Identifying factors that promote population differentiation is of interest for understanding the early stages of speciation. Gene flow among populations inhabiting different environments can be reduced by geographical distance (isolation-by-distance) or by divergent selection resulting from local adaptation (isolation-by-ecology). Few studies have investigated the influence of these factors in small oceanic islands where the influence of geographic distance is expected to be null but where habitat diversity could have a strong effect on population differentiation. In this study, we tested for the spatial divergence of phenotypes (floral morphology and floral scent) and genotypes (microsatellites) among ten populations of Jumellea rossii, an epiphytic orchid endemic to Réunion growing in three different habitats. We found a significant genetic differentiation between populations that is structured by habitat heterogeneity rather than by geographic distance between populations. These results suggest that ecological factors might reduce gene flow among populations located in different habitats. This pattern of isolation-by-habitat may be the result of both isolation-by-ecology by habitat filtering and asynchrony in flowering phenology. Furthermore, data on floral morphology match these findings, with multivariate analysis grouping populations by habitat type but could be only due to phenotypic plasticity. Indeed floral scent compounds were not significantly different between populations indicating that specific plant-pollinator mutualism does not seem to play a major role in the population differentiation of J. rossii. In conclusion, the results from our study emphasize the importance of habitat diversity of small oceanic islands as a factor of population differentiation.

Even if the persistence of the J. fragrans population is not threatened in the short term, its genetic diversity has probably been reduced by fragmentation and over-collection. In situ conservation actions for J. fragrans and ex situ cultivation of both species are recommended in order to meet the demand of local people.

Morphological differences and identification of Jumellea rossii and Jumellea fragrans (Orchidaceae) in Reunion Island : implications for conservation. — Conservation strategies are not possible when there is confusion in the taxonomic status of a group of plants. Such confusion makes difficult for systematic biologists to identify functional biological entities. This is particularly true in the case of species that diversified fast due to adaptive radiation particularly plants from the oceanic islands. It is the case of certain orchids from Reunion Island. Among them, the “Faham” complex includes several taxa whose populations are situated at various elevations with morphological and reproductive variations. These taxa are actually merged into one name : Jumellea fragrans causing confusion in their taxonomic status. This confusion has caused numerous problems of identification and errors hindering the protection status of the species. In this study, we suggest to clarify the systematic position of the taxa composing complex Jumellea fragrans using a biometric approach at population scale. The objective is to identify morphological characters that allow distinguishing the taxa of the J. fragrans complex. Morphological characters (vegetative and floral) are measured on individuals from three natural populations representative of altitudinal range of the complex. Principal component analysis made on the characters show a separation of the individuals in two groups (Mare-Longue vs Basse-Vallée and Cilaos). Nine characters (on 14 measured) are significantly different between Mare-Longue population and the populations of Basse-Vallée and Cilaos and allow identifying both groups. Population of Mare-Longue belongs to the species Jumellea fragrans (Thouars) Schltr. and populations of Basse-Vallée and Cilaos belongs to the species Jumellea rossii Senghas. In terms of conservation, the first recommendation is to recognize two different species : J. rossii and J. fragrans. Moreover, putting J. fragrans into the «vulnerable» IUCN Red List category and the adoption of a protection status are recommended. Concerning J. rossii, more studies on geographical range and population dynamics are necessary to estimate the risk of extinction. In the same way, studies on genetic variability of both species would generate useful data for implementation of conservation strategies.

Jumellea fragrans and Jumellea rossii, both named "Faham", are two epiphytic orchids endemic to the Mascarene Islands (Reunion, Mauritius) widely used for their aromatic and medicinal properties. Cultivation of these orchids is currently non-existent, so gathering and poaching in natural populations provide the supply. Continued use of this resource and the reduction of its natural habitat now result in a drastic decline of its natural populations. In order to prevent the decline of these taxa, to preserve its natural evolution in the wild, and to answer to the local consumers demand, we initiate a multidisciplinary project. The main aim of the so-called "ORCHIFAH" project is to provide the scientific background requisite for the production of Faham at an industrial level. An ecological approach is set to characterise the environmental conditions (light, temperature, watering) for an optimal biomass production. In vitro conditions of asymbiotic germination are currently determined. The biochemical components variation of populations of the two species are analysed by RMN spectrometry. The development of an appropriated extractive mode of volatile compounds is planned. All this information will help us to accurately characterise the biology of Faham and the conditions of its production, essential prerequisites for the development of an agricultural production chain. The results will also allow us to determine the conservation status of the species and recommendations for the management of wild populations. The poster will explicit the different steps of the implementation of an agricultural production chain. The first results in each field will be presented. (Texte intégral

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