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Accueil du site → Doctorat → Allemagne → 2017 → An integrative approach to epilithic diatom diversity analysis in tropical streams from the Lerma-Chapala Basin, Central Mexico

Freie Universität Berlin (2018)

An integrative approach to epilithic diatom diversity analysis in tropical streams from the Lerma-Chapala Basin, Central Mexico

Mora Hernández, Luis Demetrio

Titre : An integrative approach to epilithic diatom diversity analysis in tropical streams from the Lerma-Chapala Basin, Central Mexico

Ein integrativer Ansatz zur Analyse der Vielfalt epilithischer Diatomeen in tropischen Bächen des Lerma-Chapala Beckens, Zentralmexiko

Auteur : Mora Hernández, Luis Demetrio

Université de soutenance : Freie Universität Berlin

Grade : Doctor rerum naturalium (Dr. rer. nat.) 2017

Résumé partiel
The study and application of diatoms as biological indicators in Mexico is infrequent, despite the multiple advantages offered by these organisms in the assessment and monitoring of freshwaters. In the few diatom studies of Mexican freshwaters, there seems to be low species diversity and an inherent cosmopolitanism of taxa, contrary to what would have been expected of a megadiverse country. This was mainly because of 1) force-fitting identifications based on monographs from temperate regions and 2) the lone use of light microscopy for identifications, which not always differentiates between closely related species. In order to better assess the diatom diversity of the country and to set an identification baseline for future studies using diatoms as biological indicators, this dissertation presents an integrative approach to epilithic diatom diversity analysis in tropical streams from the Lerma-Chapala Basin, Central Mexico. This study is based on a representative sampling of diatoms from small, mostly undisturbed, mountain streams from the north and east sections of the basin, as well as samples from the west of the basin, which include the heavily polluted Lerma River and some of its major tributaries. Samples were collected during the most contrasting periods of the year, the rainy and dry seasons. In the first part of this work, the diatom samples of the small mountain streams from the north and east sections of the basin were cultivated for morphological, ecological, molecular and phylogenetic analysis. The morphological evaluation resulted in the largest diatom diversity reported for Mexico to date, 274 infrageneric taxa, including the description of two new species, Brachysira altepetlensis and Sellaphora queretana. The ecological analysis revealed that the community composition observed was mainly driven by the ionic composition of the water, with indicator taxa identified for the varying conditions in pH, conductivity and nutrients. Under the premise that diatom identifications at species level in environmental DNA (eDNA) metabarcoding studies rely heavily on the completeness of reference databases, a regional morphological and molecular taxonomic reference library was assembled by diatom cultivation

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