Date of Award
Fall 11-22-2024
Document Type
Masters Thesis
Degree Name
M.S. in Biological Sciences
Organizational Unit
College of Natural Science and Mathematics, Biological Sciences
First Advisor
Jonathan P. Velotta
Second Advisor
Erica Larson
Third Advisor
Robin Tinghitella
Copyright Statement / License for Reuse
All Rights Reserved.
Keywords
Alosa pseudoharengus, Evolution, Genetics
Abstract
The extent to which we can predict evolution is of utmost concern in our era of rapid anthropogenic change. Tests of this require a system in which independent taxa are subjected repeatedly to the same selection pressures. Migratory alewives (Alosa pseudoharengus) in the Atlantic coastal USA are a unique model, as multiple populations have been independently restricted to freshwater (landlocked) by dams built in the last 350 years. To test if recent freshwater adaptation occurs in parallel, I conducted whole genome sequencing of landlocked and anadromous (migratory from ocean to freshwater) populations of alewife. I first confirmed that landlocked populations are independently derived from an anadromous ancestor. I subsequently found that landlocked populations have lowered genetic diversity, likely caused by a combination of founder effects, bottlenecks, and/or ongoing inbreeding. I scanned for signatures of natural selection across the genome and determined that while parallel selection was rare, small regions of repeated selection occurred around genes with putative function in salt and water balance. Moreover, a suite of candidate osmoregulatory genes was under selection more frequently than other genes in the genome. This suggests that a small but functionally-relevant group of genes are repeated targets of selection. Despite this, repeated selection on any given gene was not likely to be due to shared variation at the nucleotide-level, suggesting a lack of selection from standing genetic variation. Thus, despite the likelihood of a large initial founding population, selection in response to damming is only repeatable at broader functional levels. My study highlights the need to understand both demography and physiological pathways when determining if evolution is predictable.
Copyright Date
11-2024
Publication Statement
Copyright is held by the author. User is responsible for all copyright compliance.
Rights Holder
Riley M. Corcoran
Provenance
Received from author
File Format
application/pdf
Language
English (eng)
Extent
91 pgs
File Size
4.2 MB
Recommended Citation
Corcoran, Riley M., "Rapid and Repeated Human-Mediated Selection in a Formerly Migratory Fish" (2024). Electronic Theses and Dissertations. 2515.
https://digitalcommons.du.edu/etd/2515