An inordinate fondness?: the number, distributions, and origins of diatom species

The number of extant species of diatoms is estimated here to be at least 30,000 and probably ca. 100,000, by extrapolation from an eclectic sample of genera and species complexes. Available data, although few, indicate that the pseudocryptic species being discovered in many genera are not functionally equivalent. Molecular sequence data show that some diatom species are ubiquitously dispersed. A good case can be made that at least some diatom species and even a few genera are endemics, but many such claims are still weak. The combination of very large species numbers and relatively rapid dispersal in diatoms is inconsistent with some versions of the ubiquity hypothesis of protist biogeography, and appears paradoxical. However, population genetic data indicate geographical structure in all the (few) marine and freshwater species that have been examined in detail, sometimes over distances of a few tens of kilometres. The mode of speciation may often be parapatric, in the context of a constantly shifting mosaic of temporarily isolated (meta) populations, but if our intermediate dispersal hypothesis is true (that long-distance dispersal is rare, but not extremely rare), allopatric speciation could also be maximized

Nitzschia fenestralis:A new diatom species abundant in the holocene sediments of an eastern African crater lake

Nitzschia is common in the phytoplankton of several East African lakes. A new species, Nitzschia fenestralis, sp. nov. D. Grady, D.G. Mann et Trobajo was encountered at numerous depths in a 16 m sediment core from Lake Babogaya, Ethiopia and is described using light and scanning electron microscopy. It is compared with several other morphologically similar taxa described from East and Central Africa (especially N. aequalis, N. mediocris, N. obsoleta and N. fabiennejansseniana), and from Europe (N. fruticosa). An unusual feature of some of these species (N. fenestralis, N. obsoleta and N. fabiennejansseniana) is that in the raphe canal each stria is represented by two narrower areolae (alternatively interpreted as a single subdivided areola). It is this feature that suggested the name of the new species (through the resemblance to a series of sash windows). Another characteristic of N. fenestralis and N. obsoleta, apparently never reported previously in any diatom, is that the more advalvar bands end approximately halfway along the frustules, rather than at the poles. In most respects (shape and size, stria and fibula densities, valve and girdle structure), N. fenestralis and N. obsoleta are very similar, but confusion is unlikely because they differ in whether central raphe endings are present (N. fenestralis) or absent (N. obsoleta). In Nitzschia fenestralis, and perhaps to a lesser extent in N. obsoleta, the striae usually become strongly radiate towards the poles. A preliminary assessment, based on the literature, suggests that N. fabiennejansseniana may be synonymous with N. obsoleta, which was described earlier.info:eu-repo/semantics/publishedVersio

A rapid cleaning method for diatoms

We describe here a protocol for cleaning diatoms when time is short and the amount of sample is very limited. Essentially, the method consists of drying material onto coverslips and cleaning it directly in situ using nitric acid (or hydrogen peroxide), which is evaporated to dryness. After washing twice or a few times with deionized water, the coverslips are ready for mounting in resin for light microscopy as usual, or attachment to stubs for scanning electron microscopy. Besides speed, the method has the advantage that it often preserves some frustules intact or leaves their different elements (and stages of valve formation) closely associated with each other. Examples where the method is especially advantageous are to clean small aliquots of cultures for identification or to act as vouchers, or to explore diversity of the most abundant species in natural material (e.g. periphyton). It is less suitable for counts in ecological or palaeoecological studies. We tabulate the many other cleaning methods to provide context for the new method described here.info:eu-repo/semantics/acceptedVersio

Homothallism, morphology and phylogenetic position of a new species of Sellaphora (Bacillariophyta), S. pausariae

Background and aims – The eutrophic Blackford Pond in Edinburgh has already provided the holotypes of six other Sellaphora species. A further undescribed species is present and requires description and characterization. Methods – Clones of the new species are characterized by light (LM) and scanning electron microscopy (SEM) and molecular phylogenetics (from a concatenated five-gene alignment of 18S rDNA, 28S rDNA, 23S rDNA, cox1 and rbcL, and a two-gene alignment of cox1 and rbcL). Key results – Sellaphora pausariae sp. nov. is named in honour of Dr Eileen Cox (‘pausaria’ = a lady coxswain). In molecular phylogenies, small-celled Sellaphora species (‘minima’ and ‘seminulum’ morphologies) branch off at the base of Sellaphora, though nodes are not well supported. Species and demes previously classified in either “Navicula pupula” or “Navicula bacillum” group into three very well supported clades (numbered 1–3). Although appearing in LM and SEM like a smaller, more delicate version of S. obesa, S. pausariae (clade 1) is not closely related to S. obesa (clade 2). Features of Sellaphora pausariae not confirmed previously in any Sellaphora but possibly widespread are: (a) hymenes with pores arranged in a regular scatter; (b) a stepped mantle near the poles; and (c) a ‘primodominant’ girdle comprising a wide band 1, a segmental band 2, and two extremely thin bands at the abvalvar end of the girdle. Sellaphora pausariae is homothallic; a deficiency of interclonal pairings in two-clone mixtures is interpreted as reflecting the tendency of cells to mate with their immediate neighbours. Conclusions – Morphologically, the new species can be differentiated from existing described species, though only problematically from some informally named demes. Molecularly, it is clearly characterized by the five genes sequenced. Girdle terminology needs expansion (e.g. to distinguish primodominant girdles from ‘graded’ ones, in which the bands gradually decrease in width and structural complexity from the valve outwards).info:eu-repo/semantics/publishedVersio

