mtDNA hypervariable region-1 variation in Central Africa

As a part of along term project on molecular variation in Central Africa (www.scienzemfn.uniroma1.it/labantro), we have sequenced the hypervariable region-1 of mitochondrial DNA in a Pygmy population from the Central African Republic (C.A.R), the Mbenzele Pygmies, and two Bantu-speaking 51 populations, the Bamileke and Ewondo from Cameroon. Concerning intrapopulational diversity, two results are worth noting. Firstly, the Mbenzele Pygmies have one of lowest within-population variability reported to date. In fact, smaller values of gene diversity have been reported only for the Hadza, Herero and the !Kung. A possible explanation is in the fact that mtDNA gene flow between Pygmies and neighbouring populations occurs mostly by marriages between a Pygmy female and a Bantu male, an event favored by the low bride price that the husband must pay. Thus, while the relatively small size of Pygmy make them prone to the loss of genetic variability, this is not counterbalanced by gene flow from external populations. Secondly, the examined groups differ substantially in their subsistence economy, since Pygmies are hunter-gatherers, while the two groups from Cameroon are descendants from farmers and pastoralists. As a matter of fact, this difference is reflected by their patterns of nucleotide pairwise differences. The most striking results provided by the analysis of interpopulational diversity is in the marked genetic differentiation between the Ewondo and Bamileke. This finding is in contrast to a previous microsatellite study. Pygmy-to-Bantu gene flow seems to play a role in this finding. In fact, there are three mtDNA lineages shared between Ewondo and Mbenzele. All these sequences are much more frequent in the Pygmy than 10) in the Bantu population and considering other Africans they are found only in the Biaka Pygmies from C.A.R. On the other hand, the Ewondo live in south Cameroon near the Cameroon Pygmies (who are closely related to the C.A.R. Pygmies) and they traditionally have no taboos against mixed marriages. By contrast, Bamileke and Mbenzele Pygmies shared no mtDNA sequence. This is to be expected since ethnic endogamy is rigid in the Bamileke and prevents mixed marriages with other Pygmy and Bantu groups.