On the Rat Trail in Near Oceania: Applying the Commensal Model to the Question of the Lapita Colonization

Presented here are the most recent results of our studies of Rattus exulans, one of the main commensal animals transported across the Pacific by Lapita peoples and their descendants. We sampled several locations in Near Oceania to determine distribution of R. exulans mitochondrial DNA (mtDNA) haplotypes in the region. We also obtained data regarding distribution of other introduced Rattus species to several islands in the Bismarck Archipelago. Our results suggest that there were multiple introductions of R. exulans to the region, which may suggest a more complex history for Lapita populations in Near Oceania. One of the greatest impacts of human arrival on previously uninhabited islands is the introduction of human-associated plants and animals. The species introduced by humans can include not only intentional introductions such as domesticated plants and animals, but also a range of unintentionally transported species including weeds, insects, and other pests (Kirch 1982, Lee et al. 2007). Often island ecosystems contain a naive fauna and numerous endemic species that cannot compete with the more recent introductions. Despite the often negative impacts of introduced species on island ecosystems, there were clearly good reasons for people to transport their familiar plants and animals to the new environments they occupied. The transported landscapes (Kirch 1984) of Pacific peoples also provide a valuable resource for prehistorians. Not only do they allow us to understand and appreciate how humans adapted to the various environments they encountered, but understanding the history of the plants and animals that humans transported can provide direct evidence regarding the history of the humans themselves: Where did they come from and when? How many introductions and population arrivals were there? Is the appearance of a particular species associated with any particular archaeologically definable culture? Beginning in the 1990s a program was developed at the University of Auckland focused on determining if tracking the movement of commensal animals introduced to Pacific islands by initial human colonists, through analyses of mitochondrial DNA (mtDNA) variation, might serve as a proxy for tracing human migration in the Pacific (Matisoo-Smith 1994, Matisoo-Smith et al. 1998). Pacific colonists transported, among other things, dogs, pigs, chickens, and rats when they settled the previously uninhabited islands of Remote Oceania. It is also generPacific Science (2009), vol. 63, no. 4:465–475 : 2009 by University of Hawai‘i Press All rights reserved 1 This research was funded by the Royal Society of New Zealand under Marsden Project UOA510: The Rat’s Tale: Tracking Lapita Peoples through Phylogenetic Analyses of Pacific Rats. Manuscript accepted 23 January 2009. 2 Department of Anthropology, University of Auckland, Auckland 1, New Zealand. 3 School of Biological Sciences, University of Auckland, Auckland 1, New Zealand. 4 Allan Wilson Centre for Molecular Ecology and Evolution, University of Auckland, Auckland 1, New Zealand. 5 Department of Anthropology, University of Otago, P.O. Box 56, Dunedin, Otago, New Zealand. 6 Allan Wilson Centre for Molecular Ecology and Evolution, Massey University, Palmerston North Campus, Private Bag 11222, Palmerston North 444, New Zealand. 7 Corresponding author (e-mail: e.matisoo-smith@