Book Review: Freshwater Diploneis. Two Studies.

by by Demetrio Mora |

Diploneis. Two Studies. Koeltz

Diatoms of Europe, Volume 09, Freshwater Diploneis: Two Studies. 2020. Horst Lange-Bertalot, André Fuhrmann and Marcus Werum: freshwater Diploneis: species diversity in the Holarctic and spot checks from elsewhere. 2020. 185 pls. (LM & SEM). 526 p. & Elena Jovanovska and Zlatko Levkov: the genus Diploneis in the Republic of North Macedonia. 2020. 60 pls. (LM & SEM). 162 p. Hardcover. Koeltz Botanical Books, Glashütten, Germany. ISBN 978-3-946583-30-1. Price 208.95 €, US$ 244.10 (prices in other currencies depend on current course).

Despite assertions that its diversity is predominantly marine, recent studies are demonstrating that the diatom genus Diploneis Ehrenb. ex Cleve holds a higher diversity in freshwaters environments than previously thought [1, 2]. One of the main impediments to species discovery of this genus in limnic environments might be its rarity, in the sense that it most often displays a sparse distribution and low abundances [3]. This is reminiscent of the Pinnularia borealis species complex, which is likewise a rare diatom that has been found to harbour an incredibly large cryptic species diversity [4].

According to the multipliers proposed to be applied to the number of species already known in selected genera or species complexes, to estimate their actual extant species diversity, this multiplier lies at x9.5 for the Diploneis smithii/fusca group [5]. Despite this group inhabiting the marine benthos, it seems that this multiplier might well be applicable to Diploneis from freshwater environments, as perfectly exemplified in volume 9 of Diatoms of Europe, a treatise dedicated to freshwater Diploneis, in which 75 new species are described, including eleven new species only found outside of Europe. This volume, divided into two studies, represents the most extensive work on Diploneis to date. These two studies examine 125 infrageneric taxa in total, including the description of 66 new infrageneric taxa in the first study [6], and nine in the second [7].

This volume is well organized, with very detailed morphological diagnoses, also providing comparative descriptions, as well as remarks on the ecology and distribution of the taxa. The comparative table of morphometric data included in the first study will surely be very welcomed among the users of this monograph, allowing for a quick comparison of several taxa instead of going back and forth through countless descriptions.

The main point for improvement of this volume relates to the quality of the light microscopy (LM) and scanning electron microscopy (SEM) microphotographs in the second study. They are of variable quality, offering very good resolution for some taxa (e.g. D. exigua Jovanovska, Levkov & Edlund) as well as low resolution for others*, in some cases not allowing to readily visualize the details that the authors point out to in the descriptions. In contrast, the LM and SEM microphotographs in the first study are outstanding, such as for the newly described D. galloprovincialis Lange-Bertalot, Fuhrmann & V. Peeters, as well as for D. werumiana Lange-Bertalot, Fuhrmann, E. Jovanovska & Levkov. Another point relates to the newly described D. submarginestriata Jovanovska, Lange-Bertalot & Levkov. It is confusing that both studies refer to its holotype under different slide numbers, leaving the reader to assume that the correct slide number should be the one in the protologue?

In spite of being part of the series “Diatoms of Europe”, it is of considerable value that this monograph is not limited to describing and critically comparing populations of species found in that continent, providing a more inclusive outlook to the diversity of the genus in freshwater ecosystems. This broader sampling also contributes to making more assertive claims about species distributions.

The authors of the first study propose a subdivision of the genus into three subgenera, i.e. Diploneis, Cribradiploneis Lange-Bertalot & Fuhrmann, and Volaediploneis Lange-Bertalot & Fuhrmann [6]. They also make a plea for maintaining the genus in its current circumscription, which they claim to be justified by the H-shaped silica complex that serves as a “stabilising cell skeleton” across the species that make up this genus [6]. Such a claim seems to be supported by molecular phylogenetics [8], which renders Diploneis as a monophyletic group. Despite the limited taxon sampling of the genus, this is the first molecular phylogeny presenting multiple Diploneis strains [8], i.e. 14, with all except one being marine, i.e. UTEX FD282 [9]. Apart from that strain, there are only two other Diploneis strains from freshwaters in publicly available nucleotide sequence databases [10]. This poor representation might be due to the difficulties in producing clonal cultures of this genus [11]. However, further efforts in gathering molecular data from freshwater and marine Diploneis taxa might well continue to support the monophyly of the genus, and reaffirm the recommendation of Lange-Bertalot et al. [6] maintaining its current circumscription. Additionally, integrative taxonomic approaches will most certainly further uncover the hidden diversity within this genus, in a similar way as researchers have done for other genera [12, 13].

