Developments in the taxonomy of silica‐scaled chrysophytes – from morphological and ultrastructural to molecular approaches

Abstract

Taxonomy in silica‐scaled chrysophytes has gone through three morphological phases. From primary studies of the cell morphology in the 18th century, the focus was in the 20th century replaced by studies of the silica structures of the cell envelope. Now, in the latest decades the importance of DNA sequencing has been recognized, not only to support the taxonomic framework but also to obtain new understanding of taxonomic relations among particular taxa. In the first part of this review, we provide a historical overview of the developments in the taxonomy of scale‐bearing chrysophytes. In the second part, we present a phylogenetic reconstruction of chrysophyte algae, updated by newly obtained SSU rDNA and rbcL sequences of several isolated Synura, Mallomonas and Chrysosphaerella species. We detected significant incongruence between the phylogenies obtained from the different datasets, with the SSU rDNA phylogram being the most congruent with the morphological data. Significant saturation of the first rbcL codon position could indicate the presence of positive selection in the rbcL dataset. Within the Synurales, the relationships revealed by the phylogenetic analyses highlight the artificial infragenetic classification of Mallomonas and Synura, and the occurrence of cryptic diversity within a number of traditionally defined species. Finally, three new combinations are proposed based on the phylogenetic analyses: Tessellaria lapponica, Synura asmundiae and S. bjoerkii.

Morphological delineation and distribution patterns of four newly described species within theSynura peterseniispecies complex (Chrysophyceae, Stramenopiles)

“…It is relatively easily cultivated and investigated with molecular methods (Wee et al, 2001;Boo et al, 2010;Kynčlová et al, 2010;Škaloud et al, 2012, 2013a, so it represents an ideal model taxon for investigating evolutionary patterns in protists. Particular species are relatively young in evolutionary terms, diverging on the order of several million years ago (Jo et al, 2013).…”

“…The order Synurales (Chrysophyceae, Stramenopiles) contains several genera of scale-bearing flagellates that are important components of phytoplankton communities of various freshwater bodies (Kristiansen & Preisig, 2007;Škaloud et al, 2013a). The most conspicuous genus of the order, Synura, is a colonial organism formed by a variable number of cells joined together at their posterior ends.…”

Comprehensive transcriptome analysis provides new insights into nutritional strategies and phylogenetic relationships of chrysophytes

“…However, the precise branching order of the major chrysomonad clades varies with algorithm and taxon sampling (Scoble & Cavalier-Smith, 2014; Grossmann et al, 2016; Bock et al, 2014). Current molecular phylogenetic analyses concentrate on few chrysophyte taxa such as the phototrophic genera Synura and Mallomonas  (Škaloud, Kristiansen & Škaloudová, 2013; Siver et al, 2015) and the mixotrophic genus Dinobryon  (Bock et al, 2014), as well as on mixotrophic and colourless single-celled taxa originally lumped into the genera Paraphysomonas  (Scoble & Cavalier-Smith, 2014), Spumella  (Grossmann et al, 2016) and Ochromonas (Andersen (2007) and RA Andersen, pers. comm., 2007).…”

Synurophyte Algae**This chapter is dedicated to my mother, Helen Jean Siver. THANKS, MOM.

“…"Halo" colonies, also studied by Wee (2001), formed when all cells of a colony simultaneously retracted to form a compact mass of cells within a now more distant peripheral matrix. All available evidence indicates that Tessellaria diverged early within the Synurophyceae lineage (Wee, 1997;Lavau et al, 1997;Škaloud et al, 2013). 3C-D).…”

“…Much work still needs to be done in order to determine the validity of the Synurophyceae as a class and to document the phylogenetic relationships of the group to other heterokonts, especially the Chrysophyceae (Andersen et al, 1999;Škaloud et al, 2013). Some recent molecular phylogenetic works question whether the Synurophyceae is a distinct class of heterokonts or a monophyletic clade nested within the Chrysophyceae.…”