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  • Publication
    Accès libre
    Phylogeography and biodiversity in an alpine leaf beetle genus
    (2009)
    Borer, Mattias
    ;
    Des changements dans la conformation tectonique et orbitale de la terre (excentricité, obliquité et la précession) ont entraîné des oscillations récurrentes du climat pendant le Quaternaire. Ces oscillations ont fortement influencé le paysage génétique de la flore et de la faune contemporaines, notamment en ce qui concerne le continent Européen. Pendant les périodes glaciaires, l’extension de la glace et du permafrost ont forcé un grand nombre d’espèces à migrer ou à survivre dans des refuges au sud de l’Europe, alors que pendant les épisodes interglaciaires, ces espèces ont recolonisé le nord de l’Europe au fur et à mesure que la glace se rétractait. Si ces processus ont été largement étudiés chez les espèces tempérées de basse altitude (pour lesquelles différents paradigmes ont été établis), on connaît beaucoup moins l’influence de cette migration cyclique des populations chez les espèces arctiques ou de haute altitude. Pendant ma thèse, j’ai étudié la phylogéographie (c’est-à-dire l'étude des principes et processus qui gouvernent la distribution des lignées généalogiques) de quatre espèces de chrysomèles alpines du genre Oreina (caractérisé par des espèces présentant une grande variété de couleurs) afin de mettre en évidence le rôle joué par les oscillations climatiques du Quaternaire sur des taxons de haute altitude. J’ai utilisé différentes méthodes moléculaires comme le génotypage par AFLP (amplified fragment-length polymorphism) et le séquençage de marqueurs cytoplasmiques et nucléaires afin de reconstruire la phylogénie et l’histoire évolutive des lignées. J’ai tout d’abord abordé la phylogénie d’Oreina elongata, une espèce avec une distribution restreinte aux Alpes et aux Apennins. Les résultats montrent que seules trois des sept sous-espèces décrites ont formé des clades monophylétiques. Les clades basaux se trouvent dans les Alpes de Suisse centrale et en Italie du nord. En utilisant une horloge moléculaire calibrée sur la vitesse moyenne d’évolution des gènes mitochondriaux des insectes, j’ai montré que la séparation des clades majeurs au sein de cette espèce a eu lieu bien avant le dernier maximum glaciaire, il y a environ 5 Ma. Cela indique clairement qu’Oreina elongata a persisté à la périphérie ou même à l’intérieur des Alpes et des Apennins pendant plusieurs cycles glaciaires. Ensuite, j’ai analysé la phylogénie d’Oreina gloriosa, une espèce qui présente une distribution strictement restreinte aux Alpes. Les analyses ont permis de mettre en évidence une séparation en trois clades principaux: un dans les Alpes de l’ouest, un dans les Alpes centrales et un dans les Alpes de l’est. L’estimation des temps de divergence à l’aide de l’horloge moléculaire suggère que la séparation des trois clades majeurs a débuté il y a 0.5 Ma, ce qui peut être considéré comme récent, en regard des résultats précédents sur Oreina elongata. Ce résultat est confirmé par le fait qu’il n’y a aucune variation morphologique chez ce taxon, d’un bout à l’autre de son aire de distribution. Afin d’étudier les conséquences des oscillations climatiques sur les interactions trophiques, j’ai également comparé le patron obtenu pour Oreina gloriosa avec celui de sa plante-hôte exclusive, l’impératoire Peucedanum ostruthium, en inférant la structuration génétique spatiale des deux espèces à l’aide d’un génotypage par AFLP. Les résultats montrent une incongruence partielle dans l’histoire de ces deux espèces antagonistes, ce qui suggère que la plante et l’insecte n’ont pas systématiquement emprunté les mêmes voies de dispersion. Puis, je me suis intéressé aux espèces génétiquement proches, Oreina cacaliae et Oreina speciosissima, deux taxons qui se rencontrent fréquemment en sympatrie sur leur aire de distribution (englobant la plupart des massifs montagneux européens). Alors que l’analyse d’un marqueur nucléaire – de même que des critères morphologiques – séparent nettement les deux espèces, la phylogénie basée sur trois marqueurs mitochondriaux montre une paraphylie réciproque marquée des deux espèces. Ces résultats mettent cependant en évidence la monophylie de 10 parmi 12 sous-espèces échantillonnées. L’incongruence entre la morphologie et l’information nucléaire et mitochondriale peut être expliquée par l’hybridation des lignées, éventuellement en combinaison avec un polymorphisme ancestral important. J’ai par la suite analysé la phylogéographie de deux sous-espèces d’Oreina speciosissima, sur la base de trois marqueurs d’ADN mitochondriaux et d’un génotypage AFLP. Tandis que les marqueurs mitochondriaux n’ont démontré qu’un très faible niveau de variation, la phylogénie basée sur les AFLP a permis de mettre en évidence une structuration très fortement corrélée à l’écologie, et notamment au type