Natural selection vs. random drift: evidence from temporal variation in allele frequencies in nature
Mueller, L.D.; Barr, L.G.; Ayala, F.J.
Genetics 111(3): 517-554
1985
ISSN/ISBN: 0016-6731 PMID: 4054608 Document Number: 243365
Monthly samples of Drosophila pseudoobscura and Drosophila persimilis in a natural population from Napa County, California were obtained. In each species, about 300 genes were assayed by electrophoresis for each of 7 enzyme loci in each monthly sample from Mar. 1972 to June 1975. The data were analysed to ascertain whether the allele frequencies at different loci varied in a correlated fashion. The methods used did not detect deterministic natural selection (e.g., overdominance or directional selection), but only the circumstance when alleles at different loci varied simultaneously in response to the same environmental variations. Moreover, only relatively large fitness differences (of the order of 15%) were detectable. Strong evidence of correlated allele frequency variation was found in 13-20% of the cases examined. It is concluded that natural selection plays a major role in the evolution of protein polymorphisms in nature.