Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Growth defense tradeoff theory predicts that plants in low-resource habitats invest more energy in defense mechanisms against natural enemies than growth, whereas plants in high-resource habitats can afford higher leaf loss rates. A less-studied defense against herbivores involves the synchrony of leaf production, which can be an effective defense strategy if leaf biomass production exceeds the capacity of consumption by insects. The aim of this study was to determine whether leaf synchrony varied across habitats with different available resources and whether insects were able to track young leaf production among tree habitat specialists in a tropical forest of French Guiana. We predicted that high-resource habitats would exhibit more synchrony in leaf production due to the low cost and investment to replace leaf tissue. We also expected closer patterns of leaf synchrony and herbivory within related species, assuming that they shared herbivores. We simultaneously monitored leaf production and herbivory rates of five pairs of tree species, each composed of a specialist of terra firme or white-sand forests within the same lineage. Our prediction was not supported by the strong interaction of habitat and lineage for leaf synchrony within individuals of the same species; although habitat specialists differed in leaf synchrony within four of five lineages, the direction of the effect was variable. All species showed short time lags for the correlation between leaf production and herbivory, suggesting that insects are tightly tracking leaf production, especially for the most synchronous species. Leaf synchrony may provide an important escape defense against herbivores, and its expression appears to be constrained by both evolutionary history and environmental factors.
ISSN: 1385-0237

hal-01204221
https://hal.archives-ouvertes.fr/hal-01204221
DOI : 10.1007/s11258-013-0290-y
PRODINRA : 288500

Résumé : Les mécanismes à l’origine du maintien de la forte diversité locale des arbres des forêts tropicales humides constituent encore une énigme pour les scientifiques. Cette thèse a pour but d’étudier et de comprendre certains facteurs biotiques et abiotiques qui influencent l’assemblage des communautés des forêts tropicales humides d’Amazonie. A l’aide d’une approche empirique conduite dans les forêts tropicales de Guyane française et du Loreto au Pérou, de nombreuses expériences de terrain ont été mises en place dans le but d’apporter des éléments de réponse sur les mécanismes impliqués dans le maintien de la diversité des communautés d’arbres et d’insectes des forêts amazoniennes. Dans un premier temps, cette thèse permet de souligner l’importance des pressions biotiques exercées sur les communautés d’arbres. En effet, les communautés d’insectes peuvent influencer la composition des communautés d’arbres le long d’un gradient environnemental conduisant à des compromis entre la défense et la croissance. Ces compromis ou tradeoff permettent de maintenir la coexistence des espèces de forêts tropicales humides en favorisant la spécialisation des arbres à leur habitat (Chapitre 1, Annexe 3). Cependant, de nombreux facteurs peuvent engendrer des variations dans les compromis d’allocation exhibés par les plantes, ce qui peut compliquer la validité de ces résultats. Dans ce sens, nous avons souligné l’influence du rôle de la cascade trophique et l’existence chez certaines espèces d’arbres de stratégies d’évitement des insectes (Chapitre 2). Dans un second temps, nous avons montré que les filtres environnementaux et les distances géographiques favorisent un fort turnover de la composition des arthropodes des forêts tropicales (chapitre 3, Annexe 2). Les résultats de cette étude ont des implications fondamentales sur les mécanismes qui expliquent la structuration des communautés d’insectes herbivores. Nous avons souligné l’importance de l’interaction des communautés des insectes herbivores et de leurs plantes associées. De plus, des prédictions sont présentées sur le degré de spécialisation des insectes à leur plante-hôte (Annexe 3), notamment sur les implications possibles dans les compromis d’allocation chez les plantes. Finalement, des perspectives de recherche sont proposées en vue de poursuivre ces travaux de recherche, et notamment des extensions de mes expériences vers d’autres régions tropicales et tempérées et l’intégration de la phylogénie pour comprendre des mécanismes de coévolution entre communautés d’arbres et insectes. Nous proposons également une intégration des résultats de cette thèse dans les stratégies locales et régionales de conservation des forêts tropicales du bassin amazonien.
The mechanisms underlying the maintenance of local diversity of trees in tropical rainforests remain under debate. This dissertation aims to study and understand some biotic and abiotic factors that may influence both tree and insect community assembly in lowland tropical forests of Amazonia. I used an empirical approach to study communities of trees and insects in tropical forests of French Guiana and Peru, to address the extent to which insect herbivores contribute to the turnover of tree species across strong environmental gradients. In Chapter 1, I studied how herbivorous insect communities can influence the composition of tree communities along an environmental gradient by reinforcing tradeoffs between defense and growth that promote habitat specialization (Chapter 1, Appendix 3). The complicated variation in the patterns of growth and defense from this study led me to pursue further observations of an alternative plant defense strategy of time-avoidance of herbivores, which I examined in detail in Chapter 2. I found evidence for coordinated leaf production in some tree species that was consistent with the satiation of herbivores, suggesting that multiple interactions between plants and their herbivores may be responsible for patterns of habitat specialization in trees. In the second part of the dissertation, I examined insect herbivore communities in detail to test for turnover in species composition across geographic and environmental gradients. In Chapter 3, I present evidence for substantial beta-diversity in arthropod communities throughout lowland Amazonian forests. In the discussion I propose research perspectives to complete this research, including the extension of observations to compare tropical and temperate regions and the integration of molecular phylogenetics information to study coevolution of plant lineages and their insect herbivores. I conclude with suggestions for the integration of the results of this thesis in local and regional strategies for the preservation and conservation of tropical forests in the Amazon basin.

