Reconstructing Asian faunal introductions to eastern Africa from multi-proxy biomolecular and archaeological datasets

Human-mediated biological exchange has had global social and ecological impacts. In subS-aharan Africa, several domestic and commensal animals were introduced from Asia in the pre-modern period; however, the timing and nature of these introductions remain contentious. One model supports introduction to the eastern African coast after the mid-first millennium CE, while another posits introduction dating back to 3000 BCE. These distinct scenarios have implications for understanding the emergence of long-distance maritime connectivity, and the ecological and economic impacts of introduced species. Resolution of this longstanding debate requires new efforts, given the lack of well-dated fauna from high-precision excavations, and ambiguous osteomorphological identifications. We analysed faunal remains from 22 eastern African sites spanning a wide geographic and chronological range, and applied biomolecular techniques to confirm identifications of two Asian taxa: domestic chicken (Gallus gallus) and black rat (Rattus rattus). Our approach included ancient DNA (aDNA) analysis aided by BLAST-based bioinformatics, Zooarchaeology by Mass Spectrometry (ZooMS) collagen fingerprinting, and direct AMS (accelerator mass spectrometry) radiocarbon dating. Our results support a late, mid-first millennium CE introduction of these species. We discuss the implications of our findings for models of biological exchange, and emphasize the applicability of our approach to tropical areas with poor bone preservation

Summary of results.

<p>Zooarchaeological and biomolecular results for the sites studied, with earliest dates for fauna confirmed via biomolecular analysis.</p

Results of biomolecular analyses.

<p>Results of biomolecular confirmation or negation of domestic chicken (<i>Gallus gallus</i>) and black rat (<i>Rattus rattus</i>) remains identified via zooarchaeological analyses. Sites: 1, Mulungu wa Mawe; 2. Panga ya Saidi; 3, Mtsengo; 4, Panga ya Mwandzumari; 5, Kwa Kipoko; 6, Panga ya Mizigo; 7, Mbuyuni; 8, Chombo; 9, Vumba Kuu; 10, Pango la Watoro; 11, Makangale Cave; 12, Ras Mkumbuu; 13, Fukuchani; 14, Unguja Ukuu; 15, Kuumbi Cave; 16, Juani Primary School; 17, Ukunju Cave; 18, Songo Mnara; 19, Nyamawi; 20, Sima; 21, Dembeni; 22, Mahilaka. Main figure made with Natural Earth (<a href="http://www.naturalearthdata.com/" target="_blank">http://www.naturalearthdata.com</a>); inset maps were hand-drawn.</p

Chronology of occurrences of non-native species.

<p>Approximate years of occupation at sites in the present study, with earliest confirmed occurrences of domestic chicken (<i>Gallus gallus</i>) and black rat (<i>Rattus rattus</i>).</p

Major zones of interaction and migration.

<p>Major zones of interaction and migration on the African continent from c. 3000 BCE-1000 CE, including spreads of farming and herding, and key areas of trade. Farming and Bantu language dispersal routes follow [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182565#pone.0182565.ref031" target="_blank">31</a>]. Earliest reported dates for two Asian taxa, black rat (<i>Rattus rattus</i>) and chicken (<i>Gallus gallus</i>), are based on published data [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182565#pone.0182565.ref026" target="_blank">26</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182565#pone.0182565.ref028" target="_blank">28</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182565#pone.0182565.ref030" target="_blank">30</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182565#pone.0182565.ref032" target="_blank">32</a>]. Made with Natural Earth (<a href="http://www.naturalearthdata.com/" target="_blank">http://www.naturalearthdata.com</a>).</p