Una planta exòtica s'allibera dels herbívors associats en colonitzar nous hàbitats a Catalunya

Una espècie exòtica es converteix en espècie invasora quan forma poblacions estables que s'expandeixen pel nou territori. Una de les hipòtesis que intenta explicar aquest procés prediu que les plantes exòtiques s'alliberen dels consumidors que tenien associats a l'àrea d'origen. Un estudi a nivell biogeogràfic que abraça tota l'àrea de distribució coneguda de l'arbust Senecio pterophorus mostra per primera vegada evidències consistents sobre la disminució d'herbívors després de la invasió d'aquesta espècie.Una especie exótica se convierte en especie invasora cuando forma poblaciones estables que se expanden por el nuevo territorio. Una de las hipótesis que intenta explicar este proceso predice que las plantas exóticas se liberan de los consumidores que tenían asociados en el área de origen. Un estudio a nivel biogeográfico que abarca toda el área de distribución conocida del arbusto Senecio pterophorus muestra por primera vez evidencias consistentes sobre la disminución de herbívoros después de la invasión de esta especie.An exotic species becomes an invasive one when it forms stable populations that expand on the new territory. One hypothesis attempting to explain this process predicts that exotic plants lose the herbivores associated with their area of origin. A biogeographical study covering the entire known distributional area of the shrub Senecio pterophorus shows for the first time consistent evidence of the decline of herbivores after the invasion of this species

Vers una teoria global de defensa química en plantes : el cas de alcaloides

Els alcaloides són un grup de productes del metabolisme secundari altament divers i distribuït majoritàriament en les angiospermes. En les plantes se'ls atribueix com a principal funció la defensa química contra herbívors i patògens. Les plantes alcalòidiques es localitzen preferentment a les regions tropicals i acostumen a ser plantes de creixement ràpid i de vida curta. Les concentracions d'alcaloides, més elevades en determinats òrgans i en períodes concrets del desenvolupament de la planta, sembla que són determinades pels constrenyiments evolutius ocasionats pels recursos del medi on la planta ha evolucionat, per la història coevolutiva entre plantes i fitòfags i per l'ambient físic immediat de la planta, principalment pels nutrients disponibles durant el seu cicle vital. Diverses hipòtesis han intentat explicar la variabilitat interespecífica i intraespecífica de defenses tractant aspectes particulars d'aquests factors. Basant-nos amb dades de plantes alcalòidiques, en aquest article hem elaborat una síntesi de les hipòtesis precedents i discutim la necessitat d'anar cap a una nova teoria global de defensa química. Aquesta nova visió integradora determina un marc conceptual ampli que ens ajuda a interpretar el com i el perquè de la presència i de la diversitat actual de les defenses químiques en plantes.Alkaloids are a large and very diverse group of secondary metabolites found principally in angiosperms. They play a defensive role in plants against herbivores and pathogens. Alkaloid-bearing plants are usually short life plants and they are localized preferently in tropical regions. Alkaloid concentrations vary in different plant parts and different plant development stages. They are determined by resource evolution constraints, by coevolution history between plants and animals and by plant immediate resouce availability. We present a global synthesis of previous plant chemical defense hypothesis in order to stablish a conceptual framework to understand the qualitative and quantitative diversity of plant defenses, with special emphasis on plant alkaloids

Resistance of the generalist moth Trichoplusia ni (Noctuidae) to a novel chemical defense in the invasive plant Conium maculatum

Conium maculatum is an apiaceous species native to Eurasia that is highly toxic to vertebrates due to the presence of piperidine alkaloids, including coniine and γ-coniceine. More than 200 years after invading the United States this species remains mostly free from generalist insect herbivores. The presence of novel chemical defenses in the introduced range could provide invasive species with a competitive advantage relative to native plants. The cabbage looper (Trichoplusia ni) is a generalist lepidopteran found throughout the US that occasionally feeds on C. maculatum. We evaluated the toxicity of piperidine alkaloids to T. ni and determined putative resistance mechanisms, both behavioral and physiological, that allows this insect to develop successfully on C. maculatum foliage. T. ni larvae raised on diets enriched with coniine and γ-coniceine showed a decrease in consumption and longer development time, but no effects on growth were found at any alkaloid concentration. In a diet choice experiment T. ni larvae showed no avoidance of alkaloid-enriched diets, suggesting that the deterrence produced by alkaloids was related to a post-ingestive metabolic response. The ability of T. ni to consume diets high in alkaloid content could be due to at least three different mechanisms: 1) a decreased consumption rate, 2) efficient excretion of at least 1/3 of ingested alkaloids unmetabolized in frass, and 3) partial detoxification of alkaloids by cytochrome P450s, as shown by the decreased larval growth in the presence of piperonyl butoxide, a P450 inhibitor. Even though T. ni tolerates C. maculatum alkaloids, the use of this species as a host plant could be ecologically disadvantageous due to prolonged larval growth and thus increased exposure to predators. Novel plant secondary compounds do not guarantee increased resistance to generalist herbivores

