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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
    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
    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
    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.
  • Publication
    Accès libre
    An alternative hibernation strategy involving sun-exposed 'hotspots', dispersal by flight, and host plant finding by olfaction in an alpine leaf beetle
    (2005)
    Kalberer, Nicole M.
    ;
    Turlings, Ted 
    ;
    Rahier, Martine 
    Oreina cacaliae (Schrank) (Coleoptera: Chrysomelidae) has a 2-year life cycle that it has to complete within the short warm seasons of the harsh alpine environment. Three years of field observations and experiments revealed that not all beetles overwintered in the soil next to their principal host Adenostyles alliariae (Asteraceae), as was previously assumed, but that many O. cacaliae left their host in autumn and flew to overwintering sites that were extensively sun-exposed. In spring, these individuals became active 2 months earlier than their conspecifics that had remained in the soil close to the host plant. These early beetles flew from their hibernation sites against the direction of the prevailing wind. After a random landing in snow, they walked to the spring host Petasites paradoxus (Asteraceae) and fed on its floral stalks, the only plant parts present at that time. A few weeks later, they took flight again to locate newly emerging A. alliariae on which they would feed and deposit larvae as did individuals that had overwintered close to A. alliariae. Leaves of A. alliariae contain pyrrolizidine alkaloids (PAs), which the beetles sequester for their own defence. The dominating PA (seneciphylline) was also found to be present in the floral stalks of P. paradoxus. With additional behavioural assays in the field and laboratory, we demonstrated the importance of plant odours in the short-range host location process. This study reveals a unique hibernation behaviour in which part of the beetle population uses exceptionally warm locations from which they emerge in spring, long before all the snow has melted. This early, but risky emergence allows them to exploit a second, highly suitable host plant, which they locate first by wind-guided flight and then by odour-guided walking. The well-fed beetles then use odour again to move to their principal host plant, on which they reproduce.
  • Publication
    Accès libre
    Flight polymorphism observed in an alpine leaf beetle and associated costs
    (Pensoft Publishers, 2003)
    Kalberer, Nicole M.
    ;
    Rahier, Martine 
  • Publication
    Accès libre
    Attraction of a Leaf Bettle (Oreina cacaliae) to Damaged Host Plants
    (2001)
    Kalberer, Nicole M.
    ;
    Rahier, Martine 
    ;
    Turlings, Ted 
    Early in spring, just after the snow melts, the leaf beetle Oreina cacaliae feeds on flowers of Petasites paradoxus. Later in spring they switch to their principle host plant Adenostyles alliariae. The attractiveness of short- and long-term damaged host plants was studied in a wind tunnel. The spring host P. paradoxus was more attractive to the beetles after it had been damaged overnight by conspecifics or artificially, but not when the plants were damaged half an hour before the wind-tunnel experiments. Contrary to P. paradoxus, the principle host plant, A. alliariae was more attractive shortly after an attack by conspecifics (half an hour before the experiment) compared to a undamaged plant, but lost its increased attractiveness when damaged overnight. The enhanced attraction of damaged plants was longer lasting in the spring host P. paradoxus than in the main host A. alliariae. Volatiles emitted by host plants were collected and gas chromatographic analyses of the odors collected showed qualitative and quantitative differences between damaged and undamaged plants. Among the volatiles recorded, green leaf volatiles and mono- and sesquiterpenes dominated. In overnight damaged P. paradoxus plants with an enhanced attractiveness, limonene was emitted in higher amounts. In freshly damaged A. alliariae leaves, more -humulene and germacrene D were emitted compared to (E,E)--farnesene, whereas in the less attractive A. alliariae plants, more (E,E)--farnesene was emitted compared to -humulene and germacrene D. In the field, the long lasting attraction of flowering P. paradoxus early in the season may facilitate mating in O. cacaliae after a successful overwintering.
  • Publication
    Accès libre
    Sequestration, Maintenance, and Tissue Distribution of Pyrrolizidine Alkaloid N-Oxides in Larvae of Two Oreina Species
    (1999)
    Ehmke, Adelheid
    ;
    Rahier, Martine 
    ;
    Pasteels, Jacques M.
    ;
    Theuring, Claudine
    ;
    Hartmann, Thomas
    Oreina cacaliae and O. speciosissima are leaf beetles that, as larvae and adults, sequester pyrrolizidine alkaloid N-oxides (PAs) as defensive compounds from their host plants Adenostyles alliariae and Senecio nemorensis. As in most Oreina species, O. speciosissima is also defended by autogenously produced cardenolides (mixed defensive strategy), whereas O. cacaliae does not synthesize cardenolides and is exclusively dependent on host-plant-acquired PAs (host-derived defense). Adults of the two Oreina species were found to have the same PA storage capacity. The larvae, however, differ; larvae of O. speciosissima possess a significantly lower capability to store PAs than O. cacaliae. The ability of Oreina larvae to sequester PAs was studied by using tracer techniques with 14C-labeled senecionine N-oxide. Larvae of the two species efficiently take up [14C]senecionine N-oxide from their food plants and store the alkaloid as N-oxide. In O. cacaliae, there is a slow but continuous loss of labeled senecionine N-oxide. This effect may reflect the equilibrium between continuous PA uptake and excretion, resulting in a time-dependent tracer dilution. No noticeable loss of labeled alkaloid is associated with molting. Senecionine N-oxide is detectable in all tissues. The hemolymph is, with ca. 50–60% of total PAs, the major storage compartment, followed by the integument, with ca 30%. The alkaloid concentration in the hemolymph is approximately sixfold higher than in the solid tissues. The selectivity of PA sequestration in larvae is comparable to PA sequestration in the bodies of adult beetles.
