Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

Ph.D. in Biological Science

First Advisor

Brice P. Noonan

Second Advisor

Leandro M. Sousa

Third Advisor

Susan Balenger


University of Mississippi

Relational Format



The Xingu River, one of the largest tributaries of the Amazon River, is currently in peril due to the recent construction of hydroelectric dams, but little is known about the numerous fish species it supports. This dissertation focuses on three pleco catfish species belonging to the genus Hypancistrus from the Xingu River with partially overlapping distributions: H. zebra, H. sp. (L174), and H. sp. (L66/333). Chapter 1 is a bibliographic review of Amazonian freshwater fish diversity, with the goal of discussing the hypotheses of speciation mechanisms that can be tested in this system, including the relative importance of ecological adaptation and vicariance caused by topographical divides and waterfalls and rapids, and arguing this is an important overlooked model for the study of speciation processes. The goal of Chapter 2 was to use genomic data to unravel the basic relationships among eight described and eleven undescribed species belonging to the genus Hypancistrus distributed across the Orinoco and Amazon Basins. The phylogenetic analyses support the existence of two clades corresponding to each basin, but relationships among some of the species are poorly supported. Further exploratory analyses in combination of hypotheses testing indicate there are at least four admixed lineages in the Amazon clade. Chapter 3 investigated the evolution of Hypancistrus from the Xingu River based on genomic data. With dense sampling of H. sp. (L66/333), phylogenetic and population genetic analyses reveal a gradient of genetic structure along the river, with introgression from lineages of Hypancistrus from other Amazon River tributaries close to the mouth of the Xingu. On the upstream limit of the distribution of H. sp. (L66/333), a population hybridized with H. sp. (L174) is found just upstream of waterfalls, that act as a partial barrier to gene flow. Tests for past gene flow suggest there is signal for multiple introgression events between these lineages, but the direction, timing, and intensity of these events is still unclear. Overall, these results indicate the evolution of Hypancistrus was exceptionally complex. Fascinating patterns of diversification are emerging from this system that is unfortunately in risk of extinction due to the impacts of damming.

Included in

Biology Commons



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