DNA sequences identify numerous cryptic species of the vertebrate: A lesson from the gobioid fish Schindleria

Schindleria (Gobioidei, Schindleriidae), believed to include one of the smallest and youngest reproducing vertebrates, is broadly distributed in the Indo-Pacific Oceans, inhabiting coral reef lagoons. They are all characterized by a reduced larval-like form, such as a slender translucent and scaleless body. The three nominal species recognized in the genus to date have been distinguished by only combination of dorsal and anal fin-ray counts, and the existence of some undescribed species has been suggested in Schindleria; thus a total picture of species composition of the genus is poorly known. Towards the disclosure of diversity of Schindleria, a molecular phylogenetic analysis using partial mitochondrial 16S rRNA sequences was conducted for specimens from the Ryukyu and Ogasawara Islands, Japan. This analysis showed clearly that as many as 21 genetically distinguishable species occurred within the geographical areas. The degree of species crypticness of “ S. praematura” [15.0 = 15 (new cryptic species + known species)/1 (known species)] is higher than the values of well-known animal examples, such as the pan-mesopelagic bristlemouth fish Cyclothone alba (5.0) and the South American skipper butterfly Astraptes fulgerator (10.0). This discovery of many cryptic species in Schindleria suggests that the use of DNA sequences is necessary for species identification of such morphologically conserved taxa. Because molecular analyses should increase the number of hitherto unnamed and pseudonymous species, especially in tropical areas, it is proposed that DNA-based designation is necessary for such taxa in order to compile the full “species lists”, although there is presently no consensus for the inclusion of DNA sequencing data in the formal descriptions of new species.