Date of Award

Summer 2020

Document Type

Open Access Dissertation


Biological Sciences

First Advisor

Roger Sawyer


Since the most recent major mass-extinction event ~65 million years ago, birds have expanded to now occupy a wide range of habitats and exhibit diverse lifestyles. A major reason for this evolutionary success is the mechanical resilience and diversity of their epidermal appendages such as feathers, scales, and beaks. The diversity of these appendages, specifically feathers has played a critical role in their evolutionary success. The feathers of birds vary substantially across different species, as well as at different life stages and anatomical locations on an individual bird. Several of the genetic elements involved in the development and structure of feathers are located at a specific genetic locus known as the Epidermal Differentiation Complex (EDC). To gain a better understanding of the genes and proteins involved in these processes as well as how genetic variation in these elements has accompanied the evolution of diverse lifestyles and phenotypes in birds, we have characterized the organization and architecture of the EDC locus across 48 diverse bird species. We have also investigated two specific gene families within the avian EDC, loricrins and a group of EDC genes rich in aromatic amino acids, which also contain a conserved sequence of Methionine-Threonine- Phenylalanine (MTF) residues at their start (EDAA/EDMTFs), to analyze their evolution in birds as well as their roles in epidermal development. Our results demonstrate that the avian EDC is conserved across birds and evolved from a common amniote ancestor. Furthermore, we show that these ancestral EDC genes have expanded in birds into large gene families but have not translocated to other parts of the genome. We also provide

evidence that these gene families of the EDC have expanded via significant amounts of gene loss and duplication events many of which are lineage specific. Finally, given that the amino acid compositions of structural proteins play a significant role in function, we investigate the amino acid contents of identified avian EDC genes and demonstrate that they contain amino acid residues commonly associated with epidermal development and structure. Overall, our results support that the evolution of the avian EDC accompanied the evolution of bird species with diverse feather morphologies and phenotypes, which has played a key role in their evolutionary success.

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