A Numerical Taxonomic Study of a Group of Selected Strongylates (Nematoda)

Abstract

Moss, W. W. (Div. Entomol., U. Calif., Berkeley 94720) and Webster, W. A. 1969. A numerical taxonomic study of a group of selected strongylates (Nematoda). Syst. Zool., 18: 423-443.-A preliminary study of a group of parasitic nematodes tested the usefulness of numerical taxonomy in the recognition of overall similarities and groupings. Two approaches were followed, a 7-OTU study involving average character values, and a 27-OTU study using character values taken from individual replicates. Qualitative and quantitative characters were used, with measurements expressed as percentages of total body length. Distance and correlation coefficients were structured by graphic and cluster analysis, and the various groupings obtained in the two studies were compared. [Numerical phenetics. Experimental taxonomy. Nematoda.] Chitwood (1957) has attributed much of the taxonomic confusion prevalent in modem nematology to four major causes, these being the state of preservation of the material, its interpretation, the presentation of results and, perhaps most important, a general lack of knowledge regarding the limits of intraspecific variability. Goodey (1959) attempted to alleviate some of these difficulties when he proposed numerous criteria to be followed when reporting on new taxa, although even with these precautions the recognition of species limits remains a major problem. The biological species concept has, at present, little applicability to the field of parasitic nematology, an area in which species must be recognized almost entirely on the basis of anatomical evidence. Accordingly, the morphological species concept must still be considered a practical necessity in the recognition of nematode classifications. Classical nematological taxonomies are based on the interpretation of structure, but are frequently influenced strongly by the importance placed by the taxonomist on any given structure, character complex or character. The different systems of classification derived from such interpretations are often radically opposed to each other and frequently, indeed, represent classifications of particular structures, rather than of complete organisms (i.e., they are special, rather than natural classifications in the sense of Davis and Heywood, 1963). In practical terms, when one attempts to place a given nematode in the taxonomic hierarchy, he soon learns that there are about as many systems of classification as there are monographs on the subject. It is obvious that an attempt should be made to stabilize the classification of the parasitic Nematoda, especially since the problem of instability is being constantly compounded by the appearance of additional revisionary works. Without doubt, highly valuable information is contained in many existing nematode taxonomies. However, some of these taxonomies derive largely from interpretations of supposed phylogenetic relationships among nematodes, or among parts of nematodes. This type of taxonomic work, basically authoritarian in concept, can be more detrimental than beneficial to, the progress of an expanding science. In view of the fact that the paleontological record is virtually blank for the parasitic Nematoda, the various evolutionary or phyletic relationships that have been suggested to date for this group are entirely speculative in nature and must be recognized as such. Although some progress has been made on operational phyletic studies in other taxa