Abstract
The fitness effects of extreme genetic change by selection were studied in large populations subjected to prolonged, intense selection. Two replicate populations of Drosophila melanogaster, with estimated effective sizes 500 <= N(e) <= 1000, were selected for increased performance in a wind tunnel, selecting on average the fastest 4.5% of flies. The mean apparent flying speed of both lines increased from ~2 to 170 cm/sec and continued to respond at diminishing rates, without reaching a plateau, for 100 generations. Competitive fitness tests in generations 50 and 85 showed minimal or no fitness loss in selected lines compared to controls. Sublines relaxed in generations 65 and 85 showed minimal or no regression in apparent flying speed. Hybrid lines, from a cross of selected X control lines in generation 75, responded to reselection saltationally, showing that the chromosomes of the selected lines had been assembled from alleles at many loci, from many different chromosomes in the base population. Thus, major genetic change was achieved, but without the costs usually associated with strong directional selection. Large population size has been interpreted, in opposing models, as either a brake or an accelerator in its effects on long-term change by selection. These results favor the second model, and challenge the concept of rugged fitness surfaces underlying the first model.
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Selected References
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- Brown W P, Bell A E. Genetic Analysis of a "Plateaued" Population of Drosophila Melanogaster. Genetics. 1961 Apr;46(4):407–425. doi: 10.1093/genetics/46.4.407. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Frankham R. Conservation genetics. Annu Rev Genet. 1995;29:305–327. doi: 10.1146/annurev.ge.29.120195.001513. [DOI] [PubMed] [Google Scholar]
- Hill W. G., Robertson A. The effect of linkage on limits to artificial selection. Genet Res. 1966 Dec;8(3):269–294. [PubMed] [Google Scholar]
- Jones L. P., Frankham R., Barker J. S. The effects of population size and selection intesnity in selection for a quantitative character in Drosophila. II. Long-term response to selection. Genet Res. 1968 Dec;12(3):249–266. doi: 10.1017/s001667230001185x. [DOI] [PubMed] [Google Scholar]
- Lynch M. The rate of polygenic mutation. Genet Res. 1988 Apr;51(2):137–148. doi: 10.1017/s0016672300024150. [DOI] [PubMed] [Google Scholar]
- Roberts R. C. The limits to artificial selection for body weight in the mouse. I. The limits attained in earlier experiments. Genet Res. 1966 Dec;8(3):347–360. doi: 10.1017/s001667230001020x. [DOI] [PubMed] [Google Scholar]
- Weber K. E. Increased selection response in larger populations. I. Selection for wing-tip height in Drosophila melanogaster at three population sizes. Genetics. 1990 Jul;125(3):579–584. doi: 10.1093/genetics/125.3.579. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wright S. Evolution in Mendelian Populations. Genetics. 1931 Mar;16(2):97–159. doi: 10.1093/genetics/16.2.97. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Zeng Z. B., Hill W. G. The selection limit due to the conflict between truncation and stabilizing selection with mutation. Genetics. 1986 Dec;114(4):1313–1328. doi: 10.1093/genetics/114.4.1313. [DOI] [PMC free article] [PubMed] [Google Scholar]