Melanesian and Asian origins of Polynesians: mtDNA and Y chromosome gradients across the Pacific

The human settlement of the Pacific Islands represents one of the most recent major migration events of mankind. Polynesians originated in Asia according to linguistic evidence or in Melanesia according to archaeological evidence. To shed light on the genetic origins of Polynesians, we investigated over 400 Polynesians from 8 island groups, in comparison with over 900 individuals from potential parental populations of Melanesia, Southeast and East Asia, and Australia, by means of Y chromosome (NRY) and mitochondrial DNA (mtDNA) markers. Overall, we classified 94.1% of Polynesian Y chromosomes and 99.8% of Polynesian mtDNAs as of either Melanesian (NRY-DNA: 65.8%, mtDNA: 6%) or Asian (NRY-DNA: 28.3%, mtDNA: 93.8%) origin, suggesting a dual genetic origin of Polynesians in agreement with the "Slow Boat" hypothesis. Our data suggest a pronounced admixture bias in Polynesians toward more Melanesian men than women, perhaps as a result of matrilocal residence in the ancestral Polynesian society. Although dating methods are consistent with somewhat similar entries of NRY/mtDNA haplogroups into Polynesia, haplotype sharing suggests an earlier appearance of Melanesian haplogroups than those from Asia. Surprisingly, we identified gradients in the frequency distribution of some NRY/mtDNA haplogroups across Polynesia and a gradual west-to-east decrease of overall NRY/mtDNA diversity, not only providing evidence for a west-to-east direction of Polynesian settlements but also suggesting that Pacific voyaging was regular rather than haphazard. We also demonstrate that Fiji played a pivotal role in the history of Polynesia: humans probably first migrated to Fiji, and subsequent settlement of Polynesia probably came from Fiji.     

The origins of the Polynesians: an interpretation from mitochondrial lineage analysis.

Using mitochondrial lineage analysis of 1,178 individuals from Polynesia, the western Pacific, and Taiwan, we show that the major prehistoric settlement of Polynesia was from the west and involved two or possibly three genetically distinct populations. The predominant lineage group, accounting for 94% of Polynesian mtDNA, shares a 9-bp COII/tRNA(Lys) intergenic deletion and characteristic control region transition variants, compared to the Cambridge reference sequence. In Polynesia, the diversity of this group is extremely restricted, while related lineages in Indonesia, the Philippines, and Taiwan are increasingly diverse. This suggests a relatively recent major eastward expansion into Polynesia, perhaps originating from Taiwan, in agreement with archeological and linguistic evidence, but which experienced one or more severe population bottlenecks. The second mitochondrial lineage group, accounting for 3.5% of Polynesian mtDNA haplotypes, does not have the 9-bp deletion and its characterized by an A-C transversional variant at nt position 16265. Specific oligonucleotides for this variant were used to select individuals from the population sample who, with other sequences, show that the Polynesian lineages were part of a diverse group in Vanuatu and Papua New Guinea. The very low overall diversity of both lineage groups in Polynesia suggests there was severe population restriction during the colonization of remote Oceania. A third group, represented by only four individuals (0.6%) in Polynesia but also present in the Philippines, shares variants at nt positions 16172 and 16304. Two Polynesians had unrelated haplotypes matching published sequences from native South Americans, which may be the first genetic evidence of prehistoric human contact between Polynesia and South America.     

Mitochondrial DNA data indicate an introduction through Mainland Southeast Asia for Australian dingoes and Polynesian domestic dogs

In the late stages of the global dispersal of dogs, dingoes appear in the Australian archaeological record 3500 years BP, and dogs were one of three domesticates brought with the colonization of Polynesia, but the introduction routes to this region remain unknown. This also relates to questions about human history, such as to what extent the Polynesian culture was introduced with the Austronesian expansion from Taiwan or adopted en route, and whether pre-Neolithic Australia was culturally influenced by the surrounding Neolithic world. We investigate these questions by mapping the distribution of the mtDNA founder haplotypes for dingoes (A29) and ancient Polynesian dogs (Arc1 and Arc2) in samples across Southern East Asia (n = 424) and Island Southeast Asia (n = 219). All three haplotypes were found in South China, Mainland Southeast Asia and Indonesia but absent in Taiwan and the Philippines, and the mtDNA diversity among dingoes indicates an introduction to Australia 4600-18 300 years BP. These results suggest that Australian dingoes and Polynesian dogs originate from dogs introduced to Indonesia via Mainland Southeast Asia before the Neolithic, and not from Taiwan together with the Austronesian expansion. This underscores the complex origins of Polynesian culture and the isolation from Neolithic influence of the pre-Neolithic Australian culture.     

