Population Genetics of Drosophila ananassae: Evidence for Population Sub-Structuring at the Level of Inversion Polymorphism in Indian Natural Populations

Drosophila ananassae is a cosmopolitan and domestic species distributed in the tropical, subtropical and mildly temperate regions. Population structure analysis in forty-five Indian natural populations of D. ananassae was performed employing three cosmopolitan inversions as markers. Pairwise FST analysis and genetic distance (D) values showed strong genetic differentiation. Though, lowermost values correspond to geographically closest populations, we did not find any significant ‘isolation by distance’ effect. Values of gene flow based on FST estimates are very low (Nm < 5). All these findings, viz. strong genetic differentiation and minimal gene flow indicate strong sub-structuring in Indian natural populations of D. ananassae at the level of inversion polymorphism. This finding is particularly intriguing in case of D. ananassae as it is frequently transported via human traffic. Given limited gene flow, populations are expected to diverge genetically due to drift. Low level of gene flow coupled with high degree of genetic differentiation might have occurred historically and is maintained currently. Demographic properties, historical and contemporary events and other factors are more important in shaping the patterns of population sub-structuring, genetic differentiation and gene flow than mere terrestrial habitat characteristics (un) favorable for migration.