d’habitat. Néanmoins, la présence de morphes intermédiaires à la base des clades des deux sous-espèces indique que la divergence entre ces deux sous-espèces n’est pas encore terminée. Enfin, dans un volet d’écologie comportementale, j’ai testé si la couleur pouvait être impliquée dans le choix du partenaire et si cela pouvait influencer les densités relatives des différentes couleurs au sein des populations d’Oreina gloriosa. Les résultats des expériences (au cours desquelles on a testé le choix du partenaire entre deux morphes de couleurs et d’origines populationnelles différentes) n’a pas permis de conclure à des différences significatives entre les différents types d’accouplements, et par conséquent à des préférences dans le choix du partenaire liées à la couleur. Finalement, on a réalisé une expérience de terrain pour tester si la sélection positive ″fréquence-dépendante″ des prédateurs est une force évolutive suffisante pour modifier les proportions des différentes couleurs au sein des populations d’Oreina gloriosa et maintenir le polymorphisme. Les résultats montrent que la survie du morphe le plus rare est significativement plus faible que celle du morphe le plus fréquent, indiquant par là que la prédation peut influencer le patron de coloration d’une population., Changes in tectonic conformation and orbital parameters of the Earth (eccentricity, obliquity and axial wobble) caused drastic climatic oscillations during the Quaternary. These oscillations strongly influenced the genetic landscape of the contemporary European flora and fauna. During cold periods the extending ice sheets and permafrost forced many temperate species to migrate into southern refugia. During interglacial periods these species recolonized northern Europe following the retreating ice shelf. The resulting patterns have been well demonstrated for temperate and lowland species, whereas much less is known about the effect on arctic or high altitude species. In my study we investigated the phylogeography of four alpine leaf beetles to uncover the influence of Quaternary climatic changes on high altitude species. We used AFLP (amplified fragment-length polymorphism) genotyping and single marker sequencing methods for the construction of phylogenies and the geographical distribution of lineages. In the phylogeny of Oreina elongate, a species restricted to the Alps and Apennines, only three out of seven described subspecies form monophyletic clades. The basal clades are found in the central Swiss Alps and northern Italy. Applying a molecular clock, we found that the split of the major clades occurred long before the last glacial maximum suggesting that O. elongate persisted for many glacial cycles within or at the edges of the Alps and Apennines. The phylogeny of O. gloriosa, a species with a uniquely alpine distribution, splits into three main clades, one in the western Alps, one in the central Alps (southern Switzerland) and one in the eastern Alps. The molecular clock estimates suggest that the divergence into the three main clades occurred 0.5 MYA and can be considered as recent, which concords with the lack of morphological variation across the distribution. The comparison of the phylogeography of Peucedanum ostruthium and its monophagous herbivore O. gloriosa based on AFLP genotyping suggests incongruence between the histories of these antagonistic species. Oreina cacaliae and O. speciosissimav are two closely related species occurring in sympatry and with ranges that cover most of the distribution of the genus. The analysis of a nuclear marker and morphological criteria clearly split the two species. The phylogeny of three mtDNA markers show paraphyly for both species but suggest that 10 out of 12 analysed subspecies are monophyletic. And incongruence between the makers may be a result of hybridisation or lineage sorting of the ancestral polymorphism. Further I analyzed the phylogeography of two subspecies within Oreina speciosissima based on three mtDNA markers and AFLP genotyping. The phylogeny of the mtDNA markers show very little structure whereas the AFLP phylogeny showed clear structure, strongly correlated with the ecology and particularly with the habitat. The presence of intermediate morphotypes at the base of both subspecies clades suggests that the divergence between these two subspecies is not yet complete. I tested if colour is involved in mate choice and could influence the colour pattern inO. gloriosa populations. Mate choice experiments between two colour morphs of O. gloriosa with origin in pure or mixed populations show no assortative mating and thus no preference for colour. Finally, we carried out a field experiment to test if positive frequency-dependent selection by predators drives O. gloriosa populations to monomorphism. The survival of the rare morph was significant lower than the survival of the common morph and thus suggests that predation can influence the population colour.
