Peridinium volzii

Holzer, Victoria J. C., Kretschmann, Juliane, Knechtel, Johanna, Owsianny, Paweł M. & Gottschling, Marc, 2022, Morphological and molecular variability of Peridinium volzii Lemmerm. (Peridiniaceae, Dinophyceae) and its relevance for infraspecific taxonomy, Organisms Diversity & Evolution 22 (1), pp. 1-15 : 8-9

Peridinium volzii is morphologically variable

Despite the uniqueness of P. volzii due to the small first apical plate, the morphological plasticity within the evolutionary lineage appears great. However, all this plasticity (shown within monoclonal strains and partly formalised in numerous varieties and forms) cannot be associated with other traits such as environmental conditions, geographic occurrence or genetic constitution that evolutionary adaptation appears of minor importance in P. volzii . A considerable number of infraspecific taxa have been described ( Table 2 ) and based on the microscopic study of monoclonal strains we confirm the existence of traits such as additional sutures (associated with, e.g., P. volzii forma complexum ; Fig. 3m ) and fusion of plates (associated with, e.g., P. volzii var. simplex ; Fig. 3l ). Other traits such as the shifted suture (of Peridinium guestrowiense var. betacollineatum Er.Lindem. ) having importance in species such as P. cinctum ( Izquierdo López et al., 2018 ; Romeikat et al., 2019) have not been found during the course of the present study. It is known today that varying widths of sutures, where the intercalary space becomes distinctively striate, are ontogenetically disposed (growth bands: Netzel, 1982). This trait ( Figs. 1a , 3b, e, i, k ) is associated with P. guestrowiense forma late-intercalatum and P. guestrowiense forma latissime-intercalatum Er.Lindem. and is the only one that occurs in combination with other morphological deviations.

In addition to the historically described intraspecific variabilities, we detected five cases of yet undiscovered deviation in P. volzii . The unusual epithecal configuration with plate 4″ abutting plate 3a ( Fig. 3 a-b) has to the best of knowledge never been noted in the literature before. More-over, alternate configurations between, for example, plates 3′ and 4″ (resp. 1a and 3a; Fig. 1c, f ) within monoclonal strains are reminiscent of, for example, Parvodinium mixtum Wołosz. ex Kretschmann, Zerdoner, Owsianny & Gottschling ( Kretschmann et al., 2018a). An additional suture and the split of plate 2a ( Fig. 3c ) have also not been reported from P. volzii so far. Fusion of plates regularly though rarely appears in the thecal pattern of various dinophytes, and corresponding observations in the present study do not come as a surprise. Usually, the fusion of plates takes place within plate series such as the intercalary ( Fig. 3f ), precingular ( Fig. 3d ) and antapical series (associated with P. volzii var. simplex ; Fig. 3l ). However, the fusion of plates associated with different plate series is very rare, and we found fused plates 1′″ and 1″″ ( Fig. 3e ) once only. Anyhow, also the newly discovered variability occurs in individual cells associated with all three ribotypes present in this study and does not make the recognition of corresponding taxa at an infraspecific rank seem justified either.

Figures

◂Fig.3 Historically described phenotypical variations and yet undiscovered deviations in the plate pattern of P. volzii. b–c, f, i, l–m Light microscopy, a, d–e, g–h, k scanning electron microscopy. a–f Newly identified deviations a–b plate 4′′ pentagonal in strains a GeoM*793; b GeoM*788; c plate 2a split (strain GeoK*024); d plates 2′′ and 3′′ fused (strain GeoM*866); e plates 1′′′ and 1′′′′ fused (strain GeoM*788); f plates 1a and 3′ fused (strain GeoM*788). g–m Historic infraspecific taxa; g P. guestrowiense forma lineatum (strain GeoM*866); h P. guestrowiense forma compressum (strain GeoM*866); i P. guestrowiense subvar. originale (strain GeoK*024); k P. volzii var. cinctiforme (strain GeoM*793); l P. volzii var. simplex (strain GeoM*789); m P. volzii forma complexum (strain GeoM*793). Abbreviations: n′: apical plate, n′′: precingular plate, n′′′: postcingular plate, n′′′′: antapical plate, na: anterior intercalary plate, nC: cingular plate, split or fused plates are indicated by asterisks. Scale bar=10 µm. U A=15 kV

◂Fig.1 Morphology of thecate and coccoid cells, with labelled thecal plates. a–c, i, m Light microscopy, d–h, k–l scanning electron microscopy. a Ventral view of strain GeoM*788; b dorsal view of strain GeoM*793; c apical view of strain GeoK*044; d ventral view of strain GeoK*037; e dorsal view of strain GeoM*788; f apical view of strain GeoK*024, with the dehiscence of epithecal opening indicated by a blue line; g antapical view of strain GeoK*044; h leftlateral view of strain GeoM*866; i motile cell of strain GeoK*037; k–m coccoid cells showing variability in shape and size of strains k GeoM*866, l GeoM*793 and m GeoK*024. Abbreviations: n′: apical plate, n′′: precingular plate, n′′′: postcingular plate, n′′′′: antapical plate, na: anterior intercalary plate, nC: cingular plate, Sa: anterior sulcal plate, Sd: right sulcal plate, Sp: posterior sulcal plate. Ss: left sulcal plate. Scale bar: 10 µm. UA: 15 kV