Assessing morphological congruence in Dinobryon species and their stomatocysts, including a newly established Dinobryon pediforme–stomatocyst connection

Abstract

The chrysophyte genus Dinobryon Ehrenberg consists of 44 taxa, which occur in freshwaters, rarely marine waters, mostly in temperate regions of the world. The taxa of Dinobryon produce characteristic solitary or dendroid colonies and resting stages called stomatocysts. Only 20 Dinobryon taxa have information on produced stomatocysts and only four stomatocysts are reliably linked with vegetative stages using modern identification standards employing scanning electron microscopy (SEM) analyses. In this study, an encysted material of Dinobryon pediforme (Lemmermann) Steinecke was collected in two lakes in contrasting regions of Poland. Light microscopy (LM) and scanning electron microscopy (SEM) analyses revealed that Dinobryon pediforme produces stomatocyst #61, Piątek J. that is described here as new morphotype following the International Statospore Working Group (ISWG) guidelines. This raises to five the number of reliable links between vegetative stages of Dinobryon species and corresponding stomatocysts. Phenotypic similarities between Dinobryon species and their stomatocysts, analysed for five reliably established links, showed no relationships in size and shape between loricas and stomatocysts belonging to the same species. The morphological characters of loricas and stomatocysts mapped onto the phylogenetic tree of the five Dinobryon species revealed only little congruence between their morphology and phylogenetic relationships.

Size-Fractionated Microbiome Structure in Subarctic Rivers and a Coastal Plume Across DOC and Salinity Gradients

“…Species sorting in the GWR plume with rising salinity may have especially restricted the number of taxa in this core subset. Eukaryotic OTUs in this core microbiome included taxa found commonly in freshwater such as the putative parasite Perkinsea ( Lefèvre et al, 2008 ; Jobard et al, 2020 ), many Chrysophyceae such as the mixotrophic genus Dinobryon , which produces stomatocysts ( Piątek et al, 2020 ) ensuring their survival in unfavorable conditions, and unclassified members of the freshwater Novel Clade 10 (Cercozoa), which contains biflagellate species that can feed on other flagellates ( Bass et al, 2018 ).…”

Multigene phylogeny reveals a cryptic diversity in the genus Dinobryon (Chrysophyceae) with integrative description of five new species

“…The formation of the stomatocyst has been reported in many chrysophycean genera: Ochromonas , Uroglena , Chromulina , Epipyxis , Mallomonas , and Spumella ( Scherffel, 1911 ; Pascher, 1914 ; Krieger, 1930 ; Lund, 1942 ; Hilliard and Asmund, 1963 ; Nygaard, 1979 ; Holen, 2014 ; Jeong et al., 2021 ). In the genus Dinobryon , the stomatocyst morphology was described in several species by line drawing and images using light and electron microscopes ( Krieger, 1930 ; Hilliard and Asmund, 1963 ; Sheath et al., 1975 ; Smith and White, 1985 ; Duff et al., 1995 ; Piatek et al., 2012 ; Piatek et al., 2020 ). The stomatocyst morphologies from five Dinobryon species were newly described in this study.…”

“…Especially, the three new species, D. cylindricollarium , D. inclinatum , and D. spinum , showed species-specific features in the ultrastructure of their stomatocysts. The stomatocyst of most Dinobryon species is spherical in shape without surface ornamentation and has either a cylindrical or conical collar, which is typical for D. annulatum , D. divergens , D. pediforme , D. sertularia , and D. sociale ( Krieger, 1930 ; Asmund, 1955 ; Hilliard and Asmund, 1963 ; Hilliard, 1966 ; Sheath et al., 1975 ; Sandgren, 1983 ; Duff et al., 1995 ; Piatek et al., 2012 ; Piatek et al., 2020 ). The new species D. cylindricollarium has a longer cylindrical collar length (1.5–3.3 μm) than D. annulatum (slightly raised collar), D. divergens (1.0–1.3 μm), and D. pediforme (0.2–0.5 μm), and its collar width (2.3–3.1 μm) is also narrower than that of D. sertularia (4.2–4.8 μm).…”

“…With the development of scanning electron microscopy (SEM), the ultrastructure of stomatocysts in Dinobryon species have received scientific attention, for example, as ecological paleoindicators in the sediment of certain lakes (Duff et al, 1995;Wilkinson et al, 2001). Since stomatocysts in Dinobryon species were first described by Stein (1878) and Bütschli (1878), the morphologies of stomatocysts have been reported in approximately 20 Dinobryon taxa; however, the stomatocyst ultrastructure of only five Dinobryon species have been described in detail using SEM (Sandgren, 1983;Piatek and Kowalska, 2008;Piatek et al, 2012;Piatek et al, 2020). Most of these were described from field specimens, and the cyst morphology on the basis of culture materials remains little known, except for that of D. cylindricum (Sandgren, 1983).…”

“…Because species identification based only on lorica morphology may not be accurate, the description of the cyst morphological characteristics of one species from lake sediments and preserved environmental specimens is not particularly useful for species identification. For example, Sandgren (1983) reported that D. cylindricum produces spiny spherical cysts with slightly curved collar, while others suggested that the species has a smooth, spherical cyst with a long, hooked collar ( Zeeb and Smol, 1993 ; Piatek et al., 2020 ). A way to resolve these discrepancies would be to identify the species by culturing each and observing the stomatocyst morphologies.…”