Oceanic islands provide a "natural laboratory" to study the impact of the evolutionary forces on the biodiversity. The effects of genetic drift and the impact of the natural selection appear all the more exacerbated since the islands are isolated and subjected to strong environmental gradients. Our study associates neutral molecular markers and characters related to the adaptation in order to evaluate the influence of these various forces in the insular context of New Caledonia on the forest species Santalum austrocaledonicum. The study of the nuclear and chloroplastic microsatellites shows a clear differentiation of the populations of the small Loyauté islands and isolation by distance within the largest island, Grande Terre. Moreover our study highlights an heterozygote deficit within populations which can be allotted to a spatial sub-structure or selfing. The variation of the size of the leaves and seeds, which are related to adaptation, results from the effects of drift but also from natural selection caused by environmental contrasts related to rainfall. In the same way the chemical composition of heartwood, analysed by chromatography, would undergo, in addition to the drift, a selective pressure exerted by phytophagous insects and mushrooms. This exploratory raises many prospects for research concerning evolutionary questions and insularity. This study enables to define units of management of this species associating adaptive characters and molecular variables.
Causes of molecular and phenotypic variability of an insular tree species : Santalum austrocaledonicum in New-Caledonia