Pigs settled Pacific islands alongside early human voyagers

(Press-News.org) Pigs across the Pacific can trace their ancestry to Southeast Asian domestic pigs that accompanied early Austronesian-speaking groups as they island-hopped across the region, according to a new genomic study. For thousands of years, humans have moved animals far beyond their natural ranges – sometimes accidentally and sometimes deliberately, but often with profound ecological consequences, especially on islands. Pigs are a striking example; although their home ranges lie mostly west of the Wallace Line, multiple species are now widespread across the islands of Southeast Asia and throughout Oceania. Archaeological and genetic evidence suggest that pigs were brought eastward more than 4,000 years ago, predating major Austronesian migrations, with later human expansions bringing them farther across the Pacific. However, studies show that endemic pigs in these regions carry a distinctive “Pacific Clade” genetic signature, which is shared by wild and free-living pigs elsewhere across mainland Southeast Asia. This pattern raises questions about the precise nature of the origin and dispersal of pig populations across the Pacific, and humans’ role in it.

 

To trace the origins of pigs across Wallacea, Melanesia, Micronesia, and Polynesia, David Stanton and colleagues sequenced 117 modern, historical, and ancient pig genomes spanning the last 2,900 years, and analyzed tooth shape data from 401 modern and 313 archaeological specimens. Stanton et al. found that pigs from the Philippines to Hawaii largely descended from domestic pigs brought by Austronesian-speaking groups from Southeast China and Taiwan about 4,000 years ago. Moreover, pigs in Oceania show no genetic mixing with the wild pig species native to islands along the migration route, indicating that the earliest introduced animals remained genetically isolated from local populations. Only later did isolated feral populations interbreed with endemic wild species. According to the authors, this pattern mirrors early, successive human migrations across the region, which likewise involved limited admixture with local groups, suggesting that these pigs possessed domestic traits well suited for transport and husbandry. Repeated island-to-island movement then shaped their evolution through genetic bottlenecks, selective pressures, and later gene flow, helping explain their success in spreading across Island Southeast Asia and the western Pacific.

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