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Selection affecting enzyme polymorphisms in enclosed Drosophila populations maintained in a natural environment
J G Oakeshott1, S R Wilson, W R Knibb
1Research School of Biological Sciences, Australian National University, Canberra.
Summary
Selection favors heterozygotes for Adh and Gpdh enzyme polymorphisms in Drosophila melanogaster at mid-latitudes. This explains observed allele frequency patterns, unlike Pgm and Est6 which show different responses to environmental factors.
Area of Science:
- Population genetics
- Evolutionary biology
- Molecular evolution
Background:
- Allele frequencies of enzyme polymorphisms in Drosophila melanogaster exhibit latitudinal clines.
- Understanding the mechanisms of selection driving these patterns is crucial for evolutionary studies.
Purpose of the Study:
- To investigate the role of natural selection on enzyme polymorphisms (Adh, Gpdh, Est6, Pgm) in Drosophila melanogaster.
- To determine the impact of geographic origin and latitude on selection pressures.
Main Methods:
- Collected Drosophila melanogaster from five Australasian localities across 24 degrees of latitude.
- Established experimental populations and monitored genotype frequencies over 15 months (12 generations).
- Estimated selection coefficients using maximum likelihood procedures.
Main Results:
- Adh and Gpdh polymorphisms showed significant, homogeneous selection coefficients indicating heterozygote advantage.
- Pgm showed heterogeneous selection coefficients, while Est6 had no significant coefficients.
- Predicted equilibrium allele frequencies for Adh and Gpdh matched those in natural populations.
Conclusions:
- Selection favors heterozygotes for Adh and Gpdh at intermediate latitudes in Drosophila melanogaster.
- These findings explain the observed latitudinal clines for Adh and Gpdh.
- Selection mechanisms for Pgm and Est6 appear to differ from Adh and Gpdh.