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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
    Biochemical strategy of sequestration of pyrrolizidine alkaloids by adults and larvae of chrysomelid leaf beetles
    (Elsevier, 1999)
    Hartmann, Thomas
    ;
    Theuring, Claudine
    ;
    Jürgen Schmidt
    ;
    Rahier, Martine 
    ;
    Pasteels, Jacques M.
    Tracer feeding experiments with 14C-labeled senecionine and senecionine N-oxide were carried out to identify the biochemical mechanisms of pyrrolizidine alkaloid sequestration in the alkaloid-adapted leaf beetle Oreina cacaliae (Chrysomelidae). The taxonomically closely related mint beetle (Chrysolina coerulans) which in its life history never faces pyrrolizidine alkaloids was chosen as a ‘biochemically naive’ control. In C. coerulans ingestion of the two tracers resulted in a transient occurrence of low levels of radioactivity in the hemolymph (1–5% of radioactivity fed). With both tracers, up to 90% of the radioactivity recovered from the hemolymph was senecionine. This indicates reduction of the alkaloid N-oxide in the gut. Adults and larvae of O. cacaliae sequester ingested senecionine N-oxide almost unchanged in their bodies (up to 95% of sequestered total radioactivity), whereas the tertiary alkaloid is converted into a polar metabolite (up to 90% of total sequestered radioactivity). This polar metabolite, which accumulates in the hemolymph and body, was identified by LC/MS analysis as an alkaloid glycoside, most likely senecionine O-glucoside. The following mechanism of alkaloid sequestration in O. cacaliae is suggested to have developed during the evolutionary adaptation of O. cacaliae to its alkaloid containing host plant: (i) suppression of the gut specific reduction of the alkaloid N-oxides, (ii) efficient uptake of the alkaloid N-oxides, and (iii) detoxification of the tertiary alkaloids by O-glucosylation. The biochemical mechanisms of sequestration of pyrrolizidine alkaloid N-oxides in Chysomelidae leaf beetles and Lepidoptera are compared with respect to toxicity, safe storage and defensive role of the alkaloids.
  • 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
    Selective sequestration and metabolism of plant derived pyrrolizidine alkaloids by chrysomelid leaf beetles
    (1997)
    Hartmann, Thomas
    ;
    Witte, Ludger
    ;
    Ehmke, Adelheid
    ;
    Theuring, Claudine
    ;
    Rahier, Martine 
    ;
    Pasteels, Jacques M.
    Pyrrolizidine alkaloids (PAs) are assumed to function as plant defence compounds against herbivory. A number of adapted insects are known to sequester plant derived PAs for their own benefit. Here we summarize the chemical interactions between leaf beetles of the genus Oreina (Coleoptera, Chrysomelidae) and their host plants Adenostyles spp., Senecio nemorensis, and S. fuchsii (Asteraceae, tribe Senecioneae). Seneciphylline N-oxide and senecionine N-oxide, the main PAs of Adenostyles, are sequestered in the bodies and exocrine defensive glands of the leaf beetles. The comparison with the PA patterns of the Senecio host plant indicates a selective PA uptake. The uptake into the body (hemolymph) is less specific, whereas the translocation into the defensive glands is highly specific. Only the N-oxides of macrocyclic retronecine esters of the senecionine type are found in significant amounts in the defensive secretions. Many other PAs such as monoesters and open-chain diesters as well as PAs of other structural types (e.g. monocrotaline N-oxide and senkirkine) are not transferred into the defensive glands. Leaf beetles sequester PAs exclusively as N-oxides. A novel PA not found in the food plants was detected in the defensive secretions of Oreina elongata; it was identified as 13,19-expoxisenecionine N-oxide (oreine), the epoxidation product of seneciphylline N-oxide. Besides this transformation, leaf beetles are able to catalyse further transformations such as the O-dealkylation of heliotrine N-oxide to rinderine N-oxide and the O-deacetylation of acetylseneciphylline N-oxide to seneciphylline N-oxide. The plant-beetle interactions are discussed in the functional context of PAs as powerful plant defensive chemicals.
  • Publication
    Accès libre
    Host-Plant Switches and the Evolution of Chemical Defense and Life History in the Leaf Beetle Genus Oreina
    (1996)
    Dobler, Susanne
    ;
    Mardulyn, Patrick
    ;
    Pasteels, Jacques M.
