Widespread heteroplasmy in schistosomes makes an mtVNTR marker "nearsighted"

Mitochondrial markers are often hailed as the preferred DNA elements for an alyses of population subdivision. To this end we have employed a mitochondr ial repeat element to examine the population structure in Schistosoma manso ni (human blood flukes). Schistosome isolates were collected from each of 2 1 different patients representing seven different areas of a Brazilian vill age. These parasite isolates demonstrate substantial genetic polymorphism, with an average of 10 genotypes infecting each patient, which is more readi ly detected because of high levels of heteroplasmy (i.e., 72.5% of the indi vidual worms exhibit multiple versions of this repeat region with different numbers of repeats). Due to the high number of common haplotypes in the po pulation, this repeat element from S. mansoni has a large proportion (47%) of its genetic variation described by differences among mitochondrial genom es within individual worms. However, when only rare haplotypes are consider ed, population structure can be defected. It seems that heteroplasmy in the schistosome population of Melquiades is both the source of plentiful genet ic variation and a confounding factor in the analysis of that variation. Th us the schistosome population in Melquiades may actually be more strongly s ubdivided than we are able to detect using this mitochondrial marker.