Population genetics ofDrosophila ananassae: genetic differentiation among Indian natural populations at the level of inversion polymorphism

Abstract

The present study, which is one of the longest temporal (two decades) and largest spatial (different parts of India covered) investigations on inversion polymorphism in natural populations of D. ananassae, was undertaken to understand the dynamics of inversion polymorphism in a broad and comprehensive manner. Forty-five natural populations from different ecogeographic regions of the country (covering the regions from Kashmir to Kanniyakumari and Gujarat to Nagaland) were analysed for chromosomal inversions. All the populations show the presence of the three cosmopolitan inversions, frequencies of which vary among the populations analysed. Simple correlations between frequencies of different inversions and regression analysis of inversion frequencies with latitude, longitude and altitude were insignificant. This reinforces the concept of rigid polymorphism in D. ananassae. Genetic divergence (spatial and temporal) at the level of chromosomal polymorphism among natural populations was calculated. Results show spatial divergence but no temporal divergence. Rigid polymorphic systems of D. ananassae did not show long-term directional trends. On the basis of the present study, and after including comparisons with the studies conducted more than two decades ago, the most important conclusion to be drawn is that the three cosmopolitan inversions in D. ananassae segregate within populations at fairly similar frequencies, and the general geographic pattern has remained constant.

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

“…Latitudinal clines have been detected in Indian natural populations of D. melanogaster (Das & Singh, 1991;Singh & Das, 1992). These north-south trends have also been reported with respect to inversion frequencies in natural populations of D. ananassae (Singh & Singh, 2007). These trends have persisted because of diversifying selection that acts to impede homogenization as a result of gene flow, as is commonly the case among naturally occurring clines (Endler, 1977;Arnold, 1997).…”

“…ananassae flies were collected from forty-five different eco-geographical localities of India ranging from Jammu in north to Kanniyakumari in south and Dwarka in west to Deemapur in east (see Singh & Singh, 2007 for details of collection along with their geographical locations).…”

“…Quantitative data on inversion frequencies in forty-five natural populations of Indian D.ananassae (Singh & Singh, 2007) was utilized to arrive at genetic variability estimates, F-statistics and gene flow. This is the first time that inversions as chromosomal markers have been employed for population structure analysis.…”

“…Forty-five natural populations from different eco-geographic regions of the country (covering the regions from Jammu in north to Kanniyakumari in south and Dwarka in west to Deemapur in east) were analysed for chromosomal inversions and data has been given elsewhere (Singh & Singh, 2007). In the present communication, same quantitative data on the frequencies of three cosmopolitan inversions in Indian natural populations of D. ananassae (Singh & Singh, 2007) have been used to arrive at genetic variability estimates, F-statistics and gene flow.…”

“…In the present communication, same quantitative data on the frequencies of three cosmopolitan inversions in Indian natural populations of D. ananassae (Singh & Singh, 2007) have been used to arrive at genetic variability estimates, F-statistics and gene flow. The present communication represents the most comprehensive analysis of Indian natural populations of D. ananassae using traditional genetic approach and employing chromosomal markers (inversions), genetic variability parameters (H o, H e, F) and F-statistics to infer the population structure and gene flow among D. ananassae populations from different parts of India.…”