Benthic flattened cells of the phylogenetically related marine dinoflagellates Protoceratium reticulatum and Ceratocorys mariaovidiorum (Gonyaulacales): a new type of cyst?

Abstract

A planktonic-benthic relationship has been described for many dinoflagellate species as part of their ecological strategy to overcome highly variable aquatic environments. Here, the phylogenetically and morphologically related marine dinoflagellates Protoceratium reticulatum and Ceratocorys mariaovidiorum were studied in relation to an unknown benthic life form. In vivo and fixed samples from cultures were analyzed in detail by light and scanning electron microscopy. In both species, a cell type with a morphology different from that of vegetative cells was observed in cultures grown until stationary phase. This cell type was always benthic, swimming sporadically only when it was disturbed. Its main feature included a strong dorsoventral compression. These cells originated from vegetative cells whose protoplasm underwent a progressive flattening, resulting in a gradual detachment of the reticulate and thick thecal plates and the formation of very thin non-reticulated new plates with pores. When returned to fresh fullstrength medium, the cells recovered their spherical vegetative-like morphology, including new reticulated thick plates and subsequent cell divisions. The kinetics of flattened cell formation showed that in both species, this cell type increased exponentially until the onset of the culture stationary phase and then decreased. The results of this study are discussed in the context of the planktonic-benthic coupling in dinoflagellate life cycles, including those newly appreciated to be well adapted to the benthic environment.

Ceratocorys mariaovidiorum sp. nov. (Gonyaulacales), a new dinoflagellate species previously reported as Protoceratium reticulatum

“…This cell type has recently been described by Salgado et al. () as a benthic stage of the life cycle. Sexual stages such as gamete pairs and planozygotes were also observed in both strains cultured in L1 medium.…”

“…The formation process and morphological features are described in detail by Salgado et al. (). On the other hand, no cysts resembling the typical spiny resting cysts of P. reticulatum appeared in the cultures of C. mariaovidiorum .…”

“…In addition to motile cells with a globular shape, a type of cell with a strong dorso-ventral compression was regularly present in the cultures, though in very low number. This cell type has recently been described by Salgado et al (2018) as a benthic stage of the life cycle. Sexual stages such as gamete pairs and planozygotes were also observed in both strains cultured in L1 medium.…”

Stressor-induced ecdysis and thecate cyst formation in the armoured dinoflagellates Prorocentrum cordatum

“…However, data on diverse life stages of dinoflagellates obtained over the last years, including such peculiar findings as the division of non-motile stages (division cysts) and flagellar motility in presumable cysts, have revived the discussion of the cyst concept 55 . Recently Salgado et al 55 described benthic stages of the dinoflagellates Protocerarium reticulatum and Ceratocorys mariaovidiorum which displayed characteristic features of cysts (e.g. motionless behaviour, reduction of cytoplasm and condensation of chloroplasts) but possessed flagella and were able to move when disturbed.…”

Studies on Woloszynskioid Dinoflagellates X: Ultrastructure, Phylogeny and Colour Variation in Tovellia rubescens n. sp. (Dinophyceae)

“…We were not able to link the flat cells to any particular life cycle stage, nor to any particular function in the culture batches. A recent discussion on the significance of flattened cells appearing in cultures of Protoceratium reticulatum (Clapar ede and J. Lachmann) Buetschli and Ceratocorys mariaovidiorum P. Salgado, S. Fraga, F. Rodr ıguez, Riob o and I. Bravo suggests a link to a benthic stage of these species, arguably because flat cells would be better adapted to move in the interstitial environment of the sediment, or to attach to sediment particles (Salgado et al 2018). Whether benthic flattened cells of T. rubescens n. sp.…”