http://www.theses.fr/2013AGUY0582/document

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Plants often rely on external, mutualistic partners to survive and reproduce in resource-limited environments or for protection from enemies. Such interactions, including mycorrhizal symbioses and ant-plant associations, are widespread and play an important role at the ecosystem and community levels. In ant-plant mutualisms, the plants may benefit from both the protection provided by the presence of ants and from the nutrients absorbed from insect debris. However, the role of third partners in plant nutrition, particularly ant-associated fungi, has never before been demonstrated. 2. We investigate this issue in the ant-plant Hirtella physophora. In this model system, Allomerus decemarticulatus ants are involved in two, highly specific interactions: first, with their host plant, and, secondly, with a fungus that they actively manipulate. Moreover, the ants combine both plant trichomes and fungal hyphae to make a trap to capture prey. 3. We empirically demonstrate the existence of a third type of interaction between the fungus and the plant through the use of both experimental enrichments with stable isotopes (15N) and histological approaches. The fungus growing in the galleries plays a role in providing nutrients to the host plant, in addition to the structural role it plays for the ants. Fungus-facilitated nitrogen uptake occurs mainly in old domatia, where abundant hyphae are in close contact with the plant cells. Whether the fungi inside the domatia and those in the galleries are the same is still uncertain. 4. Synthesis. Together, our results show that a fungal partner in an ant-plant mutualism can benefit the plant by improving its nutrient uptake, and they demonstrate the existence of a true tripartite mutualismin this system. Our results add further evidence to the notion that interpretations of some ant-plant symbioses as purely protective mutualisms have overlooked these nutritional aspects.
ISSN: 0022-0477

hal-00818792
https://hal.archives-ouvertes.fr/hal-00818792

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
1. Our understanding of the contribution of interspecific interactions to functional diversity in nature lags behind our knowledge of spatial and temporal patterns. Although two-species mutualisms are found in all types of ecosystems, the study of their ecological influences on other community members has mostly been limited to third species, while their influence on entire communities remains largely unexplored. 2. We hypothesized that mutualistic interactions between two respective ant species and an epiphyte mediate the biological traits composition of entire invertebrate communities that use the same host plant, thereby affecting food webs and functional diversity at the community level. 3. Aechmea mertensii (Bromeliaceae) is both a phytotelm ('plant-held water') and an ant-garden epiphyte. We sampled 111 bromeliads (111 aquatic invertebrate communities) associated with either the ant Pachycondyla goeldii or Camponotus femoratus. The relationships between ants, bromeliads and invertebrate abundance data were examined using a redundancy analysis. Biological traits information for invertebrates was structured using a fuzzy-coding technique, and a co-inertia analysis between traits and abundance data was used to interpret functional differences in bromeliad ecosystems. 4. The vegetative traits of A. mertensii depended on seed dispersion by C. femoratus and P. goeldii along a gradient of local conditions. The ant partner selected sets of invertebrates with traits that were best adapted to the bromeliads' morphology, and so the composition of the biological traits of invertebrate phytotelm communities depends on the identity of the ant partner. Biological traits suggest a bottom-up control of community structure in C. fenaoratus-associated phytotelmata and a greater structuring role for predatory invertebrates in P. goeldii-associated plants. 5. This study presents new information showing that two-species mutualisms affect the functional diversity of a much wider range of organisms. Most biological systems form complex networks where nodes (e.g. species) are more or less closely linked to each other, either directly or indirectly, through intermediate nodes. Our observations provide community-level information about biological interactions and functional diversity, and perspectives for further observations intended to examine whether large-scale changes in interacting species/community structure over broad geographical and anthropogenic gradients affect ecosystem functions.
Functional Ecology

hal-01096909
https://hal-agroparistech.archives-ouvertes.fr/hal-01096909
DOI : 10.1111/j.1365-2435-2011.01863.x