Bridging near and remote Oceania: mtDNA and NRY variation in the Solomon Islands

Although genetic studies have contributed greatly to our understanding of the colonization of Near and Remote Oceania, important gaps still exist. One such gap is the Solomon Islands, which extend between Bougainville and Vanuatu, thereby bridging Near and Remote Oceania, and include both Austronesian-speaking and Papuan-speaking groups. Here, we describe patterns of mitochondrial DNA (mtDNA) and nonrecombining Y chromosome (NRY) variation in over 700 individuals from 18 populations in the Solomons, including 11 Austronesian-speaking groups, 3 Papuan-speaking groups, and 4 Polynesian Outliers (descended via back migration from Polynesia). We find evidence for ancient (pre-Lapita) colonization of the Solomons in old NRY paragroups as well as from M2-M353, which probably arose in the Solomons ～9,200 years ago and is the most frequent NRY haplogroup there. There are no consistent genetic differences between Austronesian-speaking and Papuan-speaking groups, suggesting extensive genetic contact between them. Santa Cruz, which is located in Remote Oceania, shows unusually low frequencies of mtDNA and NRY haplogroups of recent Asian ancestry. This is in apparent contradiction with expectations based on archaeological and linguistic evidence for an early (～3,200 years ago), direct colonization of Santa Cruz by Lapita people from the Bismarck Archipelago, via a migration that "leapfrogged" over the rest of the Solomons. Polynesian Outliers show dramatic island-specific founder events involving various NRY haplogroups. We also find that NRY, but not mtDNA, genetic distance is correlated with the geographic distance between Solomons groups and that historically attested spheres of cultural interaction are associated with the recent genetic structure of Solomons groups, as revealed by mtDNA HV1 sequence and Y-STR haplotype diversity. Our results fill an important lacuna in human genetic studies of Oceania and aid in understanding the colonization and genetic history of this region.     

The impact of the Austronesian expansion: evidence from mtDNA and Y chromosome diversity in the Admiralty Islands of Melanesia

The genetic ancestry of Polynesians can be traced to both Asia and Melanesia, which presumably reflects admixture occurring between incoming Austronesians and resident non-Austronesians in Melanesia before the subsequent occupation of the greater Pacific; however, the genetic impact of the Austronesian expansion to Melanesia remains largely unknown. We therefore studied the diversity of nonrecombining Y chromosomal (NRY) and mitochondrial (mt) DNA in the Admiralty Islands, located north of mainland Papua New Guinea, and updated our previous data from Asia, Melanesia, and Polynesia with new NRY markers. The Admiralties are occupied today solely by Austronesian-speaking groups, but their human settlement history goes back 20,000 years prior to the arrival of Austronesians about 3,400 years ago. On the Admiralties, we found substantial mtDNA and NRY variation of both Austronesian and non-Austronesian origins, with higher frequencies of Asian mtDNA and Melanesian NRY haplogroups, similar to previous findings in Polynesia and perhaps as a consequence of Austronesian matrilocality. Thus, the Austronesian language replacement on the Admiralties (and elsewhere in Island Melanesia and coastal New Guinea) was accompanied by an incomplete genetic replacement that is more associated with mtDNA than with NRY diversity. These results provide further support for the "Slow Boat" model of Polynesian origins, according to which Polynesian ancestors originated from East Asia but genetically mixed with Melanesians before colonizing the Pacific. We also observed that non-Austronesian groups of coastal New Guinea and Island Melanesia had significantly higher frequencies of Asian mtDNA haplogroups than of Asian NRY haplogroups, suggesting sex-biased admixture perhaps as a consequence of non-Austronesian patrilocality. We additionally found that the predominant NRY haplogroup of Asian origin in the Admiralties (O-M110) likely originated in Taiwan, thus providing the first direct Y chromosome evidence for a Taiwanese origin of the Austronesian expansion. Furthermore, we identified a NRY haplogroup (K-P79, also found on the Admiralties) in Polynesians that most likely arose in the Bismarck Archipelago, providing the first direct link between northern Island Melanesia and Polynesia. These results significantly advance our understanding of the impact of the Austronesian expansion and human history in the Pacific region.     

