Origins and dispersals of Pacific peoples: evidence from mtDNA phylogenies of the Pacific rat.

The human settlement of the Pacific in general, and the origin of the Polynesians in particular, have been topics of debate for over two centuries. Polynesian origins are most immediately traced to people who arrived in the Fiji, Tonga, and Samoa region approximately 3,000 B.P. and are clearly associated with the Lapita Cultural Complex. Although this scenario of the immediate origins of the Polynesians is generally accepted, the debate on the ultimate origin of the Polynesians and the Lapita cultural complex continues. Our previous research has shown that analyses of mtDNA variation in the Pacific rat (Rattus exulans), often transported as a food item in the colonizing canoes, are valuable for tracing prehistoric human migration within Polynesia. Here we present mtDNA phylogenies based on approximately 240 base pairs of the d-loop from both archaeological and modern samples collected from Island Southeast Asia and the Pacific. We identify three major haplogroups, two of which occur in the Pacific. Comparing our results with Lapita models of Oceanic settlement, we are able to reject two often cited but simplistic models, finding support instead for multifaceted models incorporating a more complex view of the Lapita intrusion. This study is unique and valuable in that R. exulans is the only organism associated with the Lapita dispersal for which there are sufficient ancient and extant populations available for genetic analysis. By tracking population changes through time, we can understand more fully the settlement process and population interactions in both Near and Remote Oceania.

Unusual variations in nuclear DNA contents in the marine copepod Pseudocalanus.

Variations in DNA/nucleus within adult females are similar, when normalized for mean differences, in the copepods Pseudocalanus sp. and Eurytemora herdmani. However, Pseudocalanus shows great variation among individuals, with no evidence of significant groupings (species?), except perhaps for a few individuals with abnormally small DNA values. Body lengths of adult female Pseudocalanus are approximately proportional to the cube root of DNA/nucleus. It is inferred that nuclear size, not nuclear number, determines body size, and this is supported by generally similar nuclear counts in newly hatched nauplii and among first copepodid stages. Although body size and development rate of Pseudocalanus had earlier been shown to be strongly heritable, an offspring-parent regression reflected no heritability of DNA/nucleus (and some abnormally small offspring values) under the probably suboptimal conditions of rearing. Some variability in DNA content of adult somatic nuclei may be related to chromatin diminution during embryogenesis. An unusual loss of nonchromosomal, Feulgen-positive material is documented for first cleavage in Pseudocalanus, but not E. herdmani.