma. Parasitoid attack behavior is highly variable among species, including occasions where the wasp darts directly and holds the spider, as well as instances involving complex behavioral sequences. In the present study, we describe the attack behavior of Polysphincta sp. nr. purcelli and P. janzeni on Cyclosa fililineata and C. morretes, respectively. All attacks occurred at night. Initially, the female wasp landed on the web hub at the position occupied by the spider, with the spider always escaping from this initial attack. Subsequently, the wasp waited for up to 14 h at the web hub for the spider’s return. The wasp then inserted its ovipositor into the mouth of the spider, after which the spider became paralyzed and remained motionless for at least 30 min. The wasp laid one egg on the surface of the host’s abdomen and remained on the web for at least 1 h thereafter. The lie-in-wait and attack only after the return of the host to the web hub, as well as the permanence of the wasp on the web after the attack are not frequent behaviors described for polysphinctines. Behavioral idiosyncrasies, such as those observed here, are common among polysphinctines, suggesting a high level of specific adaptive matching of polysphinctine parasitoid behavior to their hosts’ biological characteristics.     

Influence of aging on brain and web characteristics of an orb web spider

In animals, it is known that age affects the abilities of the brain. In spiders, we showed that aging affects web characteristics due to behavioral alterations during web building. In this study, we investigated the effects of age on the associations between morphological changes to the spider brain and changes in web characteristics. The orb web spider Zygiella x-notata (Araneae, Araneidae) was used to test these relationships. Experiments were conducted on young (19 ± 2 days after adult molt, N = 13) and old (146 ± 32 days, N = 20) virgin females. The brain volume decreased with age (by 10%). Age also had an impact on the number of anomalies in the capture area generated during web building. The statistical relationships between the volume of the brain and web characteristics showed that there was an effect of age on both. Our results showed that in spiders, aging affects the brain volume and correlates with characteristics (anomalies) of the web. As web building is the result of complex behavioral processes, we suggest that aging affects spider behavior by causing some brain alterations.     

网粒体脱落有助于茶小绿叶蝉成虫逃离蜘蛛网

[目的]茶小绿叶蝉Empoasca onukii是我国茶园的重要害虫,其体表覆盖网粒体,而网粒体是否具有防御功能则知之甚少.本研究旨在明确网粒体脱落是否对该害虫逃离茶园蜘蛛网起到关键作用.[方法]将茶小绿叶蝉成虫置于草间小黑蛛Hylyphantes graminicola的不规则网内,利用高清摄像机和Vegas软件对茶...     

The Effect of Wind Exposure on the Web Characteristics of a Tetragnathid Orb Spider

Studies on spiders in their natural habitats are necessary for determining the full range of plasticity in their web-building behaviour. Plasticity in web design is hypothesised to be important for spiders building in habitats where environmental conditions cause considerable web damage. Here we compared web characteristics of the orb spider Metellina mengei (Araneae, Tetragnathidae) in two different forest habitats differing in their wind exposure. We found a notable lack of differences in web geometry, orientation and inclination between webs built along an exposed forest edge and those built inside the forest, despite marked differences in wind speed. This suggests that M. mengei did not exhibit web-building plasticity in response to wind in the field, contrasting with the findings of laboratory studies on other species of orb spiders. Instead, differences in prey capture and wind damage trade-offs between habitats may provide an explanation for our results, indicating that different species employ different strategies to cope with environmental constraints.     

