George Koki

The Genetic Structure of Pacific Islanders

Human genetic diversity in the Pacific has not been adequately sampled, particularly in Melanesia. As a result, population relationships there have been open to debate. A genome scan of autosomal markers (687 microsatellites and 203 insertions/deletions) on 952 individuals from 41 Pacific populations now provides the basis for understanding the remarkable nature of Melanesian variation, and for a more accurate comparison of these Pacific populations with previously studied groups from other regions. It also shows how textured human population variation can be in particular circumstances. Genetic diversity within individual Pacific populations is shown to be very low, while differentiation among Melanesian groups is high. Melanesian differentiation varies not only between islands, but also by island size and topographical complexity. The greatest distinctions are among the isolated groups in large island interiors, which are also the most internally homogeneous. The pattern loosely tracks language distinctions. Papuan-speaking groups are the most differentiated, and Austronesian or Oceanic-speaking groups, which tend to live along the coastlines, are more intermixed. A small “Austronesian” genetic signature (always <20%) was detected in less than half the Melanesian groups that speak Austronesian languages, and is entirely lacking in Papuan-speaking groups. Although the Polynesians are also distinctive, they tend to cluster with Micronesians, Taiwan Aborigines, and East Asians, and not Melanesians. These findings contribute to a resolution to the debates over Polynesian origins and their past interactions with Melanesians. With regard to genetics, the earlier studies had heavily relied on the evidence from single locus mitochondrial DNA or Y chromosome variation. Neither of these provided an unequivocal signal of phylogenetic relations or population intermixture proportions in the Pacific. Our analysis indicates the ancestors of Polynesians moved through Melanesia relatively rapidly and only intermixed to a very modest degree with the indigenous populations there.

Colonisation of Haemophilus influenzae and Streptococcus pneumoniae in the Upper Respiratory Tract of Neonates in Papua New Guinea: Primary Acquisition, Duration of Carriage, and Relationship to Carriage in Mothers

In order to determine the age of acquisition and duration of carriage of the first strains of Haemophilus influenzae and Streptococcus pneumoniae in the upper respiratory tract of Papua New Guinea children, 25 babies were recruited at, or shortly after birth. Nasal secretions from mothers and children were cultured at 1- to 2-weekly intervals. H. influenzae and S. pneumoniae were acquired within the neonatal period by 60% of the infants, and all were colonised by both organisms within the first 3 months of life. Carriage periods for H. influenzae ranged from 6 to 221 days (mean, 74 days), and for S. pneumoniae from 5 to 290 days (mean, 96 days). Penicillin resistance was detected in 36% of the first acquired strains of pneumococci. Mothers, generally either did not carry H. influenzae or S. pneumoniae, or harboured types different to those first acquired by their infants. However, one-third of mothers subsequently became colonised with H. influenzae and S. pneumoniae types similar to those carried by their babies.

Melanesian mtDNA Complexity

Melanesian populations are known for their diversity, but it has been hard to grasp the pattern of the variation or its underlying dynamic. Using 1,223 mitochondrial DNA (mtDNA) sequences from hypervariable regions 1 and 2 (HVR1 and HVR2) from 32 populations, we found the among-group variation is structured by island, island size, and also by language affiliation. The more isolated inland Papuan-speaking groups on the largest islands have the greatest distinctions, while shore dwelling populations are considerably less diverse (at the same time, within-group haplotype diversity is less in the most isolated groups). Persistent differences between shore and inland groups in effective population sizes and marital migration rates probably cause these differences. We also add 16 whole sequences to the Melanesian mtDNA phylogenies. We identify the likely origins of a number of the haplogroups and ancient branches in specific islands, point to some ancient mtDNA connections between Near Oceania and Australia, and show additional Holocene connections between Island Southeast Asia/Taiwan and Island Melanesia with branches of haplogroup E. Coalescence estimates based on synonymous transitions in the coding region suggest an initial settlement and expansion in the region at ∼30–50,000 years before present (YBP), and a second important expansion from Island Southeast Asia/Taiwan during the interval ∼3,500–8,000 YBP. However, there are some important variance components in molecular dating that have been overlooked, and the specific nature of ancestral (maternal) Austronesian influence in this region remains unresolved.

