Species-Specific Retinal Adaptation to Permanent Darkness in G. charrua and O. latipes

Sustained neurogenesis underlies retinal regeneration in teleosts, but is largely absent in mammals, making comparative studies of closely related fish species a powerful approach to uncover regulatory mechanisms and evolutionary constraints. Environmental cues are likely key regulators, yet their impact on plasticity and function is poorly understood. We examined the impact of prolonged darkness on retinal cell proliferation and visual performance in two closely related teleosts, the annual fish Garcialebias charrua and Oryzias latipes. EdU/BrdU labeling was used to quantify retinal cell proliferation after defined darkness periods. Visual acuity and contrast sensitivity were assessed via optomotor response assay. Both species exhibited increased cell proliferation in response to darkness; however, the affected retinal layers and dynamics differed. In G. charrua, proliferation increased in the inner nuclear layer, with decreased visual acuity and higher contrast sensitivity. O. latipes responded to shorter darkness exposure with increased cell proliferation in the outer nuclear layer, decreased acuity and, unlike in annual fish, reduced contrast sensitivity. Our results reveal species-specific recruitment of distinct progenitor/precursor cell populations in the adaptation to changes in the photic environment. Our results highlight the evolutionary relevance of retinal neurogenesis, playing a key role in the adaptation to a changing environment.