Vignette d'image

Rahier, Martine

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

Résultat de la recherche

Filtres

4
4
4
Réinitialiser les filtres

Paramètres

Voici les éléments 1 - 4 sur 4
  • Publication
    Accès libre
    Geographic variation in oviposition choice of a leaf beetle: the relationship between host plant ranking, specificity, and motivation
    (2007)
    Gotthard, Karl
    ;
    Margraf, Nicolas
    ;
    Rahier, Martine 
    The degree of adaptation of herbivorous insects to their local flora is an important component of the evolutionary processes that lead to host plant specialization in insects. In this study we investigated geographic variations in the oviposition preference of the leaf beetle Oreina elongata Suffrian (Coleoptera: Chrysomelidae: Chrysolini) in relation to differences in host plant specialization, in the field. We focused on the mechanisms of host choice and asked whether potential differences among populations are due to variations in host plant ranking and/or host plant specificity. We performed a combination of simultaneous choice and sequential no-choice experiments with two of the major host plants of the beetle [Cirsium spinosissimum (L.) and Adenostyles alliariae (Gouan) (Asteraceae)]. The results suggested that spatial variation in host plant specialization has resulted in differences between populations in some aspects of the oviposition choice of O. elongata, while other aspects seem unaffected. We found no variation in host plant ranking among populations, as estimated in simultaneous choice tests. In contrast, the sequential no-choice test indicated that host plant specificity was lower in a population that never encountered the highest ranked plant in the field. This finding agreed with our expectations, and we discuss our results in relation to the commonly used hierarchical threshold model. The results suggested that the mechanism for the differences in specificity is the variation among populations in the general motivation to oviposit, rather than quantitative differences in relative preference for the two hosts. We stress that it is essential to establish which of the two mechanisms is most important, as it will affect the probability of evolutionary change in host plant ranking.
  • Publication
    Accès libre
    The evolution of larval foraging behaviour in response to host plant variation in a leaf beetle
    (2005)
    Gotthard, Karl
    ;
    Margraf, Nicolas
    ;
    Rasmann, Sergio 
    ;
    Rahier, Martine 
    The evolutionary causes of variation in host specialization among phytophagous insects are still not well understood and identifying them is a central task in insect–host plant biology. Here we examine host utilization of the chrysomelid beetle Oreina elongata that shows interpopulation variation in the degree of specialization. We focus on larval behaviour and on what selection pressures may favour the use of two different larval host plants (Adenostyles alliariae and Cirsium spinosissimum) in one population as opposed to specialization onto one of them as is seen in other populations. The results suggest that the degree of exploratory foraging behaviour is higher in larvae from the two-host population than in single host populations, and a field survey of the two-host population also indicated that larvae do move between host species. A field experiment indicated that predation rates on O. elongata larvae in the two-host population are higher on one of the host species, A. alliariae, than on the alternative C. spinosissimum. In combination with earlier results this finding suggest that larvae move between hosts to obtain better food on one host, and to get better protection from predators on the other. It appears that in this two-host situation a single plant species does not provide the most beneficial conditions in all parts of O. elongata life cycle and individuals may obtain different plant-specific benefits by moving between host species. This heterogeneous host situation appears to have selected for the explorative larval foraging strategy seen in the in the two-host population. In general, the results support the notion that to understand patterns of host plant use in insects it is often vital to consider a range of host related selection pressures whose relative importance may vary between life stages of the insect.
  • Publication
    Accès libre
    The growth strategy of an alpine beetle: maximization or individual growth adjustment in relation to seasonal time horizons ?
    (2003)
    Margraf, Nicolas
    ;
    Gotthard, Karl
    ;
    Rahier, Martine 
    1. Life-history theory typically predicts that juvenile growth rate should be maximized and consequently juvenile period minimized. However, in several examples it has been shown that insect larvae do not always grow as fast as they can and this has been explained by costs of high growth rate, typically higher juvenile mortality rate. Hence, some insect larvae have the ability to adaptively adjust growth rate to catch up if development is delayed.
    2. The presence of such ability was tested for in the alpine beetle Oreina elongata Suffrian. In this species, the favourable period for development is relatively short and of unpredictable length, and individuals are chemically defended against predation; factors that could affect the balance between the benefits and costs of high growth rate.
    3. Here it is shown that when time stressed, O. elongata larvae were able to increase growth rate, accelerate development and reach the normal final weight.
    4. Hence, individual growth rate adjustment was present in a situation where its adaptive value appeared to be relatively weak, which supports the notion that flexible growth strategies are a common phenomenon in temperate insects.
  • Publication
    Accès libre
    Local adaptation and ecological genetics of host-plant specialization in a leaf beetle
    (2003)
    Ballabeni, Pierluigi
    ;
    Gotthard, Karl
    ;
    Kayumba, Aline
    ;
    Rahier, Martine 
    The tendency of insect species to evolve specialization to one or a few plant species is probably a major reason for the remarkable diversity of herbivorous insects. The suggested explanations for this general trend toward specialization include a range of evolutionary mechanisms, whose relative importance is debated. Here we address two potentially important mechanisms: (i) how variation in the geographic distribution of host use may lead to the evolution of local adaptation and specialization; (ii) how selection for specialization may lead to the evolution of trade-offs in performance between different hosts. We performed a quantitative genetic experiment of larval performance in three different populations of the alpine leaf beetle Oreina elongata reared on two of its main host plants. Due to differences in host availability, each population represents a distinctly different selective regime in terms of host use including selection for specialization on one or the other host as well as selection for utilizing both hosts during the larval stage.
    The results suggest that selection for specialization has lead to some degree of local adaptations in host use: both single-host population had higher larval growth rate on their respective native host plant genus, while there was no difference between plant treatments in the two-host population. However, differences between host plant treatments within populations were generally small and the degree of local adaptation in performance traits seems to be relatively limited. Genetic correlations in performance traits between the hosts ranged from zero in the two-host population to significantly positive in the single-host populations. This suggests that selection for specialization in single host populations typically also increased performance on the alternative host that is not naturally encountered. Moreover, the lack of a positive genetic correlation in the two host-population give support for the hypothesis that performance trade-offs between two host plants may typically evolve when a population have adapted to both these plants. We conclude that although there is selection for specialization in larval performance traits it seems as if the genetic architecture of these traits have limited the divergence between populations in relative performance on the two hosts.