Alain Pasquet

Web-building behaviour in the orb-weaving spider Zygiella x-notata: influence of experience.

Zygiella x-notata is an orb-weaving spider that often renews its trap daily. Web building has associated costs and benefits, and building successive webs may have consequences for lifetime reproductive success. In the laboratory, we tested the ability of Z. x-notata to modify its building behaviour in response to various stages in predation (prey detection, capture and ingestion) experienced with a previous web. We determined which stages provided information for the spiders. Spiders that detected, captured and ingested prey and then rebuilt their web used less silk and made a smaller capture area than in the previous web. There was no effect of prey detection alone on the next web. Capture without feeding gave the same results as capture followed by feeding. The spiders that ate prey without detection and capture (feeding by hand) had the same energetic gains as spiders that caught prey but delayed building a new web. The spiders thus showed plasticity in web-building behaviour and in the amount of silk used (energetic investment) in the short term (from one web to the next). Changes in body condition may therefore influence web construction. Moreover, information gained during prey capture appeared to influence the size and structure of the next web. This ability should enable spiders to adapt their web building to maximize their fitness. Copyright 2000 The Association for the Study of Animal Behaviour.

Influences of aggregative behaviour on space occupation in the spider Zygiella x-notata (Clerck)

SummaryThe distribution of the spider Zygiella x-notata was examined using field populations of adult females occupying the outside frames of windows. The structure of the populations was aggregative, and the distribution of individuals on the window frames and the size of the webs were density dependent. Also, the sizes of the webs of neighbouring spiders on the same window alternated. This spatial organization involves interactions between neighbours. If one spider out of two is removed, and if all the webs are destroyed, remaining spiders that previously had small webs significantly increase the size of their construction. In contrast, individuals that previously had large webs do not modify the size of their construction. This shows that individuals of Z. x-notata respond to the presence of neighbours. The influence of intraspecific interactions in such a population is discussed.

Body-mass-dependent cost of web-building behavior in an orb weaving spider, Zygiella x-notata.

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.

A Thesaurus for Soil Invertebrate Trait-Based Approaches

Soil invertebrates are known to be much involved in soil behaviour and therefore in the provision of ecosystem services. Functional trait-based approaches are methodologies which can be used to understand soil invertebrates’ responses to their environment. They (i) improve the predictions and (ii) are less dependent on space and time. The way traits have been used recently has led to misunderstandings in the integration and interpretation of data. Trait semantics are especially concerned. The aim of this paper is to propose a thesaurus for soil invertebrate trait-based approaches. T-SITA, an Internet platform, is the first initiative to deal with the semantics of traits and ecological preferences for soil invertebrates. It reflects the agreement of a scientific expert community to fix semantic properties (e.g. definition) of approximately 100 traits and ecological preferences. In addition, T-SITA has been successfully linked with a fully operational database of soil invertebrate traits. Such a link enhances data integration and improves the scientific integrity of data.

Colonial life versus solitary life in Cyrtophora citricola (Araneae, Araneidae)

Summary: Among spiders, some species could be qualified as colonial. Individuals may live alone or in colonies where each spider exploits its own capture web in a communal network. We compared solitary with colonial life in Cyrtophora female populations from South-East Sicily in 1992 and 1993. We used 6 parameters to describe and compare the populations: spider size, web size, egg production, prey captured, presence of kleptoparasites and their size.¶ Spiders living in colonies did not differ in size from solitary spiders.¶ The webs of colonial spiders were smaller than those of solitary spiders.¶ The number of prey captured and their size did not differ between the two types of spiders.¶ Solitary spiders produced more eggs than colonial individuals.¶ Kleptoparasite spiders Argyrodes gibbosus were more numerous in the webs of solitary spiders than in the webs of colonial spiders and there were more solitary webs infested by kleptoparasites in 1992. The kleptoparasites were larger in colonial webs than in solitary ones. Another species of spider, Holocnemus pulchei, spun its own web in the network of the web of Cyrtophora. The number of Holocnemus per web did not differ between solitary and colonial Cyrtophora.¶ Results are discussed by referring to what it is known in other temporarily social spiders.

