Genetic diversity of natural populations of the two species Naegleria
gruberi and N. australiensis
collected at the same time in the same area was studied using
multilocus enzyme electrophoresis
(MLEE analysis). Reference strains and related species were also analysed
for comparison. 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 species. 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 predominance of a few multilocus genotypes within
each species was
observed. These lines of evidence strongly suggest non-random association
of alleles, leading to the
conclusion that N. gruberi and N. australiensis
have predominantly clonal genetic structures in the
wild. Populations consist of a few major clones with some closely related
ones – a structure found
for several parasitic protozoans and bacteria. This contrasts with
the panmictic structure found for
N. lovaniensis, another species of this genus, and suggests
that closely related species within the
genus have evolved to have different reproductive strategies.