Taxonomía, sistemática y evolución del Hedera L. (araliaceae)

Dirigée par:
  1. Pablo Vargas Gómez Directeur/trice
  2. Modesto Luceño Garcés Tuteur

Université de défendre: Universidad Pablo de Olavide

Fecha de defensa: 13 juin 2008

  1. Salvador Talavera Lozano President
  2. Enrique Rico Hernández Secrétaire
  3. Pilar Catalán Rodríguez Rapporteur
  4. Gonzalo Nieto Feliner Rapporteur
  5. Inés Álvarez Fernández Rapporteur

Type: Thèses

Teseo: 161621 DIALNET


Species are basic units in studies of taxonomy, systematics, evolution, biodiversity and ecology. However, facing species definition, characterization and delimitation is a hard task that very often offers multiple final solutions and difficult decisions making. Theoretical and practical aspects intermingle when facing the "species problem" contributing this way to increase the inherent biological difficult on deciding. On the one hand, the "species concept" is something that should be clarified before addressing any particular species definition. However, this task is a long-standing problem that has focused the debate of evolutionary biologists since Darwin. Whether species do really exists in nature or not and whether achieving a general "species concept" is plausible or not, it is out of doubt the need of compartmentalization of organismal variability into distinguishable categories. A proper species definition, and consequent delimitation, should contemplate practical applicability without neglecting the underlying evolutionary history. This implies the need of detecting differences between putative species that were able to be characterized. Finding differences and establishing limits meets biological problems derived from the steady condition of evolution, different mechanisms involved in speciation processes and loss of hierarchy due to gene flow and hybridization. In addition to this biological complexity on species characterization, improvement of proper methodology for delimiting species has been systematically neglected. In the present thesis a worldwide systematic revision of the genus Hedera L. (Araliaceae) has been undertaken in order to propose an integral taxonomic treatment that contemplates morphology, cytogenetics, biogeography, and evolutionary history of the genus (Chapter 6). The main objective of the thesis is to provide a robust taxonomic treatment for ivies based on recognition of biological entities morphologically distinguishable. This purpose is addressed from both morphological and molecular perspectives. Macro- and micromorphological characters of ivies were examined, followed by the screening of their variability across the whole genus range. The resulting morphological data were statistically analysed and interpreted in a biogeographical context as well as correlated with cytogenetics, in order to evaluate recognised species by other authors and re-define biological entities, if needed. Particular adaptation of the traditional approach of delimiting species through the identification of apparently fixed, non- or partially overlapping differences are proposed for Hedera species (Chapter 3). Molecular sequences from plastid and nuclear genomes were analysed in order to understand phylogenetic relationships among species, as well as to infer the evolutionary history of the genus (Chapters 4). The species of Hedera recognised were finally analysed within an evolutionary context in order to understand the diversity distribution as well as to place them in the context of "phyletic lineages" (Chapters 4, 5).