Voici les éléments 1 - 10 sur 29
  • Publication
    Restriction temporaire
    Environmental gradients and the evolution of tri‐trophic interactions
    Long‐standing theory predicts herbivores and predators should drive selection for increased plant defences, such as the specific production of volatile organic compounds for attracting predators near the site of damage. Along elevation gradients, a general pattern is that herbivores and predators are abundant at low elevation and progressively diminish at higher elevations. To determine whether plant adaptation along such a gradient influences top‐down control of herbivores, we manipulated soil predatory nematodes, root herbivore pressure and plant ecotypes in a reciprocal transplant experiment. Plant survival was significantly higher for low‐elevation plants, but only when in the presence of predatory nematodes. Using olfactometer bioassays, we showed correlated differential nematode attraction and plant ecotype‐specific variation in volatile production. This study not only provides an assessment of how elevation gradients modulate the strength of trophic cascades, but also demonstrates how habitat specialisation drives variation in the expression of indirect plant defences.
  • Publication
    Accès libre
    Chicks of the great spotted cuckoo may turn brood parasitism into mutualism by producing a foul-smelling secretion that repels predators
    (2014-4) ;
    Canestrari, Daniela
    ;
    Bolopo, Diana
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    Marcos, José M.
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    ;
    Baglione, Vittorio
    ;
    The great spotted cuckoo (Clamator glandarius) is an important brood parasite of carrion crows (Corvus corone corone) in northern Spain. We recently found that, unlike what is commonly known for cuckoo-host interactions, the great spotted cuckoo has no negative impact on average crow fitness in this region. The explanation for this surprising effect is a repulsive secretion that the cuckoo chicks produce when they are harassed and that may protect the brood against predation. Here, we provide details on the chemical composition of the cuckoo secretion, as well as conclusive evidence that the dominating volatile chemicals in the secretion are highly repellent to model species representative of common predators of the crows. These results support the notion that, in this particular system, the production of a repulsive secretion by the cuckoo chicks has turned a normally parasitic interaction into a mutualistic one.
  • Publication
    Accès libre
    Do induced responses mediate the ecological interactions between the specialist herbivores and phytopathogens of an alpine plant?
    (2011-5) ; ;
    Naisbit, Russell E
    Plants are not passive victims of the myriad attackers that rely on them for nutrition. They have a suite of physical and chemical defences, and are even able to take advantage of the enemies of their enemies. These strategies are often only deployed upon attack, so may lead to indirect interactions between herbivores and phytopathogens. In this study we test for induced responses in wild populations of an alpine plant (Adenostyles alliariae) that possesses constitutive chemical defence (pyrrolizidine alkaloids) and specialist natural enemies (two species of leaf beetle, Oreina elongata and Oreina cacaliae, and the phytopathogenic rust Uromyces cacaliae). Plants were induced in the field using chemical elicitors of the jasmonic acid (JA) and salicylic acid (SA) pathways and monitored for one month under natural conditions. There was evidence for induced resistance, with lower probability and later incidence of attack by beetles in JA-induced plants and of rust infection in SA-induced plants. We also demonstrate ecological cross-effects, with reduced fungal attack following JA-induction, and a cost of SA-induction arising from increased beetle attack. As a result, there is the potential for negative indirect effects of the beetles on the rust, while in the field the positive indirect effect of the rust on the beetles appears to be over-ridden by direct effects on plant nutritional quality. Such interactions resulting from induced susceptibility and resistance must be considered if we are to exploit plant defences for crop protection using hormone elicitors or constitutive expression. More generally, the fact that induced defences are even found in species that possess constitutively-expressed chemical defence suggests that they may be ubiquitous in higher plants.
