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Accueil du site → Doctorat → Allemagne → Systematics, ecology and evolution of Heliotropium sect. Cochranea (Heliotropiaceae) and the biogeography of the Atacama Desert

Freie Universität Berlin (2010)

Systematics, ecology and evolution of Heliotropium sect. Cochranea (Heliotropiaceae) and the biogeography of the Atacama Desert

Luebert, Federico

Titre : Systematics, ecology and evolution of Heliotropium sect. Cochranea (Heliotropiaceae) and the biogeography of the Atacama Desert

Systematik, Ökologie und Evolution von Heliotropium sect. Cochranea (Heliotropiaceae) und die Biogeographie der Atacama-Wüste

Auteur : Luebert, Federico

Université de soutenance : Freie Universität Berlin

Grade : Doctor rerum naturalium (Dr. rer. nat.) 2010

Résumé
Heliotropium sect. Cochranea (Heliotropiaceae) is endemic to the Atacama and Peruvian Deserts. In this work, systematics, ecology and evolution of Heliotropium sect. Cochranea are studied, under the hypotheses that Heliotropium sect. Cochranea may have experienced an adaptive radiation in the Atacama Desert and section Cochranea originated and diversified in response to the development of the Atacama Desert. Following research questions were addressed : (1) Which species comprise Heliotropium sect. Cochranea ? (2) Is Heliotropium sect. Cochranea monophyletic ? (3) Which major clades can be sensibly identified within Heliotropium sect. Cochranea ? (4) To which other Heliotropium species-groups is Heliotropium sect. Cochranea related ? (5) What are the ages of diversification of the major clades of Heliotropium sect. Cochranea and of the related species-groups ? (6) Is morphological diversity in Heliotropium sect. Cochranea related to its habitat ? (7) What are the limiting climatic factors determining the distribution of the species in Heliotropium sect. Cochranea ? In order to approach these questions, several methods were employed, including modern approaches to phylogenetic systematics as well as traditional alpha taxonomy and morphological analyses. Phylogeny-based divergence time estimations and event-based biogeographical analyses were carried out. Ecological niche modelling has also been employed in an attempt at identifying climatic variables that control the distribution of the species of section Cochranea. Seventeen species are recognised and one new subspecies is described. Section Cochranea was shown to be monophyletic, and originated during the middle to late Miocene, with a major diversification event during the early Pliocene. Three major Neotropical clades of Heliotropium were identified, one of them being Heliotropium sect. Cochranea. For these clades, morphological diversity based on vegetative characters of habit and leaf was compared both among clades and among species growing in arid and humid environments of the Neotropics. Heliotropium sect. Cochranea has high leaf morphological diversity, comparable to its sister group, which is species- richer. Morphological diversity tends to be greater in arid than in humid environments, especially in leaf morphology. This difference is likely due to the contribution of section Cochranea to the overall leaf morphological diversity of the Neotropical Heliotropium species from arid habitats. At least five independent Andean and extra-Andean diversification events were detected in Neotropical Heliotropium to have taken place in the late Miocene and early Pliocene, coinciding with the hypothesis of recent and rapid Andean uplift and subsequent development of aridity in South America. Winter precipitation and winter minimum temperatures were the most important variables for most species of Heliotropium sect. Cochranea. Summer maximum temperature was also important for several species. This results are consistent with the expectation that the distribution of the species of section Cochranea is mostly controlled by seasonal variation of precipitation and, secondarily, of extreme temperatures. The results are in line with adaptive radiation as evolutionary mechanisms for the diversification of Heliotropium sect. Cochranea.

Mots clés : adaptive radiation ; Boraginaceae ; Boraginales ; Chile ; phylogeny

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Page publiée le 8 novembre 2011, mise à jour le 4 novembre 2018