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Mutualisms, or interactions between species that lead to net fitness benefits for each species involved, are stable and ubiquitous in nature mostly due to "byproduct benefits" stemming from the intrinsic traits of one partner that generate an indirect and positive outcome for the other. Here we verify if myrmecotrophy (where plants obtain nutrients from the refuse of their associated ants) can explain the stability of the tripartite association between the myrmecophyte Hirtella physophora, the ant Allomerus decemarticulatus and an Ascomycota fungus. The plant shelters and provides the ants with extrafloral nectar. The ants protect the plant from herbivores and integrate the fungus into the construction of a trap that they use to capture prey; they also provide the fungus and their host plant with nutrients. During a 9-month field study, we over-provisioned experimental ant colonies with insects, enhancing colony fitness (i.e., more winged females were produced). The rate of partial castration of the host plant, previously demonstrated, was not influenced by the experiment. Experimental plants showed higher δ¹⁵N values (confirming myrmecotrophy), plus enhanced vegetative growth (e.g., more leaves produced increased the possibility of lodging ants in leaf pouches) and fitness (i.e., more fruits produced and more flowers that matured into fruit). This study highlights the importance of myrmecotrophy on host plant fitness and the stability of ant-myrmecophyte mutualisms.
PLoS ONE

hal-00913754
https://hal.archives-ouvertes.fr/hal-00913754
https://hal.archives-ouvertes.fr/hal-00913754/document
DOI : 10.1371/journal.pone.0059405
OATAO : 10202

Éditeur(s) : HAL CCSD Royal Society, The
Résumé : Species engaged in multiple, simultaneous mutualisms are subject to trade-offs in their mutualistic investment if the traits involved in each interaction are overlapping, which can lead to conflicts and affect the longevity of these associations. We investigate this issue via a tripartite mutualism involving an ant plant, two competing ant species and a fungus the ants cultivate to build galleries under the stems of their host plant to capture insect prey. The use of the galleries represents an innovative prey capture strategy compared with the more typical strategy of foraging on leaves. However, because of a limited worker force in their colonies, the prey capture behaviour of the ants results in a trade-off between plant protection (i.e. the ants patrol the foliage and attack intruders including herbivores) and ambushing prey in the galleries, which has a cascading effect on the fitness of all of the partners. The quantification of partners' traits and effects showed that the two ant species differed in their mutualistic investment. Less investment in the galleries (i.e. in fungal cultivation) translated into more benefits for the plant in terms of less herbivory and higher growth rates and vice versa. However, the greater vegetative growth of the plants did not produce a positive fitness effect for the better mutualistic ant species in terms of colony size and production of sexuals nor was the mutualist compensated by the wider dispersal of its queens. As a consequence, although the better ant mutualist is the one that provides more benefits to its host plant, its lower host–plant exploitation does not give this ant species a competitive advantage. The local coexistence of the ant species is thus fleeting and should eventually lead to the exclusion of the less competitive species.
ISSN: 0962-8452

hal-01608641
https://hal.archives-ouvertes.fr/hal-01608641
DOI : 10.1098/rspb.2016.1679
PRODINRA : 405078

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
In mutualisms, each interacting species obtains resources from its partner that it would obtain less efficiently if alone, and so derives a net fitness benefit. In exchange for shelter (domatia) and food, mutualistic plant-ants protect their host myrmecophytes from herbivores, encroaching vines and fungal pathogens. Although selective filters enable myrmecophytes to host those ant species most favorable to their fitness, some insects can by-pass these filters, exploiting the rewards supplied whilst providing nothing in return. This is the case in French Guiana for Cecropia obtusa (Cecropiaceae) as Pseudocabima guianalis caterpillars (Lepidoptera, Pyralidae) can colonize saplings before the installation of their mutualistic Azteca ants. The caterpillars shelter in the domatia and feed on food bodies (FBs) whose production increases as a result. They delay colonization by ants by weaving a silk shield above the youngest trichilium, where the FBs are produced, blocking access to them. This probable temporal priority effect also allows female moths to lay new eggs on trees that already shelter caterpillars, and so to occupy the niche longer and exploit Cecropia resources before colonization by ants. However, once incipient ant colonies are able to develop, they prevent further colonization by the caterpillars. Although no higher herbivory rates were noted, these caterpillars are ineffective in protecting their host trees from a pathogenic fungus, Fusarium moniliforme (Deuteromycetes), that develops on the trichilium in the absence of mutualistic ants. Therefore, the Cecropia treelets can be parasitized by two often overlooked species: the caterpillars that shelter in the domatia and feed on FBs, delaying colonization by mutualistic ants, and the fungal pathogen that develops on old trichilia. The cost of greater FB production plus the presence of the pathogenic fungus likely affect tree growth.
PLoS ONE