  • Publication
    Accès libre
    Barrières linguistiques et communication dans une policlinique de médecine
    (2001) ;
    Loutan, Louis
    ;
    Stalder, Hans
    Wie steht es mit der Verantwortung, sich mit dem Gesprächspartner communis – «gemein» – zu machen, wenn der fremdsprachig ist? Wie wird die Verantwortung für die Kommunikation wahrgenommen, wenn Sprachbarrieren bestehen? Und wie sieht diese Verantwortung im Gesundheitsbereich aus? Im Universitätsspital Genf wurde dies im Rahmen eines Pflegequalitäts-Projektes untersucht. Die Studie zeigt, dass Französisch nur in 36% aller Fälle die Muttersprache der Patienten war, welche die medizinische Poliklinik während zwei Monaten (1999) aufsuchten. Zudem sprach mehr als ein Drittel der Patienten, entsprechend den Angaben der Ärzte, nicht fliessend französisch. Die Auswertung der von Patienten und Ärzten ausgefüllten Fragebogen ergab folgende Resultate: Fremdsprachige Patienten bewerteten die Kommunikation in der Sprechstunde dann am besten, wenn ein qualifizierter Dolmetscher zugegen war, weniger gut, wenn auf eine Drittsprache ausgewichen wurde, und noch weniger gut, wenn Patientenangehörige Ad-hoc-Übersetzungsdienste verrichteten. Auf der Ärzteseite wird die Kommunikation mit französisch sprechenden Patienten durchwegs besser bewertet. Was die Kommunikation mit fremdsprachigen Patienten angeht, werden oft höhere Bewertungen der Kommunikation angegeben, wenn der Arzt allein dem Patienten gegenübersitzt (d.h. also eine «Verkehrsprache» benützt), im Durchschnitt jedenfalls höher als wenn ein Dolmetscher anwesend ist. Am wenigsten gut kam auch hier, und zwar mit weit grösseren Unterschieden, die Kommunikation mittels Angehöriger weg. Die Zufriedenheit der Ärzte mit den qualifizierten Dolmetschern war sehr gross (8,8 im Durchschnitt, bei einer Skala von 1-10).
  • Publication
    Accès libre
    Coping with an antagonist: the impact of a phytopathogenic fungus on the development and behaviour of two species of alpine leaf beetle
    (2007) ; ;
    Naisbit, Russell. E.
    Herbivorous insects and phytopathogenic fungi often share their host plants. This creates a network of direct and indirect interactions, with far-reaching consequences for the ecology and evolution of all three parties. In the Alps, the leaf beetles Oreina elongata and Oreina cacaliae (Coleoptera: Chrysomelidae), and the rust fungus Uromyces cacaliae (Uredinales: Pucciniaceae) are found on the same host plant, Adenostyles alliariae (Asterales: Asteraceae). We compare the impact of rust infection on these two closely-related beetle species, one of which, O. cacaliae, is a specialist on A. alliariae, while the other, O. elongata, moves repeatedly between Adenostyles and an alternative host, Cirsium spinosissimum. Larval performance, feeding preference, oviposition choice and dispersal behaviour were studied in field and laboratory experiments. When reared on rust-infected leaves, larvae of both beetle species had lower growth rates, lower maximum weights and longer development times. Larvae and adults discriminated among diets in feeding trials, showing a preference for discs cut from healthy leaves over those bearing a patch of sporulating rust, those from elsewhere on an infected leaf, and those from an upper leaf on an infected plant. Females of the two species differed in behaviour: in O. cacaliae they favoured healthy leaves for larviposition, while in O. elongata they showed no significant preference during oviposition. In the field, larvae and adults of both species dispersed more rapidly when placed on infected host plants. The results demonstrate that rust infection reduces the quality of the plant as a host for both Oreina species, and they combine the ability to detect systemic infection with the evolution of evasive behaviours. For these beetles, competition with a rust clearly increases the difficulty of survival in the harsh conditions of alpine environments, and may have a profound impact on the evolution of their life history traits and host plant use.
