Genetic Origins of the Kiritimati Population from Central-Eastern Micronesia

Abstract

The migration of Austronesian-speaking populations through Oceania has intrigued researchers for decades. The Kiribati islands, situated along the boundaries of Micronesia and Polynesia, provide a crucial link in this migration. We analyzed the genome-wide data of the Kiritimati population of Kiribati to uncover their genetic origins and connections with other Oceanian groups. Our study reveals that the Kiritimati population primarily exhibits Remote Oceanian-related ancestry associated with ancient Lapita and present-day Polynesian populations. In addition, our identity-by-descent analysis identifies populations from the coastal southern Philippines as their closest relatives in Island Southeast Asia. The genetic links between Kiritimati, ancient Lapita, and modern Polynesians underscore the shared ancestry and continuous gene flow across these regions. This genetic continuity and ongoing links are supported by linguistic and cultural evidence, illustrating a complex history of migration and admixture in Oceania.

Keywords: Kiritimati; Micronesia; Oceania; Polynesia; human history; population genetics.

Fig. 1.

Overview of population structure and genetic relationships of Kiritimati. a) Map of Oceania indicating the location of various island groups, with Kiritimati highlighted in an inset figure. Basemap: Esri World Imagery © Esri; map rendered using Leaflet. b) Principal component analysis of worldwide populations or c) restricted to Asia-Pacific populations. Colored circular markers represent specific populations or population clusters. MI, Micronesian; PO, Polynesian.

Fig. 2.

Admixture analysis. Clustering of populations assuming K2 to K9 number of genetic ancestry components. The analysis was run for 50 iterations, with common modes of replicates for each K identified using CLUMPP. The predominant mode for each K was subsequently visualized using Pong v1.4.

Fig. 3.

Genetic affinities of Kiritimati. Levels of a) pairwise f2, b) Hudson's FST, and c) Weir and Cockerham's FST statistics indicate the top 20 populations with the highest genetic affinity with Kiritimati. Error bars represent 1.96 standard error of the estimate. d) Map of Oceania with the location of the top 20 populations represented by circular markers indicating the levels of shared genetic drift with Kiritimati based on outgroup F3 statistics in the form f3 (Mbuti; Kiritimati, X). Kiritimati is represented by the blue circular marker with red circular outline. The intensity of the blue gradient reflects the level of shared genetic drift (range: 0.28 to 0.35), with darker shades representing higher values. MI, Micronesian; PO, Polynesian; PH, Philippine.

Fig. 4.

IBD sharing with Kiritimati. a) Sharing of DNA tracts that are identical by descent with Kiritimati, top 30 populations. Numbers on the bars reflect the count of DNA segments of the corresponding length category, and error bars represent 95% confidence interval. b) Map of Oceania showing the location of the top 15 populations with circular markers indicating the levels of IBD sharing with Kiritimati. The intensity of the blue gradient reflects the level of IBD sharing with Kirtimati, based on the total number of shared segments (range: 11 to 133), with darker shades representing higher values. Asterisks represent the location of Kiritimati and Tarawa of the Gilbert Islands. MI, Micronesian; PO, Polynesian; PH, Philippine.

Fig. 5.

East Asian and Australasian-related ancestries in Kiritimati. a) Detection of Australasian-related ancestry using the test f4(Mbuti, Papuan; Kankanaey, Kiritimati). Papuans represent the Australasian-related ancestry while Philippine Cordilleran Kankanaey represent the East Asian-related ancestry. b) Detection of higher levels of East Asian-related relative to Australasian-related ancestry in Kiritimati using the test f4(Mbuti, X; Papuan, Kankanaey). c) Proportions of East Asian-related and Australasian-related ancestries estimated by qpAdm in Kiritimati and other Micronesian and Polynesian populations. Error bars represent 1.96 standard error of the estimate. MI, Micronesian; PA, Papuan; PO, Polynesian; PH, Philippine.

Fig. 6.

Level of genetic differentiation in the Kiritimati. a) Runs of homozygosity and b) inbreeding coefficient of Kiritimati and other reference populations estimated using PLINK v1.9. AM, American; EA, East Asian; MI, Micronesian; PA, Papuan; PO, Polynesian; PH, Philippine; TW, Taiwanese.