Degree
Doctor of Philosophy (PhD)
Department
Biological Sciences
Document Type
Dissertation
Abstract
Birds display a rainbow of eye colors, but this trait has been relatively little-studied. In this dissertation, I first survey eye color variation across birds and discuss its causes at three levels: mechanistic, genetic and evolutionary (Chapter 2). Then, I examine the evolutionary history of the Cassidix grackle complex, a clade that includes notable inter- and intra-specific variation in eye color, and I address questions about phylogeography and hybridization within the group (Chapter 3). Finally, I focus on Boat-tailed Grackles (Quiscalus major), which show geographic and within- population variation in eye color. I combine whole-genome sequencing and phenotypic data from field photographs to quantify eye color variation within Q. major and identify regions of the genome associated with eye color differences (Chapter 4).
In Chapter 2, I summarize the patterns of variation in eye color across birds, the pigments and structures that give bird irises their colors, the small number of genes that have been linked to eye color in domestic birds, and the evolutionary hypotheses relating eye color to both survival and signaling.
In Chapter 3, I conducted a phylogeography study using samples from all 13 subspecies of the three species in the Cassidix clade: Boat-tailed Grackle (Q. major), Great-tailed Grackle (Q. mexicanus), and the extinct Slender-billed Grackle (Q. palustris). I find no evidence of admixture between Q. major and Q. mexicanus, and find support for the monophyly of both species, contrary to evidence from mitochondrial DNA. I also show that geographic breaks, not eye color differences, structure genetic variation within Q. major.
Lastly, in Chapter 4, I took standardized eye photos of 41 Boat-tailed Grackles collected in Louisiana, Mississippi, and Alabama, and sequenced whole genomes of each individual. I used FST outlier scans to find regions of the genome that differ between light-eyed and dark-eyed individuals of the species. I then identified a set of candidate genes that may underlie eye color variation in Q. major, including some, such as KCNJ13, that have been implicated in pigmentation in other vertebrates.
Date
5-13-2025
Recommended Citation
Corbett, Eamon, "Avian Eye Color, Phylogeography, and the Genetics of Iris Variation in Grackles (Quiscalus)" (2025). LSU Doctoral Dissertations. 6796.
https://repository.lsu.edu/gradschool_dissertations/6796
Committee Chair
Brant Faircloth