Comparative Retinal Morphology of Two Sympatric Lizard Species from Distinct Microhabitats

This study investigated retinal interspecific differences between two sympatric lizards from the Turpan Basin of Xinjiang that occupy distinct microhabitats. Eremias roborowskii inhabits shrublands, while Phrynocephalus axillaris lives in open sandy areas. We adopted retinal whole-mounting, paraffin sectioning, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to compare retinal structure, oil droplet traits, photoreceptor arrangement, and ultrastructural characteristics between the two species. Both species exhibited five types of colored oil droplets, a temporal fovea, and a highly vascularized conus papillaris, confirming cone-dominant retinas. P. axillaris had larger oil droplets with an average diameter of 3.719 ± 1.100 μm. In contrast, E. roborowskii showed a higher oil droplet density of 1473 ± 1203 ind/mm². The inner plexiform layer (IPL) was significantly thicker in E. roborowskii (56.01 ± 14.76 μm) relative to P. axillaris (50.76 ± 15.25 μm). The two species also differed markedly in photoreceptor ultrastructure. E. roborowskii contained mitochondria-rich ellipsoids, while P. axillaris possessed glycogen-enriched paraboloids. These structural variations reflect compatibility with local ambient light conditions. E. roborowskii is predisposed to suit diffuse shrubland light through high droplet density and mitochondrial-dominant ellipsoids, whereas P. axillaris tends to accommodate intense open-field sunlight via larger oil droplets and well-developed paraboloids. This study provides key morphological evidence to reveal how microhabitat divergence drives retinal specialization among desert reptiles.