Probing gastrotrich taxonomy with DNA barcoding

Gastrotrichs represent a phylum of basal metazoans, living both in marine and freshwater environments, dimensionally comprised between 80 µm and 3 mm. Though taxonomic and biogeographic knowledge has been improved in the last years, little is known about the molecular aspects of this group. The aim of this study was to analyze these organisms by means of DNA barcoding which is a well-known technique consisting in the use of a gene sequence to affiliate an organism to a known species or to a new taxon. In this research, mitochondrial gene cytochrome oxidase I (COI) was used to identify gastrotrichs. It’s important to notice that no Gastrotrich COI sequence has been deposited in GenBank so far. Sampling of different populations of Turbanella cornuta and Paraturbanella teissieri, species considered to have a wide distribution, was carried out in Adriatic, Ligurian and Tyrrhenian Sea (Italy), Baltic Sea (Sweden), Atlantic Ocean (Canary Islands) and Arabian Gulf (Kuwait). DNA was extracted from some specimens, COI sequence amplified through PCR, and in the end the product was purified and sequenced. The obtained sequences were analyzed with NJ, MP and Bayesian Inference. It was possible to group in monophyletic clades, morphologically similar specimens belonging both to the same population and to diversely geographically distant populations. In particular, analyses revealed that specimens of T. cornuta from Adriatic, Ligurian, and Baltic Sea and Arabian Gulf can be considered distinct species, although similar. These results show that barcoding allows a more precise specific identification of Gastrotrichs; therefore this technique appears to be clearly useful when dealing with cryptic species, not easily distinguishable just by means of morphological characters. The wide application of this method will be of true interest also in reconsidering on new bases the paradoxical cosmopolitan distribution of several species.