Experimental study of foundation and development ofAnelosimus eximius colonies in the tropical forest of French Guiana

SummaryPossibilities for new colony foundation inAnelosimus eximius (Theridiidae) were tested with isolated females (both with and without egg sacs) and with groups of individuals (groups from 150 to 250 spiders). Experimental groups were deposited in three different habitats: within the forest, on the forest edge (where natural colonies develop most frequently) and outside the forest (low savannah or areas cleared of vegetation, but in which plant life had started to grow back between the path and the forest edge).Isolated adult females had very low founding success: less than 13 % settled and spun a web; the presence of an egg sac provided by investigators was not an influencing factor. Webs of isolated females had the same architectures as those of colonies with several hundreds of individuals. This web was a horizontal sheet linked to a thick vertical network of threads.All groups of 150 to 250 spiders established colonies in appropriate habitats. The colonies outside the forest, and more than 90 % of the colonies along the forest edges successfully developed during the one month observation period. Conversely, 35 % of the colonies in the forest disappeared either a few days after being placed there, or one or two weeks after. In the latter case, spiders apparently left their webs, and all silk structures were left intact. No dead spiders were found in the webs.Average web surface areas increased in all colony types with age, except for those placed in the forest. In these colonies, the number of individuals decreased, and there were fewer egg sacs than in the colonies placed outside the forest.Results are discussed with regard to natural colony distribution along open paths and to the dispersive characteristics of this spider species.

Modalities of Feeding Behaviour in an Orb-Weaving Spider Zygiella X-Notata (Clerck) (Araneae: Araneidae)

Prey capture and ingestion by the orb-weaving spider Zygiella x-notata have been studied in relation to prey type and to prey density (number of prey items presented/time unit). Whatever the type or the weight of a prey item (11 mg fly, 11 mg or 15 mg cricket larva), the pattern of prey capture did not vary. Ingestion rate did not vary during a meal when the prey was a fly, but this rate decreased with time when the prey was a cricket larva. This decrease was not due to satiation. When several prey items of the same type were placed simultaneously on a web, the spiders subdued them all, chose one of them (generally the first item) and then returned to its retreat to ingest it. A spider presented 3 crickets larvae at one-hour intervals, interrupted feeding on the first item when the second prey was presented. The second item was subdued more rapidly than the first one had been, but the spider left the second prey in the web and returned to its previous item. The third prey item was treated in the same manner as the second one. Spiders spent less time feeding on the first cricket larva in multi-prey tests, whatever the interval between prey arrivals, than on a cricket larva in single-prey test. On the other hand, no difference was found between the single-prey test and the multi-prey test when the prey were flies. In addition, whatever the prey type, quantities ingested (fresh weight) did not vary significantly between the single and multi-prey tests. Data presented here suggest that Zygiella x-notata can modify trade-offs obtained during prey item ingestion and that ingestion curves are good predictions of the quantity ingested in relation of time spent feeding.

The impact of management strategies in apple orchards on the structural and functional diversity of epigeal spiders

Apple orchards are agro-ecosystems managed with high levels of inputs and especially pesticides. Epigeal spider communities were sampled in three seasons using pitfall traps in 19 apple orchards with four different management strategies (abandoned, under organic, Integrated Pest Management or conventional protection) and thus significantly different pesticide usage. The abundance and diversity of the spider communities was the highest in abandoned orchards. Higher diversity and evenness values were the only difference in spider communities from the organic orchards compared to the other commercial orchards. The analysis of five ecological traits (proportion of aeronauts, type of diet, overwintering stages, body size and maternal care), however, clearly showed differences in the spiders from the organic orchards. The spider species in the other commercial orchards were smaller and have higher dispersal abilities. Seven bioindicator species were identified in abandoned orchards, two species in organic ones (only Lycosidae) and one species in conventional orchards (Linyphiidae).

Behavioural Tactics for Prey Capture and Prey Ingestion in Two Sympatric Spiders

Hunting tactics of two sympatric orb-weaving spiders Argiope bruennichi (Scopoli) and Araneus marmoreus Clerck were investigated in the field by offering them flies (40 mg) or grasshoppers (250 mg or 100 mg). For each prey item offered capture rate, spider behaviour and duration were observed. Quantities ingested by the spiders and durations of ingestion of grasshoppers were investigated in the laboratory. Spiders of both species exhibit distinct tactics for each prey type. To capture grasshoppers, spiders first wrap them and then bite their prey. After first leaving the prey, the spider returns, carries the prey to the retreat or to the hub and then ingests it. To capture flies, spiders of both species first bite it, and immediately carry it to the hub or the retreat where they eat it. A. bruennichi showed more variable tactics with flies than with grasshoppers. A. marmoreur showed more variable tactics with small grasshoppers. Total time taken for the capture of a given prey type was similar for the two spiders: for grasshoppers A. marmoreus had a longer handling time and ingested a larger part of grasshoppers, but spent less time ingesting it than A. bruennichi.

Does building activity influence web construction and web characteristics in the orb-web spider Zygiella x-notata (Araneae, Araneidae)?

BackgroundVery 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.ResultsThere 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.ConclusionsThese 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 spiders adult life does not affect a stereotyped behaviour such as the building of an orb-web.