System Analysis and Nematode Phylogeny A. R. MAGGENTI 1 The purpose here is to suggest a method The available fossils represent only a small which will permit understanding of the fraction of the former plant and animal life phylogenetic relationships of contemporary on earth. That enormous numbers of animals representatives of the phylum Nematoda and plants, important to the evolution of without fossils. It is not my intent to again contemporary forms, must have existed and (14) offer a phylogeny for the Nematoda. declined to extinction without leaving a trace To say that no real benefit or knowledge of is illustrated by an observation in recent phylogeny or evolution is possible without historical times. Of the millions of buffalo fossils is succumbing to apathy. One cannot (American Bison), some estimates in excess deny or ignore that all systems, morphologi- of 100 × l0 s, strewn over the Great Plains cal, biological and chemical manifested in scarcely three generations ago, today there modern forms developed by evolutionary is hardly a trace. The skeletons have now sequence. It is true that with a complete largely disappeared and the bones are dissolv- fossil record the rates of evolution and de- ing and crumbling into dust under the attack velopmental pressures could be accurately of weather. Without conservation of the re- evaluated. However, in the absence of a maining limited numbers, practically the only fossile record evolutionary relations and other evidence of their occurrence would be developmental tendencies can be assessed "buffalo wallows." Without supplementary by the use of direct or corollary system knowledge of the buffalo, however, these analysis. Taxonomists must not overlook would not be identifiable. systems and their analysis. The advent of sophisticated instrumenta- Obviously, confidence would be much tion has permitted new research avenues more complete in the presence of a complete heretofore impossible or impractical. Com- fossil record. The fossil record provides (in puters, electron microscopes, and the myriad addition to verification of existence) knowl- of instruments available to the biochemist edge of time of existence, rates of develop- and physiologist have facilitated significant ment, and to some extent distribution and contributions to our store of knowledge. The abundance. The latter have proven to be impact of this rapid development of method- more accurate for marine life than terrestrial ology, technology and instrumentation has fauna and flora. Though often assumed, led into an era of apparently divergent tax- frequency of occurrence of fossils is rarely onomic schools. Taxonomists are categorized correlated with former population density or as numerical phenetic, cladistic or phyloge- distribution but rather indicates areas and netic. It is indeed unfortunate that, perhaps time periods favoring preservation together through faulty communication, each school with optimum predisposal to fossilization. seems to lack appreciation for the others' attempt to attain the same goal from another Received for publication 5 September 1969. point of view. Among the various schools 1 Department of Nematology, University of California, Davis, California 95616. the phylogenetic approach has been termed 7 8 Journal of Nematology, Vol. 2, No. 1, January 1970 intuitive taxonomy because it relies upon the Schuurmans Stekhoven and De Coninck (20) experience and the judgment of the observer proposed a scheme based on amphidial to determine significance of characters. Some shapes; Steiner (21) utilized the excretory significance must be attached to the fact that system. The difficulty with a single gross the fundamental ideas of the traditional phy- morphological character analysis is the un- logenetic taxonomists have often been con- certainty whether the evolved scheme is firmed by the opposing schools. progressive or regressive. Filipjev (8), Chit- The literature suggests that all too much wood (3), Maggenti (14), Platonova (19) time is spent in argument about the theoreti- and Gerlach (9) proposed phylogenies utiliz- cal merits of the various methods of approach ing several systems for which the most in- rather than the compatibility and significance formation was available. The parasitologists of the results. Comparison of the findings of have supplemented these criteria by a cor- the various approaches and argument over relation of parasite characteristics with host areas of noncorrelation would seem to be biology and evolution. much more fruitful. As in all methodology, Goodey (10) states, "classification of any different techniques have different inherent group of organisms is a matter of conven- limitations. Therefore, it would behoove the ience" and that the "collection and catalogu- taxonomists to recognize the restricting prem- ing of nematodes have not yet progressed far ises of each particular school. It would enough for their interrelationships to be seri- then be advantageous to combine the efforts ously studied." It is essential for the growth of each system, thereby increasing the level and progress of this science that we do not of confidence in any phylogenetic conclu- allow ourselves to be deceived by this type sions. It is axiomatic in science that the of reasoning. The best classification accord- realness of any determination should be sup- ing to Mayr (16) is not that which guarantees ported by multiple evaluation using different rapid unambiguous identification but that techniques. which has the highest predictive value. Thus In attempting to form a classification of nematode taxonomists must decide to accept higher categories into phylogenetic units we the limitations enforced by the lack of a must accept certain limitations. We are al- fossil record and attempt to formalize a ways faced with insufficient knowledge of the phylogeny on the basis of tested evolutionary phylogenetically important characters of principles and methods for evolutionary many groups. In classification, phylogenies resolution or forego the phylogenetic concept must be presented in a linear sequence of of classification and replace it with a "practi- species, genera, families and so forth, while cal" classification permitting rapid identifica- the phylogenetic tree, more than a classifica- tion. tion, has the added dimension of time. There- I do not accept Goodey's philosophy; fore, no classification could be an exact therefore, the proposal here is to describe representation of the phylogeny, even if all a means whereby alternate phylogenetic the facts were known. schemes based upon thorough detailed sys- The phylogenies and the evolutionary re- tem and character group analysis can be lationships of nematodes that have been compared; the regions of superimposition proposed have usually utilized gross mor- would then suggest the most probable line of phology of a single character group. For descent. The approach is not original; it example, De Coninck (5) employed the dis- has been tested and utilized successfully in tribution of cephalic setae and papillae; other disciplines. The basic idea is to utilize SYMPOSIUM" SYSTEM ANALYSIS PHYLOGENY • Maggenti 9 diverse systems of all types, morphological, mon to all except in the systems of excretion. hormonal, chromosomal, immunological, bio- The reason for this will become obvious logical, physiological or biochemical. The when the system is discussed. In other than effectiveness of the system is predicated upon a model system many more features of each each system being analyzed independently system would have to be discussed. How- and objectively. The confidence in determi- ever, for simplicity in illustrating the feasi- nations by approaches used heretofore is bility of the approach, these were kept to a limited by the subjective decision-making minimum. These particular systems were requisite in character selection and estimation chosen because of their variability through- of profundity at each successive level. That out the Nematoda. taxonomy can and should require the use of Within Nematoda other systems have value supplemental systems and properties other at different levels of investigation. The stoma, than the gross morphology of simple char- for instance, is of little value in system analysis acters has been well established. Nadler (17) because it is likely to be greatly influenced by employed chromosomal characters in his environment. Analysis of this feature rapidly study of the taxonomy of ground squirrels; reduces to circumlocution; however, this does Kelly (12) used comparative endocrinology not negate its usefulness at lower category in his investigation of the evolution of in- levels of investigation. The same may be said vertebrates and vertebrates; and Barrington of the amphid, even though it appears to be (1) utilized comparative hormone studies in more conservative and less susceptible to his book on evolution. Within nematology, environmental influence. Until we know more immunology has been used in the systematic about amphidial structure and function this studies of both plant parasitic and free living organ does not lend itself to analysis. An nematodes by Bird (2), Lee (13), and EI- important aspect of system study is to recog- Sherif and Mai (7). nize those features which analyze in a linear Without an analysis such as employed by fashion. The position and form of cephalic the numerical taxonomists there is danger of setae and papillae is such a case. The pattern subjective bias. The model scheme being of progression is