Host plant selection by a monophagous herbivore is not mediated by quantitative changes in unique plant chemistry : Agonopterix alstroemeriana and Conium maculatum

Host plant selection by ovipositing females is a key process determining the success of phytophagous insects. In oligophagous lepidopterans, host-specific plant secondary chemicals are expected to be dominant factors governing oviposition behavior; distinctive compounds can serve as high-contrast signals that clearly differentiate confamilial hosts from non-hosts increasing the accuracy of host quality evaluation. Agonopterix alstroemeriana (Clerk) (Lepidoptera: Oecophoridae) and Conium maculatum L. (Apiaceae) form an extremely specialized plant-herbivore system, with A. alstroemeriana monophagous on C. maculatum, a plant with few other insect herbivores at least in part due to its virtually unique capacity among plants to produce piperidine alkaloids. Here we have studied the response of A. alstroemeriana oviposition to unique host plant secondary metabolites, piperidine alkaloids, and widespread compounds, mono- and sesquiterpenes, in a concentration-dependent fashion. Rates of oviposition were negatively correlated with Z-ocimene concentrations. To confirm the deterrent properties of this monoterpene for A. alstroemeriana oviposition, we conducted a choice experiment using artificially damaged C. maculatum plants, with higher emission of volatiles, and undamaged control plants. Damaged plants were less preferred as oviposition sites compared to the controls. The lack of association between oviposition and piperidine alkaloids, defenses unique to Conium species, suggests that quantitative changes of these species-specific chemicals do not play a predominant role in host selection by the monophagous A. alstroemeriana

Are invasive plants more toxic than native plants? An example of rapid evolution after invasion

Biological invasions are excellent systems to study rapid evolution of plant chemical defenses. Current hypotheses predict a divergence of plant chemical defenses in response to a decrease in herbivory after invasion (e.g. EICA hypothesis) or in response to novel climatic conditions. Post-invasive changes in plant chemistry can modify the interactions with herbivores and facilitate invasion success. However, whether plant toxicity is changed after invasion remains to be evaluated. Senecio pterophorus is a shrub native from Eastern South Africa and a recent invader in Western South Africa (~100 years ago), Australia (>70-100 years ago) and Europe (>30 years ago). These distributional regions of S. pterophorus differ in their summer drought stress and in their interactions with herbivores. As other Asteraceae, S. pterophorus contains pyrrolizidine alkaloids (PAs) toxic to vertebrate and invertebrate herbivores. Plants from 54 populations sampled throughout the entire known worldwide distributional area, including the native and three non-native ranges, were grown under controlled conditions. First, we analyzed the levels of chemical defenses and leaf morphological traits to determine whether plant genetically-based traits diverged between native and non-native populations. Second, we performed non-choice bioassays with generalist herbivores (e.g. Spodoptera sp) to evaluate changes in plant toxicity after invasion. Plants from different origins diverged in their chemical and morphological traits. Levels of chemical defenses were higher in the introduced populations, including the highly toxic 1,2-unsaturated PAs and the less toxic 1,2-saturated PAs. These results, indicative of higher toxicity in the invasive range, were consistent with the lower larval growth when insects consumed non-native plants. We discuss what factors, either chemical or morphological, determine the increase in plant toxicity after invasion. By comparing the genetic similarity across the native and non-native areas obtained by neutral markers we evaluate whether changes in toxicity are result of a rapid evolution

