Comparing Morphological and Molecular Estimates of Species Diversity in the Freshwater GenusSynura(Stramenopiles): A Model for Understanding Diversity of Eukaryotic Microorganisms

We performed a comparison of molecular and morphological diversity in a freshwater colonial genusSynura(Chrysophyceae, Stramenopiles), using the island of Newfoundland (Canada) as a case study. We examined the morphological species diversity in collections from 79 localities, and compared these findings to diversity based on molecular characters for 150 strains isolated from the same sites. Of 27 species or species-level lineages identified, only one third was recorded by both molecular and morphological techniques, showing both approaches are complementary in estimating species diversity within this genus. Eight taxa, each representing young evolutionary lineages, were recovered only by sequencing of isolated colonies, whereas ten species were recovered only microscopically. Our complex investigation, involving both morphological and molecular examinations, indicates that our knowledge ofSynuradiversity is still poor, limited only to a few well-studied areas. We revealed considerable cryptic diversity within the coreS. peterseniiandS. leptorrhabdalineages. We further resolved the phylogenetic position of two previously described taxa,S. kristianseniiandS. peterseniif.praefracta, propose species-level status forS. peterseniif.praefracta, and describe three new species,S. vinlandica,S. fluviatilis,andS. cornuta. Our findings add to the growing body of literature detailing distribution patterns observed in the genus, ranging from cosmopolitan species, to highly restricted taxa, to species such asS. hibernicafound along coastal regions on multiple continents. Finally, our study illustrates the usefulness of combining detailed morphological information with gene sequence data to examine species diversity within chrysophyte algae.