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- PublicationAccès libreFrom Parasitism to Mutualism: Unexpected Interactions Between a Cuckoo and Its Host(2014-3)
; ; - PublicationAccès libreChicks of the great spotted cuckoo may turn brood parasitism into mutualism by producing a foul-smelling secretion that repels predators(2014-4)
; ; - PublicationAccès libreBarrières linguistiques et communication dans une policlinique de médecine(2001)
; - PublicationAccès libreCoping 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. - PublicationRestriction temporaireEnvironmental gradients and the evolution of tri‐trophic interactions(2018-11-28)
; ; 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. - PublicationAccès libreSmall Emissions with Major Consequences: Specialized Malodorous Defenses in Birds(Switzerland: Springer International Publishing, 2016)
; - PublicationAccès libreEin Gesundheitsmonitoring von MigrantInnen: Sinnvoll ? Machbar ? Realistisch ?(2004)
; Die vorliegende Machbarkeitsstudie informiert über die Verwendbarkeit und Tauglichkeit von bestehenden Datenbanken für die Evaluation der Gesundheit von MigrantInnen und arbeitet verschiedene Szenarien zum Aufbau eines Monitorings des Gesundheitszustandes und –verhaltens von MigrantInnen aus. Szenario 1 schlägt vor, eine schon existierende Gesundheitsbefragung durch ein Modul migrationsspezifischer Fragen zu erweitern. Szenario 2 beinhaltet ein sogenanntes Patchwork-Monitoring, in dem schon bestehende Datenbanken migrationsspezifisch untersucht werden. Szenario 3 umfasst Entwicklung, Aufbau, Stichprobenbildung von fünf ausgewählten Migrationsgruppen und die Durchführung einer Gesundheitsbefragung von Personen mit Migrationshintergrund, unter besonderer Berücksichtigung migrationsspezifischer und sprachlich angepasster Fragenkataloge - PublicationAccès libreExperimental Growth Conditions affect Direct and Indirect Defences in two Cotton Species(2023)
; ; ; ; ; Cotton has been used as a model plant to study direct and indirect plant defence against herbivorous insects. However, the plant growing conditions could have an important effect on the outcome of such plant defence studies. We examined how common experimental growth conditions influence constitutive and inducible defences in two species of cotton, Gossypium hirsutum and G. herbaceum. We induced plants by applying caterpillar regurgitant to mechanical wounds to compare the induction levels between plants of both species grown in greenhouse or phytotron conditions. For this we measured defence metabolites (gossypol and heliocides) and performance of Spodoptera frugiperda caterpillars on different leaves, the emission of plant volatiles, and their attractiveness to parasitic wasps. Induction increased the levels of defence metabolites, which in turn decreased the performance of S. frugiperda larvae. Constitutive and induced defence levels were the highest in plants grown in the phytotron (compared to greenhouse plants), G. hirsutum and young leaves. Defence induction was more pronounced in plants grown in the phytotron and in young leaves. Also, the differences between growing conditions were more evident for metabolites in the youngest leaves, indicating an interaction with plant ontogeny. The composition of emitted volatiles was different between plants from the two growth conditions, with greenhouse-grown plants showing more variation than phytotron-grown plants. Also, G. hirsutum released higher amounts of volatiles and attracted more parasitic wasps than G. herbaceum. Overall, these results highlight the importance of experimental abiotic factors in plant defence induction and ontogeny of defences. We therefore suggest careful consideration in selecting the appropriate experimental growing conditions for studies on plant defences. - PublicationAccès libreCanopy gaps promote selective stem-cutting by small mammals of two dominant tree species in an African lowland forest: the importance of seedling chemistry(2016-1)
; Small mammals can impede tree regeneration by injuring seedlings and saplings in several ways. One fatal way is by severing their stems, but apparently this type of predation is not well-studied in tropical rain forest. Here, we report on the incidence of stem-cutting' to new, wild seedlings of two locally dominant, canopy tree species monitored in 40 paired forest understorey and gap-habitat areas in Korup, Cameroon following a 2007 masting event. In gap areas, which are required for the upward growth and sapling recruitment of both species, 137 seedlings of the long-lived, light-demanding, fast-growing large tropical tree (Microberlinia bisulcata) were highly susceptible to stem-cutting (83% of deaths) it killed 39% of all seedlings over a c. 2-y period. In stark contrast, seedlings of the more shade-tolerant, slower-growing tree species (Tetraberlinia bifoliolata) were hardly attacked (4.3%). In the understorey, however, stem-cutting was virtually absent. Across the gap areas, the incidence of stem-cutting of M. bisulcata seedlings showed significant spatial variation that could not be explained significantly by either canopy openness or Janzen-Connell type effects (proximity and basal area of conspecific adult trees). To examine physical and chemical traits that might explain the species difference to being cut, bark and wood tissues were collected from a separate sample of seedlings in gaps (i.e. not monitored for stem-cutting). These analyses suggested that, compared with T. bifoliolata, the lower stem density, higher Mg and K and fatty acid concentrations in bark, and fewer phenolic and terpene compounds in M. bisulcata seedlings made them more palatable and attractive to small-mammal predators, likely rodents. We conclude that selective stem-cutting is a potent countervailing force to the current local canopy dominance of the grove-forming M. bisulcata by limiting the recruitment and abundance of its saplings. Given the ubiquity of gaps and ground-dwelling rodents in pantropical forests, it would be surprising if this form of lethal browsing was restricted to Korup. - PublicationRestriction temporaireThe combined use of an attractive and repellent sex pheromonal component by a gregarious parasitoid(2019-3-28)
; ; ; ; ; Gregarious parasitoids usually clump their cocoons together and the adults emerge in a synchronized fashion. This makes it easy for them to find mating partners and most copulations indeed take place at the natal patch. Yet, males should leave such sites when females are no longer receptive. As yet, this decision-making process and the possible involvement of pheromones were poorly understood. Here we report on a remarkable use of attractive and repellent pheromones of the well-studied gregarious parasitoid species Cotesia glomerata (L.) (Hymenoptera: Braconidae). Virgin C. glomerata females were found to release an attractive as well as a repellent compound, which in combination arrest males on the natal patch, but after mating the females stop the production of the attractant and the males are repelled. The repellent compound was identified as heptanal, which was also released by males, probably reducing male-male competition on the natal patch. We also confirmed that the sex ratio of the emerging wasps can vary considerably among patches, depending on the relative quality of hosts and the number of females that parasitize a host. The newly revealed use of attractive and repellent pheromone compounds by C. glomerata possibly helps maximize mating success under these variable conditions.
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