As plantas, produtores da base das cadeias tróficas, apresentam diversos tipos de defesas contra a ação de consumidores, os herbívoros, podendo ser defesas físicas, químicas e bióticas. Nas defesas bióticas, plantas fornecem recursos alimentares (e.g. néctar extrafloral) e/ou moradia para predadores que em troca podem fornecer proteção contra herbívoros. Assim, a partir de comportamentos agressivos e/ou de patrulha, formigas são consideradas os principais protetores de plantas. Nessa perspectiva, a presente dissertação buscou investigar a influência que o néctar extrafloral tem sob a interação formiga-planta em uma área de Cerrado. O estudo foi realizado na Reserva Ecológica do Clube Caça e Pesca Itororó de Uberlândia, no município de Uberlândia, MG, em uma área com fitofisionomia de cerrado sentido restrito. A espécie de planta utilizada neste estudo foi Qualea multiflora (Vochysiaceae), uma das espécies mais abundantes do Cerrado, a qual apresenta nectários extraflorais (NEFs) na base do pecíolo foliar e nas inflorescências. Nossas hipóteses principais foram: a) que formigas visitantes dos NEFs de Q. multiflora impactam positivamente a planta, reduzindo a ação de herbívoros; b) que essas interações formigas-plantas são modificadas ao longo do desenvolvimento fenológico das folhas das plantas; c) que diferentes níveis de herbivoria nas plantas produzem também diferentes reações nas formigas visitantes; e d) que diferentes estruturas das plantas apresentam diferentes níveis de defesas. Os resultados demonstrados no Capítulo 1 comprovam que a herbivoria foliar em Q. multiflora foi baixa e similar nos diferentes estágios de desenvolvimento da folha, mostrando que as defesas expressas pela planta são eficientes. Das três defesas foliares avaliadas durante o desenvolvimento foliar, observou-se que a densidade de tricomas apresenta pico de efetividade no início do desenvolvimento, a defesa biótica (produtividade dos NEFs) apresenta pico de efetividade no período intermediário do desenvolvimento, e a dureza foliar apresenta pico de efetividade no período em que a folha já está adulta. Esses resultados comprovam a eficiência da variação temporal nas defesas foliares de Q. multiflora, o que interfere diretamente na interação formiga-planta. No Capítulo 2, foi mostrado que NEFs localizados em inflorescências produzem néctar mais volumoso e energético que atrai maior quantidade de formigas comparado ao néctar produzido pelos NEFs foliares. A produtividade e a atratividade dos NEFs, assim como o forrageamento de formigas, também foram afetados por variações na herbivoria (simulada experimentalmente). Esses resultados demonstram que Q. multiflora sincroniza suas defesas foliares ao longo do tempo garantindo a proteção contra herbívoros e que essas defesas (como evidenciado para defesa biótica) podem ser alteradas de acordo com o valor e probabilidade de ataque de suas estruturas. / Plants, producers of food chains, have different types of defenses against action of consumers, herbivores, which can be physical, chemical and biotic defenses. In biotic defenses, plants provide food resources (e.g. extrafloral nectar) and/or shelter for predators, which in turn may provide protection against herbivores. Thus, from patrol and/or aggressive behavior, ants are considered main plants protectors. From this perspective, the present work aimed to investigate the influence that extrafloral nectar has under ant-plant interaction in an area of Cerrado. The study was conducted in Reserva Ecológica do Clube Caça e Pesca Itororó de Uberlândia, in Uberlândia, MG, in an area with cerrado stricto sensu vegetation. The plant species used was Qualea multiflora (Vochysiaceae), one of the most abundant species of Cerrado, which has extrafloral nectaries (EFNs) at the base of leaf petiole and in inflorescences. Our main assumptions were: a) EFNs visitors ants of Q. multiflora positively impact the plant reducing the herbivore action; b) these ants-plants interactions are modified along the phenological development of plant leaves; c) different herbivory levels in plants produce different reactions in visitors ants; and d) different plant structures have different defenses levels. Results presented in Chapter 1 show that foliar herbivore in Q. multiflora was low and similar to different stages of leaf development, showing that expressed plant defenses are effective. Of the three foliar defenses evaluated during leaf development, it was observed that density of trichomes presents effectiveness peak in early development, biotic defense (EFNs productivity) in intermediated period of development and leaf toughness in the period in which the leaf is adult. These results show the efficacy of temporal variation in foliar defenses in Q. multiflora, which directly affects ant-plant interaction. In Chapter 2, it was shown that EFNs located in inflorescences produce nectar more quantitative and qualitative, which attract large amount of ants, than EFNs located in leaves. EFNs productivity and attractiveness, as well as ants foraging, were also influenced by herbivory variation (experimentally simulated). These results show that Q. multiflora synchronizes its leaf defenses over time ensuring protection against herbivores and that these defenses (as evidenced for biotic defense) can be changed according to value and attack probability of their structures.

