Cavefish as biological models in the laboratory and in the wild

Cavefish have advanced to the forefront as excellent models for laboratory studies in developmental and evolutionary biology.The iconic Mexican characid,Astyanax mexicanus,which consists of a surface-dwelling morph and about 30 interfertile cave-dwelling morphs,has become a major contributor to behavior,sensory biology,trait evolution,and biomedicine(Jeffery,2020).There are about 200 scientifically-described cavefish species distributed in karst areas on most continents(Proudlove,2015).Similar to A.mexicanus,a small subset of other cavefish taxa coupled with related surface-dwelling species are now serving as additional laboratory models to address a variety of important biological problems.A prime example is the cyprinid genus Sinocycloceilus,which contains 75 closely related surface and cave species endemic to the karst massifs of southwestern China(Jiang et al.,2019,2023;Ma et al.,2019).Comparative studies of Chinese and Mexican cavefish can be used to address a host of questions concerning the convergence and divergence of cave related traits.In the future,other Chinese cavefish species,such as the cave loach,as well as the more recently discovered European cavefishes,are likely to join the current group of excellent laboratory models.This special issue of Zoological Research presents the results of current research on these diverse cavefish species.In addition to recent research using cavefish models in laboratory studies,this issue also covers new research on cavefish in the wild.

Protection and exploration of the scientific potential of Chinese cavefish

The karst habitats of Southwest China contain the richest cavefish fauna in the world.However,many Chinese cavefish species are now at high risk of extinction.Chinese cavefish have evolved unusual traits,which are important for studying adaptive evolution and modeling human diseases.Here,we call on scientific research institutions to develop programs to conserve precious cavefish species and suggest international cooperation to promote research on cavefish in China.

Differentially expressed genes identified by cross-species microarray in the blind cavefish Astyanax

Changes in gene expression were examined by microarray analysis during development of the eyed surface dwelling(surface fish)and blind cave-dwelling(cavefish)forms of the teleost Astyanax mexicanus De Filippi,1853.The cross-species microarray used surface and cavefish RNA hybridized to a DNA chip prepared from a closely related species,the zebrafish Danio rerio Hamilton,1822.We identified a total of 67 differentially ex-pressed probe sets at three days post-fertilization:six upregulated and 61 downregulated in cavefish relative to surface fish.Many of these genes function either in eye development and/or maintenance,or in programmed cell death.The upregulated probe set showing the highest mean fold change was similar to the human ubiquitin specific protease 53 gene.The downregulated probe sets showing some of the highest fold changes corresponded to genes with roles in eye development,including those encoding gamma crystallins,the guanine nucleotide binding pro-teins Gnat1 and Gant2,a BarH-like homeodomain transcription factor,and rhodopsin.Downregulation of gam-ma-crystallin and rhodopsin was confirmed by in situ hybridization and immunostaining with specific antibodies.Additional downregulated genes encode molecules that inhibit or activate programmed cell death.The results suggest that cross-species microarray can be used for identifying differentially expressed genes in cavefish,that many of these genes might be involved in eye degeneration via apoptotic processes,and that more genes are downregulated than upregulated in cavefish,consistent with the predominance of morphological losses over gains during regressive evolution.