TESTS OF SIB DIVERSIFICATION THEORIES OF OUTCROSSING IN IMPATIENS-CAPENSIS - EFFECTS OF INBREEDING AND NEIGHBOR RELATEDNESS ON PRODUCTION AND INFESTATION

Several models of the evolution of genetic systems posit very strong frequency-dependent selection acting on small spatial scales; in such circumstances a genetically diverse sibship outperforms a genetically uniform sibship, and genes for mixis may spread in a population. Such selection regimes may derive from resource limitation and/or parasite transmission. We describe a greenhouse experiment designed to test these ideas, using the annual herb Impatiens capensis. Plants were potted in pairs; the genetic variance within pots was manipulated by using progeny from either inbred or outcrossed parents and by using either full sibs or unrelated individuals. Treatment combinations designed to increase genetic diversity resulted in greater phenotypic variance in both morphology and production, though not in the density of spider mites or whiteflies. Despite evidence of resource limitation, there was no effect of genetic diversity on productivity, nor was there an effect on infestation. These results fail to support either the sib competition or the sib contagion theory of outcrossing.