Date of Award

Spring 5-2016

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

Committee Chair

Jake Schaefer

Committee Chair Department

Biological Sciences

Committee Member 2

Brian Kreiser

Committee Member 2 Department

Biological Sciences

Committee Member 3

David Duvernell

Committee Member 4

Donald Yee

Committee Member 4 Department

Biological Sciences

Committee Member 5

Micheal Davis

Committee Member 5 Department

Biological Sciences


Headwater resident fishes may be prone to a high rate of population fragmentation within river networks because large streams have habitat conditions outside of their preferred ecological niche and may limit gene flow in the dendritic ecological network. To investigate patterns of population structure, asymmetrical gene flow, and influences on genetic distance and isolation from connecting habitat pathways, species specific ecological traits, and basin scale characteristics, a multi-species, multi-regional study was performed. Six headwater species of fish from four taxonomic groupings were sampled for genetic material in three regions of paired neighbor drainages and then genotyped for eight microsatellite loci.

All species were found to have a nested hierarchical population structure relating to regional and geographical structure of drainages. There were also differences in rates of fragmentation across the species and regions studied, with Fundulus olivaceus and the Lower Mississippi River having the lowest rates. Most of the headwater species were found to have patterns with the majority of drainages supporting asymmetrical upstream gene flow along the main stem of the networks. Five of the species were found to have significant Isolation by Distance, and four of the species were found to have significant Isolation by Resistance due to large streams. The reservoir in the Pearl River was found to not significantly increase genetic distance, while the reservoir in the Little Red River significantly increased genetic distance. Headwater specialization and a combination of opportunistic strategy and periodic strategy life history traits were found to increase isolation rates across species. The amount of available habitat within drainages and the shape of the drainage were found to have the most influence on genetic distance patterns at large scales.

This study shows that natural fragmentation of populations within networks is common across different species of headwater fishes, and is related to specific ecological characteristics of those species and regional characteristics of the drainage network. This project contributes to the understanding of how habitat preference within dendritic networks influences genetic population structure and provides a background rate of fragmentation in common headwater species that can be used for comparison with threatened or endangered species.



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