As plantas, produtores da base das cadeias tróficas, apresentam diversos tipos de defesas contra a ação de consumidores, os herbívoros, podendo ser defesas físicas, químicas e bióticas. Nas defesas bióticas, plantas fornecem recursos alimentares (e.g. néctar extrafloral) e/ou moradia para predadores que em troca podem fornecer proteção contra herbívoros. Assim, a partir de comportamentos agressivos e/ou de patrulha, formigas são consideradas os principais protetores de plantas. Nessa perspectiva, a presente dissertação buscou investigar a influência que o néctar extrafloral tem sob a interação formiga-planta em uma área de Cerrado. O estudo foi realizado na Reserva Ecológica do Clube Caça e Pesca Itororó de Uberlândia, no município de Uberlândia, MG, em uma área com fitofisionomia de cerrado sentido restrito. A espécie de planta utilizada neste estudo foi Qualea multiflora (Vochysiaceae), uma das espécies mais abundantes do Cerrado, a qual apresenta nectários extraflorais (NEFs) na base do pecíolo foliar e nas inflorescências. Nossas hipóteses principais foram: a) que formigas visitantes dos NEFs de Q. multiflora impactam positivamente a planta, reduzindo a ação de herbívoros; b) que essas interações formigas-plantas são modificadas ao longo do desenvolvimento fenológico das folhas das plantas; c) que diferentes níveis de herbivoria nas plantas produzem também diferentes reações nas formigas visitantes; e d) que diferentes estruturas das plantas apresentam diferentes níveis de defesas. Os resultados demonstrados no Capítulo 1 comprovam que a herbivoria foliar em Q. multiflora foi baixa e similar nos diferentes estágios de desenvolvimento da folha, mostrando que as defesas expressas pela planta são eficientes. Das três defesas foliares avaliadas durante o desenvolvimento foliar, observou-se que a densidade de tricomas apresenta pico de efetividade no início do desenvolvimento, a defesa biótica (produtividade dos NEFs) apresenta pico de efetividade no período intermediário do desenvolvimento, e a dureza foliar apresenta pico de efetividade no período em que a folha já está adulta. Esses resultados comprovam a eficiência da variação temporal nas defesas foliares de Q. multiflora, o que interfere diretamente na interação formiga-planta. No Capítulo 2, foi mostrado que NEFs localizados em inflorescências produzem néctar mais volumoso e energético que atrai maior quantidade de formigas comparado ao néctar produzido pelos NEFs foliares. A produtividade e a atratividade dos NEFs, assim como o forrageamento de formigas, também foram afetados por variações na herbivoria (simulada experimentalmente). Esses resultados demonstram que Q. multiflora sincroniza suas defesas foliares ao longo do tempo garantindo a proteção contra herbívoros e que essas defesas (como evidenciado para defesa biótica) podem ser alteradas de acordo com o valor e probabilidade de ataque de suas estruturas. / Plants, producers of food chains, have different types of defenses against action of consumers, herbivores, which can be physical, chemical and biotic defenses. In biotic defenses, plants provide food resources (e.g. extrafloral nectar) and/or shelter for predators, which in turn may provide protection against herbivores. Thus, from patrol and/or aggressive behavior, ants are considered main plants protectors. From this perspective, the present work aimed to investigate the influence that extrafloral nectar has under ant-plant interaction in an area of Cerrado. The study was conducted in Reserva Ecológica do Clube Caça e Pesca Itororó de Uberlândia, in Uberlândia, MG, in an area with cerrado stricto sensu vegetation. The plant species used was Qualea multiflora (Vochysiaceae), one of the most abundant species of Cerrado, which has extrafloral nectaries (EFNs) at the base of leaf petiole and in inflorescences. Our main assumptions were: a) EFNs visitors ants of Q. multiflora positively impact the plant reducing the herbivore action; b) these ants-plants interactions are modified along the phenological development of plant leaves; c) different herbivory levels in plants produce different