Molecular evidence of cryptic speciation in planktonic foraminifers and their relation to oceanic provinces

The fossil record of planktonic foraminifers is a key. source of data on th e biodiversity and evolution of marine plankton, One of the most distinctiv e foraminiferal taxa, Orbulina universa, widely used as a stratigraphic and paleoclimatic index, has always been regarded as a single species. Here we present a phylogenetic analysis of Orbulina small subunit rDNA, sequences from 25 pelagic stations covering 100 degrees latitude in the Atlantic Ocea n. The genetic data reveal the presence of three cryptic species, whose dis tribution is clearly correlated to hydrographic provinces, and particularly to sea-surface total chlorophyll a concentration. Our results, together wi th previous studies, suggest that a considerable part of the diversity amon g planktonic foraminifers has been overlooked in morphological taxonomies, Our data also support the idea that planktonic foraminifers, even if adapte d to particular hydrographic conditions, are high-dispersal organisms whose speciation may be similar to that of other high-dispersal taxa in which re productive mechanisms and behavior, rather than just geographic barriers to dispersal, play key roles in species formation and maintenance.