EVIDENCE FOR CLONAL STRUCTURE OF NATURAL-POPULATIONS OF FREE-LIVING AMEBAS OF THE GENUS NAEGLERIA

Genetic diversity of natural populations of the two species Naegleria gruberi and N. australiensis collected at the same time in the same ar ea was studied using multilocus enzyme electrophoresis (MLEE analysis) . Reference strains and related species were also analysed for compari son. Five loci were found to be polymorphic and allowed identification of 19 different multilocus genotypes among 67 isolates - eight for N. gruberi and 11 for N. australiensis - none being common to the two sp ecies. Large departures from Hardy-Weinberg equilibrium were found at all the loci, with significant heterozygote deficiencies in most cases . The two species exhibited strong linkage disequilibrium and the pred ominance of a few multilocus genotypes within each species was observe d. These lines of evidence strongly suggest non-random association of alleles, leading to the conclusion that N. gruberi and N. australiensi s have predominantly clonal genetic structures in the wild. Population s consist of a few major clones with some closely related ones - a str ucture found for several parasitic protozoans and bacteria. This contr asts with the panmictic structure found for N. lovaniensis, another sp ecies of this genus, and suggests that closely related species within the genus have evolved to have different reproductive strategies.