Understanding eye color genetics in the domestic pigeon

UNDERSTANDING EYE COLOR GENETICS IN THE DOMESTIC PIGEON Bridget Phillips, Emily Maclary, Ryan Wauer, Michael Shapiro School of Biological Sciences INTRODUCTION Across the animal kingdom, coloration and pigment pattern diversity is widespread. Despite this abundant variation, the genetic changes that lead to diversity in pigmentation are still largely unknown. Identifying specific genetic differences between different species is difficult due to the immense amount of genetic changes between them, most of which are unrelated to pigmentation. In the Shapiro lab, we use the domestic pigeon (Columbia livia) as a model system of genetic diversity. Through selective breeding, domestic pigeons show extensive variation in many traits, including pigmentation and pigment patterning. This variation within a single species recapitulates some of the pigment diversity seen across wild species. One tissue that shows extensive variation in pigmentation across species is the iris of the eye (Negro et al., 2017). Iris colors can vary from bright orange, red, or blue to dark brown. The genetics of eye color variation is poorly understood, however, because while iris color varies between species, variation within a single species is less common and typically only seen in domestic animals (Negro et al., 2017). Eye color arises from pigments in the front of the iris, which is a ring-shaped membrane that controls the amount of light that enters the eye. Iris color variation can have functional significance. For example, among mantellid frogs, tree-dwelling species are more likely to have brightly colored irises than terrestrial species, which typically have dark irises, and this bright iris coloration may serve as a defensive strategy that repels predators (Amat, 2013). Furthermore, iris color may have selective significance as there is an association between being nocturnal and having darker eye colors in owls, which is hypothesized to be beneficial for avoiding both predator and prey detection (Passarotto et al., 2018). Pigeons are one domestic species where iris color is variable, and this makes them an ideal model to understand the genetics of iris pigmentation. There are three main iris colors that have been identified by pigeon breeders: orange, pearl (white), and bull (dark brown) (Figure 1).