    ;
    Rahier, Martine 
    Insect-plant interactions have played a prominent role in investigating phylogenetic constraints in the evolution of ecological traits. The patterns of host association among specialized insects have often been described as highly conservative, yet not all specialized herbivorous insect lineages display the same degree of fidelity to their host plants. In this paper, we present an estimate of the evolutionary history of the leaf beetle genus Oreina. This genus displays an amazing flexibility in several aspects of its ecology and life history (1) host plant switches in Oreina occurred between plant families or distantly related tribes within families and thereby to more distantly related plants than in several model systems that have contributed to the idea of parallel cladogenesis; (2) all species of the genus are chemically defended, but within the genus a transition between autogenous production of defensive toxins and sequestration of secondary plant compounds has occurred; and (3) reproductive strategies in the genus range from oviparity to viviparity including all intermediates that could allow the gradual evolution of viviparity Cladistic analysis of 18 allozyme loci found two most parsimonious trees that differ only in the branching of one species. According to this phylogeny estimate, Oreina species were originally associated with Asteraceae, with an inclusion of Apiaceae in the diet of one oligophagous species and an independent switch to Apiaceae in a derived clade. The original mode of defense appears to be the autogenous production of cardenolides as previously postulated; the additional sequestration of pyrrolizidine alkaloids could have either originated at the base of the genus or have arisen three times independently in all species that switched to plants containing these compounds. Viviparity apparently evolved twice in the genus, once without matrotrophy, through a retention of the eggs inside the female's oviducts, and once in combination with matrotrophy. We hypothesize that the combination of autogenous defense and a life history that involves mobile externally feeding larvae allowed these beetles to switch host plants more readily than has been reported for highly conservative systems.
  • Publication
    Accès libre
  • Publication
    Accès libre
    Spatial genetic structure of leaf beetles species with special emphasis on alpine populations
    (1996)
    Knoll, Steffi
    ;
    Rahier, Martine 
    ;
    Mardulyn, Patrick
    ;
    Pasteels, Jacques M.
  • Publication
    Accès libre
    Relative unpalatability of leaf beetles with either biosynthesized or sequestered chemical defence
    (1995)
    Rahier, Martine 
    ;
    Pasteels, Jacques M.
    ;
    Alonso-Media, A.
    ;
    Brower, L. P.
    Defence of leaf beetles in the genus Oreina is chemically diverse. Some (e.g. O. gloriosa) rely on the secretion of small quantities of a concentrated mixture of cardenolides that are biosynthesized de novo and stored only in special glands. Others (e.g. O. cacaliae) lack cardenolides but sequester pyrrolizidine alkaloid N-oxides (PAs) and store them both in their body and in their glands. First, the impact of the defensive secretions on the palatability of the beetles to wild-caught red-winged blackbirds, Agelaius phoeniceus, was tested. The reactions of the birds to these two different types of chemicals were then compared to determine whether they grant equal protection to the beetles. Oreina gloriosa, with their secretion of cardenolides intact, were eaten in 55% of the trials. When the secretion was physically removed, 95% of the now undefended O. gloriosa were eaten. The mean handling time by the birds also decreased from 41 to 26 s. This shows that the small quantity of highly concentrated secretion produced on the surface of the beetle's body affords substantial protection against avian predators. Oreina cacaliae, with PAs in their secretion and in their body, were eaten in only 21% of the cases. When the secretion was removed, leaving PA only in the body, the number eaten rose to 36%. The time to peck and then reject the beetles with their secretions intact was less in O. cacaliae than in O. gloriosa. PAs therefore seem to provide the beetle with better protection from the birds than do cardenolides. The experiment raised the possibility that the birds may have the ability to reject beetles with PAs olfactorily.
  • 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
    A comparison between allozyme data and phenotypic distances from defensive secretion in Oreina leaf-beetles (Chrysomelinae)
    (1994)
    Rahier, Martine 
    ;
    Pasteels, Jacques M.
    The genetic relationships between five Oreina species (Chrysomelidae, Coleoptera) were studied. Of these species, four (O. bifrons, O. gloriosa, O. speciosa, O. variabilis) feed on Apiaceae and secrete mixtures of autogenous cardenolides from defensive glands, whilst the other (O. speciosissima) feeds on Asteraceae and is able both to produce cardenolides and to sequester pyrrolizidines N-oxides (PAs). A dendrogram based on the different mixtures of cardenolides produced by the different species agreed with these genetic relationships. In other words, cardenolide mixtures are good taxonomic markers, since the clustering method based on chemical defense produces a branching pattern similar to that based on genetic relationships.
  • Publication
    Accès libre