Geographical clinal variation at seven esterase-coding loci in Indian populations of Zaprionus indianus

Twelve Indian natural populations of Zaprionus indianus, collected along 22 degrees latitudinal range, were analysed electrophoretically for allozymic variation of esterase gene-enzyme system. Interestingly, all the seven Est loci were found to be highly polymorphic in all the populations of Z. indianus. The genetic structure of Z. indianus populations was characterized by extensive inter-populational genotypic as well as allelic frequency heterogeneity and higher genic differentiation at all the esterase-coding loci. All the polymorphic loci in geographical populations of Z. indianus revealed latitudinal clines, and changes in allelic frequencies were found to correlate with latitude. The occurrence of higher genetic variability in Z. indianus populations was in agreement with its habitat-generalist or broad niche-width characteristics, i.e., the species populations utilized diverse food resources and displayed adaptation to variable climatic conditions. Thus, the observed genic divergence patterns in colonizing populations of Z. indianus could be maintained by balancing natural selection varying spatially along the north-south axis of the Indian sub-continent.