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‘Overcompensation’ at an enzyme locus in Drosophila pseudoobscura*

Published online by Cambridge University Press:  14 April 2009

Mirjana Toŝić
Affiliation:
Department of Genetics, University of California, Davis, California 95616
Francisco J. Ayala
Affiliation:
Department of Genetics, University of California, Davis, California 95616

Summary

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The experiments reported in this paper are primarily addressed to test the hypothesis of overcompensation; i.e. whether polymorphic populations exploit limiting environmental resources better than populations uniform for a single genotype. Overcomposition is an ecological consequence of some models of frequency-dependent selection. Secondarily, the experiments investigate whether overdominance exists at the Mdh-2 locus in Drosophila pseudoobscura.

Two types of experimental populations are established: ‘low-variability’ populations, in which all flies in a culture are offspring from only two laboratory strains; ‘high-variability’ populations, in which the flies in a culture are derived from 20 different strains. However, the overall degree of individual heterozygosity is the same in both types of populations. Three kinds of populations with respect to the Mdh-2 locus are established within each type; two are homozygous for either the 100 or the 112 allele, the third is heterozygous. A fourth kind of population exists among the high-variability populations; namely, populations in which all three Mdh-2 genotypes are present. The experiments are done at two densities; one quasi-optimal, the other highly competitive.

Populations with high overall levels of genetic variation consistently produce more flies than low-variability populations. The differences are significant at the low, but not at the high, density. Moreover, populations polymorphic for the Mdh-2 locus generally produce more flies than populations having only one Mdh-2 genotype. At high density, the Mdh-2 polymorphic populations have greater productivity than populations with anyone of the three genotypes, and the differences are statistically significant when the polymorphic populations are compared with either one of the two homozygotes or with the average of all three genotypes. In brief, overcompensatory effects – which may account for frequency-dependent selection – are observed in the experiment and may be a common phenomenon in nature.

Populations in which all individuals are heterozygous at the Mdh-2 locus produce in every case more flies than populations with only homozygotes for one or the other allele. The superiority of the heterozygotes is statistically significant for all comparisons at low density, but at high density it is statistically significant for the comparison with the homozygote rarer in nature and only in low variability populations.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1980

References

REFERENCES

Allard, R. W. & Adams, J. (1969). Population studies in predominantly self-pollinating species. XIII. Intergenotypic competition and population structure in barley and wheat. American Naturalist 103, 621647.CrossRefGoogle Scholar
Antonovics, J. (1978). The population genetics of mixtures. Plant Relations in Pastures (ed. Wilson, J. R.). East Melbourne, Australia: C.S.I.R.O.Google Scholar
Anxolabehere, D. & Periquet, G. (1972). Variation de la valeur selective de l'heterozygote en fonction des frequencies alleliques chez Drosophila melanogaster. Compte Rendu de l'Académie des Sciences, Paris 275 (D), 27552757.Google Scholar
Ayala, F. J. (1965). Relative fitness of populations of Drosophila serrata and Drosophila birchii. Genetics 51, 527544.CrossRefGoogle ScholarPubMed
Clarke, B. & O'Donald, P. (1964). Frequency-dependent selection. Heredity 19, 201206.CrossRefGoogle Scholar
Dobzhansky, Th. & Ayala, F. J. (1973). Temporal frequency changes of enzyme and chromosomal polymorphisms in natural populations of Drosophila. Proceedings of the National Academy of Sciences, U.S.A. 70, 680683.CrossRefGoogle ScholarPubMed
Dobzhansky, Th. & Pavlovsky, O. A. (1961). A further study of fitness of chromosomally polymorphic and monomorphic populations of Drosophila pseudoobscura. Heredity 16, 169179.CrossRefGoogle Scholar
Harding, J., Allard, R. W. & Smeltzer, D. G. (1966). Population studies in predominantly self-pollinated species. IX. Frequency-dependent selection in Phaseolus lunatus. Proceedings of the National Academy of Sciences, U.S.A. 56, 99104.CrossRefGoogle Scholar
Harper, J. L. (1967). The relation of numbers and mass in plant populations. Population Biology and Evolution (ed. Lewontin, R. C.). New York: Syracuse University Press.Google Scholar
Kojima, K. & Tobari, Y. N. (1969). The pattern of viability changes associated with genotype frequency at the alcohol dehydrogenase locus in a population of Drosophila melanogaster. Genetics 61, 201209.CrossRefGoogle Scholar
Levins, R. (1965). Theory of fitness in the heterogeneous environment. V. Optimal genetic system. Genetics 52, 891904.CrossRefGoogle Scholar
Marinković, D. & Ayala, F. J. (1975 a). Fitness of allozyme variants in Drosophila pseudoobscura. I. Selection at the Pgm-1 and Me-2 loci. Genetics 79, 8595.CrossRefGoogle ScholarPubMed
Marinković, D. & Ayala, F. J. (1975 b). Fitness of allozyme variants in Drosophila pseudoobscura. II. Selection at the Est-5, Odh and Mdh-2 loci. Genetical Research 24, 137149.CrossRefGoogle Scholar
Nei, M., Maruyama, T. & Chakraborty, R. (1975). The bottleneck effect and genetic variability in populations. Evolution 29, 110.CrossRefGoogle ScholarPubMed
Petit, C. & Ehrman, L. (1969). Sexual selection in Drosophila. Evolutionary Biology 3, 177223.Google Scholar
Schultz, W. M. & Usanis, S. A. (1969). Inter-genotypic competition in plant populations. II. Maintenance of allelie polymorphisms with frequency-dependent selection and mixed and random mating. Genetics 60, 875891.CrossRefGoogle Scholar
Snyder, T. & Ayala, F. J. (1979). Frequency-dependent selection at the Pgm-1 locus of Drosophila pseudoobscura. Genetics. (In the Press.)CrossRefGoogle Scholar
Sokal, R. R. & Rohlf, F. J. (1969). Biometry. San Francisco: Freeman.Google Scholar
Spiess, E. (1957). Relation between frequencies and adaptive values of chromosomal arrangements in Drosophila persimilis. Evolution 11, 8493.CrossRefGoogle Scholar
Toŝ, M. & Ayala, F. J. (1980). Density and frequency dependent selection at the Mdh-2 locus in Drosophila pseudoobscura. Submitted to Genetics.Google Scholar
Wallace, B. (1968). Topics in Population Genetics. New York: W. W. Norton.Google Scholar
Yarbrough, K. & Kojima, K. (1967). The mode of selection at the polymorphic Est-6 locus in cage populations of Drosophila melanogaster. Genetics 57, 677686.CrossRefGoogle Scholar