Abstract
The Solomon Islands, first settled c.30,000 years ago, sits on the boundary of Near and Remote Oceania. The archipelago played a significant role in major prehistoric Pacific mobility and interactions: such as the Lapita expansion, and settlement of the Polynesian Outliers and Micronesia. Previous genetic studies of commensals have inferred large-scale human migrations across the Pacific, but few samples from the Solomon Islands were included. Here, we present the analysis of ancient DNA from twelve Rattus sp. bones excavated from Sikopo Island in the Western Solomons, dated between 850 - 500 cal. BP. Mitochondrial DNA from nine Rattus exulans (Pacific Rat) specimens were successfully sequenced and thus more than doubled the number of commensal animals sampled from the Solomon Islands. Phylogenetic analyses identified the Sikopo Island rats as more closely related to Polynesian than Near Oceanic samples and showed them to be of a different mitochondrial DNA haplogroup than previously detected in the Solomon Islands. The results are consistent with current hypotheses for multiple introductions of these rats (and therefore human movements) across the Near and Remote Oceania boundary. With consideration of archaeological and other lines of evidence, we propose three scenarios to explain how the Sikopo Island rats may have been introduced into the Western Solomons - two of which involve different long-distance connections with Remote Oceania and the other involves inter-island movements within the Solomon Islands. Overall, our results highlight the potential for further genetic commensal studies in the Solomon Islands to reconstruct prehistoric Pacific population mobility and interaction spheres.