La política lingüística en las elecciones valencianas de 2011

This article analyzes the proposals having to do with language policy put forward by the political groups that won seats in the Valencian Parliament in the May 2011 elections.  Most of these proposals originated in a document entitled Propostes d´Escola Valenciana per als programes electorals (Valencian School Proposals for Electoral Platforms). The article examines the scope of the proposals within the framework of the Valencian language policy of recent decades, and does so from a sociolinguistic perspective. In the case of those coalitions that have not been represented in the Valencian government, a comparison is made both with respect to the proposals of the majority parties and to current language policy.  In this way, the article maps out  the language policy that is possible in Valencia in the medium term.En este artículo se analizan las propuestas en materia de política lingüística de las coaliciones y partidos políticos que obtuvieron representación en las Cortes Valencianas en las elecciones de mayo de 2011. Desde una perspectiva sociolingüística, se estudiará el alcance de las propuestas, dentro del marco de la política lingüística valenciana de las últimas décadas. Eso implica que el comportamiento como gestores se tendrá en cuenta a la hora de valorar las propuestas que presentaron al programa electoral en el caso de los partidos que han tenido y tienen responsabilidades de gobierno. En el caso de los que no han tenido, el comparatisme se llevará a cabo tanto con las propuestas de los mayoritarios como con la política lingüística efectiva, dibujando así el mapa de la política lingüística posible en el País Valencià en un plazo medio.En aquest article s’analitzen les propostes en matèria de política lingüística de les coalicions i partits polítics que van obtenir representació a les Corts Valencianes en les eleccions de maig de 2011. Des d’una perspectiva sociolingüística, s’estudiarà l’abast de les propostes, dins del marc de la política lingüística valenciana de les darreres dècades. Això implica que el capteniment com a gestors es tindrà en compte a l’hora de valorar les propostes que van presentar al programa electoral en el cas dels partits que han tingut i tenen responsabilitats de govern. En el cas dels que no n’han tingut, el comparatisme es durà a terme tant amb les propostes dels majoritaris com amb la política lingüística efectiva, dibuixant així el mapa de la política lingüística possible al País Valencià en un termini mitjà

Són les plantes invasores més tòxiques que les natives?

Les plantes invasores poden modificar la composició, l'estructura i el funcionament dels ecosistemes que colonitzen i sembla que podrien canviar la seva pròpia composició química i toxicitat. Per tal d'esbrinar si es produeixen aquests darrers canvis, el grup d'Ecologia Química i Toxicologia de la UAB ha analitzat la concentració de certes molècules de l'arbust Senecio pterophorus que són tòxiques per a organismes invertebrats i vertebrats en plantes recol·lectades a la seva zona nativa i en tres regions on s'ha convertit en espècie invasora.Las plantas invasoras pueden modificar la composición, la estructura y el funcionamiento de los ecosistemas que colonizan y parece que podrían cambiar su propia composición química y toxicidad. Para averiguar si se producen estos últimos cambios, el grupo de Ecología Química y Toxicología de la UAB ha analizado la concentración de ciertas moléculas del arbusto Senecio pterophorus que son tóxicas para organismos invertebrados y vertebrados en plantas recolectadas en su zona nativa y en tres regiones donde se ha convertido en especie invasora.Exotic plants can strongly affect the composition, structure and functioning of the invaded ecosystems and it seems that they are able to change their own chemical composition and toxicity. To determine whether these changes actually take place, the Chemical Ecology and Toxicology group at the UAB analysed the concentration of certain molecules of the Senecio pterophorus shrub toxic to vertebrates and invertebrates in plants collected in their native environment and in three non-native environments

Els fenols, entre el carboni i el nitrogen : resposta als increments del CO2 atmosfèric i interacció amb el cicle del nitrogen