  • Publication
    Accès libre
    Distribution of autogenous and host-derived chemical defenses in Oreina leaf beetles (Coleoptera: Chrysomelidae)
    (1995)
    Pasteels, Jacques M.
    ;
    Dobler, Susanne
    ;
    Rahier, Martine 
    ;
    Ehmke, Adelheid
    ;
    Hartmann, Thomas
    ;
    Pasteels, Jacques M.
    ;
    Dobler, Susanne
    ;
    Ehmke, Adelheid
    ;
    Hartmann, Thomas
    The pronotal and elytral defensive secretions of 10 Oreina species were analyzed. Species feeding on Apiaceae, i.e., O. frigida and O. viridis, or on Cardueae (Asteraceae), i.e., O. bidentata, O. coerulea, and O. virgulata, produce species-specific complex mixtures of autogenous cardenolides. O. melanocephala, which feeds on Doronicum clusii (Senecioneae, Asteraceae), devoid of pyrrolizidine alkaloids (PAs) in its leaves, secretes, at best, traces of cardenolides. Sequestration of host-plant PAs was observed in all the other species when feeding on Senecioneae containing these alkaloids in their leaves. O. cacaliae is the only species that secretes host-derived PA N-oxides and no autogenous cardenolides. Differences were observed in the secretions of specimens collected in various localities, because of local differences in the vegetation. The other species, such as O. elongata, O. intricata, and O. speciosissima, have a mixed defensive strategy and are able both to synthesize de novo cardenolides and to sequester plant PA N-oxides. This allows a great flexibility in defense, especially in O. elongata and O. speciosissima, which feed on both PA and non-PA plants. Populations of these species were found exclusively producing cardenolides, or exclusively sequestering PA N-oxides, or still doing both, depending on the local availability of food-plants. Differences were observed between species in their ability to sequester different plant PA N-oxides and to transform them. Therefore sympatric species demonstrate differences in the composition of their host-derived secretions, also resulting from differences in host-plant preference. Finally, within-population individual differences were observed because of local plant heterogeneity in PAs. To some extent these intrapopulation variations in chemical defense are tempered by mixing diet and by the long-term storage of PA N-oxides in the insect body that are used to refill the defensive glands.
  • Publication
    Accès libre
    Production of cardenolides versus sequestration of pyrrolizidine alkaloids in larvae of Oreina species (Coleoptera, Chrysomelidae)
    (1994)
    Dobler, Susanne
    ;
    Rahier, Martine 
    Adult leaf beetles of the genus Oreina are known to be defended either by autogenously produced cardenolides or by pyrrolizidine alkaloids (PAs) sequestered from the food plant, or both. In this paper we analyze larvae of different Oreina species and show that the larvae contain the same defensive toxins as the adults in quantities similar to those released in the adults' secretion. Both classes of toxins are found in the body and hemolymph of the larvae, despite their different origins and later distribution in the adults. Larvae of sequestering species differed in their PA patterns, even though they fed on the same food plants. The concentration in first-instar larvae of a PA-sequestering species was similar to that in fourth-instar larvae. In all stages examined, the amount of PAs per larva did not greatly exceed the estimated uptake of one day. Eggs of two oviparous species contained large concentrations of the adult's toxins, while neonates of a sequestering larviparous species had no PAs.
  • Publication
    Accès libre
    Physiological sources of variation in chemical defense of Oreina gloriosa (Coleoptera: Chrysomelidae)
    (1993)
    Eggenberger, F.
    ;
    Rahier, Martine 
    The defensive secretion of the alpine chrysomelid Oreina gloriosa is a complex mixture of mainly cardenolides and tyrosine betaine. Individually sampled secretions of adult laboratory-reared and field-collected beetles were analyzed by reverse-phase HPLC; 16 secretion components were quantified. Quantities and concentrations of different components were significantly affected by the age, sex, and reproductive status of individual beetles. Aging was correlated with marked increases (up to 4.4-fold) and decreases (up to 2.7-fold) of quantities and concentrations of several components. Differences between the sexes were smaller, but quantities of all components and concentrations of several components were larger in laboratory-reared females than in males. There was less of one component of the secretion in mated than unmated females, but the concentrations of four secretion components were higher (up to 1.6-fold) in mated females.