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

Influence of the Stereochemical Structure on The Physicochemical Properties of Polymers Prepared by Ring-Opening Polymerization of Chiral Heterocyclic Monomers

Physico-chemical properties of polymers prepared by ringopening polymerization of heterocyclic chiral monomers with different enantiomeric composition are compared. Two general kinds of behaviour were observed for products with a monosubstituted carbon in the chain: when the substituent group is not bulky the properties of polyenantiomers and their racemic mixture are very similar ; when the substituent is a bulky group, e. g. t-butyl, many of the properties (m.p., crystalline structure, solubility, etc.) are very different for the same polymers. The corresponding statistical stereocopolymers are amorphous. For polymers with disubstituted asymmetric carbon atoms the statistical stereocopolymers are crystalline and their melting behaviour varies with the enantiomeric purity. In some cases a strong dependence of the mechanical and biological properties on the enantiomeric purity of stereocopolymers is reported

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

Robust similarity between hypergraphs based on valuations and mathematical morphology operators

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Similarity between Hypergraphs Based on Mathematical Morphology

International audienceIn the framework of structural representations for applications in image understanding, we establish links between similarities, hypergraph theory and mathematical morphology. We propose new similarity measures and pseudo-metrics on lattices of hypergraphs based on morphological operators. New forms of these operators on hypergraphs are introduced as well. Some examples based on various dilations and openings on hypergraphs illustrate the relevance of our approach

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

Les minivis orthodontiques (indications et bilan pré-chirurgical)

Les minivis fournissent un ancrage squelettique stable pour corriger la majorité des malocclusions et permettent la réalisation de mouvements orthodontiques complexes, tout en supprimant les effets parasites sur les dents voisines. Un plan de traitement doit être établi par l'orthodontiste afin de déterminer le site d'insertion idéal pour une traction orthodontique optimale. Le chirurgien-dentiste posant les minivis choisit alors leurs dimensions, suite à une analyse des structures anatomiques voisines. L'insertion se fait sous anesthésie locale, la procédure chirurgicale est simple grâce à un bilan pré-chirurgical correctement mené, diminuant le risque de complications per ou post-opératoires.NANTES-BU Médecine pharmacie (441092101) / SudocNANTES-Bib.Odontologie (441092219) / SudocSudocFranceF