Unravelling the hidden complexity in diversity and pigment composition of a colonial flagellate Synura sphagnicola (Chrysophyceae, Stramenopiles)

Abstract

In this study, we aim to taxonomically evaluate a unique example of cryptic diversity in a freshwater protist species Synura sphagnicola, occurring at two evolutionary levels. First, we characterize two species, S. sphagnicola and S. rubra sp. nov., that diverged from one another approx. 14 Mya. These species are morphologically well differentiated by the morphology of silica scales. Second, we propose seven evolutionary young, but ecologically and geographically well differentiated lineages as separate sub–species, sphagnicola, agilis, borealis (within S. sphagnicola), rubra, ampla, bella and caelica (within S. rubra). In addition, we examine the autofluorescence and pigment composition of two selected strains, identifying fucoxanthin as a predominant carotenoid. We further show that the red droplets in the cytoplasm, a prominent feature of both species, are formed by a previously unknown pigment. Finally, we identify chlorophyll–c2 in S. sphagnicola. Since the lack of this pigment represents a major distinguishing character to discriminate between classes Synurophyceae and Chrysophyceae, we formally synonymize these taxa.