Excavating Neandertal and Denisovan DNA from the genomes of Melanesian individuals

Denisovan DNA retained in Melanesians Modern humans carry remnants of DNA from interbreeding events with archaic lineages, such as Neandertals. However, people from Oceania also retain genes from a second ancient lineage, the Denisovans. Vernot et al. surveyed archaic genomic sequences in a worldwide sample of modern humans, including 35 individuals from the Melanesian Islands. All non-African genomes surveyed contained Neandertal DNA, but a significant Denisovan component was found only in the Melanesians. Reconstruction of this genetic history suggests that Neandertals bred with modern humans multiple times, but Denosivans only once, in ancestors of modern-day Melanesians. Science, this issue p. 235 Neandertal and Denisovan DNA live on in modern day Melanesians. Although Neandertal sequences that persist in the genomes of modern humans have been identified in Eurasians, comparable studies in people whose ancestors hybridized with both Neandertals and Denisovans are lacking. We developed an approach to identify DNA inherited from multiple archaic hominin ancestors and applied it to whole-genome sequences from 1523 geographically diverse individuals, including 35 previously unknown Island Melanesian genomes. In aggregate, we recovered 1.34 gigabases and 303 megabases of the Neandertal and Denisovan genome, respectively. We use these maps of archaic sequences to show that Neandertal admixture occurred multiple times in different non-African populations, characterize genomic regions that are significantly depleted of archaic sequences, and identify signatures of adaptive introgression.

A genomic history of Aboriginal Australia

The population history of Aboriginal Australians remains largely uncharacterized. Here we generate high-coverage genomes for 83 Aboriginal Australians (speakers of Pama–Nyungan languages) and 25 Papuans from the New Guinea Highlands. We find that Papuan and Aboriginal Australian ancestors diversified 25–40 thousand years ago (kya), suggesting pre-Holocene population structure in the ancient continent of Sahul (Australia, New Guinea and Tasmania). However, all of the studied Aboriginal Australians descend from a single founding population that differentiated ~10–32 kya. We infer a population expansion in northeast Australia during the Holocene epoch (past 10,000 years) associated with limited gene flow from this region to the rest of Australia, consistent with the spread of the Pama–Nyungan languages. We estimate that Aboriginal Australians and Papuans diverged from Eurasians 51–72 kya, following a single out-of-Africa dispersal, and subsequently admixed with archaic populations. Finally, we report evidence of selection in Aboriginal Australians potentially associated with living in the desert.

Genomic insights into the peopling of the Southwest Pacific

The appearance of people associated with the Lapita culture in the South Pacific around 3,000 years ago marked the beginning of the last major human dispersal to unpopulated lands. However, the relationship of these pioneers to the long-established Papuan people of the New Guinea region is unclear. Here we present genome-wide ancient DNA data from three individuals from Vanuatu (about 3,100–2,700 years before present) and one from Tonga (about 2,700–2,300 years before present), and analyse them with data from 778 present-day East Asians and Oceanians. Today, indigenous people of the South Pacific harbour a mixture of ancestry from Papuans and a population of East Asian origin that no longer exists in unmixed form, but is a match to the ancient individuals. Most analyses have interpreted the minimum of twenty-five per cent Papuan ancestry in the region today as evidence that the first humans to reach Remote Oceania, including Polynesia, were derived from population mixtures near New Guinea, before their further expansion into Remote Oceania. However, our finding that the ancient individuals had little to no Papuan ancestry implies that later human population movements spread Papuan ancestry through the South Pacific after the first peopling of the islands.

Genetic and Linguistic Coevolution in Northern Island Melanesia

Recent studies have detailed a remarkable degree of genetic and linguistic diversity in Northern Island Melanesia. Here we utilize that diversity to examine two models of genetic and linguistic coevolution. The first model predicts that genetic and linguistic correspondences formed following population splits and isolation at the time of early range expansions into the region. The second is analogous to the genetic model of isolation by distance, and it predicts that genetic and linguistic correspondences formed through continuing genetic and linguistic exchange between neighboring populations. We tested the predictions of the two models by comparing observed and simulated patterns of genetic variation, genetic and linguistic trees, and matrices of genetic, linguistic, and geographic distances. The data consist of 751 autosomal microsatellites and 108 structural linguistic features collected from 33 Northern Island Melanesian populations. The results of the tests indicate that linguistic and genetic exchange have erased any evidence of a splitting and isolation process that might have occurred early in the settlement history of the region. The correlation patterns are also inconsistent with the predictions of the isolation by distance coevolutionary process in the larger Northern Island Melanesian region, but there is strong evidence for the process in the rugged interior of the largest island in the region (New Britain). There we found some of the strongest recorded correlations between genetic, linguistic, and geographic distances. We also found that, throughout the region, linguistic features have generally been less likely to diffuse across population boundaries than genes. The results from our study, based on exceptionally fine-grained data, show that local genetic and linguistic exchange are likely to obscure evidence of the early history of a region, and that language barriers do not particularly hinder genetic exchange. In contrast, global patterns may emphasize more ancient demographic events, including population splits associated with the early colonization of major world regions.