All things considered, volume 9 of Diatoms of Europe is a valuable work presenting an excellent treatise of the genus Diploneis from freshwater environments, highly recommendable for any institution and individual dedicated to the taxonomy of diatoms. Additionally, it will certainly be a useful identification tool for ecologists, hydrobiologists and palaeolimnologists.

References

1. Jovanovska E, Levkov Z, Edlund MB (2015) The genus Diploneis Ehrenberg ex Cleve (Bacillariophyta) from Lake Hövsgöl, Mongolia. Phytotaxa 217(3): 201-248
2. Kulikovskiy MS, Lange-Bertalot H, Kuznetsova IV (2015) Lake Baikal: Hotspot of Endemic Diatoms II. Iconographia Diatomologica 26: 1-656
3. Lange-Bertalot H, Fuhrmann A (2017) Diploneis lecohuiana sp. n., D. fereparma sp. n., and D. parma Cleve: rare diatoms (Bacillariophyta) in Central European freshwater. Nova Hedwigia Beiheft 146: 33–42
4. Pinseel E, Janssens SB, Verleyen E, Vanormelingen P, Kohler TJ, Biersma EM, Sabbe K, Van de Vijver B, Vyverman W (2020) Global radiation in a rare biosphere soil diatom. Nature Communications 11:2382
5. Mann DG, Vanormelingen P (2013) An Inordinate Fondness? The Number, Distributions, and Origins of Diatom Species. Journal of Eukaryotic Microbiology 60(4): 414-420
6. Lange-Bertalot H, Fuhrmann A, Werum M (2020): Freshwater Diploneis: species diversity in the Holarctic and spot checks from elsewhere. In: Lange-Bertalot H (ed) Diatoms of Europe. Diatoms of European Inland Water and Comparable Habitats 9. Freshwater Diploneis  ̶  Two Studies. Koeltz Botanical Books, Glashütten, 1-526.
7. Jovanovska E, Levkov Z (2020) The genus Diploneis in the Republic of North Macedonia. In: Lange-Bertalot H (ed) Diatoms of Europe. Diatoms of European Inland Water and Comparable Habitats 9. Freshwater Diploneis  ̶  Two Studies. Koeltz Botanical Books, Glashütten, 527-690.
8. Sabir JSM, Theriot EC, Manning SR, Al-Malki AL, Khiyami MA, Al-Ghamdi AK, Sabir MJ, Romanovicz DK, Hajrah NH, El Omri Abdelfatteh, Jansen RK., Ashworth MP (2018) Phylogenetic analysis and a review of the history of the accidental phytoplankter, Phaeodactylum tricornutum Bohlin (Bacillariophyta). PLoS ONE 13(6): e0196744
9. Theriot EC, Ashworth M, Ruck E, Nakov T, Jansen RK (2010) A preliminary multigene phylogeny of the diatoms (Bacillariophyta): challenges for future research. Plant Ecology and Evolution 143(3): 278-296.
10. Mora D, Abarca N, Proft S, Grau J, Enke N, Carmona J, Jahn R, Zimmermann J (2019) Morphology and metabarcoding: a test with stream diatoms from Mexico highlights the complementarity of identification methods. Freshwater Science 39(3): 448-464
11. Droop SJM, Mann DG, Lokhorst GM (2000) Spatial and temporal stability of demes in Diploneis smithii/D. fusca (Bacillariophyta) supports a narrow species concept. Phycologia 39(6): 527-546
12. Jahn R, Abarca N, Kusber W-H, Skibbe O, Zimmermann J, Mora D (2020) Integrative taxonomic description of two new species of the Cocconeis placentula group (Bacillariophyceae) from Korea based on unialgal strains. Algae 35(4): 303-324
13. Maltsev Y, Maltseva S, Kociolek JP, Jahn R, Kulikovskiy M (2021) Biogeography of the cosmopolitan terrestrial diatom Hantzschia amphioxys sensu lato based on molecular and morphological data. Scientific Reports 11:4266

 

Demetrio Mora
Referat U2 – Mikrobielle Ökologie
Bundesanstalt für Gewässerkunde
Am Mainzer Tor 1
56068 Koblenz
Germany

 

Both pictures included in this review, from the front and back covers of the book, were made available by and are here reproduced with authorisation from the publisher.

*Note from the publisher: Too dark images from the book can be made available upon request. Please email the publisher.