Department of Biology

Evolution and functional characterization of olfactory receptors in birds

Dr. Robert Driver
Duke University

March 22, 2024
3-4 pm

Hosted By Dr. Tim Lee

Vertebrates detect odor molecules with olfactory receptors (ORs), a gene family expressed in the olfactory epithelium. Among species, OR diversity is associated with reliance on smell, with some mammals exceeding 1000 OR genes. Birds are the most speciose class of terrestrial vertebrates, inhabiting nearly all land environments and with diverse social structures and foraging strategies, yet were long thought to make limited use of olfactory signals. Recent behavioral work in birds has shown important roles for olfaction in foraging and species recognition, among other behaviors. Contributing to this surge of interest in avian olfaction, our recent work has shown that birds have hundreds more OR genes in their genomes than previously realized. We have examined the genomic OR repertoire of over 120 high quality long-read bird genomes spanning the avian phylogeny, revealing between 50 and 400 intact ORs in all species surveyed. Due to OR clusters within the genome, obtaining accurate OR genomic counts is only possible with long-read genomic sequencing. To discern the functional roles of ORs, we measured OR mRNA expression levels in the olfactory epithelium of four bird species and found that the majority of the bird OR genomic repertoire is expressed in tissue relevant to smell. To confirm the ability of bird ORs to detect odors, we expressed chicken ORs in mammalian cell culture, bombarded ORs with multiple odors, and measured OR activation in response to each odor. We found that chicken ORs respond to several types of pyrazines, a group of chemicals that are found in the scent of green peppers. Additionally, we show the preservation of olfactory receptor and ligand relationships between mammals and birds, showing that receptor function is conserved across hundreds of millions of years of vertebrate evolution. Together, these results show that bird ORs are diverse, evolve dynamically, are expressed in the olfactory epithelium, and are capable of functionally detecting odors. This work provides the foundation for future functional characterization of bird ORs across a variety of bird species.