Deep genome-wide divergences among species in White Cloud Mountain minnow Tanichthys albonubes (Cypriniformes: Tanichthyidae) complex: Conservation and species management implications.

Identifying cryptic species is important for the assessments of biodiversity. Further, untangling mechanisms underlying the origins of cryptic species can facilitate our understanding of evolutionary processes. Advancements in genomic approaches for non-model systems have offered unprecedented opportunities to investigate these areas. The White Cloud Mountain minnow (Tanichthys albonubes) is a popular freshwater pet fish worldwide but its wild populations in China are critically endangered. Recent research based on a few molecular markers suggested that this species in fact comprised seven cryptic species, of which six were previously unknown. Here, we tested six of these cryptic species and quantified genomic interspecific divergences between species in the T. albonubes complex by analyzing genome-wide restriction site-associated DNA sequencing (RADseq) data generated from 189 individuals sampled from seven populations (including an outgroup congeneric species, T. micagemmae). We found that six cryptic species previously suggested were well supported by RADseq data. The genetic diversity of each species in the T. albonubes complex was low compared with T. micagemmae and the contemporary effective population sizes (Ne) of each cryptic species were small. Phylogenetic analysis showed seven clades with high support values confirmed with Neighbor-Net trees. The pairwise divergences between species in T. albonubes complex were deep and the highly differentiated loci were evenly distributed across the genome. We proposed that the divergence level of T. albonubes complex is at a late stage of cryptic speciation and lacking gene flow. Our findings provide new insights into cryptic speciation and have important implications for conservation and species management of T. albonubes complex.