mtDNA lineage analyses: origins and migrations of Micronesians and Polynesians

The islands of Micronesia and Polynesia collectively comprise the last major region of the globe to be settled by humans. Both of these groups of islands were colonized within the last 4,000 years by Austronesian-speaking agriculturists. Based on biogeographic and linguistic patterns, central-eastern Micronesia and Polynesia are included by many in a single category called Remote Oceania. Similarities of biologic, linguistic, and cultural traits within Remote Oceania highlight a question central to Oceanic studies: Are similarities among islands due to a common origin of isolated communities, to ongoing interactions among islands, or both? Analyses of mitochondrial DNA (mtDNA) sequences reveal that most remote Oceanic populations are polyphyletic. These polyphyletic populations violate the assumptions of many genetic distance and population demography models and so are problematic to interpret. The majority of mtDNA sequences from Micronesian and Polynesian populations are derived from Asia, whereas others are inferred to have originated in New Guinea. These data support an Island Southeast Asian origin and a colonization route along the north coast of New Guinea. The Marianas and Yap proper (main island) appear to have been independently settled directly from Island Southeast Asia, and both have received migrants from Central-Eastern Micronesia since then. Palau clearly demonstrates a complex prehistory including a significant influx of lineages from New Guinea. Thus genetic similarities among Micronesian and Polynesian populations result, in some cases, from a common origin, and in others, from extensive gene flow.     

Mitochondrial DNA evidence for the spread of Pacific rats through Oceania

In the 10 years since we published our first full analysis of mitochondrial DNA (mtDNA) variation in Rattus exulans as a means for tracking human migration in Polynesia, we have extended the commensal approach through time and space with the use of ancient DNA (aDNA) and by analysing samples from across the Pacific. Not only can mtDNA phylogenies provide information regarding population origins and paths of migration, they have also provided information regarding degrees of contact and interaction between islands. An important extension of the R. exulans project is the creation and on-going development of a genetic database for the identification of Rattus species based on mtDNA sequences. The phylogenetic analysis of sequences from 18 species and 1 subspecies of Rattus thus far have raised some questions regarding species identification and species distributions in the Pacific.     

European Y-chromosomal lineages in Polynesians: a contrast to the population structure revealed by mtDNA.

We have used Y-chromosomal polymorphisms to trace paternal lineages in Polynesians by use of samples previously typed for mtDNA variants. A genealogical approach utilizing hierarchical analysis of eight rare-event biallelic polymorphisms, seven microsatellite loci, and internal structural analysis of the hypervariable minisatellite, MSY1, has been used to define three major paternal-lineage clusters in Polynesians. Two of these clusters, both defined by novel MSY1 modular structures and representing 55% of the Polynesians studied, are also found in coastal Papua New Guinea. Reduced Polynesian diversity, relative to that in Melanesians, is illustrated by the presence of several examples of identical MSY1 codes and microsatellite haplotypes within these lineage clusters in Polynesians. The complete lack of Y chromosomes having the M4 base substitution in Polynesians, despite their prevalence (64%) in Melanesians, may also be a result of the multiple bottleneck events during the colonization of this region of the world. The origin of the M4 mutation has been dated by use of two independent methods based on microsatellite-haplotype and minisatellite-code diversity. Because of the wide confidence limits on the mutation rates of these loci, the M4 mutation cannot be conclusively dated relative to the colonization of Polynesia, 3,000 years ago. The other major lineage cluster found in Polynesians, defined by a base substitution at the 92R7 locus, represents 27% of the Polynesians studied and, most probably, originates in Europe. This is the first Y-chromosomal evidence of major European admixture with indigenous Polynesian populations and contrasts sharply with the picture given by mtDNA evidence.     