  • Publication
    Accès libre
    Host-Plant Use in the Specialist Leaf Beetle Oreina gloriosa : the Role of Linear Furanocoumarins
    (2004)
    Nessi, Luca
    ;
    ; ; ;
    Städler, Erich
    La chrysomèle alpine Oreina gloriosa (Coleoptera: Chrysomelidae) est hautement spécialisée sur l'ombellifère Peucedanum ostruthium (Apiaceae), l'impératoire. Dans la nature, adultes et larves sont très sélectifs: les uns et les autres se nourrissent exclusivement de feuilles, mais surtout, ils choisissent certaines plantes et en ignorent complètement d'autres. En outre, des études préliminaires ont suggéré que les larves soient actives la nuit. Comme de nombreuses autres apiacées, P. ostruthium synthétise plusieurs furanocoumarines linéaires, métabolites secondaires décrits pour leur activité antiappétante et/ou toxique à l'égard d'insectes phytophages généralistes. Par ailleurs, les furanocoumarines linéaires sont connues pour leur action phototoxique: le rayonnement ultraviolet proche du spectre visible induit chez ces substances une excitation électronique qui peut déterminer différents processus toxiques au niveau cellulaire. Le but de cette étude a été de vérifier l'hypothèse selon laquelle la chimie secondaire de P. ostruthium constituerait un facteur explicatif de l'utilisation de la plante hôte par la strictement monophage O. gloriosa. Toute la recherche a été menée au sein d'une seule population de la plante et de la population du coléoptère qui lui est inféodée.

    Dans un premier temps, nous avons étudié le rythme d'activité de la chrysomèle sur les 24 heures dans son mileu. Ce travail a révélé que les larves se nourrissent exclusivement pendant la nuit et s'enfoncent dans le sol pendant le reste de la journée. Certaines jeunes larves se retirent dans les gaines ou les bourgeons. Au contraire, les adultes ont été observés sur les plantes pendant les 24 heures. Nous avons ensuite vérifié si la croissance larvaire était affectée par la photoactivation des furanocoumarines. Pour cela, les larves ont été placées dans deux environnements lumineux, avec et sans rayonnement ultraviolet. La mortalité a été plus grande dans le deuxième traitement: nous n'avons néanmoins pas pu tirer de conclusions définitives sur l'effet de la photoactivation des furanocoumarines. Dans un travail de terrain, nous avons montré que les invertébrés antagonistes de O. gloriosa sont essentiellement actifs pendant la nuit. Au vu du chevauchement entre les périodes d'activité de la chrysomèle et de ses prédateurs, nous suggérons que les ennemis naturels ne constituent pas la raison d'être du comportement des larves. Nous proposons que l'activité nocturne représente une contre-adaptation à la photoactivité des furanocoumarines. Il s'agirait alors d'un rare exemple d'adaptation comportementale chez un insecte spécialisé sur une plante hôte avec furanocoumarines linéaires. En effet, les insectes avec un régime alimentaire strictement lié à ces métabolites secondaires, disposent en général de moyens de détoxification métaboliques. La différence comportementale entre larves et adultes est probablement liée à l'épaisseur et à la pigmentation de la cuticule imaginale, vraisemblablement opaque à la lumière ultraviolette.

