Functional Ecology of Plant-Insect-Microbe interactions
Molecular Ecology, Chemical Ecology, Ecophysiology, Behavioral Ecology, Evolutionary Ecology
Nutritional Ecology of Insects
My research activity is fundamentally rooted into an ecophysiological perspective and fits into what is called Nutritional Ecology. The focus of my research is indeed to understand complex multitrophic systems and their intimate interactions based on a multidisciplinary comprehensive approach ranging from molecular biology, biochemistry and precise physiology to ecology and evolutionary biology. The second characteristic of my research is a special accent on fine and intimate physiological interactions played out on a micro-scale.
I currently develop 2 main research lines:
- Plant manipulation and nutritional strategies in plant-insect-microbe interactions
- Nutrient acquisition and allocation strategies in insects
My integrative approach is at the interface between functional and evolutionary ecology.
Nutrient acquisition and allocation strategies.
The way insects acquire, store and use nutrients has tremendous effects on their life history strategies and population dynamics. Parasitoids are of particular interest in this context, as many of them do host-feeding, often in a non-concurrent way with parasitism, on hosts. This trade-off between immediate and future reproduction relates in a most direct fashion nutrient acquisition and reproductive strategies. Such trade-off are difficult to understand without a lifelong point of view: this is necessary both because the time of death has a major influence on many decisions and also because the capital reserves, i.e. reserves accumulated during the larval stages, act as a buffer early in life.
We focus on physiological mechanisms of nutrition in Hymenopteran parasitoids and their implications for life-history traits. This research is grounded in an ecophysiological perspective as we seek to identify physiological mechanisms (nutrients acquisition and allocation rules) underlying behavioral decisions and life-history strategies in parasitoids. Our investigations mainly deal with two main evolutionary conflicts, the trade-off between investment in current reproduction and investment in potential future reproductive events on one hand, and the trade-off between the number of offspring produced and their subsequent respective fitness on the other hand. In collaboration with Prof. J. Casas, we explore fine and intimate physiological interactions at a spatial and temporal scale relevant for these organisms.
Physiological investigation of nutrient acquisition and allocation rules in the parasitoid Eupelmus vuilleti allow us today to construct one of the most complete multidimensional lifetime nutrient dynamical budgets available for any organism. We have also gained some insights on the underlying hormonal mechanisms controlling allocation.
We are currently developing futher these investigations towards ecological and biochemical mechanisms underlying lack of lipogenesis in parasitoids but also towards the implementation of acquired knowledge for applied research questions.
- Ecology & Lipogenesis: Ecological conditions underlying the lack of lipid synthesis in parasitic wasps (Projet Européen FP7-PEOPLE-IEF - Dr. D. Giron & B. Visser)
- Agroécologie: Concevoir la gestion des ravageurs en agroforesterie par la conservation de la biodiversité (Projet Région Centre - Prof. J. Casas) .
The sedentary behaviour of endophagous arthropods (i.e.; living within plant tissues) makes them ideal systems for interpreting the ecological and evolutionary mechanisms of herbivory and related questions such as plant resistance or physiological manipulation. Such intimate associations are expected to facilitate close interactions between independent genomes leading to biochemical and hormonal cross-talks between arthropods and plants, setting the ground for altered plant gene expression and changes in plant hormone activity.
We focus on understanding the adaptive significance and evolution of endophagous life history modes by studying the intimate physiological, biochemical and molecular mechanisms used by leafminer insects to manipulate their host-plant environment and their fitness consequences for the insect. Our investigation mainly deal with the understanding of how plant and herbivores interact by focusing on nutritional benefits (plant nutrients) and costs (plant defensive compounds) but also on the ancestral and convergent role of hormones (cytokinins) and the pivotal role played by endosymbiotic bacteria (Wolbachia). We also seek to estimate the impact of the internal-feeding strategy on major insect life history traits and to establish a complete nutrient budget for the endophagous insect.
Our findings reveal an unexpected capacity of leafminers to manipulate the plant physiology to their own advantages. Our results on the Malusdomestica/Phyllonorycterblancardellaplant-leaf mining system show: (i) The ability of this leafminer caterpillar to manipulate its host plant in order to generate a microenvironment with all the nutrient supply (sugars and proteins) needed for its survival. Mined areas contain more proteins and sugars than unparasitized tissues (ii) A decrease in plant defences compounds within the mined area. We recently indentified major molecular steps on which the insect can act and the metabolic consequences for the phenylpropanoids pathway. (iii) A large accumulation of cytokinins in the mined tissues which is responsible for the preservation of functional nutrient-rich green tissues at a time when leaves are otherwise turning yellow. This plant physiology manipulation is however not restricted to a specific time of the season but occurs at all stages of the plant ontogeny. (iv) The primary role played by endosymbiotic bacteria (Wolbachia) in the synthesis of these cytokinins and in the induction of nutrient-rich tissues. Removing these bacteria results in the absence of "green-island" formation on leaves, increased compensatory larval feeding, and higher insect mortality.
We are currently developing futher these investigations by investigating the chemical effectors produced by the insect and their consequences for the molecular and chemical reconfiguration of the host-plant using in particular new-sequencing technologies. We are also investigating the potential converging strategies developed by leaf-miner and gall-inducer insects.
- InsectEffect: Insect effectors involved in plant manipulation and resources exploitation (Projet Région Centre - Dr. D. Giron)
- Using three-way interactions between plants, microbes and arthropods to enhance crop protection and production (EU COST Action FA 1405 - Dr. A. Biere)
- Insect Reprogrammers: From strategies for manipulating plants to agriculture (Le STUDIUM - Dr. D. Giron & Prof. M. Harris)
My publications in high quality peer-reviewed journals ranging from field-oriented (e.g. Journal of Insect Physiology, Functional Ecology) to more general journals (e.g. Nature; Proceedings of the Royal Society London B, Ecology Letters) reflect the integrative approach characterizing my research.
To know more: http://casas-lab.irbi.univ-tours.fr/giron.html
2013 Giron D., Frago E., Glevarec G., Pieterse CMJ. & Dicke M. Cytokininsas key regulators in plant–microbe–insect interactions: connecting plant growth and defence. Functional Ecology27, 599-609
2010 Kaiser W., Huguet E., Casas J., Commin C. & Giron D. Plant green-island phenotype induced by leaf-miners is mediated by bacterial symbionts.Proceedings of the Royal Society, London B277, 2311–2319
2005 Casas J, Pincebourde S, Mandon N, Vannier F, Pujol R & Giron D. Lifetime multidimensional nutrient dynamics in a simultaneous capital and income breeding parasitoid insect. Ecology86, 545-554
2004 Giron D, Dunn DW, Hardy ICW & Strand MR. Aggression by polyembryonic wasp soldiers correlates with kinship but not resource competition. Nature 430, 676-679
2003 Giron D & Casas J. Mothers reduce egg provisioning with age. Ecology Letters6, 273-277
2002 Giron D, Rivero A, Mandon N, Darrouzet E & Casas J. The physiology of host feeding in parasitic wasps: implications for survival. Functional Ecology16, 750-757
See my CV for a complete list of publications