The Polynesian gene pool: an early contribution by Amerindians to Easter Island

It is now generally accepted that Polynesia was first settled by peoples from southeast Asia. An alternative that eastern parts of Polynesia were first inhabited by Amerindians has found little support. There are, however, many indications of a 'prehistoric' (i.e. before Polynesia was discovered by Europeans) contact between Polynesia and the Americas, but genetic evidence of a prehistoric Amerindian contribution to the Polynesian gene pool has been lacking. We recently carried out genomic HLA (human leucocyte antigen) typing as well as typing for mitochondrial DNA (mtDNA) and Y chromosome markers of blood samples collected in 1971 and 2008 from reputedly non-admixed Easter Islanders. All individuals carried HLA alleles and mtDNA types previously found in Polynesia, and most of the males carried Y chromosome markers of Polynesian origin (a few had European Y chromosome markers), further supporting an initial Polynesian population on Easter Island. The HLA investigations revealed, however, that some individuals also carried HLA alleles which have previously almost only been found in Amerindians. We could trace the introduction of these Amerindian alleles to before the Peruvian slave trades, i.e. before the 1860s, and provide suggestive evidence that they were introduced already in prehistoric time. Our results demonstrate an early Amerindian contribution to the Polynesian gene pool on Easter Island, and illustrate the usefulness of typing for immunogenetic markers such as HLA to complement mtDNA and Y chromosome analyses in anthropological investigations.     

Increased Y-chromosome resolution of haplogroup O suggests genetic ties between the Ami aborigines of Taiwan and the Polynesian Islands of Samoa and Tonga

The Austronesian expansion has left its fingerprint throughout two thirds of the circumference of the globe reaching the island of Madagascar in East Africa to the west and Easter Island, off the coast of Chile, to the east. To date, several theories exist to explain the current genetic distribution of Austronesian populations, with the “slow boat” model being the most widely accepted, though other conjectures (i.e., the “express train” and “entangled bank” hypotheses) have also been widely discussed. In the current study, 158 Y chromosomes from the Polynesian archipelagos of Samoa and Tonga were typed using high resolution binary markers and compared to populations across Mainland East Asia, Taiwan, Island Southeast Asia, Melanesia and Polynesia in order to establish their patrilineal genetic relationships. Y-STR haplotypes on the C2 (M38), C2a (M208), O1a (M119), O3 (M122) and O3a2 (P201) backgrounds were utilized in an attempt to identify the differing sources of the current Y-chromosomal haplogroups present throughout Polynesia (of Melanesian and/or Asian descent). We find that, while haplogroups C2a, S and K3-P79 suggest a Melanesian component in 23%-42% of the Samoan and Tongan Y chromosomes, the majority of the paternal Polynesian gene pool exhibits ties to East Asia. In particular, the prominence of sub-haplogroup O3a2c* (P164), which has previously been observed at only minimal levels in Mainland East Asians (2.0-4.5%), in both Polynesians (ranging from 19% in Manua to 54% in Tonga) and Ami aborigines from Taiwan (37%) provides, for the first time, evidence for a genetic connection between the Polynesian populations and the Ami.     

