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1.
The architecture of vertical aerial orb webs may be affected by spider size and gravity or by the available web space, in
addition to phylogenetic and/or developmental factors. Vertical orb web asymmetry measured by hub displacement has been shown
to increase in bigger and heavier spiders; however, previous studies have mostly focused on adult and subadult spiders or
on several size classes with measured size parameters but no mass. Both estimations are suboptimal because (1) adult orb web
spiders may not invest heavily in optimal web construction, whereas juveniles do; (2) size class/developmental stage is difficult
to estimate in the field and is thus subjective, and (3) mass scales differently to size and is therefore more important in
predicting aerial foraging success due to gravity. We studied vertical web asymmetry in a giant orb web spider, Nephila pilipes, across a wide range of size classes/developmental stages and tested the hypothesis that vertical web asymmetry (measured
as hub displacement) is affected by gravity. On a sample of 100 webs, we found that hubs were more displaced in heavier and
larger juveniles and that spider mass explained vertical web asymmetry better than other measures of spider size (carapace
and leg lengths, developmental stage). Quantifying web shape via the ladder index suggested that, unlike in other nephilid
taxa, growing Nephila orbs do not become vertically elongated. We conclude that the ontogenetic pattern of progressive vertical web asymmetry in
Nephila can be explained by optimal foraging due to gravity, to which the opposing selective force may be high web-building costs
in the lower orb. Recent literature finds little support for alternative explanations of ontogenetic orb web allometry such
as the size limitation hypothesis and the biogenetic law. 相似文献
2.
Kensuke Nakata 《Die Naturwissenschaften》2010,97(11):1029-1032
Most orb web spiders face downward on the web hub, and their webs are vertically asymmetrical, that is, the lower part of
the web is larger than the upper part and the ratio of the lower part to the whole web area increases as the spider grows.
This phenomenon may reflect biogenetic law such that young animals exhibit a general ancestral trait whereas adults exhibit
specific and derived traits. An alternative explanation is that vertical asymmetry may arise from the difference in time required
by spiders to move up or down the web to capture prey. The present study tested these two hypotheses for Eriophora sagana. Subadults of this species build their webs with reverse asymmetry in that the upper part of the web area is larger than
the lower part. In both subadults and adults, the upper proportion decreased with spider weight, and adult spiders built more
symmetric webs. These results support the capture time difference hypothesis. 相似文献
3.
Why do kleptobiotic spiders of the genus Argyrodes seem to be associated with spiders of the genus Nephila worldwide? Observations following introduction of experimental insect prey of different sizes and weights on to host webs revealed that: (1) small prey are more effectively retained on the web of Nephila clavipes than on the web of another common host, Leucauge venusta. (2) N. clavipes did not consume small prey that accumulated on the web whereas larger, heavier prey were enveloped and stored. (3) We observed clear partitioning of prey items between N. clavipes and Argyrodes spp.; diet selection by Argyrodes did not overlap with that of N. clavipes but closely overlapped with that of L. venusta. (4) L. venusta responds very quickly to prey impact whereas N. clavipes is slower, offering a temporal window of opportunity for Argyrodes foraging. (5) The ability of L. venusta to detect and respond to small items also means that it acts aggressively to Argyrodes spp., whereas N. clavipes does not. Consequently, food-acquisition behaviours of Argyrodes were clearly less risky with N. clavipes compared with L. venusta. We conclude that when a kleptobiotic organism has a choice of various host species, it will opt for the least risky host that presents the highest rate of availability of food items. The fact that Nephila species present such characteristics explains the worldwide association with Argyrodes kleptobiotic spiders. 相似文献
4.
Orb web spiders sit at the centre of their approximately circular webs when waiting for prey and so face many of the same
challenges as central-place foragers. Prey value decreases with distance from the hub as a function of prey escape time. The
further from the hub that prey are intercepted, the longer it takes a spider to reach them and the greater chance they have
of escaping. Several species of orb web spiders build vertically elongated ladder-like orb webs against tree trunks, rather
than circular orb webs in the open. As ladder web spiders invest disproportionately more web area further from the hub, it
is expected they will experience reduced prey gain per unit area of web investment compared to spiders that build circular
webs. We developed a model to investigate how building webs in the space-limited microhabitat on tree trunks influences the
optimal size, shape and net prey gain of arboricolous ladder webs. The model suggests that as horizontal space becomes more
limited, optimal web shape becomes more elongated, and optimal web area decreases. This change in web geometry results in
decreased net prey gain compared to webs built without space constraints. However, when space is limited, spiders can achieve
higher net prey gain compared to building typical circular webs in the same limited space. Our model shows how spiders optimise
web investment in sub-optimal conditions and can be used to understand foraging investment trade-offs in other central-place
foragers faced with constrained foraging arenas. 相似文献
5.
