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Ecology, forms and functions of the basal angiosperms from New Caledonia

Trueba Sanchez S.. 2016. Montpellier : Université de Montpellier, 220 p.. Thèse de doctorat -- Ecologie, évolution, ressources génétiques, paléontologie.

One of the remarkable characteristics of the New Caledonian flora is the presence of numerous angiosperm lineages recognized as the earliest divergences of the flowering plants, due to their phylogenetic positions. Within these lineages, some species are likely to bear ancestral morpho-anatomical features. Therefore, under a comparative perspective, the study of these species can provide compelling information for understanding the early evolutionary stages of angiosperms. The first part of this thesis aims to study the structural and functional characteristics of representative groups of basal angiosperms. The study of Amborella trichopoda, sister species to the remaining flowering plants, shows a covariation of functional traits (stem-leaf) and a morphological plasticity in response to changes in the light environment. This suggests that these plastic responses were already present in the common ancestor of angiosperms. In parallel, the study of the anatomical evolution of Piperales, the most diversified basal angiosperm order, suggests that their common ancestor had an active cambium. These results support the hypothesis that early angiosperms had a woody habit and that sympodial growth may have been acquired early during angiosperms evolution. Basal angiosperms are among the over-represented angiosperm lineages of New Caledonia. However, the mechanisms underlying this disharmony remain unexplored. A second component of this thesis analyzes the environmental distribution of New Caledonian basal angiosperms to know their habitat preferences and their environmental requirements. Further, we assess the influence of their drought tolerance on their environmental distribution. We show that most species have a preference for rain forest habitats with small variations in temperature. Drought-induced hydraulic vulnerability stands as a major trait that restricts the distribution of these species to humid habitats. These stable conditions seem to have persisted in refugial areas in the archipelago during the last glacial maximum, allowing the persistence of basal angiosperm species. Therefore, a past climatic stability could explain the over-representation of some groups of forest species that may have disappeared in neighboring regions. The distribution of basal angiosperms in New Caledonia, as well as their drought sensitivity, support the hypothesis suggesting that early angiosperms lived in humid and stable environments.

Mots-clés : nouvelle-calédonie; france

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