EDITORIAL

What is a Protist?

As an editor of a journal named 'Protist' one is frequently confronted with the above question posed by potential authors, apt readers of the journal, students, administrators and other paymasters, or fellow editors of other journals.

What is a protist? An editor is tempted and perhaps well-advised not to take a too restrictive stand on this matter, especially if a top-quality manuscript has been submitted. However, unless one wants to treat protists as a formal taxon (e.g. the 'Protista'), in which case, when applying phylogenetic (cladistic) classification principles all eukaryotes become protists, one needs to come up with a more practical solution to this question.

One may, of course, consult dictionaries, textbooks, scholarly treatises (as e.g. referred to in this issue's 'from the Archives' contribution by John Corliss), interview professional colleagues or trace the history of the name. In doing so, it is evident that no consensus emerges. Should we thus conclude with Mark Ragan (1998) that 'protists are what protistologists study', or that a protist qualifies as such by appearing in the pages of a journal bearing this name? Are protists just social constructs?

The problem in defining the protists in my estimation stems mainly from the misconception that protists should be treated as a taxonomic entity and is thus a consequence of that genuine human activity of classifying nature in a hierarchical manner. From Haeckel's (1866) Protista to the 'modern' > '5 kingdom' concepts (e.g. Margulis and Schwartz 1998) it has been 'convenient' to treat protists as a 'kingdom' (or a few 'kingdoms') because of the 'relative simplicity for information retrieval systems and for the education/edification of high school and college students, the general public, non-scientific professional people, and non-biological scientists' (Corliss 1998). The kingdom concept apparently also serves to raise the self-confidence of scientists who study these organisms. After all who wants to study the 'lower', 'simple' or 'primitive' organisms when others deal with the 'higher', 'complex' or 'more advanced' ones?

If one uncouples the term protist from its perpetuated taxonomic pervasion, protists much in the sense of Haeckel (but excluding the bacteria: part of Haeckel's Moneres) constitute a grade of cellular organization, namely single-celled (unicellular) eukaryotes. This is also the concept that stimulated the inauguration of the 'Archiv für Protistenkunde', the predecessor of the journal 'Protist' (Schaudinn: 'eine Sammelstelle für alle Forschungen zur Naturgeschichte der Einzelligen'). As in any biological definition the borders are blurred: are (sometimes macroscopic) coenocytic organisms unicellular and thus protists? Are cell colonies, aggregates, or simple filaments consisting of nondifferentiated cells uni- or multicellular and thus protists or not? What about organisms that have been secondarily reduced from a multicellular to a unicellular status such as Saccharomyces cerevisiae? It is clear that protists when defined as unicellular eukaryotes cut through monophyletic taxa (clades): Chlamydomonas is a protist, but the majority of taxa within the Viridiplantae are not protists, the same may be said about Porphyridium (a red alga), Chytridium (a fungus) or Monosiga (a choanoflagellate, presumably part of the animal lineage). Conversely, the brown alga Macrocystis in being a multicellular organism of considerable size (up to 50 m long) with differentiation of its thallus into organs, tissues and various cell types (thus mimicking the vascular plants), transcellular communication through plasmodesmata, and a complex life history involving specialized reproductive organs for asexual and sexual reproduction hardly qualifies as a protist.

'Protist' publishes papers that report substantial and novel findings in any area of research on protists. As 'Protist' enters its second year authors and readers will eventually decide whether 'Protist' lives up to this goal. An excellent paper will not be turned down because it does not fit a definition!

References

Corliss, JO (1998) Haeckel's kingdom Protista and current concepts in systematic protistology. Stapfia 56: 85-104
Haeckel E (1866) Generelle Morphologie der Organismen. 2 vols. G. Reimer, Berlin
Margulis L, Schwartz KV (1998) Five kingdoms: an illustrated guide to the phyla of life on earth. 3rd ed WH Freeman, New York
Ragan MA (1998) On the delineation and higher-level classification of algae. Eur J Phycol 33: 1-15

February 1999

Michael Melkonian, Editor
Cologne