Identification of four Indian ascidians based on COI gene sequences

Abstract DNA barcoding involving the sequencing of a short mitochondrial DNA segment, cytochrome c oxidase subunit 1 (COI) gene, is a specialized technique for the identification of species even at the early embryonic and larval stages, which is quite difficult in morphology-based taxonomy. Ascidians are sessile invertebrate chordates possessing numerous biochemical as well as pharmacological activities. In this study, a total of 36 ascidian samples belonging to the family Didemnidae were sequenced for a 650 bp region of the mitochondrial COI gene. All the species were represented by multiple specimens. The barcode sequences showed no stop-codons and indels in the alignments. The aligned sequences were submitted in Barcode submission tool, NCBI, and the accession numbers were obtained. The minimum intraspecific distance was found to be 0.00% and the maximum was 2.23%. Mean Kimura 2-parameter (K2P) distances within-species, genus, and family were 0.88, 5.98, and 20.03%, respectively. The mean interspecific distance is more than the mean intraspecific divergence, which indicates efficiency of DNA barcoding for identification of ascidians.