Inferring the population structure and demography of Drosophila ananassae from multilocus data.

Inferring the origin, population structure, and demographic history of a species is a major objective of population genetics. Although many organisms have been analyzed, the genetic structures of subdivided populations are not well understood. Here we analyze Drosophila ananassae, a highly substructured, cosmopolitan, and human-commensal species distributed in the tropical, subtropical, and mildly temperate regions of the world. We adopt a multilocus approach (with 10 neutral loci) using 16 population samples covering almost the entire species range (Asia, Australia, and America). Analyzed with our recently developed Bayesian method, 5 populations in Southeast Asia are found to be central, while the other 11 are peripheral. These 5 central populations were sampled from localities that belonged to a single landmass ("Sundaland") during the late Pleistocene ( approximately 18,000 years ago), when sea level was approximately 120 m below the present level. The inferred migration routes of D. ananassae out of Sundaland seem to parallel those of humans in this region. Strong evidence for a population size expansion is seen particularly in the ancestral populations.