Exploring the Matrilineal Genomic History of Aboriginal Australians through Mitochondrial DNA

Abstract

We investigated the route taken in the first human migration from southeast Asia to southern Australia. Mitochondrial DNA (mtDNA) sequences were analysed using phylogenetic trees, then a simulation study was used to identify the migration route that best described the observed data. The simulation study compared the observed mtDNA data to DNA simulated under nine different scenarios. If the actual migration history resembled one of the scenarios, we would expect the summary statistics of the observed and simulated mtDNA to be similar. The simulation study did not conclusively select one migration route, or a set of migration routes, that best described the data. To check that this was a consequence of the data and not the modelling assumptions, we considered a range of extensions to the initial simulation study. This included modifications to the time between migration events through the south-east Asian islands, exploration of the effect of different migration levels after the initial settlement of all populations, and then a more detailed haplogroup analysis. From these extended analyses, we found that increasing the length of time between migration events through the southeast Asian islands resulted in a greater ability to distinguish between migration routes. We also found that we were less able to distinguish between migration routes when identical patterns of ongoing migration were applied to all migration routes. Our further haplogroup analysis used a simulation study to compare three different migration routes. While we could not determine the geographical route taken, we could determine the patterns of ongoing migration that occurred after settlement. The observed mtDNA data was consistent with ongoing, low-level migration between northeastern Australia and New Guinea. We conjecture that rapid migration through the southeast Asian islands resulted in minimal evidence of the initial migration events in the mtDNA sequence data. When considering the phylogenetic trees, we noticed low branch support values around the time of settlement of Australia, which further supports our conjecture. Our findings suggest that small amounts of ongoing migration between northeastern Australia and New Guinea occurred. Our inability to reliably determine the initial migration route taken also illustrates the limitations of mtDNA analysis, and highlight the importance of using nuclear DNA for future studies in this area.