Nakata K 《Die Naturwissenschaften》2007,94(10):853-857
Animals obtain information from past foraging experience to adjust their foraging activity according to their environment.
The ability of spiders to obtain information from unsuccessful predation experiences was investigated by examining the effects
on web building, a significant foraging investment, of prey detection without successful capture in the orb-web spider Cyclosa octotuberculata. Four treatments were employed: (1) successful capture and feeding: one syrphid fly was allowed to be captured and consumed
by the spider on the web; (2) single prey-item detection: a syrphid fly was placed on the web to lure the spider, but was
removed before capture; (3) five prey-item detection: above prey-item detection stimulus was given five times; and, (4) control:
neither prey nor feeding on the web. While control spiders decreased the total thread length and capture area of their webs,
prey-item detection spiders in both conditions increased them, indicating that the spider obtained information from unsuccessful
predation experience to adjust their foraging investment. The fed spiders exhibited a significantly greater increase than
the prey-detection-only spiders, suggesting that prey detection alone and prey detection with consumption had different informational
effects. Total thread length did not differ between single and five prey-item detection spiders, but distance between two
adjacent sticky spirals increased only in the former spiders, possibly because five times unsuccessful predations prevented
spiders to reduce web stickiness. It suggests that the spider changed web morphology according to the number of prey detection. 相似文献
6.
Agnarsson I 《Die Naturwissenschaften》2011,98(2):163-167
How fully a suitable habitat patch is utilized by organisms depends crucially on patch size and isolation. Testing this interplay is made difficult in many systems by the arbitrariness of defining a "habitat patch", measuring its boarders, and relatively low detection probability of the inhabitants. Spider webs as habitat patches for obligate web kleptoparasites are free from these problems. Each individual web is a highly discrete and readily measured habitat patch, and the detection probability of argyrodine spider kleptoparasites is very nearly 1. Hence, spider webs emerge as simple systems for ecological models such as patch occupancy and metapopulation biology. Recently, I showed that the distribution of kleptoparasites among host webs relates both to web (patch) size as well as patch connectivity. Here, I test the relative importance of patch size versus isolation in explaining patch occupancy and abundance of inhabitants. I find that (1) web size is the better predictor of patch occupancy and abundance. (2) Web size is overall positively correlated with abundance, but predicts it most precisely among interconnected webs and not at all among the most isolated webs. Hence, patch occupancy and inhabitant abundance is explained by a rather complex interplay between patch size and isolation. 相似文献
7.
Orb-web building spiders (Araneae: Araneoidea, Uloboridae) can be considered as territorial central place foragers. In territorial
central place foragers, the optimal foraging arena is circular, with the forager sitting in its centre. In orb webs, the spider’s
orientation (head up or head down) whilst waiting for prey on the hub of its web and the downwards–upwards asymmetry of its
running speeds are the probable causes for the observed deviation of the hub from the web’s centre. Here, we present an analytical
model and a more refined simulation model to analyse the relationships amongst the spider’s running speeds, its orientation
whilst waiting for prey and the vertical asymmetry of orb webs. The results of our models suggest that (a) waiting for prey
head down is generally favourable because it allows the spider to reach the prey in its web on average quicker than spiders
waiting head up, (b) the downwards–upwards running speed asymmetry, together with the head-down orientation of most spiders,
are likely causes for the observed vertical asymmetry of orb webs, (c) waiting head up can be advantageous for spiders whose
downwards–upwards running speed asymmetry is small and who experience high prey tumbling rates and (d) spiders waiting head
up should place their hub lower than similar spiders waiting head down. 相似文献
8.
