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Rahier, Martine

Nom
Rahier, Martine
Affiliation principale
Fonction
Professeure ordinaire
Email
Martine.Rahier@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/99

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  • Publication
    Accès libre
    Counter-intuitive developmental plasticity induced by host quality
    (2007)
    Röder, Gregory 
    ;
    Rahier, Martine 
    ;
    Naisbit, Russell. E.
    Adaptation to different hosts plays a central role in the evolution of specialization and speciation in phytophagous insects and parasites, and our ability to experimentally rank hosts by their quality is critical to research to understand these processes. Here we provide a counter-intuitive example in which growth is faster on poor quality hosts. The leaf beetles Oreina elongata and Oreina cacaliae share their host plant with the rust Uromyces cacaliae. Larvae reared on infected Adenostyles alliariae show reduced growth rate, reduced maximum weight and longer development time. However, they normally respond adaptively to the rust's mid-season arrival. When switched during development from healthy to infected leaves, larvae accelerate growth and reduce development time, but pupate at lower body weight. In this novel plant–insect–fungus interaction, infection forms the cue to trade off life-history traits in order to complete development within the brief alpine summer. It represents a novel mode of developmental plasticity, which is likely to be found in other host–parasite systems whenever host quality deteriorates due to multiple infection or ageing. This phenotypic plasticity would modify competition after co-infection and the mutual selection imposed by hosts and parasites, and creates a paradoxical negative correlation between growth rate and environmental quality.
  • Publication
    Accès libre
    Ecological interactions between two species of leaf beetle, a rust fungus, and their host plant
    (2007)
    Röder, Gregory 
    ;
    Rahier, Martine 
    Les champignons parasites et les insectes herbivores sont connus pour leur influence négative sur les populations de plantes, affectant leur reproduction, leur croissance, leur survie, et interférant dans leurs relations avec d’autres espèces. En fournissant un logement, une protection et une source de nourriture pour de nombreux organismes, les végétaux représentent un élément essentiel des écosystèmes terrestres dans lesquels ils permettent la rencontre d’organismes aussi différents que des champignons pathogènes et des insectes phytophages. Les relations triangulaires qui naissent de cette proximité peuvent être directes ou indirectes lorsque la plante hôte joue le rôle de médiateur. Les insectes peuvent se nourrir du champignon ou de l’une de ses parties, comme le mycélium ou les structures reproductrices, et de ce fait réduire l’ampleur de l’infection ou de la transmission de la maladie. En revanche, d’autres espèces sont susceptibles de véhiculer des spores infectieuses et d’inoculer de nouvelles plantes. Ici, les champignons et les insectes s’influencent directement, positivement ou négativement, mais leurs relations deviennent indirectes lorsqu’ils engendrent des perturbations chez leur hôte. Une attaque fongique est susceptible de produire des changements dans la qualité de la plante hôte, mais aussi d’y activer des résistances qui peuvent également agir sur les insectes, grâce à des mécanismes de défenses croisés. Ainsi, les plantes participent activement à ces relations en mettant en oeuvre des défenses permanentes ou activables, impliquant des structures morphologiques, des substances chimiques internes ou externes, leur phénologie, ou des stratégies de tolérance. Ce travail est centré sur l’étude des relations directes et indirectes entre la plante Adenostyles alliariae, la rouille Uromyces cacaliae, et deux chrysomèles alpines Oreina elongata et Oreina cacaliae. Dans leur environnement naturel, régit par des conditions difficiles, leur relation prend une importance particulière, principalement due à une période d’activité très courte, mais aussi à cause de la stratégie de défense des chrysomèles alpines, impliquant des composés secondaires (pyrrolizidine alcaloïdes) produits par la plante et séquestrés par ces insectes pour leur propre défense. Dans ce contexte, le nombre de conséquences possibles est accru. L’influence de chacun des protagonistes sur les deux autres fut observée à l’aide d’expériences combinées entre le terrain, le laboratoire, et l’analyse de composés chimiques. Quatre sites différents furent choisis au sein les Alpes suisses et italiennes. Les résultats montrent que des interactions triangulaires influencent nos rotagonistes, avec des effets sur leur comportement, leur phénologie, leur cycle de vie, leurs performances, leur distribution et la dynamique de leurs populations. Ces conséquences sont majoritairement négatives et les rares effets positifs ne fournissent pas d’explication valable à l’apparente continuité de ce système. Néanmoins, un mélange de défenses, d’évitement et de tolérance entre les membres de ce système semble être à la base de leur coexistence., Independently, both fungal disease and herbivorous insects are considered to have major impacts on plant populations, affecting growth, survival, and reproduction, as well as modifying their interactions with other species. By providing habitats, protection, and food for numerous species, plants form an essential component of terrestrial ecosystems and constitute the convergent point for interactions between many groups, including plant pathogenic fungi and phytophagous insects. The three-way interactions resulting from this junction may be direct, plant-mediated, or both. Insects can feed on fungal mycelia and reproductive structures, reducing the infection and its transmission, or transport infectious spores to inoculate new plants. Fungi and insects exercise an influence, positive or negative, directly on each other. The relationships can be indirect if attack transforms the host plant, such as when fungal infection induces plant resistance against fungal attack, but in doing so also induces defences against herbivores by cross-effect mechanisms, and produces changes in host plant quality. The plants participate actively through their permanent and induced defences, involving morphological structures, internal, external, and emitted chemical compounds, phenology, or tolerance. This study focus on the direct and indirect interactions between the host plant Adenostyles alliariae, systemic infections of the rust Uromyces cacaliae, and attacks by the alpine leaf beetles Oreina elongata and Oreina cacaliae. In the harsh conditions of their high alpine habitats, their relations are likely to be particularly intense, due to the very short period of activity as well as to the specificity of the defence strategy used by the Oreina leaf beetles. The involvement of pyrrolizidine alkaloids (PAs), secondary compounds produced by the plant and sequestered by the leaf beetles for their own defence, increases the potential consequences of these three-way interactions beyond those typically considered. Field trials in four populations across the Swiss and Italian Alps were combined with laboratory experiments and chemical analyses to examine the influence of each protagonist on the others. The results show that the tripartite interactions affect all three participants, with implications for their behaviour, phenology, life cycle, fitness, population dynamics, and distribution. Negative impacts seem to prevail, while concrete positive interactions are weak and not sufficient to explain the apparent continuity of this system. Nonetheless, a mix of defences, avoidance and tolerance to the presence of the other members seems to be basis of their coexistence.
