The importance of systematics in parasitological research

The discipline of systematics plays a central role in all branches of biolo gy. In today's technology-orientated research world, it is important to rea lise the continuing value of systematics, the basic tenet of which is to co mbine diverse types of data to produce classifications that reflect the nat ural history of living organisms. Accurate classification systems are cruci al in the field of parasitology, not only because they provide the means to identify species and strains of parasites, but also because they provide a framework around which a parasite's biology can be studied. The constructi on of such a classification system is often hampered by the parasite's biol ogy, which may preclude the application of traditional techniques of concep ts (such as morphological differentiation or the biological species concept ) to delineate species. It is often the case that these difficulties can be overcome by the use of molecular systematic techniques. In this paper, it is proposed that a detailed understanding of the phylogeny of a group of or ganisms can be used as a basis to examine other aspects of their systematic s. This is illustrated using the protozoan parasite Giardia intestinalis. D ata gathered using the complementary techniques of allozyme electrophoresis and nucleotide sequencing have been used to infer the phylogenetic relatio nships of G. intestinalis isolated from various host species. The results, supported by biological data, suggest that G. intestinalis is a species-com plex. As we move towards the year 2000, molecular systematics will play an increasingly important role in elucidating host-parasite relationships. How ever, its use as a taxonomic tool will require a general acceptance by para sitologists and the adoption of formal procedures to allow the description of new species by these methods. The aim of this approach is not to dismiss traditional methods, but to use them in combination with contemporary meth ods in the true spirit of the discipline of systematics. (C) 1999 Australia n Society for Parasitology. Published by Elsevier Science Ltd. All rights r eserved.