TRYPANOSOMA-BRUCEI SL - EVOLUTION, LINKAGE AND THE CLONALITY DEBATE

The Index of Association (I,) has been proposed by Maynard Smith et al . (1993) as a general method for characterizing the population structu res of microorganisms as either: clonal, epidemic, cryptic species or panmictic. With reference to the current debate surrounding the mode o f reproduction in parasitic protozoa, this study explores (i) the suit ability and limitations of the I, for characterizing populations of Ty panosoma brucei s.l., and (ii) the idea that the significance of genet ic differences between populations may be better understood if the evo lution, spread and temporal stability of certain parasite genotypes ar e also considered. Four populations of T. brucei from Cote d'Ivoire, U ganda and Zambia are analysed using the I, and a complementary test fo r linkage disequilibrium, test f of Tibayrenc, Kjellberg & Ayala (1990 ). The two populations from Uganda are characterized as epidemic, whil e the others appear more or less clonal; the merits of the two methods are compared. The implications of the various population classificati ons are discussed with reference to genotype longevity in each region; the evolutionary and biomedical consequences of the genetic non-homog eneity of T. brucei are reviewed.