ELUCIDATING GLOBAL PATTERNS IN FUNCTIONAL DIVERSITY OF MARINE CHROMOPHYTIC PHYTOPLANKTON BASED ON RBCL DEEP PHYLOGENY

Global patterns of functional diversity of chromophytic phytoplankton using robust bioinformatics analyses including deep phylogeny based on form ID rbcL gene across different ecologically significant oceanographic ecoregions were undertaken as part of this study. A total of 2476 uncultured form ID rbcL sequences were retrieved from GenBank representing seven major oceanographic ecoregions around the world. In addition, 12 form ID rbcL clone libraries were generated and analyzed from Sundarbans Mangrove Biosphere Reserve in this study. Phylogenies were constructed using RAxML method. Bioinformatics and statistical analyses such as Operational taxonomic unit (OTUs) calculation, beta diversity matrices, AMOVA, ANOSIM, LIBSHUFF and UniFrac were undertaken. Natural selection pressure on form ID rbcL sequences were investigated for the first time from environmental form ID rbcL sequences using maximum likelihood based SLAC methodology. Global phylogenetic analyses recovered 11 major clades of chromophytic phytoplankton in varying proportions with several novel form ID rbcL sequences in each of the seven targeted ecoregions. In beta-diversity analysis, majority of OTUs of each targeted ecoregions were found to be restricted within their respective ecosystems, whereas some were shared by two or more habitat types. Natural selection pressure on form ID rbcL datasets showed that dN/dS ratio varied from 0.124-0.158 with few evidences of positive selection. Present phylogenetic and bioinformatics analyses provided a strong statistical support for the hypothesis that different oceanographic regimes harbor distinct and coherent groups of chromophytic phytoplankton. We show that different selection pressure on form ID rbcL gene under different environmental conditions could lead to functional differences and ultimately overall fitness of chromophytic phytoplankton populations.