Microstructure and transcriptomics reveal rapid light-induced visual plasticity in the non-obligate cave dweller Oreolalax rhodostigmatus (Megophryidae, Anura).

BACKGROUND: Phenotypic plasticity is a specific area of interest that refers to the ability of an organism to alter its phenotype in response to environmental changes. Adaptive visual plasticity is a fascinating phenomenon observed in various animal species. Cave-dwelling organisms often exhibit visual degeneration, but non-obligate species like Oreolalax rhodostigmatus may retain adaptive plasticity. Currently, no laboratory simulations of light-induced conditions have been reported. This study investigated the morphological, histological, and molecular responses of O. rhodostigmatus tadpoles to prolonged light exposure, hypothesizing structural retinal remodeling and upregulation of phototransduction genes reflecting reversible plasticity. RESULTS: Histological analysis revealed significant thickening of retinal layers (particularly inner retinal and ganglion cell layers) and structural refinement of photoreceptor outer segments in light-exposed (3- and 10-week) groups compared to dark-adapted controls (0-week). Immunohistochemistry showed restoration of organized rod and cone morphology after light exposure. Transcriptomic profiling identified 2,937-4,847 differentially expressed genes (DEGs) between groups. Key phototransduction genes (GNAT1, GRK7, CRYBA2, BEST2, MYO3B) were significantly upregulated in light-exposed tadpoles, while the cave-adaptation associated photoreceptor gene s26 was downregulated. Ultrastructural analysis indicated increased mitochondrial density and improved photoreceptor structure following light treatment. CONCLUSION: Prolonged light exposure induces significant structural, ultrastructural, and molecular adaptations in the visual organs of O. rhodostigmatus tadpoles, including retinal layer thickening, photoreceptor regeneration, and upregulation of phototransduction pathways. The downregulation of s26 and absence of mutations common in obligate cavefish suggest retained latent pathways enabling reversible plasticity, rather than irreversible degeneration. This adaptive plasticity allows non-obligate cave dwellers to balance energy conservation in darkness with functional vision restoration upon light exposure, representing a distinct evolutionary strategy compared to obligate cave species.