Date of Graduation

12-2019

Document Type

Thesis

Degree Name

Master of Science in Cell & Molecular Biology (MS)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

R. Michael Ceballos

Committee Member

Douglas D. Rhoads

Second Committee Member

David S. McNabb

Third Committee Member

Daniel D. Magoulick

Keywords

Lower Mekong River, Pangasiidae, Pangasius, rag1

Abstract

The Mekong River located in Southeast Asia is a global “hotspot” for aquatic biodiversity. It includes an extensive variety of fish species second only to the Amazon River in South America. Recent studies have revealed the impacts of anthropogenic and climate factors on this river system. Such impacts can result in the formation of barriers, which divide a species population and impede gene flow between separated sub-populations. Barriers influence evolutionary trajectories resulting in the generation of geographic variants or subspecies from an ancestral population. Catfish (Teleostei: Siluriformes) are a key species of the Mekong River ecosystem and are an essential component of southeast Asian commercial fisheries. Using catfish as an indicator species for Mekong River ecosystem stability has proved challenging due to use of different genetic markers by different research groups and the unsuitability of some markers to resolve differences at distinct taxonomic levels. In this study, a subset of samples from a larger group of more than 800 fish specimens from 19 sampling sites in the Lower Mekong Basin were used to examine the suitability of the recombination activating gene 1 (rag1), a nuclear gene, for differentiating phylogenetic and biogeographic relationships. Specifically, 183 samples from four phenotypically identified Pangasiid species were used to compare marker fidelity between a mitochondrial gene (i.e., 16S rDNA) and rag1, which was previously reported to resolve interspecies differences. Phylogenies based on 16S rDNA were used to reveal species level relationships and to correct misclassifications based on phenotypic identification of fish species. Two of the four species – Pangasius macronema and Pangasianodon hypophthalmus - were further studied to determine if the rag1 gene can serve as a robust genetic marker for evaluating phylogeographic patterns. Discernable biogeographic trends for P. hypophthalmus were not resolved using rag1 as a marker. However, a phylogenetic cluster was resolved for P. macronema that mapped to geography suggesting that rag1 may be useful in resolving biogeographic structure for this species of catfish. If catfish are to be used as indicator species for river system stability, establishing reliable genetic markers for rapid analysis of biogeographic trends is essential.

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