The Pacific Rat Race to Easter Island: Tracking the Prehistoric Dispersal of Rattus exulans Using Ancient Mitochondrial Genomes

Katrina West,Jennifer Kahn,David V Burley,Terry L Hunt,Elizabeth Matisoo-Smith,Olga Kardailsky,Catherine Collins

doi:10.3389/fevo.2017.00052

Abstract

The location of the immediate eastern Polynesian origin for the settlement of Easter Island (Rapa Nui), remains unclear with conflicting archaeological and linguistic evidence. Previous genetic commensal research using the Pacific rat, Rattus exulans; a species transported by humans across Remote Oceania and throughout the Polynesian Triangle, has identified broad interaction spheres across the region. However, there has been limited success in distinguishing finer-scale movements between Remote Oceanic islands as the same mitochondrial control region haplotype has been identified in the majority of ancient rat specimens. To improve molecular resolution and identify a pattern of prehistoric dispersal to Easter Island, we sequenced complete mitochondrial genomes from ancient Pacific rat specimens obtained from early archaeological contexts across West and East Polynesia. Ancient Polynesian rat haplotypes are closely related and reflect the widely supported scenario of a central East Polynesian homeland region from which eastern expansion occurred. An Easter Island and Tubuai (Austral Islands) grouping of related haplotypes suggests that both islands were established by the same colonization wave, proposed to have originated in the central homeland region before dispersing through the south-eastern corridor of East Polynesia.

Highlights

The expansion of modern humans into the wider Pacific, culminating with the colonization of eastern Polynesia within the last 1,000 years, represents one of the last major migrations in human history (Duggan et al, 2014; Matisoo-Smith, 2015)
27 samples were removed post-sequencing as a result of missing large fragments and low read depth (
Complete mitochondrial genome sequencing provides a higher degree of molecular resolution that can be used to distinguish Pacific rat populations across Remote Oceania

Summary

Introduction

The expansion of modern humans into the wider Pacific, culminating with the colonization of eastern Polynesia within the last 1,000 years, represents one of the last major migrations in human history (Duggan et al, 2014; Matisoo-Smith, 2015). The timing and sequence of settlement across many of the major archipelagos of central East Polynesia remain largely unresolved, with conflicting estimates of initial colonization varying by more than 1,000 years (Wilmshurst et al, 2008, 2011). A two-phase sequence of settlement has been proposed—establishment in the Society Islands ∼925–830 B.P. before a widespread radiation toward the Marquesas, ∼750– 673 B.P.; Easter Island, ∼750–697 B.P.; Hawai’i, ∼731–684 B.P.; New Zealand, ∼720–668 B.P.; Southern Cooks, ∼700– 669 B.P.; and the Line Islands, ∼675–657 B.P. There are still irreconcilable differences in the chronological boundaries of some island groups, with some researchers advocating for an earlier settlement of the Cook Islands, the Marquesas, Hawai’i and Mangareva (Gambier Islands; Kirch et al, 2010; Allen and McAlister, 2013; Athens et al, 2014; Conte and Molle, 2014; Weisler et al, 2015)

Methods

Results

Discussion

Conclusion