Maeda Obregon, Alejandro; (2025) Biodiversity assessment of fish and amphibian communities from the Valley of Mexico: An environmental DNA approach. Doctoral thesis (Ph.D), UCL (University College London).

Text Thesis Submission Final Version.pdf - Accepted Version Access restricted to UCL open access staff until 1 July 2026. Download (58MB)

Abstract

Freshwater ecosystems and their associated fauna rank among the most impacted natural resources amid the ongoing global biodiversity crisis. The circumstances are even more critical for native amphibian and fish species inhabiting urban freshwater ecosystems. The Basin of the Valley of Mexico, situated in the central Mexican highlands, is considered extinct due to prolonged desiccation processes resulting from the expansion of Greater Mexico City. Remnants of the freshwater system persist, harbouring endemic freshwater fauna, including two axolotl species and the mexclapique fish. Despite their biocultural significance, these ecosystems have undergone varying degrees of modification, complicating the implementation of traditional survey methods. Environmental DNA is a robust tool for assessing biodiversity and the ecological status across diverse ecosystems. The sensitivity, cost-efficiency, repeatability, and reduced reliance on taxonomic expertise of eDNA methods make them a powerful alternative that can be implemented in challenging scenarios. Chapter 1 introduces the research area, delineating the prevalent issues and existing knowledge gaps. Chapter 2 uses eDNA metabarcoding to assess the ecological status of amphibian and fish species at Lake Xochimilco, with particular emphasis on native species and analysing the impacts of alien fish species such as the African tilapia and Old-World carps. Chapter 3 shifts attention to the River Magdalena, investigating the ecological effects on endemic amphibian species caused by the rainbow trout invasion. Concerning the critically endangered axolotl, a species-specific qPCR assay was developed in Chapter 4 to corroborate the findings presented in the preceding Chapters. Chapter 5 presents the set of conclusions and future directions for the study's findings and research area. Despite the challenges posed by the degradation of these urban freshwater ecosystems, this thesis elucidates the efficacy of eDNA methodologies in assessing the status of rare fish and amphibian species, even amid the predominance of invasive fish species. Furthermore, the results of this research underscore the potential of eDNA applications to contribute to the conservation of endangered species.

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