ARTICLE Updates on the status of giant clams Tridacna spp. and Hippopus hippopus in the Philippines using mitochondrial CO1 and 16S rRNA genes Apollo Marco D. Lizano 1,2 and Mudjekeewis D. Santos 1 * 1 Genetic Fingerprinting Laboratory, Marine Fisheries Research Division, 1 National Fisheries Research and Development Institute 2 The Marine Science Institute University of the Philippines, Diliman Quezon City, Philippines T he CO1 and 16S rRNA genes of six of the possible eight species of giant clams (Hippopus hippopus, Tridacna gigas, T. crocea, T. squamosa, T. derasa, and Tridacna sp.YCT-2005) under the Tridacnidae family found in the Philippines were sequenced for molecular approach-based species identification. We first report- ed here the CO1 sequence of H. hippopus and made it available online through GenBank. We also reported the first sighting of Tridacna sp. YCT-2005 in Philippine waters, an undescribed species of giant clam, which has initially been reported to be a potentially new species that was thought to be found only in Tai- wan. Phylogenetic trees of CO1 and 16S rRNA gene sequences of giant clam samples from the Philippines were constructed using both the Neighbor -Joining approach and the Maximum- Likelihood approach. Both trees showed similar topology in which Tridacna and Hippopus formed two distinct clades. T. crocea, T. squamosa, T. maxima, T. costata, and Tridacna sp. YCT-2005 showed monophyletic grouping under subgenus Chametrachea confirming the recognized groupings of giant clams based on morphology. On the other hand, restriction site mapping based on the 16S rRNA gene showed a unique recogni- 187 Vol. 7 | No. 1 | 2014 Philippine Science Letters *Corresponding author Email Address: mudjiesantos @yahoomail.com Submitted: March 13, 2013 Revised: January 23, 2014 Accepted: April 9, 2014 Published: May 24, 2014 Editor-in-charge: Gisella P. Padilla-Concepcion tion site at 367-370 bp (5’AGCT3’) for the species of T. maxima as opposed to the species of Tridacna sp. YCT-2005. Alu I re- striction endonuclease was identified as a candidate diagnostic enzyme to differentiate between these species. This study con- firmed the identity of giant clams found in the Philippines using molecular techniques. The use of DNA barcoding can be a useful tool to identify different species of giant clams which is needed for their proper management and conservation in the Philippines, since they are all declared as endangered. INTRODUCTION Giant clams are one of the world’s largest bivalves, ranging from 15 cm for Tridacna crocea Lammarck 1819 to 150 cm for Tridacna gigas Linnaeus 1758 (Juinio et al. 1989, Lucas 1988). These clams belong to the subfamily Tridacninae, which has two genera namely: Hippopus and Tridacna (Othman et al. 2010). Two species belong to Genus Hipopopus: Hippopus hippopus Linnaeus 1758 and Hippopus porcellanus Rosewater 1982. Three subgenera belong to Genus Tridacna : Tridacna sensu stricto which is composed of one species (T. gigas); Chametra- chea which is composed of four species (Tridacna maxima Rod- ing 1798, Tridacna squamosa Lamarck 1819, Tridacna crocea Lamarck 1819, and Tridacna costata Roa-Quiaoit, Kochzius, KEYWORDS Giant clams, Philippines, mitochondrial DNA CO1, phylogenetic tree, 16S rRNA