Behavioural analysis of web building anomalies in the orb-weaving spider Zygiella x-notata (Araneae, Araneidae)

Among animal constructions, spider’s orb webs represent regular geometrical architecture models. Their construction is the result of successive, simple and reproducible behavioural patterns, often considered as stereotyped. It has recently been shown that spider’s building behaviours vary, which can alter web regularity. The final capture spiral results from the laying of successive threads between two radii, here termed ‘spiral units’. We defined a theoretical normal web, as a web in which each turn of the final spiral should be parallel to the preceding one. Weaving of the spiral units sometimes leads to anomalies in the orb web. Anomalies were identified and analysed in the orb-weaving spider Zygiella x-notata (Clerck, 1757). From video recordings of web construction, we noted the displacements of the legs and of the abdomen of the spider. We compared the frequency of displacements, and their duration, between the construction of spiral units that produce a normal turn and ones that produce an anomalous turn. The position of the legs on the web’s threads was also analysed. Results showed that anomalies were not the consequences of a modification in activity but more likely the result of the position on the radii of the fourth leg. These results suggest that spiders use local information to build the final capture spiral

Maintenance of polymorphism in the orb weaving spider species Agalenatea redii (Araneae, Araneidae)

The maintenance of polymorphism within populations may be the consequence of several elements of species life history such as use of space, activity rhythms, predation, parasitism and reproduction. The present study focuses on the latter aspect using an orb weaving spider, Agalenatea redii, which presents five different morphs of the opisthosoma pattern in the adult stage. Over the course of four years, from 2008 to 2011, adult spiders (males, females and pairs) were observed at different sites. In 2011, we also conducted a six-week survey of a single population, observing the number of spiders of each morph and the morph of paired spiders. We collected field data on the spatial and temporal distribution of spiders based on their sex and morph. Using a distance analysis, we compared the field distribution with a simulated one in which pairs were associated at random. The results showed that although there were changes over time and space in the proportions of females of the different morphs, as well as in the proportion of the pair associations, pairing according to morphs probably occurs at random

La communication chez les Araignees : etude des phenomenes vibratoires transmis par les toiles lors du rapprochement des sexes chez quelques Dictynidae et Agelenidae

SIGLECNRS T 66454 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Stratégies comportementales et modèle d'optimisation dynamique à horizon non fini (succession des constructions de toiles chez une araignée orbitèle "Zygiella X-Notata" (Clerck))

Dans ce travail, nous avons cherché à tester l'hypothèse selon laquelle les araignées femelles adultes d'une espèce orbitèle, Zygiella x-notata, construisent leurs toiles successives de manière à maximiser leur fitness. Après avoir mis au point un outil méthodologique permettant d'estimer la longueur de la spirale d'une toile, l'aspect dynamique des constructions a été étudiée à court terme. Nos résultats montrent que les araignées utilisent des informations relatives aux événements de capture et de consommation de proies associés à une toile lors de la construction de la toile suivante. La dynamique des constructions a ensuite été étudiée à plus long terme, entre la mue imaginale des femelles et leur première ponte. Ce travail a nécessité de préciser les coûts et bénéfices associés au comportement de construction et de réaliser un modèle prédictif de la stratégie optimale de construction des toiles. Cette stratégie a pu être comparée aux comportements des araignées. Les données recueillies suggèrent que le risque de prédation encouru durant la construction d'une toile sont faibles et révèlent que les dépenses énergétiques associés à la construction d'une toile augmentent à la fois avec la quantité de soie mise en place et avec le poids des araignées. Les probabilités de capture de proies (bénéfices énergétiques) augmentent avec la taille des toiles. Les données de terrain et de laboratoire révèlent que les araignées réduisent leur activité de construction au cours de leur développement. En accord avec ces observations, le modèle prédit que les araignées devraient réduire leur activité de tissage quand leur poids devient élevé. Par ailleurs nos résultats suggèrent que la pression de sélection exercée sur le comportement de construction est faible au cours d'une grande part du développement des araignées femelles adultes, ce qui pourrait expliquer en partie la diversité des comportements de construction exprimés par celles-ci.This study aims to test the hypothesis that adult female spiders of the orb-weaving species Zygiella x-notata build their successive webs according to rules that allow them to maximise their fitness. A non invasive method was first set up to estimate the total capture thread length of a web. Short term web building dynamics could be then investigated. Our results showed that informations linked to capture events and to prey ingestion with a given web influence following web building. Long term web building dynamics was studied through a longitudinal study of spiders between their final moult and their first egg-laying. Cost and benefits of web-building behaviour had to be estimated before setting up a predictive model of web-building optimal strategy. Predictions of this model could then be matched with observed behaviour. Behavioural data suggest predation risk occurring during web building to be weak, and energetic expenditure to increase both with the amount of silk set up per web and with spider's body weight. Probability of prey catching -that is, energetic expected gains- increased together with web size. Both field and laboratory data showed that adult female spiders reduced their web building activity throughout their development. Results of the predictive model also suggest that when their body weight increased, optimal spiders should reduce their building activity. Furthermore, we could make the following hypothesis: selective pressures should remain weak over web-building behaviour during most of adult female spider's development. This could explain, at least partly, the great diversity of observed web-building behaviours.NANCY1-SCD Sciences & Techniques (545782101) / SudocSudocFranceF

Loss of legs: is it or not a handicap for an orb-weaving spider?

