Molecular Phylogeny of the Parasitic Dinoflagellate Chytriodinium within the Gymnodinium Clade (Gymnodiniales, Dinophyceae)

Abstract

The dinoflagellate genus Chytriodinium, an ectoparasite of copepod eggs, is reported for the first time in the North and South Atlantic Oceans. We provide the first large subunit rDNA (LSU rDNA) and Internal Transcribed Spacer 1 (ITS1) sequences, which were identical in both hemispheres for the Atlantic Chytriodinium sp. The first complete small subunit ribosomal DNA (SSU rDNA) of the Atlantic Chytriodinium sp. suggests that the specimens belong to an undescribed species. This is the first evidence of the split of the Gymnodinium clade: one for the parasitic forms of Chytriodiniaceae (Chytriodinium, Dissodinium), and other clade for the free-living species.

Phylogeny, evidence for a cryptic plastid, and distribution of Chytriodinium parasites (Dinophyceae) infecting copepods

“…As expected, our isolates branched with C. affine (and one environmental sequence), while sequences from Chytriodinium roseum and several uncultured isolates obtained in other studies formed the remainder of the well-supported clade and branched with Dissodinium within the Gymnodinium clade (Daugbjerg et al 2000). Monophyly of Chytriodinium and Dissodinium (Chytriodiniaceae) remained unsupported, but the same branching pattern has been seen consistently in both maximum likelihood and Bayesian analyses (Gómez et al 2009;Gomez and Skovgaard 2015). A split into the parasitic Chytriodiniaceae and the free-living Gymnodinium clade members was not recovered, as also shown by Gómez et al (2009) but conflicting with the tree inferred by Bayesian analysis (Gomez and Skovgaard 2015), so the question as to whether the Gymnodinium clade is bifurcated into parasites and free-living forms cannot be answered at present.…”

“…The size distribution is in agreement with the different prevalent life stages of Chytriodinium, i.e., free-living spores and host-associated sporangia. In this context, it is noteworthy that in this study, the sporangium seemed to be attached to a copepod nauplius and not to an egg or egg sac of a brood-carrying copepod species (Gomez and Skovgaard 2015). Unfortunately, however, due to difficult conditions at sea, the authors failed to take more high quality pictures and to further investigate the characteristics of a feeding tube connecting host and parasite.…”

“…Monophyly of Chytriodinium and Dissodinium (Chytriodiniaceae) remained unsupported, but the same branching pattern has been seen consistently in both maximum likelihood and Bayesian analyses (Gómez et al 2009;Gomez and Skovgaard 2015). A split into the parasitic Chytriodiniaceae and the free-living Gymnodinium clade members was not recovered, as also shown by Gómez et al (2009) but conflicting with the tree inferred by Bayesian analysis (Gomez and Skovgaard 2015), so the question as to whether the Gymnodinium clade is bifurcated into parasites and free-living forms cannot be answered at present. The maximum likelihood tree inferred from concatenated SSU/LSU alignment of the Gymnodinium clade did not show such a split, but the nodes in question remained unsupported (Fig.…”

“…This phylogeny suggests an affiliation of Chytriodinium to the Gymnodinium clade (Daugbjerg et al 2000), and a split of this clade into free-living and parasitic subgroups; the latter comprising Chytriodinium and Dissodinium in the family Chytriodiniaceae. Monophyly of Chytriodiniaceae, however, was not statistically supported and could also not be confirmed using LSU rRNA gene sequences as phylogenetic marker (Gomez and Skovgaard 2015).…”

“…Morphological data are limited to light-microscopic investigations, and their apparently complex life cycle resulted in contradicting phylogenetic assignments at various taxonomic ranks within the Dinophyceae (see Gómez et al 2009 and references within). Molecular sequence data should resolve this question, but sequence data for this genus is rare, and consequently, the most recently published SSU rRNA gene based tree illustrating its phylogenetic position contains only a single full-length and two partial Chytriodinium sequences (Gomez and Skovgaard 2015). This phylogeny suggests an affiliation of Chytriodinium to the Gymnodinium clade (Daugbjerg et al 2000), and a split of this clade into free-living and parasitic subgroups; the latter comprising Chytriodinium and Dissodinium in the family Chytriodiniaceae.…”