Melanesian origin of Polynesian Y chromosomes

BACKGROUND: Two competing hypotheses for the origins of Polynesians are the 'express-train' model, which supposes a recent and rapid expansion of Polynesian ancestors from Asia/Taiwan via coastal and island Melanesia, and the 'entangled-bank' model, which supposes a long history of cultural and genetic interactions among Southeast Asians, Melanesians and Polynesians. Most genetic data, especially analyses of mitochondrial DNA (mtDNA) variation, support the express-train model, as does linguistic and archaeological evidence. Here, we used Y-chromosome polymorphisms to investigate the origins of Polynesians. RESULTS: We analysed eight single nucleotide polymorphisms (SNPs) and seven short tandem repeat (STR) loci on the Y chromosome in 28 Cook Islanders from Polynesia and 583 males from 17 Melanesian, Asian and Australian populations. We found that all Polynesians belong to just three Y-chromosome haplotypes, as defined by unique event polymorphisms. The major Y haplotype in Polynesians (82% frequency) was restricted to Melanesia and eastern Indonesia and most probably arose in Melanesia. Coalescence analysis of associated Y-STR haplotypes showed evidence of a population expansion in Polynesians, beginning about 2,200 years ago. The other two Polynesian Y haplotypes were widespread in Asia but were also found in Melanesia. CONCLUSIONS: All Polynesian Y chromosomes can be traced back to Melanesia, although some of these Y-chromosome types originated in Asia. Together with other genetic and cultural evidence, we propose a new model of Polynesian origins that we call the 'slow-boat' model: Polynesian ancestors did originate from Asia/Taiwan but did not move rapidly through Melanesia; rather, they interacted with and mixed extensively with Melanesians, leaving behind their genes and incorporating many Melanesian genes before colonising the Pacific.     

Molecular Identification of Bacteria by Total Sequence Screening: Determining the Cause of Death in Ancient Human Subjects

Research of ancient pathogens in ancient human skeletons has been mainly carried out on the basis of one essential historical or archaeological observation, permitting specific pathogens to be targeted. Detection of ancient human pathogens without such evidence is more difficult, since the quantity and quality of ancient DNA, as well as the environmental bacteria potentially present in the sample, limit the analyses possible. Using human lung tissue and/or teeth samples from burials in eastern Siberia, dating from the end of 17^th to the 19^th century, we propose a methodology that includes the: 1) amplification of all 16S rDNA gene sequences present in each sample; 2) identification of all bacterial DNA sequences with a degree of identity ≥95%, according to quality criteria; 3) identification and confirmation of bacterial pathogens by the amplification of the rpoB gene; and 4) establishment of authenticity criteria for ancient DNA. This study demonstrates that from teeth samples originating from ancient human subjects, we can realise: 1) the correct identification of bacterial molecular sequence signatures by quality criteria; 2) the separation of environmental and pathogenic bacterial 16S rDNA sequences; 3) the distribution of bacterial species for each subject and for each burial; and 4) the characterisation of bacteria specific to the permafrost. Moreover, we identified three pathogens in different teeth samples by 16S rDNA sequence amplification: Bordetella sp., Streptococcus pneumoniae and Shigella dysenteriae. We tested for the presence of these pathogens by amplifying the rpoB gene. For the first time, we confirmed sequences from Bordetella pertussis in the lungs of an ancient male Siberian subject, whose grave dated from the end of the 17^th century to the early 18^th century.     

The ants of remote Polynesia revisited

The islands of remote Polynesia (east of Rotuma, Samoa, Tonga and New Zealand) have long been thought to contain few, if any, native ants. The findings of recent sediment core studies, however, challenge this conventional wisdom and indicate some species may be native. The majority of ant species in remote Polynesia, however, are introductions from tropical and subtropical regions around the world. Despite this diversity of origins, and the lack of a common coevolutionary history in the region, patterns of organization in remote Polynesian ant communities are generally similar to those observed in coevolved continental areas. The distribution of ant species across Polynesia is consistent with a primary mechanism of anthropogenic introductions, with the availability of suitable habitat as a secondary mechanism. The species-area relationship for better-collected Polynesian islands reveals these islands are depauperate compared to Melanesian islands with endemic species. Four out of five of the “world’s worst” invasive ant species are present in remote Polynesia. Recent studies have documented how range expansions of such ant species have had detrimental effects on native arthropod populations, although the overall effects of introduced ants per se on naïve endemic island arthropods may never be known with certainty. Considering the relatively fragile nature of island ecosystems, and the potential transformative effects of invasive ants on arthropod communities, vigilance is required to prevent the spread of invasive ant species across Polynesia.     

