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

Abstract

Drosophila ananassae is a cosmopolitan and domestic species distributed in the tropical, subtropical and mildlytemperate regions. Population structure analysis in forty-five Indian natural populations of D. ananassae was performedemploying three cosmopolitan inversions as markers. Pairwise FST analysis and genetic distance (D) values showed stronggenetic differentiation. Though, lowermost values correspond to geographically closest populations, we did not find anysignificant ‘isolation by distance’ effect. Values of gene flow based on FST estimates are very low (Nm < 5). All thesefindings, viz. strong genetic differentiation and minimal gene flow indicate strong sub-structuring in Indian naturalpopulations 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 divergegenetically due to drift. Low level of gene flow coupled with high degree of genetic differentiation might have occurredhistorically and is maintained currently. Demographic properties, historical and contemporary events and other factors aremore important in shaping the patterns of population sub-structuring, genetic differentiation and gene flow than mereterrestrial habitat characteristics (un) favorable for migration.