    Nous avons également vérifié l'hypothèse selon laquelle O. gloriosa dans la nature sélectionnerait les plantes en fonction de leur attributs chimiques. Nous avons échantillonné des plantes fortement consommées et des plantes libres de toute attaque d'O. gloriosa. Les feuilles ainsi récoltées ont été extraites et analysées par chromatographie liquide pour déterminer la composition qualitative et quantitative en furanocoumarines linéaires. La chimie secondaire a permis de bien discriminer plantes consommées et non consommées. O. gloriosa est probablement à même de reconnaître certaines de ces substances comme signaux ou elle est en mesure de mieux en tolérer certaines plutôt que d'autres dans leur action toxique. De toute façon, la chimie secondaire explique, du moins en partie, l'utilisation de la plante hôte par ce coléoptère strictement monophage au sein d'une population de sa plante nourricière. Cet exemple révèle la nécessité d'approfondir l'investigation, trop souvent négligée, du rôle de la variation chimique intrapopulationnelle dans les études concernant la convenance de l'hôte pour des insectes spécialistes., The alpine leaf beetle Oreina gloriosa (Coleoptera: Chrysomelidae) is highly specialized on the umbelliferous plant Peucedanum ostruthium (Apiaceae). Adults and larvae feed on leaves and clearly discriminate between individual plants in nature. Preliminary studies suggested that the larvae are active at night. Like many other apiaceous plants, P. ostruthium produces several linear furanocoumarins, secondary metabolites shown to be deterrent and/or toxic to generalist herbivorous insects. Moreover, linear furanocoumarins are well known as phototoxins: when irradiated with long-wave ultraviolet light, these compounds enter an excited state which can mediate different within cell toxic processes. The aim of the present thesis was to verify the hypothesis that the secondary chemistry of P. ostruthium is a factor explaining the actual host-plant use by the strictly monophagous O. gloriosa. All of our work concentrated on a single plant population and its affiliated beetle population.

    We firstly investigated the daily activity rhythm of the beetles in the field. Larvae have been shown to feed exclusively at night and to burrow into the soil for the remainder of the day. Some young larvae hid within sheaths or buds during daylight. In contrast, adults were found on the plants over the 24 hours. We further verified if the performance of the larvae was affected by the photoactivation of the linear furanocoumarins. Larvae were forced to remain in two different light environments, with and without ultraviolet radiation. O. gloriosa was shown to suffer higher mortality when forced under light with ultraviolet radiation. Nonetheless, we were not able to draw definitive conclusions on the effect of the furanocoumarin photoactivation. In a field study, we showed that invertebrate natural enemies of O. gloriosa are mainly active at night. Because of the congruence in time between the beetle and the predators activities we suggest that natural enemies should not be considered as a driving force for the larval night behaviour. We propose that night activity counteracts the photoactive furanocoumarins and should be considered a rare example of behavioural adaptation in a linear furanocoumarin-specialized insect. In fact, specialists are reported to rely on metabolic detoxification. The difference in the behaviour between larvae and adults may be related to the thick and pigmented cuticle of the latter, probably opaque to ultraviolet light.

    Finally we tested the hypothesis that individual plants remain free from O. gloriosa attack due to their chemical attributes. Samples of plants hosting actively feeding O. gloriosa (strongly consumed leaves) and plants exhibiting no damage (unattacked leaves) were collected in the field and examined by HPLC for their qualitative and quantitative linear furanocoumarin composition. The secondary chemistry allowed us to clearly segregate attacked and unattacked plants. We suggest that plant chemistry, relative to the ability of O. gloriosa to tolerate or recognise plant chemicals, can to some extent explain the host use of this monophagous leaf beetle within a population of its host plant. This shows the need for further work on the neglected impact, for specialists, of intrapopulation variation in secondary chemistry on host suitability., Il crisomelide alpino Oreina gloriosa (Coleoptera: Chrysomelidae) è altamente specializzato sull'ombellifera Peucedanum ostruthium (Apiaceae), l'imperatoria vera o erba rena. Adulti e larve in natura sono estremamente selettivi: gli uni e le altre si nutrono solo di foglie, ma distinguono tra le singole piante cibandosi di alcune e trascurandone completamente altre. Inoltre indagini preliminari hanno suggerito che le larve siano attive di notte. Analogamente ad altre ombellifere, P. ostruthium contiene varie furanocumarine lineari, metaboliti secondari con effetto deterrente e/o tossico per insetti fitofagi generalisti. Le furanocumarine lineari sono pure note per la loro fototossicità: la luce ultravioletta di lunghezza d'onda vicina allo spettro visibile induce in queste sostanze un'eccitazione elettronica che può provocare vari processi tossici a livello cellulare. La nostra tesi aveva lo scopo di verificare l'ipotesi secondo cui la chimica secondaria di P. ostruthium spiegherebbe l'utilizzazione della pianta ospite - così come l'osserviamo oggi - da parte dello specialista O. gloriosa. Per l'insieme della ricerca ci siamo concentrati su una singola popolazione della pianta e sulla popolazione dell'insetto ad essa legata.