Affinities among Melanesians,Micronesians, and Polynesians: a neutral biparental genetic perspective

The human colonization of Remote Oceania, the vast Pacific region including Micronesia, Polynesia, and Melanesia beyond the northern Solomon Islands, ranks as one of the greatest achievements of prehistory. Many aspects of human diversity have been examined in an effort to reconstruct this late Holocene expansion. Archaeolinguistic analyses describe a rapid expansion of Austronesian-speaking "Lapita people" from Taiwan out into the Pacific. Analyses of biological markers, however, indicate genetic contributions from Pleistocene-settled Near Oceania into Micronesia and Polynesia, and genetic continuity across Melanesia. Thus, conflicts between archaeolinguistic and biological patterns suggest either linguistic diffusion or gene flow across linguistic barriers throughout Melanesia. To evaluate these hypotheses and the general utility of linguistic patterns for conceptualizing Pacific prehistory, we analyzed 14 neutral, biparental genetic (short tandem repeat) loci from 965 individuals representing 27 island Southeast Asian, Melanesian, Micronesian, and Polynesian populations. Population bottlenecks during the colonization of Remote Oceania are indicated by a statistically significant regression of loss of heterozygosity on migration distance from island Southeast Asia (r = 0.78, p < 0.001). Genetic and geographic distances were consistently correlated (r > 0.35, p < 0.006), indicating extensive gene flow primarily focused among neighboring populations. Significant correlations between linguistic and geographic patterns and between genetic and linguistic patterns depended upon the inclusion of Papuan speakers in the analyses. These results are consistent with an expansion of Austronesian-speaking populations out of island Southeast Asia and into Remote Oceania, followed by substantial gene flow from Near Oceanic populations. Although linguistic and genetic distinctions correspond at times, particularly between Western and Central-Eastern Micronesia, gene flow has reduced the utility of linguistic data within Melanesia. Overall, geographic proximity is a better predictor of biparental genetic relationships than linguistic affinities.     

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 approximately 30-50,000 years before present (YBP), and a second important expansion from Island Southeast Asia/Taiwan during the interval approximately 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.     

Biogeography of the fauna of French Polynesia: diversification within and between a series of hot spot archipelagos

The islands of French Polynesia cover an area the size of Europe, though total land area is smaller than Rhode Island. Each hot spot archipelago (Societies, Marquesas, Australs) is chronologically arranged. With the advent of molecular techniques, relatively precise estimations of timing and source of colonization have become feasible. We compile data for the region, first examining colonization (some lineages dispersed from the west, others from the east). Within archipelagos, blackflies (Simulium) provide the best example of adaptive radiation in the Societies, though a similar radiation occurs in weevils (Rhyncogonus). Both lineages indicate that Tahiti hosts the highest diversity. The more remote Marquesas show clear examples of adaptive radiation in birds, arthropods and snails. The Austral Islands, though generally depauperate, host astonishing diversity on the single island of Rapa, while lineages on other islands are generally widespread but with large genetic distances between islands. More recent human colonization has changed the face of Polynesian biogeography. Molecular markers highlight the rapidity of Polynesian human (plus commensal) migrations and the importance of admixture from other populations during the period of prehistoric human voyages. However, recent increase in traffic has brought many new, invasive species to the region, with the future of the indigenous biota uncertain.     

Genome-wide analysis indicates more Asian than Melanesian ancestry of Polynesians

Analyses of mitochondrial DNA (mtDNA) and nonrecombining Y chromosome (NRY) variation in the same populations are sometimes concordant but sometimes discordant. Perhaps the most dramatic example known of the latter concerns Polynesians, in which about 94% of Polynesian mtDNAs are of East Asian origin, while about 66% of Polynesian Y chromosomes are of Melanesian origin. Here we analyze on a genome-wide scale, to our knowledge for the first time, the origins of the autosomal gene pool of Polynesians by screening 377 autosomal short tandem repeat (STR) loci in 47 Pacific Islanders and compare the results with those obtained from 44 Chinese and 24 individuals from Papua New Guinea. Our data indicate that on average about 79% of the Polynesian autosomal gene pool is of East Asian origin and 21% is of Melanesian origin. The genetic data thus suggest a dual origin of Polynesians with a high East Asian but also considerable Melanesian component, reflecting sex-biased admixture in Polynesian history in agreement with the Slow Boat model. More generally, these results also demonstrate that conclusions based solely on uniparental markers, which are frequently used in population history studies, may not accurately reflect the history of the autosomal gene pool of a population.     