New JC virus (JCV) genotypes from Papua New Guinea and Micronesia (type 8 and type 2E) and evolutionary analysis of 32 complete JCV genomes

Summary. The JC virus (JCV) is a ubiquitous human polyomavirus that frequently resides in the kidneys of healthy individuals and is excreted in the urine of a large percentage of the population. Geographic-specific JCV variants, isolated from urine and from brain of progressive multifocal leukoencephalopathy (PML) patients, have been grouped into seven distinct genotypes based on whole genome analysis and by individual polymorphic nucleotides (typing sites) in the VP1 coding region. Mutations in the archetypal regulatory region, sometimes consisting of deletions and/or duplications, are also useful taxonomic characters for further characterizing and subdividing genotypes. Investigation of JCV variation in Papua New Guinea (PNG) revealed three distinct variants called PNG-1, PNG-2, and PNG-3. These variants exhibited consistent coding region and regulatory region mutations. Evolutionary analysis of 32 complete JCV genomes including six new viral genomes from the western Pacific suggests that the new PNG JCV variants are closely associated with the broad group of Type 2 strains of JCV found throughout Asia, forming a monophyletic group with the Northeast Asian strains (Type 2A). Within the Type 2 clade, however, the PNG JCV variants cluster as two distinct groups and are therefore described here as new JCV genotypes designated Type 2E and Type 8.

Maternal History of Oceania from Complete mtDNA Genomes: Contrasting Ancient Diversity with Recent Homogenization Due to the Austronesian Expansion

Archaeology, linguistics, and existing genetic studies indicate that Oceania was settled by two major waves of migration. The first migration took place approximately 40 thousand years ago and these migrants, Papuans, colonized much of Near Oceania. Approximately 3.5 thousand years ago, a second expansion of Austronesian-speakers arrived in Near Oceania and the descendants of these people spread to the far corners of the Pacific, colonizing Remote Oceania. To assess the female contribution of these two human expansions to modern populations and to investigate the potential impact of other migrations, we obtained 1,331 whole mitochondrial genome sequences from 34 populations spanning both Near and Remote Oceania. Our results quantify the magnitude of the Austronesian expansion and demonstrate the homogenizing effect of this expansion on almost all studied populations. With regards to Papuan influence, autochthonous haplogroups support the hypothesis of a long history in Near Oceania, with some lineages suggesting a time depth of 60 thousand years, and offer insight into historical interpopulation dynamics. Santa Cruz, a population located in Remote Oceania, is an anomaly with extreme frequencies of autochthonous haplogroups of Near Oceanian origin; simulations to investigate whether this might reflect a pre-Austronesian versus Austronesian settlement of the island failed to provide unequivocal support for either scenario.

Human polyomavirus JC variants in Papua New Guinea and Guam reflect ancient population settlement and viral evolution

The peopling of the Pacific was a complex sequence of events that is best reconstructed by reconciling insights from various disciplines. Here we analyze the human polyomavirus JC (JCV) in Highlanders of Papua New Guinea (PNG), in Austronesian-speaking Tolai people on the island of New Britain, and in nearby non-Austronesian-speaking Baining people. We also characterize JCV from the Chamorro of Guam, a Micronesian population. All JCV strains from PNG and Guam fall within the broad Asian group previously defined in the VP1 gene as Type 2 or Type 7, but the PNG strains were distinct from both genotypes. Among the Chamorro JCV samples, 8 strains (Guam-1) were like the Type 7 strains found in Southeast Asia, while nine strains (Guam-2) were distinct from both the mainland strains and most PNG strains. We identified three JCV variants within Papua New Guinea (PNG-1, PNG-2 and PNG-3), but none of the Southeast Asian (Type 7) strains. PNG-1 strains were present in all three populations (Highlanders and the Baining and Tolai of New Britain), but PNG-2 strains were restricted to the Highlanders. Their relative lack of DNA sequence variation suggests that they arose comparatively recently. The single PNG-3 strain, identified in an Austronesian-speaking Tolai individual, was closely related to the Chamorro variants (Guam-2), consistent with a common Austronesian ancestor. In PNG-2 variants a complex regulatory region mutation inserts a duplication into a nearby deletion, a change reminiscent of those seen in the brains of progressive multifocal leukoencephalopathy patients. This is the first instance of a complex JCV rearrangement circulating in a human population.