Rao D Ceballos Fernandez O Castañeda-Barbosa E Díaz-Fleischer F 《Die Naturwissenschaften》2011,98(8):699-703
Most orb-web spiders face downwards in the web. A downward orientation has been proposed to be the optimal strategy because
spiders run faster downwards and thus can catch prey quicker. Consequently, orb-web spiders also extend their web in the lower
part, leading to top-down web asymmetry. Since the majority of orb-web spiders face downwards, it has been difficult to test
the effect of orientation on prey capture and web asymmetry. In this study, we explored the influence of reverse orientation
on foraging efficiency and web asymmetry in Verrucosa arenata, a neotropical orb-web spider that faces upwards in the web. We show that reverse orientation does not imply reverse web
asymmetry in this species. V. arenata spiders captured more prey in the lower part of the web but more prey per area on the upper part. The average running speeds
of spiders did not differ between upward and downward running, but heavier spiders took longer to capture prey while running
upwards. We discuss these findings in the context of foraging efficiency and web asymmetry. 相似文献
9.
Marija Majer Ingi Agnarsson Jens-Christian Svenning Trine Bilde 《Die Naturwissenschaften》2013,100(11):1031-1040
Latitude, rainfall, and productivity have been shown to influence social organisation and level of sociality in arthropods on large geographic scales. Social spiders form permanent group-living societies where they cooperate in brood care, web maintenance, and foraging. Sociality has evolved independently in a number of unrelated spider genera and may reflect convergent evolutionary responses to common environmental drivers. The genus Anelosimus contains a third of approximately 25 described permanently social spider species, eight to nine species that all occur in the Americas. To test for environmental correlates of sociality in Anelosimus across the Americas, we used logistic regression to detect effects of annual rainfall, productivity, and precipitation seasonality on the relative likelihood of occurrence of social and non-social Anelosimus spiders. Our analyses show that social species tend to occur at higher annual rainfall and productivity than non-social species, supporting the hypothesised effects of these environmental variables on the geographical distribution of social species. We did not find support for the hypothesis that permanently social species occur in areas with low precipitation seasonality. High annual precipitation and, to less extent, high productivity favour the occurrence of permanently group-living Anelosimus spiders relative to subsocial and solitary species. These results are partially consistent with previous findings for the Old World spider genus Stegodyphus, where a link between high habitat productivity and sociality was also found. Unlike Anelosimus, however, Stegodyphus typically occur in dry habitats negating a general importance of high precipitation for sociality. Sociality in spiders thus seems to be strongly linked to productivity, probably reflecting the need for relatively high availability of large prey to sustain social colonies. 相似文献
10.
Wind has previously been shown to influence the location and orientation of spider web sites and also the geometry and material
composition of constructed orb webs. We now show that wind also influences components of prey-catching behaviour within the
web. A small wind tunnel was used to generate different wind speeds. Araneus diadematus ran more slowly towards entangled Drosophila melanogaster in windy conditions, which took less time to escape the web. This indicates a lower capture probability and a diminished
overall predation efficiency for spiders at higher wind speeds. We conclude that spiders’ behaviour of taking down their webs
as wind speed increases may therefore not be a response only to possible web damage. 相似文献
11.
Parasitoid-induced mortality of Araneus omnicolor (Araneae, Araneidae) by Hymenoepimecis sp. (Hymenoptera, Ichneumonidae) in southeastern Brazil 总被引:1,自引:0,他引:1
All species included in the Polysphincta genus-group develop as ectophagous parasitoids of active spiders, killing their hosts prior to pupation. However, little
information regarding natural history and ovipositing behavior of most species are available. In this study we inspected 85
webs of Araneus omnicolor to evaluate the frequency of parasitism and host size preferences of the wasp Hymenoepimecis sp. We also described the web characteristics of normal and parasitized spiders and the wasp ovipositing behavior. About
41% of the adult females of A. omnicolor inspected were parasitized. The highest incidence of parasitism was observed among relatively small females while no egg
or larva was found in large individuals. Araneus omnicolor builds a strong web composed of an orb and barrier threads, where the spider rests within a curled leaf. The parasitoid larva
builds its cocoon within this refuge, and modified cocoon webs were not observed. The ovipositing behavior of Hymenoepimecis sp. was very similar to that of Hymenoepimecis argyraphaga parasitizing Leucauge argyra, including the position of the sting, the killing of a previously attached larva, and the expelling of the egg from the base
of the ovipositor. 相似文献
12.