Proceedings of the SMBE Tri-National Young Investigators' Workshop 2005. Reconstructing the origins and dispersal of the Polynesian bottle gourd (Lagenaria siceraria)

The origin of the Polynesian bottle gourd (Lagenaria siceraria), an important crop species in prehistoric Polynesia, has remained elusive. Most recently, a South American origin has been favored as the bottle gourd could have been introduced from this continent with the sweet potato by Polynesian voyagers around A.D. 1,000. To test the hypothesis of an American origin for the Polynesian bottle gourd, we developed seven markers specific to bottle gourd (two chloroplast and five nuclear). The nuclear markers were developed using a new technique where polymorphic inter simple sequence repeat (ISSR) markers are converted into single-locus polymerase chain reaction and sequencing markers--an approach that will be useful for developing markers in other taxa. All seven markers were sequenced in 36 cultivars of bottle gourd from Asia, the Americas, and Polynesia. The results support a dual origin for the Polynesian bottle gourd: the chloroplast markers are exclusively of Asian origin, but the nuclear markers show alleles originating in both the Americas and Asia. Because hybridization of Polynesian bottle gourds with post-European introductions cannot be excluded, ancient DNA from archaeological material will be useful for further elucidating the prehistoric movements of this species in Polynesia. This work has implications not only for the dispersal of the Polynesian bottle gourd but also for the domestication and dispersal of the species as a whole.     

Ancient voyaging and Polynesian origins

The "Polynesian motif" defines a lineage of human mtDNA that is restricted to Austronesian-speaking populations and is almost fixed in Polynesians. It is widely thought to support a rapid dispersal of maternal lineages from Taiwan ~4000 years ago (4 ka), but the chronological resolution of existing control-region data is poor, and an East Indonesian origin has also been proposed. By analyzing 157 complete mtDNA genomes, we show that the motif itself most likely originated >6 ka in the vicinity of the Bismarck Archipelago, and its immediate ancestor is >8 ka old and virtually restricted to Near Oceania. This indicates that Polynesian maternal lineages from Island Southeast Asia gained a foothold in Near Oceania much earlier than dispersal from either Taiwan or Indonesia 3-4 ka would predict. However, we find evidence in minor lineages for more recent two-way maternal gene flow between Island Southeast Asia and Near Oceania, likely reflecting movements along a "voyaging corridor" between them, as previously proposed on archaeological grounds. Small-scale mid-Holocene movements from Island Southeast Asia likely transmitted Austronesian languages to the long-established Southeast Asian colonies in the Bismarcks carrying the Polynesian motif, perhaps also providing the impetus for the expansion into Polynesia.     

Population structure of Pacific Cordyline fruticosa (Laxmanniaceae) with implications for human settlement of Polynesia

The Polynesian-introduced Cordyline fruticosa is used as a proxy for reconstructing human colonization patterns in Oceania. Because of its material, nutritional, medicinal, and religious importance, green-leaved C. fruticosa was transferred by Polynesian settlers to virtually every habitable Pacific island before European contact. Previous studies propose that green-leaved C. fruticosa is unable to reproduce sexually. To confirm sterility, crosses between fertile and putatively sterile forms were performed. To look for population structure in C. fruticosa that might confirm sterility as well as illustrate patterns of human migration, amplified fragment length polymorphism data were generated. Genotypic similarities were visualized using neighbor joining phenograms and analyses of molecular variance and principal components. The results from greenhouse crosses show that the Eastern Polynesian form is sterile; this finding is corroborated by a lack of genetic variability in Eastern Polynesian accessions. Sterile C. fruticosa appears to have been preferentially transferred throughout Eastern Polynesia; selection for the sterile form may be related to consumption of its rhizomes. Identification of a sterile form of C. fruticosa, possibly developed within Western Polynesia, may be significant to the systematics of Cordyline because it raises the possibility that the fertile form may actually be native to some Pacific islands.