  • Publication
    Accès libre
    A quantitative genetic analysis of leaf beetle larval performance on two natural hosts: including a mixed diet
    (2001)
    Ballabeni, Pierluigi
    ;
    Rahier, Martine 
    Published quantitative genetic studies of larval performance on different host plants have always compared performance on one host species or genotype vs. performance on another species or genotype. The fact that some insects may feed on more than one plant species during their development has been neglected. We executed a quantitative genetic analysis of performance with larvae of the leaf beetle Oreinaelongata, raised on each of two sympatric host plants or on a mixture of them. Growth rate was higher for larvae feeding on Adenostylesalliariae, intermediate on the mixed diet and lowest on Cirsium spinosissimum. Development time was shortest on A. alliariae, intermediate on mixed diet and longest on C. spinosissimum. Survival was higher on the mixed diet than on both pure hosts. Genetic variation was present for all three performance traits but a genotype by host interaction was found only for growth rate. However, the reaction norms for growth rate are unlikely to evolve towards an optimal shape because of a lack of heritability of growth rate in each single environment. We found no negative genetic correlations for performance traits among hosts. Therefore, our results do not support a hypothesis predicting the existence of between-host trade-offs in performance when both hosts are sympatric with an insect population. We conclude that the evolution of host specialized genotypes is unlikely in the study population.
  • Publication
    Accès libre
    Performance of leaf beetle larvae on sympatric host and non-host plants
    (2000)
    Ballabeni, Pierluigi
    ;
    Rahier, Martine 
    Studies asking the ability of insects to utilize novel host plants often use novel hosts that are allopatric with the insect population under investigation. However, since the outcomes of species interactions are often site-specific, such studies cannot tell us whether a plant would actually be used by a given insect population if the plant grew sympatrically with it. We therefore performed a quantitative genetics experiment to analyse the performance of larvae of the leaf beetle Oreina elongata Suffrian (Coleoptera: Chrysomelidae, Chrysomelinae) on two host and three non-host plants, collected from a site where insects and plants co-occur in the Western Alps. When raised on the non-host Petasites albus (L.), larvae were able to survive equally well as on the two hosts, Adenostyles alliariae (Gouan) and Cirsium spinosissimum (L.), whereas they did not survive on the two other non-hosts, Peucedanum ostruthium (L.) and Rumex alpinus L. On P. albus, growth rate was slightly lower and development time slightly longer than on the two hosts. We found a genotype by environment interaction only for growth rate but not for development time and survival. However, the shape of the reaction norms of growth rates suggests that it is unlikely that selection could favour the inclusion of P. albus into the host range of the study population.Studies asking the ability of insects to utilize novel host plants often use novel hosts that are allopatric with the insect population under investigation. However, since the outcomes of species interactions are often site-specific, such studies cannot tell us whether a plant would actually be used by a given insect population if the plant grew sympatrically with it. We therefore performed a quantitative genetics experiment to analyse the performance of larvae of the leaf beetle Oreina elongata Suffrian (Coleoptera: Chrysomelidae, Chrysomelinae) on two host and three non-host plants, collected from a site where insects and plants co-occur in the Western Alps. When raised on the non-host Petasites albus (L.), larvae were able to survive equally well as on the two hosts, Adenostyles alliariae (Gouan) and Cirsium spinosissimum (L.), whereas they did not survive on the two other non-hosts, Peucedanum ostruthium (L.) and Rumex alpinus L. On P. albus, growth rate was slightly lower and development time slightly longer than on the two hosts. We found a genotype by environment interaction only for growth rate but not for development time and survival. However, the shape of the reaction norms of growth rates suggests that it is unlikely that selection could favour the inclusion of P. albus into the host range of the study population.Studies asking the ability of insects to utilize novel host plants often use novel hosts that are allopatric with the insect population under investigation. However, since the outcomes of species interactions are often site-specific, such studies cannot tell us whether a plant would actually be used by a given insect population if the plant grew sympatrically with it. We therefore performed a quantitative genetics experiment to analyse the performance of larvae of the leaf beetle Oreina elongata Suffrian (Coleoptera: Chrysomelidae, Chrysomelinae) on two host and three non-host plants, collected from a site where insects and plants co-occur in the Western Alps. When raised on the non-host Petasites albus (L.), larvae were able to survive equally well as on the two hosts, Adenostyles alliariae (Gouan) and Cirsium spinosissimum (L.), whereas they did not survive on the two other non-hosts, Peucedanum ostruthium (L.) and Rumex alpinus L. On P. albus, growth rate was slightly lower and development time slightly longer than on the two hosts. We found a genotype by environment interaction only for growth rate but not for development time and survival. However, the shape of the reaction norms of growth rates suggests that it is unlikely that selection could favour the inclusion of P. albus into the host range of the study population.