Evolutionary diversity and function of odorant receptors in birds

Odorant receptors (ORs) form one of the largest gene families in vertebrates; most mammals have hundreds of intact OR genes. Although birds display diverse breeding and foraging behaviors, they were long assumed to rely minimally on olfaction. Here we show that, similar to mammals, bird genomes often encode hundreds - and in some species, thousands - of intact ORs. We further present evidence that most avian ORs within the bird-specific gamma-c subfamily have undergone extensive gene conversion. We show that avian ORs are expressed in olfactory sensory neurons and respond to defined odorants. Notably, we identify ligands for avian ORs, revealing both unique functions within the gamma-c clade and functional conservation with a deeply divergent mammalian OR. These findings uncover unexpected parallels between mammals and birds in olfactory system organization while revealing a distinctive evolutionary feature: widespread gene conversion shaping the majority of avian ORs.