reactions in visitors ants; and d) different plant structures have different defenses levels. Results presented in Chapter 1 show that foliar herbivore in Q. multiflora was low and similar to different stages of leaf development, showing that expressed plant defenses are effective. Of the three foliar defenses evaluated during leaf development, it was observed that density of trichomes presents effectiveness peak in early development, biotic defense (EFNs productivity) in intermediated period of development and leaf toughness in the period in which the leaf is adult. These results show the efficacy of temporal variation in foliar defenses in Q. multiflora, which directly affects ant-plant interaction. In Chapter 2, it was shown that EFNs located in inflorescences produce nectar more quantitative and qualitative, which attract large amount of ants, than EFNs located in leaves. EFNs productivity and attractiveness, as well as ants foraging, were also influenced by herbivory variation (experimentally simulated). These results show that Q. multiflora synchronizes its leaf defenses over time ensuring protection against herbivores and that these defenses (as evidenced for biotic defense) can be changed according to value and attack probability of their structures.

Le métabolisme secondaire joue un rôle écologique majeur dans les interactions des organismes avec leur environnement. Une étude intégrée de la biologie, de l’écologie des organismes et des variations de leur métabolisme est essentielle pour comprendre le rôle des métabolites secondaires au sein des écosystèmes. Or ce type d’approche est rare en milieu marin.Le petit clade d’éponges Homoscleromorpha constitue un vrai potentiel de découverte de nouvelles espèces et de molécules bioactives valorisables. Par ailleurs, leur position de dominance dans certaines communautés benthiques de Méditerranée en faisait un modèle de choix pour démarrer des recherches en écologie chimique marine.Ce travail a débuté avec la description d’une espèce du genre Oscarella, O. balibaloi ainsi que de nouvelles molécules produites par cet organisme. Cette nouvelle espèce avec deux autres espèces communes du même genre, O. tuberculata et O. lobularis constituent parfois de vrais faciès au sein des communautés du coralligène et des grottes semi-obscures. L’étude comparée du cycle de vie de ces Oscarella a montré dans tous les cas une reproduction saisonnière, avec des différences dans les périodes de gamétogénèse et d’émission des larves, et des sensibilités variables face aux changements des conditions de régime thermique. Deux composés majoritaires de type lysophospholipides ont été isolés et caractérisés pour la première fois dans O. tuberculata, et retrouvés dans O. lobularis. Leur rôle potentiel de médiateurs moléculaires impliqués dans le processus de reproduction (embryogenèse et développement) a été proposé, et devra être confirmé par des études expérimentales. Une nouvelle famille de sesterterpènes glycosylés (dénommés balibalosides) a été découverte dans O. balibaloi.Une étude pluriannuelle des variations du métabolisme de ces espèces a été réalisée à travers trois approches complémentaires permettant de tester les modalités d’allocation des ressources à la production de métabolites secondaires. Les patrons de variation des niveaux d’expression de métabolites ciblés, des signatures métaboliques et des bioactivités des extraits d’éponges ont montré une influence significative du cycle de reproduction sur le métabolisme secondaire. Les méthodes globales (métabolomique et bioactivité) ont permis de montrer que le cycle de variation du métabolisme secondaire était marqué par une modification importante de sa production accompagnée par une baisse de bioactivité pendant les périodes les plus coûteuses de la reproduction (reproduction asexuée, embryogenèse et développement larvaire). Ces résultats montrent un compromis d’allocation des ressources entre un métabolisme primaire (la reproduction) et la production des métabolites secondaires, et soutient ainsi la théorie de défense optimale.L’approche de métabolomique s’est