Demographic reductions and genetic bottlenecks in humans: minisatellite allele distributions in Oceania

Polynesians have lower heterozygosities at minisatellite VNTR (Variable Number of Tandem Repeat) loci than have Melanesians; this has been taken as evidence of population-size bottlenecks during the colonisation of Polynesia. We have analysed the allelic distribution of several minisatellite loci in the population of Rapa, a Polynesian island that is known to have undergone a demographic reduction of approximately 95% since first contact with European explores 200 years ago, leaving a surviving population of 120. We found that the minisatellite diversity of this population does not differ significantly from that of other Polynesian populations, and appears consistent with the neutral expectation of diversity assuming the infinite alleles model. This suggests that the demographic crisis that Rapa underwent did not perturb the allele distribution to the extent that the tests used here could detect. Thus we cannot say that a demographic change of this magnitude constitutes a genetic bottleneck detectable at these loci. The reduced diversity seen in Polynesia must therefore be explained either by more severe bottlenecks as might be expected during colonisation, or else by other causes.