The diversity and distribution of modern planktic foraminiferal small subunit ribosomal RNA genotypes and their potential as tracers of present and past ocean circulations

Molecular phylogenetic analysis of the small subunit ribosomal RNA gene of planktic spinose foraminifers shows that morphospecies may represent clusters of different and often highly divergent genotypes. In some cases the level of divergence may justify separate taxonomic status as distinct "cryptic" species. Molecular evolution rate estimates, based on fossil record evidence, suggest that the cryptic divergences may have occurred many millions of years ago. An investigation of their distribution in the Caribbean (tropical zone), Coral Sea and Mediterranean Sea (subtropical zone), and Southern California Eight (transitional zone) indicates that genotypes are transported across water mass boundaries, and it is proposed that the direction of gene flow follows the prevailing global ocean surface circulation pattern. At the present time the prevailing currents transport tropical/subtropical genotypes from the Pacific to Atlantic around the South African Cape. Cooler water transitional genotypes may transit from Pacific to Atlantic in gene corridors opened during glacial periods.