Els fenols són metabòlits secundaris d'un gran interès en ecologia ja que poden regular la intensitat de diverses interaccions entre la planta i el seu entorn. Les concentracions de fenols en planta estan determinades per factors abiòtics, especialment per la relació entre la disponibilitat de C i la disponibilitat de N per a la planta. Així doncs, una major disponibilitat de C, per exemple com a resultat d'un increment de les concentracions de CO2 atmosfèric, podria determinar una estimulació de la síntesi de fenols. Els canvis en les concentracions de fenols en un escenari de canvi global podrien tenir conseqüències en els processos ecològics relacionats amb el metabolisme secundari. En aquesta tesi doctoral hem estudiat, en primer lloc, les variacions de les concentracions de fenols en espècies mediterrànies sotmeses a concentracions elevades de CO2 i crescudes en competència per llum, aigua i nutrients. Amb aquests estudis volem esbrinar si un augment de CO2 atmosfèric tendeix a incrementar les concentracions de fenols, tal com prediuen les hipòtesis fenotípiques d'assignació de recursos, quan les plantes creixen en condicions properes a les naturals. En concret, hem volgut saber i) si la resposta dels fenols a concentracions elevades de CO2 és variable a nivell intraespecífic i interespecífic, ii) com afecta la diversitat vegetal en aquesta resposta, i iii) si els canvis en les concentracions de fenols es mantenen quan les plantes han estat sotmeses a concentracions elevades de CO2 durant llargs períodes de temps. Els nostres resultats mostren que, a curt termini, les concentracions de fenols tendeixen a incrementar en plantes crescudes a concentracions elevades de CO2, i que aquesta resposta és independent dels genotips, dels grups funcionals i de la diversitat de la comunitat, però dependent de les espècies. A llarg termini, les concentracions de fenols no incrementen a elevat CO2. A la segona part de la tesi ens hem interessat en el paper dels fenols com a reguladors del cicle del N en dos ecosistemes (boreal i mediterrani) caracteritzats per una limitació de N al sòl. Així doncs, hem estudiat els efectes de la presència de capçada en dues espècies vegetals amb grans concentracions de fenols en fulla, Ledum palustre i Cistus albidus, i els efectes de l'addició de lixiviats d'aquestes espècies -els quals contenen fenols- en el cicle del N. Els nostres resultats mostren que els lixiviats d'ambdues espècies poden modificar significativament el cicle del N del sòl adjacent, però que aquests efectes no estan causats per la fracció fenòlica dels lixiviats. En conclusió, hem vist que en condicions naturals els fenols no són el principal factor que controla la disponibilitat de N inorgànic per a la vegetació.Phenolic compounds are plant carbon-based secondary metabolites of high interest in ecological studies because they can regulate the strength of some biotic interactions. At specific level, phenolic compound concentrations are determined by abiotic factors such as plant C and N availability. An increasing atmospheric CO2 could influence the synthesis of phenolics and these changes could have further consequences in ecological processes highly related to secondary metabolism. We first studied changes in phenolic concentrations in Mediterranean species growing at elevated CO2. It is generally accepted that increased carbon source for plants results in an increase of carbon-based secondary compounds when growth is limited by other resources. However, the validity of this response is mainly unknown in plants growing in natural conditions. We wanted to know: i) whether there was a genetic variability in the response of phenolic compounds at elevated CO2, ii) the effects of plant diversity in the response of phenolics at elevated CO2, and iii) the long term response of phenolic compounds in plants submitted to elevated CO2. Our results show that, at short term, phenolic concentrations increased under elevated CO2 in plants growing close to natural conditions, and this response was related to the studied species but not to the genotypes, functional groups or plant diversity. At long term, phenolic concentrations had no significant increase in plants growing in naturals conditions. We second studied the role of phenolic compounds in controlling N cycling in Boreal and Mediterranean ecosystems, where soil is N limited. Thus, we analyzed the effects of plant presence from two phenolic compound-bearing species (Ledum palustre and Cistus albidus) on N cycling, as well as the effects of leaf leachates containing high phenolic compound concentrations. Our results shown that leachates can change soil N cycling under both plant species, but these effects are not due to phenolic compounds. We conclude that phenolic compounds are not the main drivers controlling soil N availability in natural conditions

Contemporary evolution of Senecio pterophorus in Response to climate but not to herbivory

Divergence in plant traits and trait plasticity after invasion has been proposed as an important mechanism favoring invasion success. Current hypotheses predict a rapid evolution in response to changes in the abiotic conditions after invasion, or to changes in the herbivore consumption pressure caused by a decrease in the enemies associated at the area of origin (e.g. evolution of increased competitive ability -EICA- hypothesis). Here we have evaluated, simultaneously, the role of climate and herbivore consumption on the rapid geographical divergence in plant traits and trait plasticity of the exotic plant Senecio pterophorus (Asteraceae). S. pterophorus is a perennial shrub native from Eastern South Africa and a recent invader in Western South Africa (~100 years ago), Australia (>70-100 years ago) and Europe (>30 years ago). In Australia it has been declared a noxious weed subject to eradication. The four distributional regions of S. pterophorus differ in their summer drought stress and in their interactions with herbivores. We performed a common garden experiment with plants sampled throughout the entire known distributional area of S. pterophorus in the native and non-native ranges to test geographical differences in individual-level traits, leaf-level traits and reproductive-level traits, and their plastic response to water availability. Native and non-native populations differed in plant traits, but not in trait plasticity, in response to their local climatic conditions. However, our results are contrary to the role of herbivory as a selective factor after invasion