Vision is critical for foraging, avoiding predators, and finding mates in many species. Despite the importance of vision, visual acuity is highly variable across species, and the relative contributions of different selective pressures and developmental processes to this variation are still unclear. Many vertebrates have specialized high visual acuity regions in the retina, such as an area centralis (region of high retinal ganglion cell density), a horizontal streak (elongated region of high density stretching across the retina), or a fovea (physical indentation in the retina surrounded by a region of high density). Many have proposed hypotheses regarding the ecological drivers that select for these retinal specializations. For example, the fovea is thought to help with vision in complex three-dimensional environments or dim light environments. However, these hypotheses had not been tested using phylogenetic comparisons across multiple species. Additionally, vision is a complex sensory system that requires the successful integration of molecular, cellular, and morphological traits, which may impose constraints on each other. It is unclear how selective pressures on vision act at these different biological scales. I am using phylogenetic comparative approaches to uncover the ecological selective pressures and functional constraints shaping the evolution of retinal specializations in both fish and mammals.