avérée un bon indicateur de la chimio-diversité. Appliquée à l’étude des relations inter-spécifiques, cette méthode de chimio-systématique a permis de proposer une classification des espèces méditerranéennes d’Homoscleromorpha. Cette classification soutient les résultats les plus récents de phylogénie moléculaire et propose la restauration de deux anciens clades au sein des Homoscleromorpha: les Plakinidae, un groupe qui ne contient aujourd’hui que des espèces à squelette, et les Oscarellidae qui ne contient que des espèces sans squelette. Les approches développées au cours de cette thèse permettent de nombreuses perspectives en chimio-systématique et écologie chimique marine. L’utilisation des signatures métaboliques peut être transposée à d’autres questions de systématique, particulièrement pour démontrer l’existence d’espèces cryptiques, et pour soutenir des hypothèses phylogénétiques au sein d’autres clades problématiques [...] / Secondary metabolism plays a major ecological role in the interactions between the organisms and their environment. An integral study of the organisms’ biology and ecology and the variations of their metabolism is essential for understanding the role of secondary metabolites in the ecosystems. This kind of approach is rare in the marine environment. Small sponge clade Homoscleromorpha constitutes a real potential for the discovery of new species and potentially bioactive molecules. In addition, its dominance in some Mediterranean benthic communities makes it a good model in marine chemical ecology research. This work has started with a description of new species of Oscarella genus, O. balibaloi. This new species forms sometimes, with two other commun Oscarella species, O. tuberculata and O. lobularis, special facies within the coralligenous and semi-dark cave communities. All three Oscarella species are caraterized by a seasonal reproductive cycle with differences in the period of gametogenesis and larval emission as well as the variation in sensitivity facing the changes in thermal regime. Two major lysophospholipid compounds were isolated and caracterized for the first time in O. tuberculata and confirmed in O. lobularis. Their potential role as signal molecules in the reproduction process (embryogenesis and development) was proposed and should be confirmed by experimental studies. One new familly of glycosilated seterterpens (named balibalosides) was found in O. balibaloi. A pluriannual study of species metabolism was performed using three complementary approaches and enabled to test the models of resource allocation to secondary metabolite production. Variation patterns in the expression level of target metabolites, in the metabolic fingerprints and the bioactivities of sponge extracts reflected the significant influence of the reproductive cycle to the secondary metabolite production. Holisitic approaches (métabolomics and bioactivity) pointed out the important modification in the secondary metabolism variation pattern followed by the decrease in bioactivity during the costly period of reproduction (asexual reproduction, embryogenesis and larval development). These results highlight the trade-off in resource allocation between the primary (reproduction) and secondary metabolism and therefore support the Optimal Defense Theory. Metabolomic approach applied to the study of interspecific relations turned out as a good indicator of chemical diversity which allowed the classification of Mediterranean Homoscleromorpha sepcies. The obtained classification was congruent with recent molecular phylogeny results proposing the restauration of two ancient clades within Homoscleromorpha, the Plakinidae, a group of species possesing skeleton and the Oscarellidae, a group of species lacking skeleton. Approaches developed during my thesis opened a numerous perspectives in chemosystematics and marine chemical ecology. The use of metabolic fingerprints can be transposed to other questions in systematics, particularly to demonstrate the existance of cryptic species and to support phylogenetic hypothesis within other problematic clades. [...]