On a Genetic Model of Intraspecific Competition and Stabilizing Selection

Buerger, R. (2002). On a Genetic Model of Intraspecific Competition and Stabilizing Selection. IIASA Interim Report. IIASA, Laxenburg, Austria: IR-02-062

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Abstract

A genetic model is investigated in which two recombining loci determine the genotypic value of a quantitative trait additively. Two opposing evolutionary forces are assumed to act: (i) stabilizing selection on the trait, favoring genotypes with an intermediate phenotype, and (ii) intraspecific competition mediated by trait, favoring genotypes whose effect the trait deviates most from that of the prevailing genotypes. Accordingly, fitness of genotypes have a frequency-independent component describing stabilizing selection, and a frequency- and density-dependent component modeling competition. We study how the underlying genetics, in particular recombination rate and relative magnitude of allelic effects, interacts with the conflicting selective forces and derive the resulting, surprisingly complex, equilibrium patterns. It is investigated under which conditions disruptive selection on the phenotypes can be observed, and how much genetic variation can be maintained in such a model. A number of unexpected phenomena are discovered, for instance that with little recombination the degree of stably maintained polymorphism and the equilibrium genetic variance can decrease as the strength of competition increases relative to the strength of stabilizing selection. In addition, mean fitness at the stable equilibria is usually much lower than the maximum possible mean fitness, and often lower than the fitness at other, unstable, equilibria. Thus the evolutionary dynamics in this system is almost always nonadaptive.

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