Molecular phylogeny of Philippine freshwater sardines based on mitochondrial DNA analysis

The commercially important Sardinella species (family Clupeidae or herrings ) usually thrive in marine environments, An exception is Sardinella tawilis of Taal Lake, Batangas, Philippines, the only known freshwater sardine, Th is species is believed to have immigrated from Balayan Bay to the lake when it was formed in the course of volcanic eruptions some 240 years ago. To d etermine the relationship of S, tawilis to the marine species S. albella, S . fimbriata, and S. longiceps from the Balayan Bay we sequenced 358 bp of t he cytochrome b gene and the mitochondrial control region. The cytochrome b gene was highly conserved and contained little phylogenetic information. T he control region sequences, however, demonstrated two highly diversified m ain haplotypes grouping S. tawilis with S,albella, as shown by maximum pars imony and neighbor-joining analysis. The haplotypes are characterized by th e presence of an 81 bp indel and up to eight 35 bp tandem repeat elements. The repeat copy number varied within individuals of S. tawilis and S. albel la, thus showing heteroplasmy in these two species only. The analysis of tw o subpopulations of S. tawilis revealed restricted substitutions that may i ndicate the beginning of genetic differentiation of the two subpopulations.