SOME MOLECULAR INSIGHTS INTO SCHISTOSOME EVOLUTION

Robust phylogenies based on molecular data for species within the genu s Schistosoma have been generated in recent years. The considerable pr ogress made in understanding the relationships between many of the 19 recognised species of Schistosoma is reviewed with particular attentio n being given to the detection and analysis of parasite variation as s hown by studies on ribosomal RNA genes, mitochondrial DNA and RAPDs. F or the most part, molecular phylogenies agree with observations based on morphological or life-history characteristics. It is clear that the parasites of man do not form a monophyletic group and that close rela tionships exist between parasites within species groups, especially in the S. haematobium group of species. The S. japonicum group appears t o be the most divergent of the species groups and yet little DNA seque nce variation has been observed between various isolates of S. japonic um. Some of the less studied schistosomes have yet to be examined at t he molecular level and may prove to be interesting links between the s pecies groups as has recently been shown with S. hippopotami. The powe r of molecular approaches for the analysis of schistosomes at the popu lation and individual level is now apparent, especially for S. mansoni . Important questions remain concerning the maintenance of parasite di versity and how schistosomes respond to selection pressures imposed ei ther during natural progression through the life-cycle or through drug treatment or vaccination. Gene discovery and gene mapping projects ar e leading to a better understanding of the schistosome genome and can be expected to contribute significantly to future comparative evolutio nary studies. Copyright (C) 1997 Australian Society for Parasitology. Published by Elsevier Science Ltd.