The genetic structure of Drosophila ananassae populations from Asia, Australia, and Samoa

Information about genetic structure and historical demography of natural populations is central to understanding how natural selection changes genomes. Drosophila ananassae is a widespread species occurring in geographically isolated or partially isolated populations and provides a unique opportunity to investigate population structure and molecular variation. We assayed microsatellite repeat length variation among 13 populations of D. ananassae to test the hypothesis that they are highly structured and we then make inferences about their ancestry and historic biogeography. High levels of genetic structure are apparent among all populations particularly in Australasia and the South Pacific, and patterns are consistent with the hypothesis that the ancestral populations are from Southeast Asia. Analysis of population structure and using F-statistics and Bayesian analysis suggest that the range expansion of the species into the Pacific is complex with multiple colonization events evident in some populations represented by lineages that show no evidence of recent admixture. The demographic patterns show isolation-by-distance among populations and population expansion within all populations. A morphologically distinct sister species, D. pallidosa collected in Malololelei, Samoa, appears to be more closely related to some of the D. ananassae populations than many of the D. ananassae populations are to one another. The patterns of genotypic diversity suggest that many of the individuals we sampled may be morphologically indistinguishable nascent species.

Key Words: Drosophila ananassae, Drosophila pallidosa, biogeography, microsatellite, population structure

Online ISS 1091-6490
Copyright 2008 by the Genetics Society of America
phone: 412-268-1812   fax: 412-268-1813   email: genetics-gsa{at}andrew.cmu.edu