Evolution and intraspecific exploitative competition. II. A two-locus model for additive gene effects.

A two-locus model corresponding to the model of Christiansen and Loeschcke (1980, theoret, Popul. Biol. 18, 297-313) is analysed. The two loci each have two alleles, and the loci influences a character which determines the utilization of resources in a one-dimensional continuum. The analysis of the model is supported by numerical iterations of the recurrence equations. The previous prediction of high linkage disequilibrium for small allele contributions to the character and close linkage between the loci is confirmed. For larger allele contributions results comparable to those for the symmetric viabilities model are obtained. The model degenerates when the allele contributions at the two loci are equal, i.e., in the most symmetric situation. The results are discussed as the outcome of a balance between optimizing selection and disruptive selection. For small allele contributions the results are virtually independent of which genotype is most favoured by the optimizing aspect of the selective forces.