International audienceLeg loss is a common phenomenon in spiders, and according to the species 5% to 40% of the adults can present at least one missing leg. There is no possibility of regeneration after adult moult and the animal must manage with its missing appendages until its death. With the loss of one or more legs, female orb-weaving spiders can be penalized twice: firstly, because the legs are necessary for web construction and secondly, the legs are essential for the control of the prey after its interception by the web. During development, spiders may be also penalized because regeneration has energetic costs that take away resources for survival, growth and reproduction. All these consequences should influence negatively the development of the spider and thus its fitness. We investigated the impact of leg loss in the orb-weaving spider, Zygiella x-notata by studying its frequency in a natural population and web building and prey capture behaviours in laboratory. In field populations, 9.5% to 13%, of the adult females presented the loss of one or more legs; the majority of individuals had lost only one leg (in 48% of cases, a first one). Leg loss seems to affect all the adult spiders, as there is no difference of mass between intact spiders and those with missing leg. Data obtained with laboratory-reared spiders, showed that the loss of legs due to the moult is rare (less than 1%). Considering changes in web design, spiders with missing legs decreased their silk investment, increased the distance between spiral turns but did not change the capture surface of the web. Under our laboratory experimental conditions, spiders with one or two lost legs did not present any difference in prey capture efficiency. In laboratory conditions, spiders with lost leg(s) did not show any difference in egg sac production or in longevity (adult lifespan) compared to intact spiders

Kleptoparasites influcence foraging behaviour of the spider Stegodyphus lineatus (Araneae, Eresidae)

International audiencePrey captured by a predator may attract kleptoparasites which could significantly reduce the amount of food consumed. Stegodyphus lineatus, a cribellate spider, builds an energetically costly web. Ants raid the webs of S. lineatus to steal prey and behave as kleptoparasites. We investigated ant raids in a natural population of S. lineatus and their influence on the spider's foraging behaviour. Considering spiders that had captured a prey, 31.2% suffered an ant raid within 24 h after the prey capture. Experimental tests showed that the response to ant raid is to delay web rebuilding and this was independent of a spider's previous foraging success. There was a tendency for spiders that were exposed to ants to build larger webs. Neither prey-handling duration nor prey consumption was modified after exposure to ants. These results suggest that Stegodyphus lineatus adapt its webbuilding behaviour in response to the risk of kleptoparasitism

Time till death affects spider mobility and web-building behavior during web construction in an orb-web spider

International audienceIt is well known that age influences organism mobility. This was demonstrated in vertebrates (such as mammals and birds) but has been less studied in invertebrates with the exception of Drosophila and the nematode Caenorhabditis elegans. Here we studied the influence of age on the mobility of the orb-weaving spider Zygiella x-notata during web construction. The orb-web is a good model because it has a characteristic geometrical structure and video tracking can be used to easily follow the spider's movements during web building. We investigated the influence of age (specifically chronological age, life span, and time till death) on different parameters of spider mobility during the construction of the capture spiral (distance traveled, duration of construction, spider velocity, spider movement, and spider inactivity) with a generalized linearmodel (GLM) procedure adjusted for the spidermass. The results showed that neither chronological age, nor life span affected the mobility parameters. However, when the time till death decreased, there was a decrease in the distance traveled, the duration of the construction of the capture spiral, and the spider movement. The spider velocity and the time of inactivity were not affected. These results could be correlated with a decrease in the length of the silky thread deposited for the construction of the capture spiral. Spiders with a shorter time till death built smaller web using less silk. Thus, our study suggests strongly that time till death affects spider mobility during web construction but not the chronological age and thus may be a good indicator of senescence

Aging and foraging efficiency in an orb-web spider

International audienceAging is often associated with reduced behavioral performance such as decreased locomotion or food consumption, related to a deterioration in physiological functions. In orb-web spiders, webs are used to capture prey and aging can affect web-building behavior and web structure. Here, we investigated the effect of aging on prey capture in the orb-web spider Zygiella x-notata. The ability of adult females to capture flies was examined at different ages. The rate of prey capture did not change with age, but older spiders took more time to subdue and capture the prey. Alterations which appeared in web structure with age (increase in the number of anomalies affecting radii and capture spiral) affected prey capture behavior. Furthermore, the analysis of individual performance (carried out on 17 spiders at two different ages) showed that older females spent more time handling the prey and finding it in the web. Our results suggest that, in the laboratory, age does not affect prey capture rates but it influences prey capture behavior by affecting web structure or/and spider motor functions