Conclusions
Beyond confirming the usefulness of uniparental genetic markers to identify past contact events, this study provides the first clear evidence for the presence of Austronesian genetic input in Eastern Africa and South Arabia, beyond the African offshore islands of Madagascar and the Comoros. This input may have spread firstly during an early stage (prior to the late eighteenth century) and secondly at a later stage (end of the nineteenth century) from the Austronesian presence in the Western Indian Ocean region, from Madagascar and directly from an unknown location in Island Southeast Asia. Moreover, this suggests that beyond the main and early well identified Austronesian dispersal event westward into the Indian Ocean, later and more specific small scale events (e.g., Arab trading activities, diaspora communities) favor limited genetic exchanges and spread of the Austronesian genetic component within the Western Indian Ocean rim populations. More genetic data from the Indian Ocean rim populations are necessary to better understand and model these multiple episodes of Austronesian genetic admixture within the Indian Ocean, including their date of admixture, routes taken, and the population and geographic scale of these contact events.