Signaling by decorating webs: luring prey or deterring predators?

SUMMARYA spider orb web is an extended phenotype; it modifies and interacts with the environment, influencing spider physiology. Orb webs are plastic, responding to variations in prey parameters. Studies attempting to understand how nutrients influence spider orb-web plasticity have been hampered by the inability to decouple prey nutrients from other, highly correlated, prey factors and the intrinsic link between prey protein and prey energy concentration. I analyzed the nutrient concentrations of cockroaches, and adult and juvenile crickets to devise experiments that controlled prey protein concentration while varying prey size, ingested mass, energy concentration and feeding frequency of the orb web spider Argiope keyserlingi. I found that A. keyserlingi alters overall architecture according to feeding frequency. Decoration length was inversely related to ingested prey mass and/or energy density in one experiment but directly related to ingested prey mass in another. These contradictory results suggest that factors not examined in this study have a confounding influence on decoration plasticity. As decorations attract prey as well as predators decreasing decoration investment may, in some instances, be attributable to benefits no longer outweighing the risks. Web area was altered according to feeding frequency, and mesh size altered according to feeding frequency and prey length. The number of radii in orb webs was unaffected by prey parameters. A finite amount of silk can be invested in the orb web, so spiders tradeoff smaller mesh size with larger web capture area, explaining why feeding frequency influenced both web area and mesh size. Mesh size is additionally responsive to prey size via sensory cues, with spiders constructing webs suitable for catching the most common or most profitable prey.

Section: Introductionmentioning

confidence: 99%

Plasticity in extended phenotypes: orb web architectural responses to variations in prey parameters

Blamires

2010

“…Cheng and Tso provided direct field evidence that A. aemula on webs with cruciate decorations experienced significantly more wasp attacks than those on undecorated webs (Cheng and Tso, 2007). These results (Cheng and Tso, 2007) and those of laboratory studies using Y-mazes (Bruce et al, 2001;Seah and Li, 2001) showed that predators may use cruciate form decorations to locate the spiders. However, responses of wasps to Argiope spiders on webs with linear decorations seem to differ.…”

Section: Discussionmentioning

confidence: 90%

“…According to the morphological phylogeny of the family Araneidae (Scharff, 1997), decoration building evolved independently several times among various genera. Most genera of spiders build linear decorations, and the cruciate form decorations can only be found in certain subadult and adult Argiope spiders The ratio of probabilities of two certain events is designated as e Cheng and Tso, 2007). The intergenus evolutionary relationship of decoration forms within the family Araneidae is congruent with the intra-genus evolutionary relationship of decoration forms in Argiope spiders.…”

Section: Discussionmentioning

confidence: 97%

“…One of the proposed functions of decorations is to visually attract prey thereby enhancing the spiders' foraging success. The prey-luring function of decorations has been demonstrated in several spider genera [Cyclosa (Tso, 1998a); Octonoba (Watanabe, 1999); Araneus (Bruce et al, 2004)], especially in those Argiope species building either discoid [early juveniles (Li et al, 2004;Li, 2005)], linear (Tso, 1996;Tso, 1998b) or cruciate form decorations (Craig and Bernard, 1990;Craig, 1991;Herberstein, 2000;Bruce et al, 2001;Cheng and Tso, 2007). Currently there are around 80 species documented in the genus Argiope (Platnick, 2009 Recent neuroethological studies on insect form vision suggest that the visual effect of linear and cruciate decorations on the behavior of prey might vary.…”

Section: Introductionmentioning

confidence: 99%

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Insect form vision as one potential shaping force of spider web decoration design

Cheng

Yang

Lin

et al. 2010

SUMMARYProperties of prey sensory systems are important factors shaping the design of signals generated by organisms exploiting them. In this study we assessed how prey sensory preference affected the exploiter signal design by investigating the evolutionary relationship and relative attractiveness of linear and cruciate form web decorations built by Argiope spiders. Because insects have an innate preference for bilaterally symmetrical patterns, we hypothesized that cruciate form decorations were evolved from linear form due to their higher visual attractiveness to insects. We first reconstructed a molecular phylogeny of the Asian members of the genus Argiope using mitochondrial markers to infer the evolutionary relationship of two decoration forms. Results of ancestral character state reconstruction showed that the linear form was ancestral and the cruciate form derived. To evaluate the luring effectiveness of two decoration forms, we performed field experiments in which the number and orientation of decoration bands were manipulated. Decoration bands arranged in a cruciate form were significantly more attractive to insects than those arranged in a linear form, no matter whether they were composed of silks or dummies. Moreover, dummy decoration bands arranged in a cruciate form attracted significantly more insects than those arranged in a vertical/horizontal form. Such results suggest that pollinator insects' innate preference for certain bilateral or radial symmetrical patterns might be one of the driving forces shaping the arrangement pattern of spider web decorations.

“…Only when spiders had stayed on their webs for more than 4 h, were their data used in data analyses (Cheng and Tso, 2007). Data from 174 h of video recording of spiders were used to investigate the effect of decoration on the predation and prey interception rate of webs.…”

Section: Field Observationsmentioning

confidence: 99%

Detritus decorations of an orb-weaving spider,Cyclosa mulmeinensis(Thorell): for food or camouflage?

Tan

2009

SUMMARYMany species of the orb-web spider genus Cyclosa often adorn their webs with decorations of prey remains, egg sacs and/or plant detritus, termed 'detritus decorations'. These detritus decorations have been hypothesised to camouflage the spider from predators or prey and thus reduce predation risk or increase foraging success. In the present study, we tested these two alternative hypotheses simultaneously using two types of detritus decorations (prey remain and egg sac) built by Cyclosa mulmeinensis (Thorell). By monitoring the possible responses of predators to spiders on their webs with and without decorations in the field, we tested whether web decorations would reduce the mortality of spiders. Wasp predators were observed to fly in the vicinity of webs with decorations slightly more often than in the vicinity of webs without decorations but there were very few attacks on spiders by wasps. By comparing the insect interception rates of webs with and without decorations in the field, we tested whether web decorations would increase the foraging success. Webs decorated with prey remains or egg sacs intercepted more insects than those without in the field. By calculating colour contrasts of both prey-remain and egg-sac decorations against spiders viewed by bird (blue tits) and hymenopteran (e.g. wasps) predators as well as hymenopteran (bees) prey, we showed that C. mulmeinensis spiders on webs with egg-sac decorations were invisible to both hymenopteran prey and predators and bird predators over short and long distances. While spiders on webs with prey-remain decorations were invisible to both hymenopterans and birds over short distances, spiders on webs with prey-remain decorations were visible to both predators and prey over long distances. Our results thus suggest that decorating webs with prey remains and egg sacs in C. mulmeinensis may primarily function as camouflage to conceal the spider from insects rather than as prey attractants, possibly contributing to the interception of more insect prey. However, the detritus decorations exhibit varying success as camouflage against predators, depending on whether predators are jumping spiders, wasps or birds, as well as on the decoration type.