The glue-coated and wet capture spiral of the orb web of the garden cross spider Araneus diadematus is suspended between the dry silk radial and web frame threads. Here, we experimentally demonstrate that the capture spiral is electrically conductive because of necks of liquid connecting the droplets even if the thread is stretched. We examine how this conductivity of the capture spiral may lead to entrapment of charged airborne particles such as pollen, spray droplets and even insects. We further describe and model how the conducting spiral will also locally distort the Earth's ambient electric field. Finally, we examine the hypothesis that such distortion could be used by potential prey to detect the presence of a web but conclude that any effect would probably be too small to allow an insect to take evasive action. 相似文献
13.
Spiders are fascinating model species to study information-acquisition strategies, with the web acting as an extension of the animal’s body. Here, we compare the strategies of two orb-weaving spiders that acquire information through vibrations transmitted and filtered in the web. Whereas Araneus diadematus monitors web vibration directly on the web, Zygiella x-notata uses a signal thread to remotely monitor web vibration from a retreat, which gives added protection. We assess the implications of these two information-acquisition strategies on the quality of vibration information transfer, using laser Doppler vibrometry to measure vibrations of real webs and finite element analysis in computer models of webs. We observed that the signal thread imposed no biologically relevant time penalty for vibration propagation. However, loss of energy (attenuation) was a cost associated with remote monitoring via a signal thread. The findings have implications for the biological use of vibrations by spiders, including the mechanisms to locate and discriminate between vibration sources. We show that orb-weaver spiders are fascinating examples of organisms that modify their physical environment to shape their information-acquisition strategy. 相似文献
14.
In numerous spider species, reproductive success of adult females has been shown to be positively correlated with their body mass. We suggest, however, that spiders may incur greater foraging costs as their body mass increases due to the numerous and complex locomotor bouts needed to build an orb-web. Such a body-mass-dependent cost should, in turn, affect the web-building decisions of spiders. In the laboratory, we tested the influence of body mass on energetic expenditure (measured as mass loss) during web-building behavior in Zygiella x-notata. Our results showed (1) that energetic costs associated with web-building were closely related to body mass and to web-building activity, and (2) that as their body mass increased, spiders reduced the amount of silk used per web, while their foraging effort simultaneously increased. This work gives new insights into web-building behavior and energy allocation strategies of weaving spiders. 相似文献
15.
Carmen Reyes-Alcubilla Miguel A. Ruiz Joaquín Ortega-Escobar 《Die Naturwissenschaften》2009,96(4):485-494
Previous studies on the homing of the wolf spider Lycosa tarantula have shown that it is carried out by path integration. Animals using this mechanism must measure the distance walked and
the angles turned. This study aims to understand if wolf spider L. tarantula is able to estimate the walked distance in an outward path. As this information is more likely obtained by proprioceptive
mechanisms, active or passive displacements have been performed. An active locomotion was found essential to estimate distances.
During passive locomotion, spiders searched for their burrows near the release point while when displaced actively the inbound
journey was longer than the outbound one. The possible use of visual landmarks near the burrow was also tested as a cue to
complete the inbound journey. Our results did not show that L. tarantula used these visual landmarks to find the burrow. L. tarantula seems to use only proprioceptive information obtained during the outbound path to estimate the distance traveled. 相似文献
16.
We studied the abilities of the garden cross spider Araneus diadematus regarding adaptation of web geometry to spatial constraints. Spiders reacted to a spatial reduction in their building site
from a square-shaped frame to a slimmer, rectangular frame (side ratio 1 : 2) by maintaining overall web geometry while reducing
the web area covered by the sticky capture spiral. However, when the frames were changed further to a rectangular side ratio
of 1 : 3, the spiders changed specific web properties in such a way that a further reduction in the capture spiral area was
prevented. Construction of the threads making up the web frame and the auxiliary spiral requires that the spider explores
the spatial constraints of its building site. The geometry of both frame and auxiliary spiral threads in turn determine the
geometry of the capture threads. Since in very narrow frames the spider adjusted the auxiliary to suit the subsequent capture
spiral, we suggest that an initial spatial survey led to the final adaptation of overall web geometry to a web site.
Received: 26 April 1999 / Accepted in revised form: 26 November 1999 相似文献
17.
