Considérations sur l’histoire naturelle des Ranunculales

Abstract : Ranunculales are an order of angiosperms comprising ca. 4,500 species including common plants like buttercups and poppies. Their flowers are highly diversified and have raised the interest of botanists for decades. Each of the seven families of the order is easily recognizable in the field, but paradoxically some families lack floral synapomorphies and have unclear ancestral states, like Ranunculaceae (ca. 2,500 species). This floral diversity may be linked to pollination and innovations may have been driven by this interaction. In addition, the plants of this group produce a variety of secondary compounds, some of which having been known for ages for their properties, like morphine or curare. Those substances could play a role in defense against herbivores. Both floral and chemical characters are thus good candidates to produce adaptive hypotheses. Here we used modern analytical methods to understand the the evolutionary patterns accounting for the extant distribution of diversity and evolution of Ranunculales flowers and toxins. A new synthetic phylogenetic framework of the Ranunculales based on already available sequences of 144 species was produced. Sixteen characters of the flower, and the presence of selected secondary metabolites were reconstructed on this tree using parsimony, and Reversible Jump Monte Carlo Markov Chains. A new scenario for floral evolution was produced, where Ranunculales had a trimerous perianth with three whorls of tepals ancestor, and the ancestors of the families evolved by losing and/or differentiating perianth whorls. The evolutionary patterns of toxins showed variability, some appearing and disappearing randomly (such as saponins), others being well-supported synapomorphies (such as aconitine-like diterpens for the tribe Delphinieae). These results offer a better understanding of the natural history of Ranunculales. Furthermore, this order is the sister-group of all other eudicots, and thus has a key position to understand the early evolution of this clade. These results will provide a deeper understanding of the floral and chemical changes that took place at the base of eudicots, which contains 70% of living angiosperms.
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Laetitia Carrive. Considérations sur l’histoire naturelle des Ranunculales. Botanique. Université Paris-Saclay, 2019. Français. ⟨NNT : 2019SACLS177⟩. ⟨tel-02276988⟩

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