Stéphanie Barthe

Post-doc at EcoFoG : September 2013 - April 2014

Demographic transition signature of tropical rain forest trees on the Guiana plateau

PhD thesis defended on December, 14th 2012.

The present species constitution of the Amazonian tropical rain forest results from the occurrence of past perturbations. These environmental changes have various origins such as entropic activity or climatic modifications and leave a phylogeographical signature in tree genomes.

The DNA imprint allows for the rebuilding of the demographic history of each present species. The aim of the study is to trace back these signals for many species with different ecological patterns of behavior. In French Guiana, Scotti-Saintagne et al. (In prep, 2010) gave prominence to an expansion of three species of pioneering tree probably between the last glacial maximum and a most recent historical time. Certain species possessing some ecological characteristics underwent a fast expansion, while the others remained common over the studied period. The aim is to know if these French Guiana expansions concerned all forest species and if they are bound to major climate changes and/or to deep modifications of the Amazonian forest landscapes by the pre-Colombian populations.

Human activity’s impact on forest populations is assessed for 4 species on 5 Amerindian sites, from 7 nuclear microsatellite regions. The impact of climatic events is assessed on Guiana for 15 species, with 3 to 5 specific nuclear and universal chloroplastic markers. Inter-specific genetic diversity is studied and demographic evolutions are tested and dated according to a typical model of intrusive species. These analytical methods of demographic changes are based on the measure of molecular diversity within the framework of Bayesian approaches for the coalescent analysis. Then expansion dates are compared either with estimated periods of Amerindian occupation by archaeologists, or with paleontological dating of major climatic events. Unfortunately studied species are often unrecognized and hard to identify in forest. And it would be necessary as well as gather more past climatic information in French Guiana.

Keywords : Population genetics, Demographic signature, Entropic and climatic perturbations, Tropical rain forest.



Ivan Scotti

Bruno Hérault

FSE Guyane {PNG}Union Européenne {PNG}

Cette thèse a été cofinancée par l’Union Européenne.

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