Cryptic species in White Cloud Mountain minnow, Tanichthys albonubes: Taxonomic and conservation implications

Cryptic species describe two or more species that had mistakenly been considered to be a single species, a phenomenon that has been found throughout the tree of life. Recognizing cryptic species is key to estimating the real biodiversity of the world and understanding evolutionary processes. Molecular methods present an unprecedented opportunity for biologists to question whether morphologically similar populations are actually cryptic species. The minnow Tanichthys albonubes is a critically endangered freshwater fish and was classified as a second-class state-protected animal in China. Previous studies have revealed highly divergent lineages with similar morphological characters in this species. Herein, we tested for cryptic species across the ranges of all known wild populations of this minnow. Using multilocus molecular (one mitochondrial gene, two nuclear genes and 13 microsatellite loci) and morphological data for 230 individuals from eight populations, we found deep genetic divergence among these populations with subtle morphological disparity. Morphological examination found variance among these populations in the number of branched anal-fin rays. Based on genetic data, we inferred eight monophyletic groups that were well supported by haplotype network and population clustering analyses. Species delimitation methods suggested eight putative species in the T. albonubes complex. Molecular dating suggested that these cryptic species diverged in the period from the Pliocene to the Pleistocene. Based on these findings, we propose the existence of seven cryptic species in the T. albonubes complex. Our results highlight the need for a taxonomic revision of Tanichthys. What is more, the conservation status of and conservation strategies for the T. albonubes complex should be reassessed as soon as possible.