  • Publication
    Accès libre
    Formal comment to Soler et al.: Great spotted cuckoo nestlings have no antipredatory effect on magpie or carrion crow host nests in southern Spain
    (2017-9-18)
    Canestrari, Daniela
    ;
    Bolopo, Diana
    ;
    ; ;
    Marcos, José
    ;
    Baglione, Vittorio
    Replicating research is crucial to assess the generality of findings. Yet, in ecology, the complexity of data collection and experimentation often precludes the possibility of going beyond single–population studies. The study by Soler et al. is therefore most welcome, as it provides new insights on the possible role of great spotted cuckoo in protecting the nest of its corvid hosts. In a previous article, we suggested a mechanism based on the malodorous secretion of great spotted cuckoo chicks to explain why the presence of the parasite in the nests of carrion crows in northern Spain increased the probability of nest success (i.e. fledging at least one host chick) as compared to non-parasitized nests. Soler et al. found no evidence supporting an anti-depredatory function of cuckoo chicks in their studied populations and proposed an alternative mechanism that may explain our experimental results. Here we would like to address a) the differences between the results of the two studies and b) the proposed interpretation of our translocation experiment. We will also respond to the concerns raised by Soler et al. on some of the analyses presented in our paper.
  • Publication
    Métadonnées seulement
    Nests, Floral Preferences, and Immatures of the Bee Haetosmia vechti (Hymenoptera: Megachilidae: Osmiini)
    (2014-7-21)
    Gotlieb, Ariella
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    Pisanty, Gideon
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    Rozen, Jerome G, Gideon
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    Mueller, Andreas
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    Sedivy, Claudio
    ;
    Herein we describe the nests (including structure, closure, orientation, and depth of cells) of the bee Haetosmia vechti Peters found nesting in Rehovot, Israel. The nesting biology of H. vechti mirrors the ancestral nesting biology within the Osmia group of the Osmiini. Nests in sandy soil consist of an excavated burrow, ending below in a small cluster of vertical cells. The cells possess firm walls of masticated leaf pulp of Centaurea procurrens Spreng. and Heliotropium suaveolens M. Bieb., and are covered with pebbles and sand grains. The last larval instar and pupa of Haetosmia vechti are described, as is its cocoon. The "immature stages exhibit the basic features of megachilid bees, but tend to have a thinner body vestiture compared to other studied taxa. In addition, we report new information on and review published accounts concerning the pollen collecting behavior of the genus Haetosmia Popov, which contains three species. Pollen taken from scopal hairs of 68 females collected at 17 sites in Turkestan, Morocco, Israel, and the United Arab Emirates was identified as originating solely from Heliotropium L. (Boraginaceae), which strongly suggests that all three Haetosmia species are narrowly oligolectic on this plant genus. In females of all three species, the second segment of the labial palpus is densely covered with rather long, apically curved and capitate bristles, an adaptation to collect Heliotropium pollen from anthers that are hidden inside the narrow corolla tube. Similar pollen-harvesting bristles specifically adapted to exploit flowers of He/iotropium seem to have evolved independently a number of times on different continents, in bees of four families.
  • Publication
    Accès libre
    Insights into the encapsulation process of photovoltaic modules: GCMS analysis on the curing step of poly(ethylene-co-vinyl acetate) (EVA) encapsulant
    (2012)
    Heng-Yu, L.
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    Théron, R
    ;
    ; ;
    Lange, R.F.M.
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    Ballif, C.
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    Perret-Aebi, L.-E.
    Appropriate encapsulation schemes are essential in protecting the active components of the photovoltaic (PV) module against weathering and to ensure long term reliability. For crystalline cells, poly(ethylene-co-vinyl acetate) (EVA) is the most commonly used PV encapsulant. Additives like peroxides and silanes are formulated in EVA encapsulants to obtain the desired properties, e.g. the desired gel content value and sufficient adhesion after the encapsulation process etc. The identification and control of volatile organic compounds (VOCs) released by the polymeric encapsulant during PV module encapsulation is important for understanding and optimizing processes in order to enhance the encapsulation quality of the manufactured modules. The authors demonstrate how gas chromatography and mass spectrometry (GC-MS) techniques can be used to help understand the curing process, mainly by identifying the VOCs emanating from EVA under the effect of temperature and pressure. The results provide chemical insights into the EVA encapsulation process, which are valuable for further optimisation of the PV module manufacturing process and evaluation of its environmental impact. 26 Refs.