Generalized entropy and Noether charge

We find an expression for the generalized gravitational entropy of Hawking in terms of Noether charge. As an example, the entropy of the Taub-Bolt spacetime is calculated.Comment: 6 pages, revtex, reference correcte

Eileen J. Cox: her journey with diatoms

Eileen already had a keen interest in science during her school years. She studied Botany at Bristol University from 1967–1970, and it was her University teacher, Professor Frank Round, who inspired her interest in diatoms. During her PhD at Bristol under Frank Round’s supervision (1970–1975) she investigated the biology of tube-dwelling diatoms. At the same time, she worked as Departmental Demonstrator in the Botany Department. She left Bristol University in 1976 and became a Claridge Druce Research Fellow at the University of Oxford (1977–1980). Her investigations focused on the genus Navicula and the ultrastructure of diatom cells more generally. From 1979–1980 Eileen took up a post as lecturer at Pembroke College, University of Oxford. In 1980 Eileen moved to Germany and worked as a Royal Society European Exchange Research Fellow at the Litoralstation, Biologische Anstalt Helgoland. Here her studies focused on living diatoms, in particular the genus Donkinia, and she explored the value of live-cell features as diagnostic characters. From 1982–1985 she worked as a Max Planck research fellow at the Max-Planck-Institute at Plön, and from 1985–1988 as a Fellow of the German Research Foundation at the Max-Planck-Institute of Limnology, River Station, in Schlitz. During these years Eileen’s research on Navicula continued, but she also worked on the genera Placoneis, Parlibellus and Pinnularia, and studied relationships between diatom distributions and the environment. In 1989 Eileen returned to the UK to join the University of Sheffield, first as Research Associate, then as NERC Advanced Research Fellow and Honorary Lecturer, and carried out ecotoxicological studies on zooplankton. In 1992 she joined the Natural History Museum as Research Botanist to continue her research on diatoms. Here Eileen made many important contributions to diatom taxonomy and systematics. She carried out important studies on the naviculoid diatoms, and on live diatoms including her novel research on valve morphogenesis. Eileen has been involved in the organisation of many scientific meetings. In 1987 she organized the first meeting of the German-speaking diatomists in Schlitz, Germany, a meeting that has subsequently developed to include a much larger group of scientists from across Europe and from 2020 onwards will be the European Diatom Meeting. Other meetings she has helped organize include those held by the British Phycological Society, British Diatom Meetings, a NorthWest and Midlands Freshwater Group meeting, the Van Heurck Symposium on Taxonomy, a SETAC Europe meeting, a Society for the History of Natural History Meeting, and several European and International Phycological Congresses. Eileen has taught extensively; hosted 7 post-doctoral fellows and many research visitors to the Natural History Museum; supervised 10 PhD students, 4 M.Sc./M.Phil. students, 1 M.Res. student, and 4 final year B.Sc. students; and examined 9 PhDs and 1 DSc. She is currently a member of six learned societies, has refereed manuscripts for 31 scientific journals, has been invited speaker at 32 scientific meetings, gave 28 invited lectures at universities and research institutes, and presented at 56 national and international conferences. Eileen has given great service to several scientific societies, as council member, secretary or president. These include the British Phycological Society (president 2001–2002), the International Society for Diatom Research (president 2000– 112 Pl. Ecol. Evol. 152 (2), 2019 2002), the Systematics Association, and the International Phycological Society. Since 2007 Eileen has been Head of Postgraduate Studies in the Science Directorate of the Natural History Museum. As part of her role she develops and implements the training programmes of students at NHM, is responsible for strategic planning, and coordinates with research and training partners at universities and research institutions across the UK. Eileen is currently Editor in Chief of Diatom Research, and was previously Associate Editor (2011–2014), she is a board member of Fottea (since 2010), was guest co-editor of the Journal of the North American Benthological Society (Special Issue on Ecology of Springs), guest co-editor of the Journal of Limnology (Special Issue on Spring Biodiversity and Conservation), and Co-Editor-in-Chief of the European Journal of Phycology (2004–2009). Private hobbies include gardening, crafts such as cross stitching and sewing, visiting art museums and travelling, especially river and ocean cruises that have taken Eileen and Elliot recently to Alaska, the Caribbean, Germany, the Czech Republic, France and Portugal. Readers may like to read Eileen’s own description of her journey in diatoms, written for the young diatomists’ blog (available at https://youngisdr.blogspot.com/p/blog-page_12. html or in this volume supplementary information).info:eu-repo/semantics/publishedVersio