    Per prima cosa abbiamo studiato il ritmo di attività dei coleotteri in natura. Abbiamo mostrato che le larve si nutrono esclusivamente di notte e passano il resto della giornata nel suolo. Alcune giovani larve si ritirano dentro le guaine o i germogli. Gli adulti invece sono presenti sulle piante durante tutte le 24 ore. In una ricerca successiva abbiamo verificato se la crescita larvale sia compromessa dalla fotoattivazione delle furanocumarine lineari. Abbiamo tenuto le larve in due distinti ambienti luminosi, con e senza radiazione ultravioletta. Quest'ultima ha determinato una maggiore mortalità di O. gloriosa, tuttavia non siamo stati in grado di formulare conclusioni definitive sull'effetto della fotoattivazione. Un lavoro sul campo ha mostrato che gli invertebrati antagonisti del crisomelide sono essenzialmente attivi di notte. Dato che i periodi di attività di O. gloriosa e dei suoi predatori si sovrappongono, suggeriamo che i nemici naturali non costituiscano il fattore selettivo all'origine del comportamento notturno delle larve. Proponiamo che questa limitazione notturna nell'attività trofica rappresenti un'acquisizione adattativa contro la fotoattività delle furanocumarine. Si tratterebbe allora di un raro esempio di adattamento comportamentale in un insetto specializzato su una pianta contenente furanocumarine lineari. In effetti, in generale gli insetti con un regime alimentare strettamente legato a queste sostanze dispongono di strumenti di detossificazione metabolici. La differenza comportamentale tra larve e adulti potrebbe essere ricondotta al tegumento spesso, colorato e probabilmente opaco alla luce ultravioletta di questi ultimi.

    Abbiamo infine verificato l'ipotesi secondo cui la chimica secondaria determinerebbe l'idoneità delle singole piante per la crescita di O. gloriosa. Abbiamo proceduto ad un campionamento sul campo di piante fortemente consumate e di piante prive di qualsiasi segno d'attacco del crisomelide. Le foglie così raccolte sono state estratte e analizzate con la cromatografia liquida per determinare la composizione qualitativa e quantitativa delle furanocumarine. La chimica secondaria ha permesso di ben caratterizzare le piante consumate rispetto a quelle non utilizzate. O. gloriosa è probabilmente in grado di riconoscere talune di queste sostanze quali segnali o di tollerarne alcune piuttosto di altre nella loro azione di tossine. In ogni caso, la chimica secondaria permette di spiegare perlomeno in parte l'utilizzazione della pianta in seno ad una popolazione da parte di questo coleottero altamente specializzato. Questo risultato rivela l'interesse di ulteriori ricerche su un aspetto spesso ignorato quale è l'impatto, per artropodi specialisti, della variazione intrapopolazionale nella chimica secondaria sull'idoneità della pianta ospite.
  • Publication
    Accès libre
    Mate Choice and Toxicity in Two Species of Leaf Beetles with Different Types of Chemical Defense
    (2003)
    Labeyrie, Estelle
    ;
    Blanckenhorn, Wolf U.
    ;
    Evidence for the use of defensive compounds for sexual purposes is scarce, even though sexual selection might have some importance for the evolution of defensive traits. This study investigates the effect of defense-related traits and body size on mating success in two sister species of leaf beetle differing in their type of chemical defense. Oreina gloriosa produces autogenous cardenolides, whereas O. cacaliae sequesters pyrrolizidine alkaloids from its food plant. Larger O. gloriosa males with more toxin or higher toxin concentration had a mating advantage, likely due to direct or indirect female choice. In the laboratory, particular pairings recurred repeatedly in this species, indicating mate fidelity. O. gloriosa females were also subject to sexual selection, possibly by male choice, because larger females and those with higher toxin concentration mated more readily and more often. In O. cacaliae, in contrast, sexual selection for toxicity and body size was not detected, or at best was much weaker. Because toxicity is heritable in O. gloriosa but environment-dependent in O. cacaliae, individuals of the former species could be choosing well-defended partners with good genes. Our study suggests that sexual selection may contribute to the maintenance of heritable defensive traits.
