Comparative histological and ultrastructural studies on the retina and kidney among some amniotes

Background: Ecological adaptations among amniotes are intricately linked to the functions of the retina and kidneys. Light exposure patterns influence the distribution and specialization of photoreceptors in the retina, while nutrition strategies and water availability dictate nephron architecture. Objective of the study: This study sought to compare the histological and ultrastructural features of the retina and kidney among three species of amniotes: the fruit-eating bat (Rousettus aegyptiacus), quail (Coturnix coturnix), and house gecko (Hemidactylus turcicus). Results: The bat's retina is predominantly composed of rods adapted for night vision, whereas the quail's retina contains a higher proportion of cones suited for color vision in daylight. The nocturnal gecko exhibits an intermediate adaptation, featuring rods with cone-like properties to improve sensitivity in low-light conditions. The bat's kidney features a well-developed cortex and medulla, with brief loops of Henle that enhance urine concentration ability through increased metabolic activity and water conservation during flight. The quail kidney contains both reptilian and mammalian nephrons, facilitating water reabsorption, which is advantageous for terrestrial and diurnal species. The gecko kidney features poorly differentiated cortical and medullary regions and lacks loops of Henle, which diminishes its capacity to concentrate urine; however, it conserves water by excreting uric acid. Conclusion: The retina and kidney of amniotes exhibit notable differences in their histological and ultrastructural characteristics, reflecting adaptations to their respective habits and habitats.