Journal of Nematology Volume 47 March 2015 Number 1
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JOURNAL OF NEMATOLOGY VOLUME 47 MARCH 2015 NUMBER 1 Journal of Nematology 47(1):1–10. 2015. Ó The Society of Nematologists 2015. Utility of Classical a-Taxonomy for Biodiversity of Aquatic Nematodes 1,2 1,3 WILFRIDA DECRAEMER AND THIERRY BACKELJAU Abstract: ‘‘Classical a-taxonomy’’ has different interpretations. Therefore, within the framework of an integrated taxonomic ap- proach it is not relevant to divide taxonomy in different components, each being allocated a different weight of importance. Preferably, taxonomy should be seen in a holistic way, including the act of delimiting and describing taxa, based on different features and available methods, and taxonomy can not be interpreted without looking at evolutionary relationships. The concept of diversity itself is quite diverse as is the measure of diversity. Taxonomic descriptions of free-living aquatic nematodes are very valuable as they provide basic phenotypic information that is necessary for the functional ecological, behavioral, and evolutionary interpretation of data gathered from molecular analyses and of the organism as a whole. In general, molecular taxonomic analyses have the advantage of being much faster and of being able to deal with a larger number of specimens but also possess the important advantage of dealing with a huge amount of features compared to the morphology-based approach. However, just as morphological studies, molecular analyses deal only with partial of an organism. Key words: morphology, molecular analyses, taxonomic descriptions. The authors, having expertise in taxonomy based on informative illustrations, and nomenclatural rules to morphology as well as on molecular data, were invited follow. The second part of this paper then deals with to discuss the future role, if any, of a-taxonomy for the current/future role of a-taxonomy in nematode biodiversity assessment of aquatic nematodes in the biodiversity assessments in which species distributions, current era of molecular/genetic data-based research community structures, and ecosystem functioning are and metadata. analysed. Nematodes are an ubiquitous and very At the beginning of the 21st century, many discus- abundant group of metazoans, which play an important sions on the taxonomic impediment and the advantage role in the nutrient mineralization process and cycling. of molecular identification techniques emphasized the Hence, to understand aquatic ecosystem functioning, shortcomings and pitfalls of a-taxonomy, questioning one must first address nematode diversity (Ristau et al., its utility and future (Tautz et al., 2002). Remedies have 2013). However, the concept of diversity itself is quite been proposed and new technologies have been de- diverse, as is the measure of diversity (Hodda et al., veloped to counter the negative perspective of taxon- 2009). We will discuss the role of a-taxonomy in nema- omy (Will et al., 2005) and create fast-track taxonomy tode biodiversity assessments in which species distribu- by combining digital imaging, molecular techniques, tions, community structures, and ecosystem functioning and highly accurate diagnoses in online wiki databases are analysed. (Riedel et al., 2013). To have a sound discussion, one must be clear on the terminology used. Therefore, we a-TAXONOMY will first look at the different interpretations of the terminology used through time, more particular how The study of aquatic nematode biodiversity starts do we define taxonomy and systematics? Why differ- with an inventory of the nematodes in the environ- entiate taxonomy into subdisciplines/sublevels as, e.g., ment. The first approach is a phenotypic one. Although a-taxonomy, descriptive taxonomy, molecular taxon- each specimen is unique, in reality specimens are omy, and integrated taxonomy? Despite the nature, sorted and grouped into taxonomic units and ordered definition and delimitation of species remain contro- (classified) on the basis of phenotypic, usually mor- versial issues, one can nevertheless provide guidelines phological characteristics, similarity, and contiguity, for a good nematode species level taxa descriptions, a methodology indicated as a-taxonomy by Simpson (1960). Names of the taxa thus defined are given by Received for publication February 16, 2015. applying the Linnean nomenclature. 1Royal Belgian Institute of Natural Sciences, Vautierstraat 29, B-1000 Brussels, The term a-taxonomy was first coined by Turrill Belgium. a 2Department of Biology, Ghent University, Ledeganckstraat 35, B-9000 (1935) who distinguished -taxonomy or ‘‘traditional Ghent, Belgium. taxonomy’’ based on morphology and V-taxonomy or 3Evolutionary Ecology Group, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium. ‘‘perfected taxonomy’’ which is more inclusive and This paper was written in the context of the FWO research community W0. builds upon a broader base of information from mor- 009.11N ‘‘Belgian Network for DNA Barcoding (BeBoL).’’ E-mail: [email protected] phology, physiology, ecology, genetics, and including This paper was edited by Jyotsna Sharma. relationships. Later on, different interpretations of 1 2 Journal of Nematology, Volume 47, No. 1, March 2015 taxonomy/a-taxonomy were given, thereby dividing taxonomy into two or three main components (Fig. 1). Mayr (1969) recognized three levels of taxonomy: a-taxonomy involves the characterization and naming of species, b-taxonomy deals with the arrangement of species into a natural system, and g-taxonomy refers to studies of various biological and evolutionary aspects. More recently, taxonomy is seen as consisting of basic taxonomy s.s., also referred to as descriptive taxonomy, complemented by taxonomy s.l. or phylogenetic tax- onomy that deals with the study of diversity, classifica- tion, and relationships (Godfray, 2002). The latter part was named biosystematics by Tillier et al. (2000), which together with taxonomy (read a-taxonomy) constitutes the discipline systematics. Dayrat (2005) introduced the term integrative taxonomy for a holistic approach based on multiple and complementary perspectives; he also provided seven guidelines for naming a species, e.g., taking into account the necessary number of spec- imens to obtain information on possible intraspecific and interspecific variations of characters; the need for FIG. 1. Chart on evolution in interpretation of taxonomy. support based on broad evidence provided by mor- phology, ecology, etc; or the preservation of type speci- mens in museum collections and their availability for molecular studies. In general, a-taxonomy stands for the diagnostic characters, analyse relationships and establish process of species discovery, description, and naming a classification. E-taxonomy or web-based taxonomy re- (Luc et al., 2010). Martens and Segers (2005) defined fers to the advantages of the Internet as a medium to a-taxonomy as the basic and classical description of new connect taxonomists and facilitate access to larger taxa and considered it a basic methodology in which the amount of different type of data. description of taxa is comparable with obtaining DNA Morphology is the basis for understanding animal sequences, an opinion we do not share. a-Taxonomic structures and ‘‘basic’’ or ‘‘classical’’ description is the data, similar to DNA sequences, provide the tools for term for a morphology-based description. Considering future analyses of, for example, phylogenetic relation- a-taxonomy sensu ‘‘basic’’ species description as a basic ships or the development of integrated databases which methodology is somewhat misleading since especially can be used to analyse distribution patterns or in mon- with small animals, such as free-living aquatic nema- itoring aquatic ecosystem health. In their recommen- todes, light microscopy (LM) observations have to be dations, they confirm that a-taxonomy sensu basic and interpreted and made visible via drawings or pictures, classical description remains a vital part of inventory and depending on the observer’s precision, are more or biodiversity but unlike sequence data stored in a web- less subjective. Anyway, species descriptions are not based database, a-taxonomy should result in publica- similar to obtaining DNA sequences since DNA se- tions and be seen as a direct means to be able to conduct quences are objective strings of nucleotides, indepen- further analyses such as phylogenetic reconstructions. dent from how or by whom they were determined. Yeates et al. (2011) referred integrative taxonomy to as Species descriptions, in contrast, depend on the per- iterative taxonomy because it lacked statistical evidence. son who produces them and on the methodology by Currently, integrative taxonomy is widely used for which morphological features were assessed. a combined morphology- and molecular data-based ap- proach when delimitating and describing taxa. The term THE SPECIES AS A TAXONOMIC UNIT ‘‘integrative’’ highlights what any science, including taxonomy, should be, i.e. not just descriptive but hy- The majority of definitions of a-taxonomy include as pothesis driven and based on a holistic approach to test last step the naming of species. Naming a species im- the hypothesis of for example, a new taxon. Taxonomy plies the knowledge on how to determine species should combine different types of features, at different boundaries. Species descriptions rarely indicate ex- levels of biological organization (from morphological plicitly how species boundaries were determined (i.e., features to genes) as well as search for new advanced under