The austral biflagellateChloromonas rubroleosa(Chlorophyceae) is the closest relative of the unusual quadriflagellate genusChlainomonas, both found in snow

Abstract

AbstractThe quadriflagellate genusChlainomonasfrequently dominates red snow globally. It is unusual in several respects, with two separated pairs of flagella, apparent cell division via extrusion of cytoplasmic threads, and being nested phylogenetically within the biflagellate genusChloromonas. Here, we showed that the austral speciesChloromonas (Cr.) rubroleosa, originally described from Antarctic red snow, is a close biflagellate relative ofChlainomonas, challenging the monophyly ofChlainomonasas currently conceived. Sequences of the 18S rRNA gene robustly linkedCr. rubroleosawith near‐identical environmental sequences from Antarctic red snow andChlainomonasfrom North America, Japan, and Europe. Furthermore, the 18S rRNA andrbcL gene sequences ofCr. rubroleosawere almost identical to New Zealand and North American collections ofChlainomonas.Cr. rubroleosaand New ZealandChlainomonasare separated by only a single‐base substitution across the ITS1‐5.8S‐ITS2 rRNA loci (and according to ITS2, the North American collection is the next closest relative). This again raises the possibility thatChlainomonasis a life‐cycle stage of vegetatively biflagellate organisms, although this remains confounded by the scarcity of biflagellates in field populations, the apparent cell division by quadriflagellates, and the absence ofChlainomonas‐type cells in cultures ofCr. rubroleosa. The latter species is broadly similar toChlainomonas, being poor at swimming, with similar pigment, chloroplast arrangement and ultrastructure, and is relatively large.Increased size is a feature of the wider clade of “Group D” snow algae. A synthesis of field and laboratory investigations may be needed to unravel the life cycle and correct the systematics of this group.