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 Composition of the Theme - Projects - Phd theses in progress

Head: Gilles Le Moullac (IFREMER)

Scientific context and aims

The islands of French Polynesia are spread over a maritime area of more than 5 million km² and are characterised by highly contrasting situations from the ecological, geomorphological and thus environmental points of view.  This highly fragmented territory (118 islands, 5 archipelagos), isolated from other continents, has thus been the site of intensive speciation resulting in a high degree of endemism, and also phenomena of local adaptation for the most ubiquitous species.  This diversity, whether of species, of biological processes or of chemical processes, has always been exploited by Polynesian populations for food, health and cosmetic resources, and today represents a major source of revenue for the territory via the wide range of ecosystem services which it supports.  Certain of these resources have already been valorised locally or internationally, but many biological issues remain to be solved with regard to the sustainability and the development of these sectors.

In this ecological, biological, social and economic context, the main objective of Theme 1 is the acquisition of knowledge for the valorisation of the marine and terrestrial resources of French Polynesia.  In order to achieve this aim, the theme is subdivided into three complementary research axes: i) Dynamic and diversity of populations; ii) Physiological processes; iii) Exploitation of biodiversity. Our approach is integrated at several scales (spatial and temporal, from molecules to populations) and involves various disciplines (human sciences, molecular chemistry, eco-physiology, cellular biology, 'omics', etc.).

Axis 1 : Dynamic and diversity of populations

The core of this research axis is the study of the diversity and the dynamic of wild or farmed populations in relation with their environment. For example, the study of the genetic diversity of wild populations can provide a basis for partially explaining phenotypes of interest and is necessary for the maintenance of the resource at an optimum productivity rate. The sustainable exploitation of these resources also requires the characterisation of their dynamic in time and space.  Thus, two main types of studies are carried out. At terrestrial level, the chemical diversity of Polynesian plants and their distribution dynamic are studied by combining chemical screening, measurement of biological activity and landscape dynamics. At marine level, and depending on the study model, we develop approaches aiming to characterise the genetic diversity of wild and farmed populations, or to explain and characterise certain phenotypes of interest via the study of genotypical and epi-genotypical diversity selected by the environment. Among the questions to be dealt with in priority:

  • to provide support for pearl farming, this involves pursuing the genetic characterisation of pearl oyster populations by developing at genome scale tools to link the genetic diversity and genes involved in the expression of phenotypes of interest. This approach is supported by the first studies of the epigenetics of populations enabling the understanding of genotype/environment interactions in the mechanisms controlling the expression of these phenotypes;
  • in the field of fish farming, we have undertaken the first studies on the genetic diversity of wild and farmed populations of the fish Platax orbicularis, with the zoo-technical objective of optimising breeding among the genitors in a hatchery.
  • the characterisation of the chemical diversity occurring in marine and terrestrial plants in French Polynesia. In complement to this approach, the dynamic of the distribution of species identified as potentially of interest will be studied, in order to assess the capacity for tolerance of these populations for sustainable development.

Axis 2 : Physiological processes

In general, the optimum valorisation of a natural resource often involves the mastery and detailed understanding of certain stages of its biological cycle, of certain physiological processes or of the mode of action of certain molecules. In the context of aquaculture, the full understanding of the physiological functions of the reproduction and nutrition of stocks from the point of view both of underlying processes and of their control factors (in particular environmental), represent fundamental issues. This is in particular the case in French Polynesia with regard to three models of interest for aquaculture: two bivalves Pinctada margaritifera and Tridacna maxima (giant clam), and one fish Platax orbicularis (vernacular name: paraha peue). For example, the understanding of the mechanisms of control of sexual differentiation in the pearl oyster (a protandrous hermaphrodite), and in particular the role of temperature, is of primordial importance in the context of climate change.  From the applied point of view, these results constitute a preliminary step towards the development of genetic enhancement programmes. While certain natural resources are valorised in toto, in the case of others, only the secondary product derived from this resource has any commercial interest, such as the pearl or the biologically active molecules isolated from the Polynesian flora. In these two cases, research is under way to study the fundamental processes of biomineralisation, in the first case, and the mode of cellular action for the second.  

In general, our work is focused in priority on the detailed characterisation of the processes of sexual differentiation, of biomineralisation, of nutrition and of biological activity, taking into account the interactions between functions, but also the influence of the environment on these processes. To meet these objectives, whether fundamental or applied, this research axis relies on the complementary competences of the team members in the fields of ecophysiology, cellular biology, functional genomics and epigenetics. The work of this research axis is carried out in close collaboration with Theme 3, in which environmental variability is taken into account.    

Axis 3 : Exploitation of biodiversity

This third, well-developed research axis involves the assessment of the potential for improvement of the already existing sectors or the emergence of new sectors of valorisation of natural resources, in close interaction with the extensive panel of private sector and institutional partners of the EIO research unit. There is real potential for pharmaceutical or cosmetics applications for many natural substances derived from terrestrial or marine plants.  For example, the Polynesian flora is rich and original, with 885 native vascular plants, of which 550 are endemic, and the ethnobotanical work carried out by our laboratory has shed light on several plants with high biological activity potential, on which in-depth phyto-chemical research is required. With regard to the marine flora, 309 species of macro-algae have been recorded as well as a wide range of cyanobacteria, upon which similar studies have been carried out, with in addition the potential for the development of seaweed farming and combined macroalgae / fish or shrimp farming. Another part of this research is focused on investigation of the potential as feed of the microalgae that are sometimes abundant in the lagoons of the Polynesian atolls and islands. Naturally consumed by the pearl oyster, these taxons may prove to be better suited for the breeding of bivalves in the hatchery than the strains that are currently used. Finally, the use of the intra-specific biodiversity represents a crucial pathway for the genetic enhancement of the pearl oyster, by organising the restructuring of the sector via the emergence of ad hoc structures (e.g. hatcheries, on-growing centres) for the valorisation of lines selected locally.