hal-00912399
https://hal.archives-ouvertes.fr/hal-00912399
https://hal.archives-ouvertes.fr/hal-00912399/document
DOI : 10.1371/journal.pone.0020538
OATAO : 10156

Éditeur(s) : HAL CCSD Frontiers Media
Résumé : "Candidatus Liberibacter solanacearum" (Lso) has emerged as a serious threat world-wide. Five Lso haplotypes have been identified so far. Haplotypes A and B are present in the Americas and/or New Zealand, where they are vectored to solanaceous plants by the potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae). The fastidious nature of these pathogens has hindered the study of the interactions with their eukaryotic hosts (vector and plant). To understand the strategies used by these pathogens to infect their vector, the effects of each Lso haplotype (A or B) on psyllid fitness was investigated, and genome-wide transcriptomic and RT-qPCR analyses were performed to evaluate Lso gene expression in association with its vector. Results showed that psyllids infected with haplotype B had significantly lower percentage of nymphal survival compared to psyllids infected with haplotype A. Although overall gene expression across Lso genome was similar between the two Lso haplotypes, differences in the expression of key candidate genes were found. Among the 16 putative type IV effector genes tested, four of them were differentially expressed between Lso haplotypes, while no differences in gene expression were measured by qPCR or transcriptomic analysis for the rest of the genes. This study provides new information regarding the pathogenesis of Lso haplotypes in their insect vector.
ISSN: 2235-2988

hal-01512244
https://hal.archives-ouvertes.fr/hal-01512244
https://hal.archives-ouvertes.fr/hal-01512244/document
https://hal.archives-ouvertes.fr/hal-01512244/file/Yao%202016%20Frontiers%20in%20Cellular%20and%20Infection%20Microbiology_%7BD6ACF6EB-9794-4F27-AB84-9EF4099B6D78%7D.pdf
DOI : 10.3389/fcimb.2016.00062

Éditeur(s) : HAL CCSD
Résumé : Neotropical forests shelter an astonishing and underrated biodiversity. The integrity and stability of these natural ecosystems are threatened by human-induced environmental changes. Therefore, highlighting the determinants of ecosystem functioning, be they natural or anthropogenic, is a daunting but paramount scientific challenge. The intrinsic complexity of highly diversified ecosystems arouses both conceptual and logistical difficulties, which we handle, by manipulating tiny ecosystems, the tank bromeliads. The leaves of tank bromeliads form wells that hold rainwater and intercept leaf litter, allowing for a simple invertebrate aquatic community to thrive. These plants can be exhaustively sampled, are naturally replicated, and widely distributed.From local to biogeographic scales, this thesis aims at understanding how these communities respond to the natural heterogeneity of Amazonian forests, and at predicting the impacts of human-induced disturbances on the structure and functioning of these communities, using in situ and lab experiments. Particular focus is attributed to the influence of some aspects of climate changes (e.g., warming, and various precipitations scenarios) on individual physiology, behavior, and trophic interactions.
Les forêts néotropicales accueillent une importante biodiversité encore méconnue. L’intégrité des écosystèmes naturels est menacée par les changements environnementaux (e.g., réchauffement climatique, destruction des habitats), par conséquent, identifier les facteurs structurants, naturels et anthropiques, du fonctionnement des écosystèmes, représente un défi scientifique crucial. L’inhérente complexité de ces milieux diversifiés pose de nombreux problèmes conceptuels et logistiques comme un échantillonnage exhaustif et/ou l’identification des espèces. Les broméliacées à réservoirs sont des écosystèmes miniatures adéquats pour pallier ces difficultés, car elles retiennent de l’eau de pluie et accumulent de la matière organique au creux de leurs feuilles, permettant ainsi de supporter des réseaux trophiques simples d’invertébrés aquatiques. Elles peuvent être échantillonnées exhaustivement, ont une forte abondance locale, et une large aire de répartition. De l’échelle locale à biogéographique, les travaux de cette thèse visent d’abord à comprendre comment ces communautés se structurent en réponse à l’hétérogénéité naturelle des forêts amazoniennes (e.g., ouverture de la canopée, fluctuations climatiques saisonnières), puis tente de prédire, par le biais d’expérimentations in situ et au laboratoire les réponses structurelles et fonctionnelles de ces communautés à divers scénarios de changement climatique. Une attention particulière a été portée sur l’impact de la température et des précipitations sur la physiologie et le comportement d’espèces clefs, et sur les interactions trophiques au sein des communautés.
https://tel.archives-ouvertes.fr/tel-01405025