Felix G. Marx Mónica R. Buono R. Ewan Fordyce R. W. Boessenecker 《Die Naturwissenschaften》2013,100(3):257-261
The origin of the pygmy right whale (Caperea marginata) has long been one of the most vexing conundrums of marine mammal evolution. The extremely disparate skeletal structure of Caperea and a patchy fossil record have left morphology and molecules at odds: whereas most morphological analyses ally Caperea with right whales (Balaenidae), most molecular studies instead suggest a close relationship with rorquals (Balaenopteridae) and grey whales (Eschrichtiidae). The morphological evidence supporting a Caperea-balaenid clade consists of several shared features of the skull and mandible, as traditionally observed in adult individuals. Here, we show that at least two of these features, the ascending process of the maxilla and the coronoid process, arise from substantially different precursors early during ontogeny and therefore likely do not represent genuine synapomorphies. Both of these juvenile morphologies have adult counterparts in the fossil record, thus indicating that the ontogenetic variation in the living species may be a genuine reflection of differing ancestral states. This new evidence contradicts previous morphological hypotheses on the origins of Caperea and may help to reconcile morphological and molecular evidence. 相似文献
18.
Temporal variation in size-assortative mating and male mate choice in a spider with amphisexual care
Males should be more selective when they have a high investment in reproduction, especially in species with biparental or paternal care. In this context, male mate choice can promote size-assortative mating (SAM) when (1) large males win intrasexual disputes, (2) large females are more fecund, and (3) males prefer larger females to smaller ones. In the spider Manogea porracea, males exhibit high reproductive investment by building their webs above those of females and exhibiting extended care of offspring in the absence of females. Under these circumstances, we expect the occurrence of SAM and male preference for large females. Herein, we performed observations and experiments in the field to evaluate the hypotheses that (1) M. porracea mates assortatively by size and (2) SAM is influenced by male mate choice. Furthermore, we measured variables that could affect mating patterns, the sex ratios, and densities of both sexes. Pairing in M. porracea was positively size-assortative in 2012, but not in 2013. Large males won most disputes for mates and preferred larger females, which produced more eggs. The inconsistency in detection of SAM was due to population dynamics, namely variations in sex ratio and population density across the breeding season. Furthermore, we found that the significance of male mate choice on sexual selection of body size in M. porracea strongly depends on the competition intensity for mating opportunities. The traditional sexual selection hypothesis of SAM needs to be reviewed and must include measures of competition intensity. 相似文献
19.
Mature colonies of Discothyrea oculata were observed nesting in cribellatid spider oothecas where they found both shelter and food although these oothecas, installed
in preexisting cavities, were protected with crimped silk. Workers of colonies bred in test tubes during laboratory experiments
recuperated the silk from spider oothecas introduced into their foraging area, using their mandibles and forelegs, to operculate
and line the test tubes. Also, colonies left the test tubes to shelter in the cribellatid spider oothecas. The term "arachnolesty"
is proposed for this new kind of lestobiosis.
Received: 20 April 1998 / Accepted in revised form: 16 October 1998 相似文献
20.
Julien Cucherousset Jean-Marc Paillisson Jean-Marc Roussel 《Die Naturwissenschaften》2013,100(8):761-768
Natal departure timing represents one of the first crucial decisions for juveniles born in spatially varying environments that ultimately disappear, but our knowledge on its determinants is limited. The present study aimed at understanding the determinants of juvenile natal departure by releasing individually tagged juvenile pike (Esox lucius L.) with variable body size and trophic position in a temporary flooded grassland. Specifically, we investigated whether natal departure depends on individual competitive status (‘competition hypothesis’), physiological tolerance to environmental conditions (‘physiological hypothesis’) or individual trophic position and the spatial heterogeneity of trophic resources (‘trophic hypothesis’). The results indicated that departure timing was negatively correlated with body size at release, showing that the dominance status among competing individuals was not the main trigger of juvenile departure. A positive correlation between departure timing and individual body size at departure was observed, suggesting that inter-individual variability in physiological tolerance did not explain departure patterns. While individual growth performances were similar irrespective of the timing of natal departure, stable isotope analyses revealed that juveniles with higher trophic position departed significantly earlier than individuals with lower trophic position. Therefore, the trade-off driving the use of spatially varying environments was most likely dependent upon the benefits associated with energetic returns than the costs associated with inter-individual competition or physiological stress. This result highlighted how ontogeny, and particularly ontogenetic niche shift, can play a central role in juvenile’s decision to depart from natal habitats in a predatory species. 相似文献