Phylogenetic Analysis And Expression Differences Of Eye-Related Genes In Cavefish Genussinocyclocheilus

The adaptive evolution of visual systems has been observed in many cavefish. However, little is known about the molecular mechanisms underlying these adaptations, which include regressive changes such as eye degeneration. Here, we analyzed phylogenetic and expression patterns of 6 eye-related genes (crx,foxg1b,opn1sw2,otx2,rhoandsox2) in 12Sinocyclocheilusspecies from China, including 8 stygobionts and 4 stygophiles, and examined photoreceptor cell morphology of these species. Those eye-degenerated species ofSinocyclocheiluswere polyphyletic and showed different degrees of photoreceptor defects in responses to cave environments. The eye loss and degeneration are the result of convergent evolution. AlthoughS. anophthalmusgrouped with the eye-normal species, it displayed not only a high degree of eye degeneration but also significant expression differences in eye-related genes compared with the eye-normal species. The genefoxg1b, which was determined to be under positive selection, might play an important role in the process of eye degeneration inS. anophthalmusbased on differential expression. Eye-related gene expression and selection may have contributed to the polyphyly of the cave species. We examined gene expression and duplication in 6 eye-related genes and revealed that these genes displayed considerable diversity in relative expression inSinocyclocheilusfishes.Otx2andsox2were significantly up-regulated in individual cave species, while the other 4 genes (crx,foxg1b, opn1sw2andrho) were significantly down-regulated. These findings provide a valuable resource for elucidating molecular mechanisms associated with visual system evolution in cavefish.