NNT : 2015YANE0003
tel-01405025
https://tel.archives-ouvertes.fr/tel-01405025
https://tel.archives-ouvertes.fr/tel-01405025/document
https://tel.archives-ouvertes.fr/tel-01405025/file/These-DEZERALD-Diffusion.pdf

Éditeur(s) : HAL CCSD Taylor & Francis
Résumé : International audience
ISSN: 1559-2316

hal-01086786
https://hal-agroparistech.archives-ouvertes.fr/hal-01086786
DOI : 10.4161/psb.4.9.9423

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Myrmecophytism occurs in plants that offer ants a nesting space and, often, food rewards in exchange for protection from predators and competitors. Such biotic protection by ants can, however, interfere with the activity of pollinators leading to potential negative consequences for the plant’s reproduction. In this study, we focused on the association between the understory myrmecophyte, Hirtella physophora (Chrysobalanaceae), and its obligate ant partner, Allomerus decemarticulatus (Myrmicinae). We investigated the reproductive biology of H. physophora and the putative mechanisms that may limit ant–pollinator conflict. Our results show that H. physophora is an obligate outcrosser, self-incompatible, and potentially insect-pollinated species. The reproduction of H. physophora relies entirely on pollen transfer by pollinators that are likely quite specific. Potential interference between flower-visiting insects during pollination may also be lessened by a spatial and temporal segregation of ant and pollinator activities, thus enabling pollen transfer and fruit production.
ISSN: 1872-8855

hal-01140817
https://hal-sde.archives-ouvertes.fr/hal-01140817
DOI : 10.1007/s11829-014-9352-x

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
BACKGROUND AND AIMS: Determining the sources of variation in floral morphology is crucial to understanding the mechanisms underlying Angiosperm evolution. The selection of floral and reproductive traits is influenced by the plant's abiotic environment, florivores and pollinators. However, evidence that variations in floral traits result from mutualistic interactions with insects other than pollinators is lacking in the published literature and has rarely been investigated. We aimed to determine whether the association with either Camponotus femoratus or Pachycondyla goeldii (both involved in seed dispersal and plant protection) mediates the reproductive traits and allocation of Aechmea mertensii, an obligatory ant-garden tank-bromeliad, differently. METHODS: Floral and reproductive traits were compared between the two A. mertensii ant-gardens. The nitrogen flux from the ants to the bromeliads was investigated through experimental enrichments with stable isotopes ((15)N). KEY RESULTS: Camponotus femoratus-associated bromeliads produced inflorescences up to four times longer than did P. goeldii-associated bromeliads. Also, the numbers of flowers and fruits were close to four times higher, and the number of seeds and their mass per fruit were close to 1*5 times higher in C. femoratus than in P. goeldii-associated bromeliads. Furthermore, the (15)N-enrichment experiment showed that C. femoratus-associated bromeliads received more nitrogen from ants than did P. goeldii-associated bromeliads, with subsequent positive repercussions on floral development. Greater benefits were conferred to A. mertensii by the association with C. femoratus compared with P. goeldii ants. CONCLUSIONS: We show for the first time that mutualistic associations with ants can result in an enhanced reproductive allocation for the bromeliad A. mertensii. Nevertheless, the strength and direction of the selection of floral and fruit traits change based on the ant species and were not related to light exposure. The different activities and ecological preferences of the ants may play a contrasting role in shaping plant evolution and speciation.
ISSN: 0305-7364

hal-00819112
https://hal.archives-ouvertes.fr/hal-00819112
DOI : 10.1093/aob/mcr253
PUBMED : 21984729