The Taxonomic Significance of Species That Have Only Been Observed Once: The Genus Gymnodinium (Dinoflagellata) as an Example

Université Paris Sud, France
PLoS ONE (Impact Factor: 3.23). 08/2012; 7(8):e44015. DOI: 10.1371/journal.pone.0044015
Source: PubMed


Taxonomists have been tasked with cataloguing and quantifying the Earth's biodiversity. Their progress is measured in code-compliant species descriptions that include text, images, type material and molecular sequences. It is from this material that other researchers are to identify individuals of the same species in future observations. It has been estimated that 13% to 22% (depending on taxonomic group) of described species have only ever been observed once. Species that have only been observed at the time and place of their original description are referred to as oncers. Oncers are important to our current understanding of biodiversity. They may be validly described species that are members of a rare biosphere, or they may indicate endemism, or that these species are limited to very constrained niches. Alternatively, they may reflect that taxonomic practices are too poor to allow the organism to be re-identified or that the descriptions are unknown to other researchers. If the latter are true, our current tally of species will not be an accurate indication of what we know. In order to investigate this phenomenon and its potential causes, we examined the microbial eukaryote genus Gymnodinium. This genus contains 268 extant species, 103 (38%) of which have not been observed since their original description. We report traits of the original descriptions and interpret them in respect to the status of the species. We conclude that the majority of oncers were poorly described and their identity is ambiguous. As a result, we argue that the genus Gymnodinium contains only 234 identifiable species. Species that have been observed multiple times tend to have longer descriptions, written in English. The styles of individual authors have a major effect, with a few authors describing a disproportionate number of oncers. The information about the taxonomy of Gymnodinium that is available via the internet is incomplete, and reliance on it will not give access to all necessary knowledge. Six new names are presented - Gymnodinium campbelli for the homonymous name Gymnodinium translucens Campbell 1973, Gymnodinium antarcticum for the homonymous name Gymnodinium frigidum Balech 1965, Gymnodinium manchuriensis for the homonymous name Gymnodinium autumnale Skvortzov 1968, Gymnodinium christenum for the homonymous name Gymnodinium irregulare Christen 1959, Gymnodinium conkufferi for the homonymous name Gymnodinium irregulare Conrad & Kufferath 1954 and Gymnodinium chinensis for the homonymous name Gymnodinium frigidum Skvortzov 1968.

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Available from: Anne Thessen, Oct 05, 2015
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    • "How common are synonyms? For the well studied dino flagellate genus Gymnodinium, an autotroph common in coastal waters, of the 268 described species 103 have never been observed since their description, so called oncers, and a large portion are likely synonyms (Thessen et al., 2012). A very similar level of synonymy or dubious species was found for another genus of dinoflagellates, the relative ly rare Histioneis, heterotrophic dinoflagellates found in open waters. "
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    • "Some museums have amassed material from across the globe with the intention of documenting the existence of all unique forms of life. As a consequence, collections frequently house many poorly known, rare, endangered, and extinct taxa, some of which may not have been seen again subsequent to their initial collection (Sinha, 1973; Novotny & Basset, 2000; Thessen, Patterson & Murray, 2012). Aside from the importance of museum collections for research and education, they may also represent *Corresponding author. "
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