Persistence of heterozygosity owing to balancing selection at allozyme loci in laboratory populations of Drosophila ananassae
DOI:
https://doi.org/10.14456/gag.2019.2Keywords:
Allozyme polymorphism, Mass culture stocks, Random genetic drift, Drosophila ananassaeAbstract
Drosophila ananassae is one of the widely occurring species in Indian subcontinent. Its genetic polymorphism has been studied extensively by considering commonly occurring inversions. However, the genetic polymorphism of this species at the molecular level has not been investigated substantially. The present study reveals the persistence of enzyme variants (allozymes) in the laboratory stocks of this species. Fifteen mass culture stocks of D. ananassae established from the flies collected from natural populations were reared in laboratory for more than 25 generations. Based on the frequency of enzyme variants of 12 enzyme loci, the different parameters of genetic variability were tested. The results obtained indicate that most of the mass culture stocks do not show conformity with HWE, at many loci. In a number of mass culture stocks, many allozyme loci showed monomorphic appearance. Estimates of genetic variability and inbreeding coefficient clearly specified that majority populations of mass culture stocks show higher level of F value (0.315 to 0.556) indicating that the mass culture stocks experienced more inbreeding. The reduction in the level of observed heterozygosity in mass culture stocks might be due to inbreeding caused by random genetic drift. However, occurrence of heterozygotes still at considerable range (0.313 to 0.339) at some enzyme loci in mass culture stocks proves that heterozygotes are subject to selection even in the laboratory conditions. When the level of heterozygosity of natural populations and their mass culture stocks were compared, it was found that number of heterozygotes have become lesser in mass culture stocks than their respective natural populations. None of the populations were found to become monomorphic for all allozyme loci studied which shows that irrespective of strong founder events, there is still heterosis, demonstrating that the populations are under substantial balancing selection. Genetic distance (D) between natural and their respective mass culture stocks (laboratory populations) have also been computed to study the level of genetic differentiation between the two.
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