  • Publication
    Accès libre
    A quantitative genetic analysis of leaf beetle larval performance on two natural hosts: including a mixed diet
    (2001)
    Ballabeni, Pierluigi
    ;
    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
    ;
    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.
  • Publication
    Accès libre
    Distribution of genetic variance and isolation by distance in two leaf beetle species: Oreina cacaliae and Oreina speciosissima
    (1998)
    Knoll, Steffi
    ;
    The distribution of genetic variance was investigated in two closely related Oreina leaf beetle species, Oreina cacaliae and Oreina speciosissima, Populations of these alpine beetles were sampled in mountainous areas of Western Europe, the total sampling area ranging from the Pyrenees to the Czech Republic. Allozyme electrophoresis of 21 (O. cacaliae) and 16 (O. speciosissima) loci revealed high genetic variability as expressed in a high percentage of polymorphic loci (only one monomorphic locus was found in each species) and high heterozygosities. No overall linkage disequilibrium was found in either species. Extensive heterozygote deficits were observed in several samples as reflected by high FIS-values and high overall inbreeding coefficients (FIT) of 0.349 (O. cacaliae) and 0.503 (O. speciosissima). The overall inbreeding coefficient was mainly attributable to within-population differentiation. The high heterozygote deficits are explained by a combination of inbreeding resulting in kinship groups and a sampling effect over several such kinship groups. No explanation of the observed patterns could be found in the host plant use or altitudinal location of the samples. For O. cacaliae, isolation by distance was found, but not for O. speciosissima. Gene flow estimates were in the range of Nm = 0.8 to 1.5.
  • Publication
    Accès libre
    Selective sequestration and metabolism of plant derived pyrrolizidine alkaloids by chrysomelid leaf beetles
    (1997)
    Hartmann, Thomas
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    Witte, Ludger
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    Ehmke, Adelheid
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    Theuring, Claudine
    ;
    ;
    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.
    ;
    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
    Reproductive biology of viviparous and oviparous species of the leaf beetle genus Oreina
    (1996)
    Dobler, Susanne
    ;
    In five species of the genus Oreina Chevrolat (Coleoptera, Chrysomelidae) we compared the size of offspring, the fecundity of the females, the timing of offspring production and female investment over the season. Two of the species, O. elongata and O. luctuosa, laid eggs, while O. cacaliae, O. gloriosa and O. variabilis gave birth to larvae. Offspring size corrected for female size was similar in the two oviparous species and in the viviparous O. cacaliae. In the two other viviparous species the larvae were two to three times bigger in relation to the female. The greater size of the offspring was not traded off for lower fecundity in these latter two species, yet the production of bigger larvae was associated with a longer laying period and thereby a spreading of reproductive investment over the season. The prediction of life history theory that higher investment in individual offspring should be traded off for lower fecundity could not be confirmed. The investigation of egg and larval development showed that in one of the oviparous species, O. luctuosa, the length of the egg stage was more variable. This corroborates the view that in this species the eggs can be retained for varying times before being laid. Greater size at birth does not necessarily lead to shortened developmental times: the larval periods of O. cacaliae, O. elongata, O. gloriosa and O. variabilis were all comparable although the larvae of the first two species were relatively smaller when laid; only the small larvae of O. luctuosa needed significantly longer for their development. For all growth parameters examined the differences between species were larger than the differences between populations. A comparison of larval growth of the oligophagous species O. cacaliae on three plant genera showed that larval growth rate is influenced by the food plant. However, the plant on which the larvae grew worst is apparently not chosen for oviposition in the field. A comparison with a phylogeny of the species based on allozymes suggests that species with similar reproductive parameters are closely related, yet that viviparity evolved independently in O. cacaliae on one hand and O. variabilis and O. gloriosa on the other.
  • Publication
    Accès libre
    A comparison between allozyme data and phenotypic distances from defensive secretion in Oreina leaf-beetles (Chrysomelinae)
    (1994) ;
    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.