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

3
3
3
Réinitialiser les filtres

Paramètres

Voici les éléments 1 - 3 sur 3
  • Publication
    Accès libre
    Conserved oviposition preferences in alpine leaf beetle populations despite host shifts and isolation
    (2007)
    Verdon, Aline
    ;
    Margraf, Nicolas
    ;
    Davison, Anthony C.
    ;
    Rahier, Martine 
    ;
    Naisbit, Russell. E.
    1. Choosing the plant on which to lay their eggs is the last act of care that most female herbivorous insects bestow upon their offspring. These decisions play a pivotal role in insect–plant interactions, placing host preference under strong selection and contributing to the diversity of phytophagous insects as one of the first traits to adapt to new hosts.
    2. This study presents a test of whether extreme isolation and exposure to different host plants can produce intra-specific divergence in oviposition preference in alpine insects. Geographic variation should impose selection to fine-tune host plant ranking and specificity to the plants normally encountered, to avoid wasting time during the very limited reproductive season experienced at high altitudes.
    3. Beetles from five populations of Oreina elongata differing in host availability were offered three natural hosts: Cirsium spinosissimum, Adenostyles alliariae, and Adenostyles glabra. A novel application of a continuation ratio model (logistic regression) was made to sequential no-choice experiments, combined with quasi-likelihood analysis of multiple-choice experiments.
    4. The results show little geographic variation in host plant choice: all populations strongly preferred Cirsium in multiple-choice trials, and in no-choice experiments laid around 47% of their remaining eggs during each stage, almost regardless of the host present.
    5. Enemy-free space seems to explain the preference for Cirsium, but isolation and exposure to different plants has clearly not caused local adaptation in host plant ranking or specificity. Reasons for this conservatism despite divergence in other characteristics are discussed.
  • 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
    Isolation and characterization of microsatellite loci in the Alpine leaf beetle, Oreina elongata
    (2005)
    Margraf, Nicolas
    ;
    Gautschi, B.
    ;
    Rahier, Martine 
    For a study of local adaptations in the Alpine leaf beetle, Oreina elongata, we developed six microsatellite loci and screened them in 305 individuals from 13 populations. All markers were polymorphic with three to 15 alleles per locus. Average observed and expected heterozygosity values were 0.14 and 0.62, respectively. Four markers showed heterozygote deficiency and deviated significantly from Hardy–Weinberg expectations, indicating the presence of null alleles.