| Summary: | Accurate species delimitations are important to understand factors driving diversification, and have implications for ecological and conservation studies. However, to give a definition of what is a “species”, which would be valid and applicable to all organisms, is challenging. Today the biologists tend to consider the species as a diversified " phenomenon " which can be characterized, morphologically, biologically, genetically, etc. rather than defined in its wholeness. Fungi rise particular problems in the determination of their "status" of species. Their range of intra-specific variations (both genetical and morphological) was poorly studied, what makes very difficult the determination of the significant characters for the establishment of diagnostic criteria. In this study we first tried to integrate the different species concept’s approaches (morphological, phylogenetical, biological, ecological etc.) in order to improve the understanding of “what is a specie” and create a “holistic” species concept. Moreover, the geographical distributions of most fungal species are also still poorly known; consequently, their origins and historical distributions remain largely understudied. High levels of cryptic diversity, scarce fossil records and poorly sampled regions can explain some of these shortcomings. Both issues were developed on an iconic group of wood decaying fungi, the genus Fomitiporia Murrill (Hymenochataceae), which includes parasitic and saprophytic species worldwide distributed. The genus was extensively sampled worldwide , in order to infer evolutionary patterns on a global scale. Fomitiporia, constitutes one of the main genera of poroid Hymenochaetaceae. The particular interest in Fomitiporia also results from the importance of several species as primary etiological agents causing diseases of economically important perennial crops or trees. Taxonomy, phylogeny and biogeography of Fomitiporia were in “chaotic” state of flux. The application of an “holistic” species concept to this genus, allowed us to evidence and at least partially resolve its complex phylogenetic / biogeographic structure. The collecting effort, mostly in tropical or subtropical areas, allow us to gather more than 300 specimens representing 98% of the species actually considered belonging to the genus. Thanks to this integrative approach, seven new species and two new combinations were described, two species proposed as new, three new combination proposed and ultimately fifteen unnamed taxa were evidenced and still need to be described and named in the Linnean system. Several morphological features, to date considered discriminating at species or genus level, such as the presence of hymenial setae or the dextrinoid basidiospores were demonstrated to be variable characters. Therefore the genus Fomitiporia was redefined on the basis of these findings. Furthermore, this study represent one of the firsts attempts to investigate fungal distributions in an evolutionary context. We used the “state of the art” phylogenetic techniques in order to investigate evolutionary relationships and historical biogeography. Molecular clock dating and ancestral area reconstruction analyses were carried out, as well as the most comprehensive phylogenetic analysis of the genus, based on the most complete taxon sampling to date. The results evidenced, for the first time, several phylogenetic lineages within Fomitiporia, with a strong biogeographical structure, resulting from a complex evolutionary history. Our results suggest a probable Neotropical origin (Palaeocene–Eocene) followed by an early dispersal to the Andean cordillera (Eocene). From the ancestral Neotropical species, the Antarctic land bridge may have provided a corridor for migration between South America and Australia (early Miocene). Subsequently, our data strongly support the hypothesis of a boreotropical dispersal model, from South America to Africa via North America and Eurasia (passing trough the North Atlantic land Bridge). From here, several dispersion events, back and forth to Asia, and ultimately an extreme long-range trans-Atlantic dispersal to the Neotropics, accompanied by a recent radiation were hypothesized. (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2016
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