Evolution of olfactory receptors in birds

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Robert Driver (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: Olfaction is an evolutionary ancient sensation, and is the perception and interpretation of chemical stimuli from surrounding air or water. Olfaction is an essential sensory modality for nearly all animals, and is used to define territories, to identify kinship, to navigate to breeding sites, to select mates, and when selecting mates. Unlike vision, which detects different wavelengths of a single particle, the photon, olfaction must detect a wide range of odor molecules. Odor molecules can be simple or complex, be large or small, and have a wide range of elements and chemical structures. To detect these diverse compounds, animals employ olfactory receptors, which constitute the largest gene family in all vertebrates. The total number of olfactory receptors that a species possesses can be used as a measurement of that species’ reliance upon smell in ecology and behavior. Despite the importance of smell and olfactory receptors in mammals, little is known about olfactory receptors in birds.\n\nThe lack of knowledge of olfactory receptors in birds stems from centuries old misconceptions about birds relying on vision over olfaction in their behavior, leading scientists to historically overlook the use of smell in birds. Recent behavioral work is gradually debunking the notion that birds cannot smell, showing that birds use smell in similar ways to mammals, in foraging, individual recognition, and mate choice. However, research into olfactory receptors in birds continues to lag behind other vertebrate classes.\n\nMy dissertation shows that birds have much larger olfactory receptor repertoires than the scientific community previously appreciated. In chapter 1, I show the discovery of hundreds of new olfactory receptors in birds, overlooked in previous studies, and show that olfactory receptors in birds, particularly the bird-specific gamma-c OR subfamily, can only be properly counted using genome assemblies that employ long-read sequencing technology. Knowing the importance of long-read assemblies for obtaining accurate olfactory receptor counts, I then expand olfactory receptor counts to 70 bird species with publicly available long read genomes, showing large olfactory repertoires across the bird phylogeny. I also show the dynamic birth and death of olfactory receptors through bird evolution, with a particularly high rate of death in the early lineages of the Neoaves bird group. However, our genomic counts only tell us the number of olfactory receptor genes in the genome, and do not directly implicate the olfactory receptors in a role specific to smell. To do this, in chapter 3, I show that the vast majority of olfactory receptors detected in the genomes of birds are indeed expressed in the olfactory epithelium, the tissue located inside the bird’s bill that is relevant to smell and the olfactory system. I further show that the gamma-c olfactory receptor subfamily is expressed in the olfactory epithelium, and that certain members of the family are expressed at high levels. These findings show that birds across the phylogeny likely use smell in their behavior and ecology, and that this sensory modality should not be overlooked in birds. My research paves the way for future studies to match bird olfactory receptors to the odors they respond to and to discover the odors that birds detect.

Additional Information

Publication

Dissertation

Language: English

Date: 2023

Subjects

olfaction, birds, olfactory receptors

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