A new view of orb webs: multiple trap designs in a single structure

Spider orb webs are impressive for their apparently uniform geometric patterns. There are, however, consistent, substantial and taxonomically widespread periphery‐to‐hub differences in the distances between both adjacent radii and between sticky spiral lines. Radii in typical orbs were on average about 4–5 times farther apart at the outer edge than the inner edge of the area covered by sticky lines. Distances between sticky spiral loops were on average about two times larger near the outer edge than in more inner portions. This pattern in sticky spiral spacing was absent in the modified orbs of Nephila clavipes, in which distances between radii varied less. Thus, patterns in sticky spiral spacing may be related to inter‐radial spacing; there is, however, probably no single explanation for all of the different patterns of sticky spiral spacing. The patterned differences in radius and sticky spiral spacing have important consequences for understanding orb function, because the lines in a prey's immediate vicinity largely determine whether it will be stopped and then retained, and elementary physics dictates that contact with more lines will tend to increase prey being stopped and retained. Rather than being a unit trap with a single set of prey capture properties, an orb has locally different trapping properties in different sectors. Abandoning the previous typological style of discussion of ‘the’ ability of a given design to stop and retain prey promises to lead to improved understanding of orb web designs. Published 2014. This article is a U.S. Government work and is in the public domain in the USA, Biological Journal of the Linnean Society, 2014, 111 , 437–449.     

Signals and Signal Choices made by the Araneophagic Jumping Spider Portia fimbriata while Hunting the Orb-Weaving Web spiders Zygiella x-notata and Zosis geniculatus

Portia fimbriata is a web-invading araneophagic jumping spider (Salticidae). The use of signal-generating behaviours is characteristic of how P. fimbriata captures its prey, with three basic categories of signal-generating behaviours being prevalent when the prey spider is in an orb web. The predatory behaviour of P. fimbriata has been referred to as aggressive mimicry, but no previous studies have provided details concerning the characteristics of P. fimbriata 's signals. We attempt to determine the model signals for P. fimbriata 's 'aggressive mimicry' signals. Using laser Doppler vibrometer and the orb webs of Zygiella x-notata and Zosis geniculatus , P. fimbriata 's signals are compared with signals from other sources. Each of P. fimbriata 's three categories of behaviour makes a signal that resembles one of three signals from other sources: prey of the web spider (insects) ensnared in the capture zone of the web, prey making faint contact with the periphery of the web and large-scale disturbance of the web (jarring the spider's cage). Experimental evidence from testing P. fimbriata with two sizes of lure made from Zosis (dead, mounted in a lifelike posture in standard-size orb web) clarifies P. fimbriata 's signal-use strategy: (1) when the resident spider is small, begin by simulating signals from an insect ensnared in the capture zone (attempt to lure in the resident spider); (2) when the resident spider is large, start by simulating signals from an insect brushing against the periphery of the web (keep the resident spider out in the web, but avoid provoking from it a full-scale predatory attack); (3) when walking in the resident spider's web, regardless of the resident spider's size, step toward the spider while making a signal that simulates a large-scale disturbance of the web (mask footsteps with a self-made vibratory smokescreen).     

Effect of abiotic factors on the foraging strategy of the orb‐web spider Argiope keyserlingi (Araneae: Araneidae)

Abstract Environmental conditions such as light level, background contrast and temperature might influence a spider's prey capture success and risk of predation. Thus it may often be advantageous for spiders to adjust web‐building behaviour in response to variation in these environmental conditions. This hypothesis was examined in a study of the construction of webs and web decorations (conspicuous strands of silk at the hub of the web) of the orb‐web spider Argiope keyserlingi. Web decorations are thought to have one or more separate functions. They may attract prey, deter predators or advertise the web to oncoming birds, thus preventing web damage. In this series of experiments, relationships between weather parameters and the construction of webs and web decorations were considered. In complementary laboratory experiments, A. keyserlingi spiders were exposed to two different light levels (700 and 90 lx), background contrasts (black and white) and temperature conditions (20 and 26°C). Of the available weather parameters, only temperature was significantly related to web decorating behaviour but not to web size. In the laboratory, temperature also influenced web‐decorating behaviour, and spiders in dim light (700 lx) constructed larger webs and longer decorations. Background contrast did not significantly alter web size or web decorations. These data suggest that when prey availability is reduced at low temperatures, spiders may use web decorations to attract prey to the web. Similarly, in dim light, spiders may build more and larger decorations to increase the visual signal to approaching prey or to advertise the web to oncoming birds.